This is chapter 4, part A, Functional Anatomy of Prokaryotic and Eukaryotic Cells. So there are two main types of cells in biology. Prokaryotes, coming from the Greek words for pre-nucleus, so meaning prokaryotes do not have a nucleus. Eukaryotes, coming from the Greek words for true nucleus, so eukaryotes do have a nucleus.
The nucleus is just where the DNA is going to be stored and protected inside the cell. Some other similarities and differences that we'll look at include the cell membrane, DNA, ribosomes, and the organelles. When you're comparing and contrasting your prokaryotes and eukaryotes, prokaryotes are things like bacteria.
Eukaryotes are... pretty much everything else. So plants, animals, protists, fungi. Prokaryotes have one circular chromosome. And again, it's not in a nucleus.
Prokaryotes do not have a nucleus. Prokaryotes also do not have histones. So histones are what help package the DNA inside the nucleus into chromosomes.
So because they don't have a nucleus, And they don't undergo cell division the way that eukaryotic cells do. They don't have histones. They don't really need them.
They have no organelles. So organelles are like the little organs of the cell. So prokaryotes and bacteria are very simple cells.
So they don't have any of these more complex structures and organelles. There are two main types of prokaryotes. So bacteria and archaea.
Bacteria. are characterized by cell walls made out of peptidoglycan. Archaea cell walls are made out of pseudomurine.
All prokaryotes divide and multiply by binary fission, so meaning they essentially split in half and multiply that way. Eukaryotes contain paired chromosomes protected in that nucleus and nuclear membrane. Why do we have pairs of chromosomes?
because you get one set from mom and one set from dad. So because our DNA is arranged in these more organized chromosome structures, we do have those histones to help package that DNA molecule. Eukaryotes do also have organelles or mini organs.
So we'll look at the function of each of the major organelles or organs of the cell. Eukaryotes don't always have a cell wall, so animal cells, we don't have cell walls, but some do, like plants, but their cell walls are made out of polysaccharides, like cellulose or chitin. And eukaryotes divide and multiply by mitosis. So within eukaryote cells, there are two main types.
So we have plant cells and animal cells. So there are a lot of shared structures and organelles that both types will have, and then there are a few specialized features for each one. So like chloroplasts are only found in plant cells.
Plant cells also contain a cellulose cell wall, where animal cells have no cell wall. Some animal cells may have a flagella, so like a sperm cell. Those were only in animal cells, so plants do not have flagella.
Both plant and animal cells will have structures like a nucleus, endoplasmic reticulum, mitochondria, and plasma membranes. So some external structures of eukaryotic cells include flagella and cilia. So these are projections coming off of the external surface of a cell used for either locomotion, so moving the cell through a substance or a fluid, or moving substances along the cell surface. So flagella are the long, whip-like, tail-like extensions. So think again like a sperm cell has a flagella on its little tail.
Cilia are more numerous, short projections. So kind of like little short hairs. Flagella are more for helping a cell swim through a fluid. The cilia are more for helping fluid move around the cell. So an example in humans, our respiratory tract is lined with cilia.
So it's going to help to sweep and propel mucus up and out of the respiratory tract. So structurally, flagella and cilia are very similar. They're both composed of microtubules that are made of a protein called tubulin.
So they're little tiny tubes within tubes that act kind of like little motors. Microtubules are arranged in organized pairs. So we have nine outer pairs and then a single pair in the center. So sometimes referred to as a nine plus two array. But again, working like a small engine, it allows the flagella to move in a wave-like manner.
The cell wall is found in plants, algae, and fungal cells. So when we said the bacteria, prokaryotes can have a cell wall made out of peptidoglycan or pseudomurine. But in eukaryotes, any cell walls would be made out of some type of carbohydrate or polysaccharide.
So in plants, their cell walls are made out of cellulose. Fungi use chitin. So this is showing the structure of a plant cell wall. So we have all of these polysaccharide rods or cellulose microfibrils. kind of just arranged and stacked and staggered to make this layer, this protective cell wall layer outside the plasma membrane.
