Hey, it's Mr. W from learn-biology.com. The AP Bio exam is coming up and you're going to need a plan to prioritize what you study. That's what this video is designed to give you. Here's your review plan. Download this checklist at apbiosuccess.com checklist.
Get three highlighters, red, green, and yellow. Follow along with me during the video. Use the stoplight method to identify items that you know well. Mark those in green.
That you know a little bit, mark those in yellow. and that you don't know at all mark those in red prioritize your studying study the red items first then the yellow and then just to keep the topics fresh study the green as you study here are some resources that you can use to help fill the gaps in your knowledge and move those red items over to green first the tutorials and comprehensive ap buyer reviews on learn-biology.com second the unit and topic reviews on the science music videos channel and third, the ongoing live reviews that I'll be doing between now and the AP Bio exam. The schedule and all other links can be found below. Let's do this.
AP Bio Unit 1, Chemistry of Life. Topic 1.1, water and hydrogen bonding. Water is a polar molecule.
It forms hydrogen bonds, which are weak intermolecular bonds. Because of water's polarity and hydrogen bonding, water acts as the universal solvent and water's key properties include cohesion, adhesion, surface tension, high specific heat. You don't only see hydrogen bonds between water molecules. Hydrogen bonding is everywhere in biology.
You see it in DNA, you see it in RNA, forming RNA specific shapes, you see it in proteins, you see it in so many intermolecular interactions. Topics 1.2 to 1.3, elements of life, et cetera. The molecules of life are built from monomers that combine into polymers.
You combine monomers into polymers through dehydration synthesis. You take polymers apart through hydrolysis. Carbohydrates are used for energy storage and they create key structures. That includes monosaccharides, which are used for energy storage, disaccharides for energy transport, and polysaccharides, which can store energy like starch.
or make structures like cellulose, which makes up cell walls. Lipids are nonpolar. Their key unit is the fatty acid. They can be saturated or unsaturated. Saturated fatty acids are more solid.
Unsaturated fatty acids, which have bends and kinks, are more liquid. Their functions include energy storage in the fats and oils, waterproofing in waxes, membrane formation in phospholipids, and signaling in steroids. Phospholipids have a dual nature.
They have a hydrophobic nonpolar tail, that's seen at number three. They have a hydrophilic polar head at one. When mixed with water, the heads bond with water while the tails form a water-free zone.
This creates a phospholipid bilayer, which is the basis of membranes. We'll talk about this much more in unit two. Proteins have diverse functions that includes motion, as in muscle tissue.
enzymes. Proteins also build structures. They're used for transport. They're used for energy storage and for signaling.
Proteins are composed of amino acids. That's their monomer. They have an amino group, a carboxyl group, and most importantly, they have an R group, a side chain that can vary in chemistry. You put those amino acids together through four levels of structure, and that includes primary structure, the linked...
genetically determined sequence of amino acids, the alpha helices and the beta pleated sheets that form between interactions between amino acids in the polypeptide backbone. Then you have the complex turns and loops that form as R groups interact with one another through a variety of bonds that might include hydrogen bonds and covalent bonds, as well as hydrophobic interactions and ionic bonds. And then you have the aggregation of multiple polypeptide. chains forming quaternary structure. Nucleic acids are the molecules of heredity, especially DNA, which plays that role in cells.
RNA can be the hereditary material in some viruses, but it's more important as an information transfer molecule, as in messenger RNA. And RNA can catalyze reactions, sort of like enzymes. And you see that in ribosomes, spliceosomes, and microRNAs. and the ability of RNA to do that will come back later when we talk about the origin of life in unit seven. Nucleic acid monomers are nucleotides, and that consists of a five carbon sugar, a nitrogenous base, and a phosphate group.
The nucleotides that make up DNA and RNA are subtly different. There's a different sugar, deoxyribose, versus ribose in RNA. And the bases are different, ATCG in DNA, AUCG in RNA. In terms of DNA structure, know that DNA is famously double-stranded.
That's why it's the double helix. It has two sugar phosphate backbones, sugar phosphate, sugar phosphate. The base pairing rules for DNA are adenine bonds with thymine and cytosine.
bonds with guanine, and it has an anti-parallel structure. Anti-parallel is like this. Note that in one strand, this is the five prime end, this is the three prime end.
In the other strand, this is five prime, and this is three prime. Unit two, cell structure and function. Know the difference between prokaryotic and eukaryotic cells in terms of size, structure, and the way they package their DNA.
AP biology is a cell biology class. while you might not be asked specific questions on the AP exam about specific organelles, you will need to know the overall geography of cells. Know the parts on this slide that relates to animal cells. Many of those parts are also found on plant cells, and I've highlighted the parts that are different in plant cells in bold on this diagram.
Topic 2.3 is cell size, and the key idea is that cells are small to maximize their surface area to volume ratio. As objects get bigger, the amount of surface area they have relative to their volume goes down. That's why cells need to be small, so they can have lots of surface area to allow for lots of diffusion. There are many, many adaptations that relate to surface area.
