The next chapter we're going to cover is the chemical level of organization. And the first thing we're going to talk about is matter and mass. Matter is anything that has mass and occupies space. There is three states of matter that we will examine. Mass is the quantity of matter in an object.
Mass is basically the amount of material in matter. It's a physical property and it determines the weight of an object in the Earth's gravitational field. But for our purposes in this course, the mass of an object is the same as its weight.
However, mass and weight are not always equivalent. So the three states of matter are solid, liquid, and gas. Solid is something that has a definite shape. volume.
Liquid has a definite volume but has a changeable shape. Gas has a changeable shape and a changeable volume. Water is the only substance that exists in all three states of matter at temperatures compatible with life.
We have solid, ice, liquid, water, and gas, water vapor. We will examine some important properties of water a little bit later on. Now matter is composed of elements, and elements cannot be broken down by ordinary chemical means. Elements have unique...
Physical properties and chemical properties. The physical properties of elements are those things that we can detect with our senses, and they're measurable. The chemical properties are how atoms interact or bond with one another.
Each element has a unique chemical symbol, and there are some important elements that we will examine because they are predominantly found in the human body. Oxygen, carbon, hydrogen, and nitrogen are among the 11 principal elements that are most abundant in the human body. There is others like calcium, phosphorus, potassium, sodium, and chlorine to give you a few examples.
And here's the periodic table of elements. You will not be responsible. for memorizing periodic table of elements, but you should recognize the major elements and recognize them by their chemical symbol. For example, oxygen is O, carbon is C, calcium C-A, potassium K. If you look at the elements of the human body, we can see that oxygen, carbon, hydrogen, nitrogen make up the predominant portion of our body's mass.
Lesser elements, calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium, iodine, and iron make up a smaller percentage. And then we have trace elements. They make up less than 1% or 0.01%.
A lot of the trace elements as you will see are part of enzymes. Some of the trace elements are zinc, chromium, manganese, to give you a few examples. Now atoms and molecules are the basic components of matter. Chemicals are composed of atoms, and atoms are the smallest stable units of matter.
Atoms are also composed of subatomic particles. The nucleus of an atom consists of neutrons and protons. A neutron has no charge, a proton has a positive charge, and the electrons orbit the nucleus.
They are equal in number to the protons in an atom. If the... Adam is balanced and uncharged.
Electrons, however, have a negative charge. And you can see some examples here showing how the atom can be divided into the various regions. You can see the protons and neutrons in the nucleus, and the electrons, which orbit around the nucleus, in spheres, or sometimes referred to as an electron cloud.
Here is two models representing atomic structure. We have the planetary model and the electron cloud model. And the electron clouds can be represented as electron shells.
You may have learned about the various electron shells and how the electrons pair up with one another in the various electron shells. depending on how many electrons can be held in each shell. The electrons are very important in understanding chemistry and the chemical reactions that occur in the human body because it's the electrons that will participate in those chemical reactions.
Now molecules are when atoms interact they can produce larger more complex structures. All matter is composed of varying arrangement of atoms, and the variation in matter gives characteristics that result from the types of atoms and the way they interact. So some terms that we need to identify are the atomic number, mass number, and an element.
The atomic number is the number of protons a nucleus. The mass number is the mass of the protons and neutrons. Mass numbers of atoms of an element are not all identical. The atomic weight is the average number of mass numbers of all the isotopes. And an isotope is an atom with the same number of protons but has different numbers of neutrons.
They have identical chemical properties, but different mass numbers. Hydrogen is a good example of an isotope. Isotopes that are radioactive will spontaneously decay.
And these are valuable tools that can be used in biological research and medicine. But radioisotopes can also cause damage to living tissue. However, radioisotopes in medicine are very useful against localized cancer. The atomic weight, the actual mass of an atom, is expressed in Daltons. One Dalton is very close to the weight of one proton or neutron, and as noted before, the atomic weight is the average mass number reflecting the proportion of different isotopes.
So you can see, for example, hydrogen has an atomic number of one, a mass number of one, but its atomic weight is slightly more than one, which represents or reflects the different proportion. isotopes. And here's another example showing that.
A PET scan is shown here. PET scan highlights different areas in the body and can be used as a diagnostic tool, for example, to look for areas that have high glucose use. Glucose is the preferential food source for cancer, and so this is generally characteristic of parts of the body that might have cancerous tissue. And in this case, we can see the PET scan shows the spread of different tumors to other parts of the body. Now, atoms are electrically neutral.