Glycocalyx found in some eukaryotic cells is composed of carbohydrates that are bonded to proteins or lipids within that plasma membrane. So glyco meaning sugar, calyx meaning case or coat. So it's just the sugar case or sugar coat.
on the outside of a cell. So we have different proteins and lipids kind of sticking out and projecting off the surface of the cell membrane. And some of these have just these sugars or these glycoproteins or glycolipids attached to them. So under the microscope, this glycocalyx is shown kind of as this fuzzy outer layer of the cell membrane. The cell membrane is similar in structure between prokaryotes and eukaryotes.
It's composed of that phospholipid bilayer. So we have a double layer of phospholipids. Remember, we have the hydrophilic heads and the hydrophobic tails.
So the tails turn in toward one another. So they're insulated and protected against the fluids surrounding the membrane inside and outside the cell. Cell membrane is also composed of proteins.
So you can have integral proteins that kind of span the entire length or thickness of the membrane. Or you can have some peripheral proteins that are just kind of on the sides or the edges of the membrane. Where eukaryote cell membranes differ from prokaryotes is that they have some cholesterols within the membrane to help stabilize it. They also contain some carbohydrates for attachment and cell-to-cell recognition. So again, some of these little projections coming off the cell membrane can act as ID markers.
or flags for other cells to recognize. The cell membrane has similar functions in both eukaryote and prokaryote cell membranes. It's going to serve as that selective barrier, so it only lets certain things in and out of the cell.
Both prokaryotes and eukaryotes are able to undergo different types of diffusion and active transport. Where they differ in function is that eukaryotes are able to undergo endocytosis. The two types of endocytosis are phagocytosis and penocytosis.
So phagocytosis just means cell eating. With phagocytosis, pseudopods or extensions of the cell membrane will kind of reach out and wrap around and engulf a particle or another cell. So this is an actual picture of immune cell, a macrophage in your immune system that's chasing a bacterial cell. So it kind of reaches out and then swallows it whole.
Penocytosis is still bringing substances or particles inside of the cell, but instead of reaching out to grab those particles, we're going to suck in some of the fluid from outside the cell. So this is sometimes called cell drinking. So we had cell eating and cell drinking. So with penocytosis we're kind of sucking up some of that fluid and anything that may be in that fluid as well.
So all cells contain cytoplasm. So this is just the kind of viscous gooey substance inside the plasma membrane in the cell. The cytosol is the actual water or fluid portion of the cytoplasm. So the cytoplasm includes the cytosol and then any organelles or dissolved substances or particles kind of floating or embedded.
within that fluid. The cytoskeleton is also found within the cytoplasm. So we have various microfilaments span throughout the cell giving it its overall shape and some structural support.
Cytoplasmic streaming is movement of this cytoplasm fluid throughout a cell. So maybe we want to move some substances in the fluid over to this side of the cell. All cells also contain ribosomes.
So all cells require proteins, and ribosomes make proteins. So we'll talk about this later in the semester. But essentially, the ribosome reads a copy of the DNA sequence, so the instructions in the DNA, and it translates that into an amino acid chain that makes a particular protein. So one difference between prokaryotes and eukaryotes is eukaryote ribosomes are slightly larger. So they consist of a 60S and smaller 40S.
So they're considered to have an 80S. So just a larger size ribosome than prokaryotes. So prokaryotes have the 70S. So theirs are a little bit smaller.
Ribosomes in eukaryotes may be either membrane bound. So they're attached to the membrane of another organelle called the endoplasmic reticulum. Or they could just be freely floating in the cytoplasm.
These smaller prokaryotic ribosomes are also found in chloroplasts of plant cells and mitochondria in plant and animal cells. So some organelles have their own ribosomes, so they make their own proteins. The nucleus is that hallmark feature of a eukaryotic cell. So that's what's going to distinguish between your prokaryotes and your eukaryotes. So the nucleus is a double membrane structure called the nuclear envelope.
It's going to contain all of the cell's genetic information in the DNA. The DNA will be combined with histone proteins to form chromatin. So we said prokaryotes don't have histone proteins because their DNA doesn't need to be as organized into chromosomes or packaged into a nucleus like eukaryotes.