Structures like gills or the big, flat ears of elephants or the inner folding of the mitochondrial membrane or the lining of the intestine, that's all about increasing the surface area to allow for... for increased amounts of diffusion, either of molecules or in the case of elephant ears, of heat. Things can also evolve so that there's less surface area. That's why whales have evolved to be so big because with less surface area in their huge bodies, they lose less heat, which is an important consideration for a mammal.
Topics 2.4 to 2.9, membrane structure and function. We'll start with membrane function. It's all about selective permeability.
controlling what can enter and leave the cell. Phospholipids form the framework, but because we already talked about that in Unit 1, you can go back and look at that. The overall structure is a fluid mosaic model.
And what that means is that there's not only phospholipids, there's also protein and cholesterol, and they're all moving around. The membrane molecules and their functions include the phospholipids, which form the framework of the membrane, cholesterol, which acts as a fluidity buffer. buffer. What that means is that it keeps the membrane stable at high temperatures and fluid at low temperatures and proteins which are involved in transport, cytoskeleton attachment, membrane embedded enzymes, signal transduction and cell-cell recognition. Membrane transport.
A lot of things go through cells just based on diffusion, movement of molecules from higher to lower concentration. It happens spontaneously. The cell doesn't need to exert energy for diffusion to happen, and molecules flow down their concentration gradients. In passive transport, the cell is allowing diffusion. It's passive about what it's letting come in, but there's simple diffusion and facilitated diffusion.
Simple diffusion is for small, nonpolar molecules, oxygen, carbon dioxide, but also for the lipids, which can diffuse directly through the phospholipid bilayer. That includes steroids. steroids, and fats. Polar molecules and ions can't diffuse through the phospholipid bilayer, so they need channels.
The channels are made of protein and they facilitate these molecules passage. That's why it's facilitated diffusion. Again, it's for polar molecules and ions.
Not everything, however, can get into cells by diffusion. Sometimes cells need to take things that are in low concentration and actively pump them in. That's called called active transport.
Active transport requires energy in the form of ATP, which gets broken down to ADP, to power some kind of pump. Instead of flowing down a concentration gradient, in active transport, molecules are being pumped up a concentration gradient. You can also have things move into cells by bulk transport. The two forms are endocytosis, where the membrane buckles in, takes the fluid and materials that are outside.
side and brings it into a vest. inside the cell or exocytosis which is the reverse those vesicles fuse with the membrane dumping their contents outside osmosis is the diffusion of water just like everything else water will flow down a concentration gradient from higher to lower concentration that's what you see happening over here water's in higher concentration here because there's less solute. It's in lower concentration here because there's more solute. Therefore, water will flow through this selectively permeable membrane that allows water to pass, but not the solute, from this side to this side. Another way to say that, is that water will flow from hypotonic to hypertonic.
You'll need to be able to predict the effect of osmosis on plant and animal cells, explaining things like what kind of environment would cause this plant cell's membrane to shrink away from its wall? What's the favorite environment for a plant cell? It happens to be a hypotonic environment because that's where water flows into cells.
And over here in this red blood cell, an animal cell, what conditions would be causing... these red blood cells to be bursting if you can answer that then you understand the effect of osmosis on animal and plant cells that leads us to the topic of water potential it's a more formal way to talk about osmosis and the movement of water it has an equation water potential equals solute potential plus pressure potential and the idea is that adding solute to water decreases its water potential and this device called a youtube no kidding the water Water is flowing from the hypotonic side to the hypertonic side because this has more solute. But another way you can say that is that the addition of solute lowered the water potential. So therefore, water is flowing from higher water potential to lower water potential.
If you add pressure, then you'll note that pressure increases water potential and water will flow away from an area of high pressure. Topics 2.10 through 11, cellular compartmentalization. Cellular compartmentalization. is exactly what it sounds like.
Cells have internal compartments that can have special pH, special chemistry, and that allows for different parts to do different things. That in and of itself explains a lot of cell structure and function, in particular, the endomembrane system, which consists of things like the nuclear membrane, the rough ER, the smooth ER, various vesicles, the Golgi, and lysosomes. Two compartments that are not part of the endomembrane system are mitochondria and chloroplasts. That's because they're endosymbionts. They're the descendants of organisms that were once independent that now live inside our cells, kind of a mind-blowing idea.
Both of these organelles evolved from free-living bacteria. The evidence for that is abundant. Each of them has their own circular DNA.
They replicate through binary fission. Those are both features that are found in bacteria. They have bacteria like ribosomes and they perform protein synthesis.
They have two membranes and the outer membrane is a vestige of the fact that they were at one point taken up by another cell. Do you have questions? Please leave them in the comments. I promise that I'll respond to them and I might even be able to respond to them in one of the live review sessions that I'll be doing as we get ready for the AP Bio exam.
AP Bio Unit 3, Cellular Energetics. Enzymes are protein lower the activation energy of reactions that occur within cells. Enzymes are highly specific.