The positive protons are balanced by the negative electrons. Remember the electrons occupy different energy levels within the electron cloud or electron spheres. The first one is closest to the nucleus and has the lowest energy level.
The number of electrons in the outermost shell is characteristic of the chemical properties of that particular element. So let's review the energy levels. The outermost energy level is called the valence shell.
Atoms with unfilled outer shells are reactive. Electrons want to pair up with one another. They don't want to be in a shell by themselves, so they usually are found in pairs.
If an atom has a full outer shell, meaning all electrons are paired, the atom is said to be inert. It means it's not going to readily react with another atom and it's very stable. The noble gases in the periodic table are considered to be inert. Other atoms that don't have a paired electron in their outer shell are reactive. And here's some examples.
So hydrogen has one electron. Helium has two electrons. It's paired. Carbon has four lone electrons in its outer shell. Neon is completely paired.
It has 10 electrons. Now ions are charged atoms and cations are atoms that have gained or lost an electron and so this would be a ion and it's no longer electrically neutral. Remember an electron has a negative charge.
Losing an electron means that you have fewer electrons, negative charges, than protons, which have positive charges. This would give you an overall net positive charge. If we have a positively charged ion, it is known as a cation.
So an example shown here is the sodium atom. The loss of an electron from a sodium atom. An atom forms a sodium cation, giving it a positive charge. An anion is another type of charged atom.
In this case, they have gained an electron. More electrons, negative, than protons. So we have an overall net negative charge. And an example would be chlorine. Chlorine has an extra electron, giving it an overall net negative charge.
Molecules are different from compounds. A molecule is a chemical substance that consists of atoms of one or more elements held together by covalent bonds. Compounds are chemical substances made up of two or more atoms from different elements. And molecules and compounds can participate in chemical reactions.
Let's examine some types of chemical bonds, starting with an ionic bond. An ionic bond is a chemical bond created by the transfer of electrons from one atom to another atom. In this case, the attraction of the opposite charges might result in an ionic bond. So ions are formed by transfer of those valence shell electrons between atoms. So an anion, something that has a negative charge, has gained one or more electrons.
A cation, remember, has a positive charge and it's lost one or more electrons. Sodium chloride is an example of that that we looked at previously. So if sodium, which has a positive charge, gets an electron from chlorine, which has a negative charge, now we have a balanced molecule, sodium chloride. And we have an ionic compound.
that results from sodium and chloride coming together. And ionic compounds often form crystals, as shown in the diagram. Covalent bonds are another type of chemical bond, but in this case, they're formed by the sharing of electrons between atoms. and we can have different types of chemical bonds. In this case, it allows each atom to fill its valence shell, that outermost shell of electrons, at least part of the time.
A single covalent bond is when one pair of electrons are shared. A double covalent bond is when two pairs of electrons are shared. And you can even have a triple covalent bond, where three pairs of electrons are shared. Now, sometimes the sharing is not equal.
So the sharing of electrons may be equal or unequal. Equal sharing produces electrically balanced nonpolar molecules. And we'll examine an example of that in just a moment. Unequal sharing by atoms produces polar molecules, and water is an excellent example of that.
This means that the electrons are not being shared equally between the atoms. So, for example, the oxygen may have a little bit more of the electrons. most of the time and that creates an electronegativity of the oxygen atom.
The positive may be a little bit more close to the hydrogen. The polarity of water molecules actually contributes to a lot of the characteristics of water that we will be examining. So we have in a polar covalent bond, unequal sharing of electrons, we will generally see a slight negative charge at one end of the molecule and a slight positive charge at the other end of the molecule. A nonpolar covalent bond, we have equal sharing of the electrons and the charge is balanced among the atoms.
And this is represented here in oxygen and carbon dioxide. So here's the polarity for the water molecule. The hydrogen atom has a slight positive charge.
The oxygen atom has a slight negative charge. Now, hydrogen bonds... form between water molecules.
And this gives, or you'll notice, that the bonds occur between the positive charge on the hydrogen atom and the negative charge on the oxygen atom. Hydrogen bonds by themselves are relatively weak, but in a water molecule, because you've got so many hydrogen bonds forming and breaking, it does contribute to some of the characteristics of water, and it creates a stronger force. So a hydrogen bond, again, is the attraction of the positive charge on the hydrogen atom to the negative charge on the oxygen.