So during cell division, mitosis and meiosis, this chromatin will condense down into... those stereotypical little X-shaped chromosomes that we're used to seeing under the microscope. So when a cell is not dividing, it's just doing its everyday cell thing, the DNA is more kind of loosely arranged in the nucleus, kind of like loose pasta or spaghetti noodles.
So when the cell gets ready to divide, we have to package our DNA. So When the cell divides, we're splitting up the DNA. We don't want to leave any genes or pieces of DNA behind.
So everything has to be packaged nice and neat and tight so all the genetic information makes it to the next generation of cells. So DNA double helix will coil and wrap around those histone proteins and form these nucleosomes, so these little bundles or balls of DNA and protein. So as that starts to coil and twist into a coil structure, those coils start to coil on themselves and form the supercoils.
And then we get eventually this nice, neat, compact X-shaped chromosome that would be visible under the microscope. Endoplasmic reticulum is a folded transport network. So it is a membrane-bound organelle. part of that endomembrane system of the eukaryotic cell.
So there's two types of endoplasmic reticulum. The rough ER is called rough because it's studded with ribosomes. Remember we said ribosomes are where proteins are made, so this is kind of a major protein factory of the cell. The smooth ER is smooth because it does not have ribosomes.
So the smooth ER is more concerned with synthesizing lipids for the cell membranes, other fats, or hormones. Remember we said ribosomes can be either membrane bound to the rough endoplasmic reticulum, or they can be freely floating in the cytoplasm. The Golgi complex, sometimes called the Golgi apparatus, is a transport organelle.
So it's kind of like the post office of the cell. So all of these proteins... that are freshly synthesized from the rough endoplasmic reticulum with those ribosomes will be packaged from the rough ER and delivered to the Golgi.
The Golgi will then modify and package and sort all of these proteins into new secretory vesicles and ship them off to their final destination. Lysosomes are organelles or vesicles that are formed off of that Golgi complex. So they're basically little sacks of digestive enzymes, so things like lysozyme. So you can think of them kind of like the stomachs of the cell. Vacuoles are storage organelles, so small cavities, storage containers of the cell.
So they can help bring food and other nutrients into the cell, as well as provide overall shape and storage for the cell. So like in plant cells, they have a very large central vacuole that keeps the plants from becoming wilted. So when plants start to wilt, they need water.
It's because of that large central vacuole has become dehydrated and shrunk the overall size of the cell. Mitochondria are double-membraned organelles. that are the sites of ATP synthesis.
So all of the major energy in the cell is produced by the mitochondria. So they're going to use cellular respiration, which we'll talk about later in the semester involving the breakdown of sugar or glucose into this chemical energy ATP. So inside the mitochondria are multiple folds, so it has lots of surface area for that cellular respiration. So these inner folds are called Christie and the fluid inside is the mitochondrial matrix. Chloroplasts are the organelles for photosynthesis in plants and algae.
So they contain flattened membranes called thylakoids. So these kind of green pancakes, stacks of green pancakes. They contain the chlorophyll or the green pigment that absorbs the radiation energy from sunlight. and uses that energy to convert carbon dioxide in the atmosphere into glucose, sugar. Some other organelles in eukaryotic cells include peroxisomes.
So these are similar to lysosomes in that they're going to help get rid of waste. So they're going to oxidize fatty acids and destroy hydrogen peroxide, a waste product. Centrosomes are composed of protein fibers and centrioles.
So these are important during cell division. They're going to form the mitotic spindle. So when the cell divides and we're shuffling all of those chromosomes around, these centrioles will form mitotic spindle, which will grab the chromosomes and kind of position them where they need to go through each stage in the cell division process.
So comparing prokaryotic and eukaryotic cells size-wise, prokaryotes are about one-tenth. the size of a eukaryotic cell. So their average size is 0.2 to 2 micrometers.
So here's the size of a bacteria, about the size of a mitochondria, which is just one part of a large eukaryotic cell. But they're slightly bigger than viruses and other biological molecules. So an animal cell, plant cell, is at least around 10, about 10 times the size of a prokaryotic cell.