They bind with their substrates at an active site, and generally every enzyme has a specific substrate. Enzymes are sensitive to changes in their environment. They can be denatured by changes in pH or temperature.
What does denaturing mean? It means that the shape of their active site changes so that they can no longer interact with their substrate. and that causes the activity of the enzyme to plummet. Enzymes can also be inhibited by molecules that are in their environment. In competitive inhibition, a molecule that is not the enzyme substrate competes with the substrate for the active site.
That keeps the enzyme from catalyzing whatever reaction it was gonna catalyze with its substrate. In non-competitive inhibition, there's an allosteric site, a second site that another molecule binds with. It's not competing for the active site.
active site, but because of the way proteins are and because of the chains of amino acids and how those amino acids interact with one another, binding over here can change the active site over here. Similar processes can be used for regulation, and we'll see that there's a kind of regulation that's called allosteric regulation that can be used to modulate the activity of enzymes. Topic 3.4, cell energy. A lot of what you learn about in Unit 3 are Metabolic pathways.
Metabolic pathways are linked series of reactions, all controlled by enzymes, where the product of one reaction becomes the reactant for the next reaction. So here's the product, and it's the reactant for the next. These metabolic pathways can be linear, like glycolysis, or it can be cyclical, like the Krebs cycle or the Calvin cycle.
And in that case, the ending compound is also the starting compound. Reactions can be exergonic or endergonic. Exergonic reactions release energy and therefore can drive cellular work. Endergonic reactions require energy.
Reactions are often coupled through ATP. ATP consists of a five carbon sugar called ribose. It consists of a nitrogenous base and three phosphate groups. ATP without these two phosphates over here is adenine, one of the monomers of RNA.
Here's how it works in terms of energy coupling. Energy in from a process like cellular respiration powers the creation of ATP from ADP and phosphate. That is an endergonic reaction that requires energy.
ATP can be broken down to ADP and phosphate, and as it does, energy is made available for cellular work. So in this case, an exergonic reaction can power endergonic processes. Every time you move your arm, you're hydrolyzing ATP, you're removing this third phosphate, and that's making movement possible. Topic 3.5, photosynthesis. Photosynthesis is a process in which photoautotrophs, self-feeders using light, use light energy to combine carbon dioxide and water to create carbohydrates.
Oxygen is released as a waste product. Photosynthesis is the source of biomass and the basis of almost every food chain on this planet and its formula is 6 co2 plus 6 h2o plus light energy creates glucose and oxygen there are two phases of photosynthesis the first of these are the light reactions and in light reactions light energy shown coming in over here is converted into chemical energy in the form of atp which we just discussed and nadph NADPH is a mobile electron carrier. It can carry electrons, it can carry reducing power, if you want to talk about it chemically, from one area of the cell to another. In the Calvin cycle, the energy in ATP and NADPH is converted into carbohydrate. Here we see this over here.
It's often represented as glucose, but as we'll see in a minute, it's actually a molecule called G3P. What the Calvin cycle does is it fixes carbon dioxide. converting it from a low energy gas into high energy sugars. The light reactions. In the light reactions, light powers an electrical current that powers proton pumps that pump protons into the thylakoid space.
Facilitated diffusion through ATP synthase generates ATP. This is a photo system over here. It's a very complex assemblage of proteins that's packed with chlorophylls. It's capable of taking light energy and making it into this flow of electricity that flows down an electron transport chain. On the way, it passes through these proton pumps that pump protons from the stroma into the thylakoid space.
Stroma, thylakoid space, stroma, thylakoid space. The protons accumulate here and they can only diffuse out through the ATP synthase channel. At the same time, When these chlorophylls lose an electron, another part of this photosystem breaks apart a water molecule.
That's the source of the oxygen released during the light reactions, and it also creates additional protons that enhance this gradient, so more ATP is produced. What about the second product of the light reactions? Electron flow from this photosystem to another electron transport chain flows to NADP+, which gets reduced to NADPH.
That's how we get the two products of the light reaction. In the Calvin cycle, there are three distinct phases that enable carbon dioxide to be converted into G3P, glyceraldehyde 3-phosphate. The first phase is carbon fixation.
Carbon dioxide gets pulled into the cycle and incorporated into originally a six carbon compound, which then gets broken into this three carbon compound over here. That's the carbon fixation phase. Carbon's entering the biosphere, it's entering the system.
Now there's energy investment. The products of the light reactions, ATP and NADPH, are used to energize this compound, and we wind up with G3P. That G3P can be harvested from the cycle and made into sugars or anything else the cell needs.
In the last phase, that G3P, a three-carbon molecule, is combined and changed in various ways so that we wind up with a bunch of RuBP, a five carbon molecule, and more ATP is required to make that happen. That's the Calvin cycle. That's how the carbon in you originally got into the biosphere.