And you can see the attraction of the hydrogen bonds between the different water molecules. The effects of the hydrogen bonds do contribute to some of the properties of water. They're constantly forming and breaking when water is in its liquid form.
However, when frozen, they lock in place, and this accounts for the expansion of water upon freezing. When water goes to the vaporous state, all hydrogen bonds are broken. This slows the rate of evaporation, And this also contributes to the surface tension property that we see with water.
Okay, chemical reactions. Chemical reactions are defined when chemical bonds form between atoms or existing bonds between atoms are broken. So we're either making or breaking bonds. These changes occur in the reactant substances, which are called the reactants, and they are rearranged to form what we call the products.
All of the reactions that occur in the human body at any given time is what is referred to as our metabolism. And there's many reactions that occur in the body at any one given time. Now chemical reactions allow us to do work.
Work is the movement of an object or change in the physical structure of matter. And we need energy, which is the capacity to form work. Now, energy comes in a couple of different forms.
There is kinetic energy, which is the energy in motion. For example, when your skeletal muscles contract, when water is flowing down a waterfall, electricity in a wire. Those are all examples of energy in motion.
Potential energy is stored energy. It also goes by another name called latent energy. Latent energy or stored energy has the potential to do work. The food you eat is a form of potential energy. The gasoline you put in your car is a form of potential energy.
Now whenever we convert energy to another form, it's never 100% efficient. We're always going to have a byproduct of heat in any chemical reaction. Think about the gasoline in your car.
You put it in your car, you turn the engine on, you drive around. When you get out of the car, stop, get to your destination. If you touch the hood of the car, the engine is hot. That's heat, which is a byproduct.
When we move about, our body temperature rises because our muscles are contracting. Now, energy cannot be created nor destroyed. It can only change forms. So here's some summaries of chemical reactions. And there's a couple of different reactions that we're going to talk about.
Synthesis reactions. which are also known as combination reactions, decomposition reactions, and exchange reactions. So a synthesis reaction, we're taking smaller particles and bonding them together to form larger more complex molecules. So in the example shown here, note plus book equals notebook. A plus B yields AB.
Synthesis reactions always involve bond formation, and they're anabolic. We're building something. In a decomposition reaction, bonds between components of a larger molecule are broken down.
They're basically the reverse of synthesis reactions. They involve the breaking of bonds, and they're catabolic. In an exchange reaction, which are also called displacement reactions, bonds are being made and broken.
So we're taking notebook plus worm and creating note plus bookworm. So you can see that we're both breaking. making bonds. Now most chemical reactions do not occur spontaneously.
Most chemical reactions will require an enzyme, which is a protein, to lower the reaction activation energy. And there's different factors that can influence the rate of reactions in the body. Temperature, for example. particle size, the concentration of the reactant, and whether an enzyme is present. So enzymes lower the activation energy and they can promote a chemical reaction by doing that.
The reaction may still occur without the enzyme but it would take a long time for that to happen. So with the help of an enzyme, the activation energy is lowered, and the reaction can proceed much more faster or quickly. Now, in the body, we have many complex reactions occurring.
Many of the reactions interlock with other steps further down in the reaction pathway. These reactions may be controlled by specific enzymes, and these reactions may either absorb or release energy. An exergonic reaction releases energy.
An endergonic reaction is where the products contain more potential energy than did the reactants. Exergonic reactions are catabolic reactions. they're breaking something down.
Endergonic reactions are anabolic reactions. They're building something up. Enzymatic reactions are necessary to the processing of metabolites in the body.
The metabolites include all of the molecules that can be synthesized or broken down. by chemical reactions in our body and we have different types of nutrients in the body. We have organic nutrients that possess carbon and hydrogen and these might form the structure of sugars, fats, proteins things we might use for energy sources. So organic compounds, organic nutrients they must contain carbon.
They're generally formed through covalent bonds, and the major classes that we'll talk about in this course are carbohydrates, fats, proteins, and nucleic acids. Inorganic nutrients or compounds do not contain carbon. They're generally formed via ionic bonding between metals and nonmetals. And they're found in smaller amounts in living organisms. Now I mentioned earlier that water is very important to life.
And water does have some unique properties that you need to be familiar with. First of all, water is called the universal solvent. And that's because water dissolves substances. Polar charges the polar charges on water. that we saw previously allow the disruption of ionic bonds of a variety of compounds.