Most bacteria are monomorphic, meaning they only have a single shape. They don't change the shape as they multiply. Although there are a few that can exhibit many shapes or pleomorphic.
We're looking at the size, shape, and arrangement of bacterial cells. So bacteria cells are classified and referred to different than karyotic cells or organisms. Bacterial cells are classified based on their shape.
and arrangement in relation to other cells. Bacillus are rod-shaped cells. So bacillus or rods is generally used kind of interchangeably.
So like in lab, you could refer to a gram-positive bacillus or you could refer to it as gram-positive rods and it would be the same answer. Caucus cells are round, spherical-shaped cells. And a cocco bacillus is kind of an intermediary between the spherical coccus and the rod-shaped bacillus.
We also have some spiral-shaped bacteria. So vibrio are kind of like little curved rods. Spirillum and spirochetes are your spiral-shaped bacteria. Something interesting about the vibrio, they have a symbiotic relationship with a squid. So like the cuttlefish.
Allows them to produce this bioluminescence and glow in the dark. There are also a few rare star or rectangular irregular shaped bacteria So here's your curved rod vibrio Cholera is also a type of vibrio bacteria spirulina spirochetes Star shaped bacteria rectangular shaped bacteria. These are more common in like soil Tyria we said we can also classify bacteria based on their arrangements. So how are they organized in their colonies, in their groups, in relation to other cells? So they may be organized in pairs, so referred to as a diplococci or a diplobacilli.
Bacteria may be arranged in clusters. So a cluster would be a staphylococcus. So it tells us it's a cluster of those spherical-shaped cells. Bacteria may be arranged in chains, also referred to as streptococci or streptobacilli. Sometimes you may see tetrads or groups of four or cube-like sarcinase.
So this is something you may see in labs. So it would be described as a gram-positive streptobacillus, or you could describe it as gram-positive rods in chains. Glycocalyx is external to the cell wall.
So it's similar to the glycocalyx we saw with eukaryotic cells. So it's that same sugar. So glycocalyx, sugar case, sugar coat.
But in prokaryotes, it can have a different function. So some prokaryotes glycocalyx may become viscous and gelatinous and form like a slimy layer to help with biofilms. Capsule glycocalyx would be a more structurally organized, firmly attached glycocalyx to form a heart.
hardened protective layer around the cell. So these capsules can help prevent phagocytosis and enhance virulence. This is a capsule stain, again something we'll get to do in lab.
So the capsule is so thick the stain can't penetrate through it, so it just appears as these little halos or clear zones around the cell body. So streptococcus pneumoniae is a capsulated bacteria. So your immune system cells would have a harder time eating or breaking down that hard capsule.
Flagella, similar to eukaryotic cells, are those tail-like extensions to help propel the cell through a fluid. So the prokaryotic flagella is made of three parts. The filament is your outermost region, so the actual tail or the hair portion coming off. The hook is what's going to attach to that filament.
And then the basal body is the actual motor of the flagella. So it consists of essentially just rods and rings that are going to anchor the flagellum to the cell wall and cell membrane. So depending on the type of cell wall the bacteria has, they may have different flagella structures. So this is showing how the flagella motor essentially works.
So all of those rods. and rings will be spinning through the cell wall. So there are also different arrangements of flagella for different bacteria. So a peritrichus would have flagella kind of all around, all around its perimeter. A monotrichus just has a single monofilament or flagella.
A lofotrichus has a tuft. or just a small little group of flagella on one end of the cell. An amphitrychus has flagella on both ends. So amphi meaning both, so think like amphibian. So it has flagellas or little tufts of flagella on both ends.
So flagella allow the bacteria to move either toward or away from a stimulus, so whether food or predators. So it could be a chemical stimulus. something like food or a light stimulus. So phototaxis or chemotaxis. When flagella rotate, it causes the cell to either run or tumble.
So run is when they're swimming kind of in one straight direction. Tumble is when they kind of spin around a bit and reorient themselves to change directions. Some of these flagella proteins can also be used as identifying antigens to distinguish between different cerevars or strains of certain bacteria. Axial filaments are sometimes called endoflagella.