Topic 3.6, cellular respiration. Cellular respiration is how cells take glucose and convert it ultimately into ATP. Note that animals just do cellular respiration, but plants do both cellular respiration.
respiration and photosynthesis. Cellular respiration comes in four stages or phases. Those are glycolysis, the link reaction, the Krebs cycle, and the electron transport chain. You should know the inputs and the outputs for glycolysis, the link reaction, and the Krebs cycle, but you don't need to know all of the stuff that goes on in the inside.
And to step back a little bit, note that all of these reactions are doing... similar things, which is that they're oxidizing food. Here's glucose. It's food. They're oxidizing it.
They're taking away its electrons, and they're creating these mobile electron carriers. In cellular respiration, they're NADH and FADH2. Remember, we had NADPH in photosynthesis.
Glycolysis and the Krebs cycle also make a little bit of ATP. However, most of the ATP in cellular respiration is created through oxidative phosphorylation. phosphorylation and the electron transport chain, which you see happening here, wondrously complex. These electron carriers, what they do is they power an electrical current that flows through an electron transport chain in the inner mitochondrial membrane.
Along the way, that electron energy is used to pump protons from the matrix to the intermembrane space. In the same way as there was proton accumulation during photosynthesis, that happens during cellular respiration. respiration. The sequestered compartment is the intermembrane space.
These protons can only diffuse out through the ATP synthase channel. As they do, their kinetic energy is used to combine ADP and phosphate into ATP. That's how cellular respiration makes ATP. Why do we need oxygen?
Because oxygen is the final electron acceptor in the electron transport chain, essentially pulling electrons down the entire. length of the chain respiration can also happen without oxygen that's anaerobic respiration and it creates much less ATP no oxygen required it generates only two ATP's both from glycolysis and it's combined with fermentation and fermentation is a process that regenerates an ad-plus so here's glycolysis pyruvic acid or pyruvate is the three carbon output of glycolysis and in fermentation reactions that pyruvate is basically changed into ethanol. What happens?
The pyruvate is reduced so that NADH can be oxidized back to NAD+. Why? Because NAD+, is one of the substrates of glycolysis, and glycolysis can't produce its two ATPs unless NAD+, is around.
That's true of lactic acid fermentation, which happens in our muscle cells when we're doing anaerobic respiration. It also happens in yogurt as they create the lactic acid that makes yogurt sour. Here's a quick review tip as you try and fill those gaps that you're discovering through this process.
Note that there are many links on the Ultimate Review page. Use those links to go to learn-biology.com. That's where you'll see tutorials.
And each unit review, which is shown up here, has flashcards, multiple choice quizzes, and practice FRQs, and click on challenges. It's the most efficient way for you to fill those gaps, and I'll tell you more about that a little bit later. APBio Unit 4, cell communication, feedback, and the cell cycle.
Cells constantly communicate with one another. They can do that directly by touching one another, or they can do that through signals. In APBiology, we're mostly focused on this through signals.
The signals are ligands or ligands. Ligands are complementary to specific receptors. Here the circle binds with this receptor over here because their shape is complementary and the binding leads to a cellular response. There are three phases of cell communication when it happens through ligands. The first is reception of the ligand.
The second is signal transduction. That's taking the initial signal making it into another kind of signal and that's often accompanied by amplification of the signal and finally there's a cellular response of which there can be two kinds the first is gene activation the second is enzyme activation i encourage you to learn about g protein coupled receptors there's a tutorial on learn-biology.com it's available in your textbook if you're using it because it's important in its own right it has shown up on the ap bio exam and it's an example of the monstrously complex kind of visual representation that the College Board will throw at you on the test steroid hormones work somewhat differently than the polar hormones that I've demonstrated in the previous slides the reason is that because they're steroids they can diffuse right through the phospholipid bilayer once they're in there they bind with cytoplasmic receptors they can then as a receptor hormone complex diffuse into the nucleus and activate genes topic 4.5 homeostasis and feedback homeostasis Stasis is maintaining internal conditions at a relatively constant optimal level. You experience this all the time. Your body temperature is 37 degrees Celsius, despite the fact that you might be in a cold place or a warm place or change from one to another. Feedback is when the output of a system is also an input to the system.
Feedback can be negative, and that's when the output quiets the system, kind of steps on the brakes. And positive feedback accelerates internal changes and drives the process forward. A feed. The feedback system that you should know about involves glucose homeostasis, which involves insulin and glucagon, two hormones.
Insulin lowers blood sugar back to the set point. Glucagon raises it when your blood sugar gets low. And when these systems break down, it results in the disease diabetes. Type 1 diabetes is because there's a breakdown in insulin production.
Type 2 diabetes is when there's a problem with cells responding to the insulin signal. There are also positive feedback loops. One to know about involves oxytocin and childbirth, and it works like this.
As the baby grows, it activates stretch receptors in the uterus. That causes the release of the hormone oxytocin, which then feeds back to the uterus, increasing contractions, activating the stretch receptors. That process culminates in childbirth.