Our body fluids contain many dissolved elements, so water is generally considered to be the universal solvent. Polar substances are also hydrophilic. And you can see the role of hydration that forms in the spheres, in the ionization of an ionic compound, and in the solution of an organic molecule containing a polar covalent bond. So now we can see glucose molecules in solution, and the hydration spheres that are forming around sodium chloride in solution.
Polar substances being hydrophilic are going to be important when we get to talking about the cell membrane and things that can get across the cell membrane. Nonpolar molecules are hydrophobic. So many of the organic molecules, they lack polar covalent bonds and they don't tend to interact with water. Hydro means water and phobic. is fearing.
So they're sometimes referred to as water theory. Now our body fluids, as noted previously, contain many different electrolytes. And these electrolytes have a number of important functions in the body, which you will learn about throughout your study of anatomy and physiology. Sodium chloride, for example, is involved in... the membrane potential of our cells.
Potassium, calcium, these are electrolytes that are involved in many organ systems, like the cardiovascular system, the nervous system, your skeletal muscle system. Now, water is important for pH regulation. The disassociation of a water molecule produces a hydrogen ion and a hydroxide ion.
And it's important that the body is able to maintain an appropriate pH because that contributes to the efficiency of chemical reactions that occur in the body. We also can't have our body fluids becoming too acidic or too basic. So it's important that you understand the pH scale.
And the pH scale is shown here. The pH scale runs from 0 to 14. Acids are from 0 to just before 7, which is neutral. And anything above 7 up to 14 is considered to be basic. Now acids...
electrolytes that release hydrogen ions when placed in a solution. They're also considered to be proton donors. Again they have a pH of less than 7 and a good example of a strong acid is hydrochloric acid. As the hydrogen ion concentration increases of a solution, the acidity also increases.
Bases are compounds that release hydroxide ions in solution. They tend to be known as proton acceptors. As the hydroxide ion concentration increases, alkalinity or basic nature of the solution also increases. And sodium hydroxide is a good example of a strong base.
So acids and bases are shown here. An acid plus water would release a lot of hydrogen ions in solution. A base plus water would release a lot of hydroxide ions in solution.
Now salt is an electrolyte that disassociates to form ions that might be able to conduct electricity. They're not reflected on the pH scale. Sodium chloride is a salt. When it's placed in solution, It releases sodium ions and chloride ions.
And there's many common salts that are dissolved in the body, like sodium chloride. Electrolytes, as you saw previously, there's a number of them that occur in the body. And they are important.
to many vital functions within the human body, such as muscle contraction, nerve impulse conduction, blood clotting, bone development, and many others that you will learn about later on. Now, buffers are substances that can resist changes in pH, and we have buffers in our body fluids. that release hydrogen ions when the pH begins to rise and become more basic. and they can also take hydrogen ions out of solution when the pH begins to fall.
So buffers are substances that can absorb or liberate hydrogen ions to maintain a constant pH and resist changes in pH. Many buffers are made by adding a weak acid with the salt of that acid. All of our body fluids contain... buffers. And you can see examples here. Carbonic acid is a weak acid and the salt, sodium bicarb, another example.
Now organic compounds. As I mentioned previously, organic compounds contain carbon. They're unique to living systems. Many Organic compounds are polymers, meaning they're chains of similar units. So they're built from smaller building blocks or monomers.
And they can be synthesized by dehydration synthesis or broken down by a hydrolysis reaction. Many organic compounds are also soluble in water. And they have certain functional groups associated with them. There is four groups of organic compounds that we will talk about.
Carbohydrates, proteins, lipids, and nucleic acids. Because these are important compounds in the body. Carbohydrates.
Carbohydrates contain carbon, hydrogen, and oxygen, and they do that in a unique ratio. One carbon for two hydrogens to one oxygen, and there can be any number of repeating units of that combination. There's three classes, monosaccharides, disaccharides, and polysaccharides.
And the function of carbohydrate is usually a major source of our cell's fuel in the form of glucose. They also can form structural molecules like the ribose sugar that's found in RNA. So let's look at some examples, starting with monosaccharides. Monosaccharides are simple sugars containing three to seven carbon atoms.