They are the mechanism of locomotion for your spirochetes or the spiral-shaped bacteria. So their flagella, instead of coming off of the cell body, wrap around the length of the cell and are anchored at one end. So when they rotate, when these flagella rotate, it causes the entire cell to move like a corkscrew motion. Fimbriae and pili are some other cellular extensions of prokaryotes.
Fimbriae are the longer hair-like appendages that allow for attachment. So they make the cell more kind of spiky, something of those little spiky balls that stick to your pants leg. So these help with attachment to form biofilms attached to other surfaces. Pili are more involved in motility, so either gliding or twitching motility.
So similar to a flagella, but not as coordinated. Pili can also function as conjugation pili, so for DNA transfer from one cell to another. So this is sometimes referred to as a sex pili or sex pili.
So bacteria don't undergo sexual reproduction in the true sense of the word, but they are capable of directly exchanging genetic material, essentially through insertion from one cell to another via these pili. pili, these conjugation pili. So just like in eukaryotes, the cell wall in prokaryotes is going to help add an extra layer of protection for the overall cell and prevent that osmotic lysis while protecting the cell membrane. The distinguishing feature between the prokaryote bacterial cell wall, though distinguished from plant cells, was that bacteria cell wall is made of peptidoglycan.
So our plant cell walls, eukaryotic cell walls, are made out of polysaccharides like cellulose. So bacteria, our hallmark characteristic is peptidoglycan in their cell walls. This is also going to contribute to the pathogenicity of certain bacteria. So the structure of the cell wall can determine how we treat certain infections.
Peptidoglycan, if we break down the name, peptido tells us it contains proteins or peptides. Peptides are just proteins. Glycan, so similar to glyco, glucose means sugar. So it's basically a protein-sugar molecule. So we have these polymers of repeating disaccharides in rows, so kind of like logs in a raft.
And then we have polypeptides, or these little proteins. that are going to link our logs together and tie them together and form our peptidoglycan raft. There are two main types of bacterial cell walls that we'll focus on.
So gram-positive cell walls are characterized by a thick layer of peptidoglycan. So we have multiple layers stacked on top of each other of our peptidoglycan rafts. They also contain...
Tychoic acids. Two types of tychoic acids on gram-positive cell walls. Your lipotychoic acid are going to help link and connect and anchor this cell wall, this peptidoglycan, to the plasma membrane. So you see it reaches all the way down into our phospholipid bilayer. The wall tychoic acids are going to link the different layers of peptidoglycan.
So we're linking all of the rafts together. Some of these polysaccharides and tychoic acids can also provide antigenic specificity, meaning they can act kind of like identification markers. Gram-negative cell walls have a thin layer of peptidoglycan, so just a single layer sometimes of this peptidoglycan that's going to be sandwiched between an inner and an outer membrane.
So gram-positive... had a single plasma membrane and a thick cell wall. Gram-negative has two plasma membranes that are going to sandwich a very thin peptidoglycan cell wall.
So the periplasm is just the space between these two membranes, so our inner and outer membranes. The outer membrane also contains polysaccharides, some lipoproteins, and phospholipids. So this outer layer kind of forms an extra layer or barrier of protection to the internal structures of the cell.
So it can help protect against some phagocytes or other immune responses and antibiotics. The distinguishing feature of the gram-negative cell wall is the lipopolysaccharide layer. So again, breaking down the word lipo, meaning fat or lipid.
polysaccharide meaning a complex sugar the o polysaccharide on the end or the tip of the structure it's going to function as our antigen so again just an identification marker, something that can elicit an immune response or an antibody generating molecule. Lipid A, so the lipo part of our LPS, is an endotoxin that's embedded within this top layer. The core polysaccharide is just the core to help stabilize the structural component.
So kind of a built-in defense mechanism for these gram-negative cells. We have this extra layer or barrier protecting the internal structures. So if an antibiotic or a phagocyte gets to this outer membrane, when this outer membrane dissolves, it's going to release this lipid A endotoxin.
The outer membrane also contains some porin proteins that are just going to form channels or passageways for certain molecules and substances to pass through.