A similar positive feedback loop works with fruit ripening and the gaseous hormone ethylene. Topical Topic 4.6 to 4.7, the cell cycle. This includes the phases of mitosis, which you can remember by the mnemonic, I put my apple there, Charlie, for interphase, prophase, metaphase, anaphase, telophase, cytokinesis. Remember that most of mitosis, everything after interphase, is all just a sliver of the process.
Most of the cell cycle is interphase, which can be divided into growth one, general growth, synthesis of DNA, and then growth two. which is preparation for the M phase. Cells can also enter into this G0 phase when they become highly specialized, essentially leaving the cell cycle.
The process is regulated by various checkpoints where the cell checks for various conditions along the way. If those conditions are met, the cell proceeds through the cell cycle. If they're not, these checkpoints enable the cell to pause. The cell cycle is regulated both externally and internally, externally by signals coming from outside the cell. cell.
There's also internal regulation and that regulation happens through cyclin and then cyclin dependent kinases. Cancer is caused by unregulated cell division. You can see here that cancer starts with mutations.
The cells grow in one location forming a tumor when they spread to other sites that's called metastasis. Mutations in genes called proto-oncogenes increase the rate of cell division and mutations in tumor suppressor genes remove cell division in here. they undermine the checkpoints that we just talked about. You can think about that with a gas pedal and a brakes analogy.
AP Bio Unit 5, Heredity. Diploid germ cells, germ cells that would be in the ovaries and the testes, create haploid sperm and egg cells with one chromosome set. Meiosis begins with germ cells, again in the testes or the ovaries, that start by replicating their DNA just like at the start of mitosis that creates cells that are diploid with doubled chromosomes. In meiosis one, homologous pairs, these pairs that are inherited from the mother and the father, the matched chromosomes wind up being separated and in meiosis two the sister chromatids are pulled apart.
Meiosis, just to put that in context, involves the same phase phases as mitosis, but they're double. In prophase 1, here's where you see the homologous pairs pairing up, and two important things happen. One is that as they pair up, they wind up exchanging pieces of DNA.
That's a process that's called crossing over. The other thing that happens is that as these homologous pairs are pulled to the cell equator, what every chromosome pair does is independent of every other pair, and that creates tremendous variation in the gametes of the homologous pairs. The rest of meiosis, we see the homologous pairs being separated in meiosis one, and here we see the sister chromatids being separated for haploid gametes result. Meiosis and sexual reproduction generate diversity in three ways. The first is independent assortment.
It's how these maternal and paternal homologous chromosomes can be sent to the next generation independently of one another, leading to many combinations of chromosomes. The second is crossing over and genetic recombination. Finally, during fertilization, a gamete from the father winds up fertilizing the gamete from the mother.
That combines the genomes of two individuals, creating even more variation. That's distinct from mitosis, in which the daughter cells are clones of the parent cell. Once we understand meiosis, we can look at sex determination in mammals and birds. In mammals, there's an XXXY sex determination system. In birds, there's a ZWZZ sex determination system.
system. Not all animals have chromosome determination of sex. For example, in various kinds of reptiles, the temperature at which an embryo develops determines whether that embryo will be male or female. And in bees and wasps and several other insects, the males are haploid, every cell in their body is haploid, and the females are diploid.
Once we understand meiosis, we can also look at what happens when the process does not proceed correctly. One major disorder is called nondisjunction, and that's when either homologous pairs don't separate correctly or sister chromatids don't separate. After fertilization, that can have a variety of consequences, one of which is a trisomy, where one of the chromosomes instead of a homologous pair will have three chromosomes. That's the cause of Down syndrome.
Or there could be a monosomy, where instead of a homologous pair, there's one chromosome. I believe that's only survivable. in the sex chromosomes, the XX chromosome in mammals, and that causes a condition called Turner syndrome. Topics 5.3 to 5.5, genetics. What is a gene?
It's the basic unit of heredity passed from parent to offspring. It determines a trait. Seen from the viewpoint of molecular genetics, our next topic, it's a sequence of nucleotides that codes for RNA or protein. Genetics, key concepts. You should know Mendel's principle of segregation of alleles.
The... the difference between homozygous and heterozygous, dominant and recessive, genotype and phenotype. Monohybrid crosses you should easily be able to handle. That's a cross between two heterozygotes and you can expect a three to one ratio in terms of the phenotype and a one to two to one ratio in terms of the genotype.
Sex-linked genes involve genes that are on the X chromosome so they're not passed on by the father, they're passed on by the mother. the mother who has the allele on one of her or both of her X chromosomes. Males can't be heterozygous.
They either have the allele or they don't. Everything we've talked about so far has involved one gene going from parents to offspring. What if there are two gene pairs as with this parental genotype over here?
In that case, independent assortment is the rule that needs to be applied. What every gene pair does is independent of every other gene pair. there.
That leads to dihybrid crosses, which result in a 9 to 3 to 3 to 1 phenotypic ratio in the offspring. If you have more than two genes, then you don't do a Punnett square. You use things like the rule of multiplication.