They can be straight chains or rings as shown here. A triose, tri meaning three, would be a three carbon sugar. A pentose would be a five carbon sugar. And a hexose is a six carbon sugar, which is actually the most common in nature.
glucose would be an example of that. Fructose is a hexose in fruits. Other examples of monosaccharides are glucose, fructose, galactose, deoxyribose, and ribose, which are found in our nucleic acids. Now isomers are compounds that have the same molecular formula, but they have a different structural arrangement. Glucose and fructose are isomers.
They both have the molecular formula C6H12O6, but the structure of them are different, as you saw in the previous slide. Disaccharides, are a combination of two monosaccharides. So they contain two monosaccharides, and they have been formed by the removal of a water molecule and forming a covalent bond via dehydration synthesis. Disaccharides are too large to pass through cell membranes, and if you want to break apart a disaccharide, water is inserted into that... carbon-oxygen-carbon covalent bond via a reaction called hydrolysis.
So hydrolysis is used to break them back down into their monosaccharides. So you can see here dehydration synthesis creates sucrose from glucose and fructose. If we want to break sucrose down via hydrolysis reaction, we can do that by adding water and we get glucose and fructose. Polysaccharides are polymers of simple sugars.
Starch and glycogen are two good examples. These are generally formed from eight or more monosaccharides joined together again by dehydration synthesis to form a long chain. Polysaccharides can again be broken down back into simple sugars by the addition of water. So you Some polysaccharides, starch to be aware of, mostly a straight chain.
It's the form of sugar storage in plants. Glycogen is the form of sugar storage in animals, in our liver and muscle cells. And cellulose is another example shown here of a polysaccharide. Polysaccharide.
Cellulose is indigestible to humans and is found in plant cell walls. We don't have the enzyme to break down cellulose. Lipids.
Lipids are a diverse group containing carbon, hydrogen, and oxygen atoms. Lipids are nonpolar substances that are insoluble in water. The main chemical difference between lipids and sugars is that lipids do not follow the 2 to 1 hydrogen ratio that we saw in sugars and carbohydrates.
They contain much less oxygen compared to carbohydrates. Now lipids may also contain other substances like... phosphorus, nitrogen, or sulfur.
Examples are fats, oils, and waxes. And in our bodies, we need a special transport mechanism for lipids to travel in our blood. Now lipids have a number of important functions in the body.
They are an essential component of all our cells. They are a reserve. energy supply. They provide twice as much energy as carbohydrates.
They can function as chemical messengers. They're the components of cellular structures, so they help to form our cell membranes. And that allows for the separation of a unique environment both inside our cells and outside our cells. Now there's different types of lipids.
Fatty acids are the first group that we will talk about. Fatty acids are long chains with attached hydrogen atoms. So fatty acids have both a head and a tail. The head, as you can see in the figure, has a carboxylic acid group, COOH. It's hydrophilic.
Remember that means water loving. The tail is hydrophobic, meaning water-fearing. Now fatty acids can be saturated or unsaturated.
A saturated fatty acid has no double bonds between the carbons of the fatty acid. This means the acid has the maximum number of hydrogens. Saturated fatty acids are generally your solid animal fats like butter. Saturated fats have implications in the increased risk of heart diseases, high blood pressure, and other cardiovascular disorders.
Unsaturated fatty acids are generally liquid at room temperature, and they have one or more double bonds between the carbon atoms. Your plant oils, like olive oil, are unsaturated. Glycerides, like a triglyceride, is a lipid produced by dehydration synthesis between a glycerol molecule and three fatty acids.
So one glycerol plus one fatty acid would be a monoglyceride. One glycerol plus two fatty acids would be a diglyceride. and a glycerol plus three fatty acids would be a triglyceride. The glycerides mainly function in energy storage, insulation, and protection in the body. Phospholipids and glycolipids are modified triglycerides.
They contain two fatty acid chains and a phosphorus containing group attached to a glycerol back. so the head and the tail regions have different properties and phospholipids are important in cell membrane structure as you see here phospholipids have a hydrophilic head and a hydrophobic tail steroids are interlocking four ring structures. So they contain four interlocking hydrocarbon rings forms a steroid. Cholesterol is the basis for all steroids that are formed in the body and you can see the ring structure shown there. Another type, a couple of other types of lipids are Leukotrienes and prostaglandins.
We won't focus so much on these types of lipids. They're derived from arachidonic acid. Leukotrienes are produced by cells in response to some form of injury or disease and in ANP2 you will discuss those in a little bit of detail.