All of the genes that we've looked at so far have involved genes that are on different chromosomes, but genes can be linked on the same chromosome. In fact, that's the rule, not the exception, because we have 20,000 genes that are distributed among 20,000. 23 chromosome pairs. So here are linked genes in a Drosophila.
What do you need to know? Linked genes are mostly inherited together. They're on the same chromosome.
As they get sent to the next generation, they'll travel together. However, they can be separated because of crossing over. To make this a little clearer, look at this example. Linked genes that are close together usually get inherited together.
So B and C, very close together. Unlikely that they'll be separated by crossing over. But genes that are further apart, like A and E most likely will be separated by crossing over.
As a result of this, you can look at the amount of recombination that happens in various crossing experiments and you can use those recombination frequencies to generate chromosome maps. like this one, which show the distance in terms of recombination between two alleles that are on the same chromosome. Here are some additional genetic topics. There's non-nuclear inheritance, which are genes that are on mitochondria, not on.
one of the chromosomes in the nucleus. There's incomplete dominance where there's a blending effect between the two alleles. And there's genotype environment interaction where it's the environment that determines the phenotype much more than the genes. You should know how to do chi-square to analyze the results of genetic crosses. I totally recommend that you set up tables like this one, and you can see a tutorial about that on learn-biology.com.
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The AP Bio exam is coming up, so go to learn-biology.com slash student sign up to find out how learn-biology.com can help you crush the AP Bio test and master AP Biology. AP Bio Unit 6, Gene Expression. We handled most of the first topic in this unit, DNA and RNA Structure, back in Unit 1. Now we're in Topic 6.2, DNA Replication. The main thing to note is that DNA replication is semi-conservative.
The original strand separates and each strand serves as a template for synthesis of a new strand. The result is that the daughter strands are half new and half old, hence semi-conserved. DNA replication is counterproductive.
carried out by a team of enzymes. The ones that you should know include helicase, DNA polymerase, primase, ligase, and others. Because DNA polymerase, the main enzyme involved in DNA replication, can only synthesize in the five prime to three prime direction, replication occurs differently on the two strands. It's continuous on what's called the leading strand, and it's fragmentary on the lagging strand, composed of short segments that are called Okazaki fragments that are later sealed.
together topic 6.3 is transcription which is the making of rna from a dna template you should be able to take any sequence of rna and translate it into amino acids using a genetic code dictionary and you should be able to explain the details of protein synthesis itself these are all fantastic processes topic 6.5 to 6.6 gene regulation operons are important gene regular systems in prokaryotes. Eukaryotes don't use operons. A key principle in multicellular eukaryotes like you and me is that all cells in the same organism are genomically equivalent. This neuron, this epithelial cell, they're quite different phenotypically, but they have the same genes.
They're different because they express different genes. Acetylation and methylation are two of the many mechanisms that eukaryotes use to control. control gene expression. Acetylation turns genes on. Methylation turns genes off.
That leads to the entire field of epigenetics, changes in DNA expression that involve reversible chemical modifications in DNA or changes in DNA packaging, but not changes in the DNA sequence. A key difference between eukaryotes and prokaryotes is that eukaryotic genes are interspersed with introns, which makes phenotypic variation possible. because of alternative splicing of exons. Exons are expressed sequences. They wind up being translated into proteins.
Introns are intervening sequences that get edited out. Topic 6.7, mutation. We'll start with point mutations, which are changes where one nucleotide changes to another. They can have a variety of effects, ranging from nothing, because there's redundancy in the genetic code, to nonsense, where a stop codon gets inserted, to. missense where we change the amino acid.
Frame shift mutations are another kind of point mutation, but instead of a substitution, frame shift mutations change the reading frame, so they have more extensive effects. Imagine you have a sentence and you just delete one of the letters, you make the rest of the sentence nonsense. That's what frame shift mutations do.
Mutations can be positive, which makes them adaptive. They can be negative or harmful, or they can be neutral, having no effect. whatsoever. It completely depends on the context and mutations are the source of the variation that makes evolution possible. Horizontal gene transfer also changes genomes but by a different mechanism than mutation.
It's where one individual transmits genes to another organism of the same generation. It's as if you touch someone and we're able to transfer genes to them. Kind of weird.
It includes conjugation in bacteria, transformation, transduction, which involves viruses. and viral recombination. Unit six ends with topic 6.8, genetic engineering and biotechnology. Here are some of the techniques that you should be familiar with. Those are PCR used for amplifying DNA, restriction enzymes and gel electrophoresis for analyzing DNA.
recombinant DNA and engineering plasmids, which enables us to do amazing things like put human genes into bacteria so they can produce gene products like insulin. And finally, DNA sequencing, which is giving us huge amounts of information that's being used in medical research, evolutionary biology, every biological field. Unit seven, evolution. Gotta say, the college board's name for this is natural selection, and that's a bad name because much of evolutionary change is new. not about natural selection, write the College Board, demand a change.
This unit begins with the material that was figured out by Charles Darwin way over 100 years ago. That includes natural selection, which brings about adaptations through survival of the fittest, artificial selection in which humans select favorite traits in our domesticated animals and plants, and sexual selection, which is selection for reproductive advantage. The effects of selection can include directional selection, where the populations meet. is pushed in one direction, stabilizing selection against the extremes, and disruptive selection, which is against the mean. Topics 7.4 to 7.5, population genetics.
This is the study of how allele frequencies change in gene pools. That's the lens in which population genetics looks at evolution. I want to start by eliminating the biggest misconception that students have in AP biology courses, and that is the wrong idea. that the dominant allele has to be more common than the recessive allele.
Somehow people confuse dominance with frequency, but that is not true. The frequency of an allele is based on the advantage or harm it confers to its associated phenotype or random historical factors. Dominant alleles are not necessarily common and they don't grow in frequency over time. An example for that is the allele that causes achondroplasia is a dominant allele.
and it's exceedingly rare. Population genetics is one of the most mathematical parts of the course. It's based in two equations developed by Hardy and Weinberg. The first is p plus q equals one, and the second is p squared plus 2pq plus q squared equals one, and there's an associated Hardy-Weinberg principle.
In this system, p represents the frequency of the dominant allele, q represents the frequency of the recessive allele. You can set this all up at a cross cross multiplication table that looks like this. And when you do population genetics analysis, the thing to do is to figure out the frequency of recessives in the population.
Once you do that, if for example, it's 0.49, then you know that if this is Q squared, then Q is the square root of that. So this is 0.49, this is 0.7, that enables you to figure out the frequency of the dominant allele and everything else. According to the Hardy-Weinberg principle, the frequency of The frequency of alleles and gene pools will stay constant unless one or more of the following conditions is not met.
This is a fictional, non-evolving population. Its characteristics are that it's infinitely large, it has no harmful or beneficial alleles, there's random mating, there's no emigration or immigration, there's no net mutation of one allele to another. This enables us to identify the factors that cause evolution.
These are are genetic drift, random change in small populations that's caused by things like population bottlenecks or the founder effect, natural selection. Some alleles are harmful. Some alleles are beneficial. Sexual selection.
Some phenotypes are more attractive than others. Gene flow, where genes move from one population to another, or directional mutation, where one allele mutates into another. These are all the factors that cause evolution.
There's a a mountain of evidence that establishes that evolution is true. This is why it's a theory, not merely a hypothesis. That evidence includes fossils.
homologous features which are derived from a common ancestor, vestigial features which no longer have a function, molecular homologies, similarities in amino acid sequences, DNA sequences or evolution that we continue to observe such as resistance to pesticides and mosquitoes antibiotics in bacteria and so on these are all evidence that descent with modification has occurred and is occurring phylogeny is evolutionary history but as an ap bio student you mostly have to grapple with it in terms of these wonderful branching diagrams that show evolution in process the key concepts include the concept of a clade of a group of organisms that is derived from a common ancestor. Other concepts include nodes, shared derived features, very important, ancestral features, outgroups, and molecular clocks. Topic 7.10 to 7.12, Speciation, Variation, and Extinction. We begin with the biological species concept, the idea that a species is a group of organisms that can naturally interbreed to produce fertile offspring. A mallard and a pintail are both ducks, but they're different species because they don't interbreed.
Why not? Because of reproductive isolating mechanisms. Those can be prezygotic barriers that keep a zygote from forming. For example, the markings on this male mallard might make him unattractive to the female pintail, which would make her uninterested in mating with him.
That's a behavioral barrier. There are also post-zygotic barriers where if some confusion arose and these two did mate, then the zygote might not be able to develop or if it did develop it wouldn't be fertile. There are two kinds of speciation to know about. There's allopatric speciation which involves a kind of geographic barrier here that's represented as a kind of mountain but it could just as easily be a river or a canyon where there's differentiation on each side of the barrier and ultimately the two subpopulations become so different they can no longer interbreed. Sympatric speciation happens without a barrier.
There's a variety of mechanisms that can lead to it. One to know about is chromosomal changes that happen particularly in plants where there's a doubling of chromosomes caused by an error in meiosis and that leads to single generation speciation. Mass extinctions are events usually caused by geological or even astronomical factors that cause a mass die-off of huge numbers of species all at one time. Five have been identified within Earth history. This one over here, 65 million years ago or so, is the one that killed off the dinosaurs caused by an impact of an asteroid.
A key thing to know is that these mass extinctions cause vast decreases in biodiversity. Look at all this diversity here in this phylogenetic tree. And then it's cut down to just two clades that make it through.
But then there's subsequent adaptive radiation and reestablishment of biodiversity. Top. Topic 7.13 is the origin of life. The key question is how did life naturally emerge in the absence of life?
After the earth became habitable, geological processes, chemical processes led to the abiotic synthesis of monomers, things like amino acids and monosaccharides and nucleotides. There must have been some process that led those monomers to then be formed into polymers. RNA, nucleic acids, proteins, so on and so forth.
That has to happen in the absence of life, and that's complicated because that process happens through enzymes. Now, how does it happen without enzymes? Some kind of geological process at a hydrothermal event, something like that.
Eventually, these polymers become encapsulated within a membrane that forms a kind of protocell, and eventually that protocell becomes something that can reproduce itself, and we have the last. universal ancestor of all life, last universal common ancestor, Leuka, and that gives rise to the three domains of life. The Miller-Urey experiment performed in the 1950s is the prototype for successful abiotic synthesis of amino acids in a simulated early Earth environment. This apparatus resulted in the production of amino acids.
This has become the model for many subsequent experiments that have produced other monomers, more complex substances, but these experiments are still a long way from generating life in a test tube a key concept to know about related to the origin of life is the rna world and luka and the idea is that rna was probably the first genetic molecule why because unlike dna which is purely informational rna is also catalytic. It can also act as an enzyme and catalyze reactions. So the scenario is something like this.
There are the inorganic precursors, carbon dioxide, methane, other molecules that combine to form RNA monomers. Those become combined to form RNA polymers, which wind up folding into complex shapes that have catalytic ability. Eventually, you have self-replication of RNAs, and those RNAs that are self-replicating become encapsulated.
in protocells. Eventually, we have the last universal common ancestor. And if you can go through this diagram and identify all the numbers, then you're doing pretty well on your march to AP bio success.
AP bio unit eight ecology. Topic 8.1 responses to the environment. Unlike every other topic in the AP bio curriculum, this one is very hard to give you guidance about because the college board's description of this topic. is extremely vague.
I've taught this topic through case studies, really fascinating stuff that involves great data sets. These are available on learn-biology.com. You can learn about explaining monogamy and promiscuity in voles, how ants are able to find their way back to their nest after foraging by counting their steps, how turtles can migrate back to the nest where they were born through detection of magnetic fields, why animals form schools and flocks.
and how honeybees communicate. My main advice to you is that learn how to be analytical, carefully read the question and do your best. Topic 8.2 is about energy flow in individual organisms and entire ecosystems. The topics covered include metabolic rate and size and the relationship between the two, why animals like shrews have such a higher metabolic rate than large animals like elephants. The flow of energy through food webs including the concept of a trophic or a feeding level the idea of the pyramid of energy and how only 10% of the energy gets passed from trophic level to trophic level for example from producers to primary consumers and then other ecological pyramids not limited to but including the pyramid of numbers topics 8.3 and 8.4 are about population growth that includes the exponential growth model and and the logistic model, which includes the idea of carrying capacity.
Some key concepts are biotic potential, how fast a population is capable of growing, and limiting factors, things that keep a population at or below its carrying capacity, and those can be density dependent or density independent. Topic 8.5 is species interactions. You should know all of the interactions that are in this chart.
You should know their definition. And you should know And you should know what the effect is on the two interacting species, whether it's positive, negative, or neutral. That's usually represented with a minus sign, a zero, or a plus sign. Many of these interactions lead to important evolutionary consequences. For example, competition leads to character displacement and niche partitioning.
A niche is the way an organism makes a living. So like, for example, if you look at shorebirds, different kinds of shorebirds evolve different beaks to exploit different. parts of the sandy beach environment.
On the other hand, interactions such as predation, herbivory, parasitism, and parasitoidism result in evolutionary arms races that lead to wondrous and amazing adaptations on the parts of each of the interacting species. Community structure is also strongly influenced by certain species that act as keystone species. These are often predators that control herbivores and by doing so they increase the overall biodiversity of the ecosystem.
Ecology also includes understanding and measuring biodiversity. Biodiversity includes both species richness, the number of species and species evenness, how evenly species are spread out. You have to be able to use the Simpson's diversity index.
The formula will be given to you in the AP bioformula sheet. Finally, human impacts on diversity. They have not been good.
Humans have been decreasing biodiversity through destruction of habitat, through habitat fragmentation. When one big habitat gets cut up into smaller pieces, it simply can't support the same spread of species, many of which, particularly large predators, need huge amounts of area in order to have the available niche that they need. Introduction of invasive species has been a huge problem that's been intentional and unintentional. We've participated in destructive exploitation of reef.
resources by logging too much over fishing and clear cutting forest. This is creating an extinction vortex where populations are getting smaller. That leads to genetic drift and inbreeding. These species lose genetic diversity.
They become less fit. There's less reproduction, more mortality, and that leads to a smaller population. A key idea of this course is that variation is good and many human activities wind up reducing the risk of death. reducing variation.
That is a dour note upon which to end the course, but I want you to feel hopeful and I want you to feel optimistic because now that you've gone through this video, you can fill the gaps and crush the AP bio exam. Your first step, go to learn-biology.com slash AP biology, sign up for an account so you can get the feedback and interaction that you need to really master the concepts that we've discussed in this video. I'll be doing live reviews on the science.
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