Prostaglandins are compounds released by cells to coordinate cellular activity and they're very powerful even in small quantities. Proteins are substances that contain carbon, oxygen, hydrogen, nitrogen and other substances like sometimes sulfur or phosphorus. They're made by combining different combinations of 20 different naturally occurring amino acids. and the polymers of amino acids are joined together by peptide bonds to form proteins. And again, amino acids are linked together by the removal of water, dehydration synthesis, and proteins can be broken down by the insertion of water, hydrolysis, into the peptide bond.
So the structure of an amino acid is shown here. And an amino acid contains an amine group plus a unique group of carbon, hydrogen, sulfur, phosphorus, and a carboxylic acid group. It also has a side chain, which is variable. Now proteins can be joined together. And the peptide linkage refers to the carbon-nitrogen linkage of amino acid side chains as shown in the diagram.
A dipeptide contains two amino acids. A tripeptide contains three amino acids. And a polypeptide contains many amino acids.
And you can see... Polypeptides contain peptides of over 100 amino acids called proteins. Now proteins can fold in different ways and there's four levels of protein structure that you should be familiar with.
The primary structure of a protein, the secondary structure of a protein, the tertiary structure, and the quaternary structure are all shown here. The primary structure of a protein or of a polypeptide is just the amino acid side chain. The secondary structure of a polypeptide is when the polypeptide chain is coiled into a helix or pleated into sheets with hydrogen bonds between the turns or folds to hold it in place. Sometimes the form is held together by a disulfide bridge.
The tertiary structure of a protein is when the primary structure is folded to expose certain amino acids, while other amino acids are folded to the inside. Hydrogen bonds hold this form structure together. And you can see here the unique structure, tertiary structure, showing the alpha helixes and the heme unit. So this would be one part of a hemoglobin molecule. Now the quaternary structure is shown here with the complete hemoglobin, which contains four polypeptide subunits.
The quaternary structure of a polypeptide... the combining of four or more proteins to form a more complex structure. This level of structure is not very common and fibrous structural proteins as seen here, collagen, they're strand-like, water insoluble, very stable, or you can have globular functional proteins which are compact, spherical in shape, water soluble, and they usually have specific functional regions or active groups, like the heme unit shown in the diagram. Now, proteins can be denatured, and denaturing a protein breaks the bonds holding the folds and coils.
It ultimately changes the physical and chemical shape of the protein. There's different ways that proteins can be denatured. Reversible changes can occur in some cases if normal conditions are restored fairly quickly.
High heat, for example, denatures proteins. It's irreversible if the extreme changes damage the structure beyond repair. Think of when you cook an egg.
It's liquid. and then when it's done cooking, it's semi-solid in structure, and so you have irreversibly damaged the shape and the proteins. Acids also denature proteins through a change in pH, and these physical and chemical changes destroy the protein's function, which is usually dependent upon its precise, unique structure.
That's why it's important to keep a protein structure intact. Now, enzymes facilitate most everything that occurs in the body. Remember, enzymes are catalysts which can speed up the rate of a reaction in the body. Each reaction has a specific enzyme or catalyst that will only work for that reaction due to its unique primary, secondary, tertiary structure. Any change which alters the structure of a protein denatures it.
So we have substrates that are reactants in enzyme reactions. We have the active site, the specific region where the enzyme must bind the substrate. We have control of reaction rates where multiple enzymes in a cell with each enzyme being under its own set of conditions. And there's a saturation limit. There's a substrate concentration required to have a maximum rate of reaction.
Enzymes are proteins. And again, they have important biological functions. To summarize, they act as catalysts.
They can accelerate the rate of a biochemical reaction by lowering the amount of energy required to start the reaction. That's the activation energy. They possess an active site, as shown here. That may be a groove or a pocket where substrates bind and undergo a chemical reaction.
The substrate binding... produces an enzyme substrate complex. Denaturation of the enzyme typically prevents the enzyme substrate complex from forming so the chemical reaction would shut down or not occur.
Nucleic acids are the final category of compounds, organic compounds, that we're going to discuss. And nucleic acids are our DNA. RNA and ATP.
Our DNA and RNA are the largest molecules in the body. They contain carbon, oxygen, hydrogen, nitrogen and phosphorus. The building blocks are the nucleotides, which is composed of a nitrogenous containing base, a pentose sugar and a phosphate group, as shown in the diagram. DNA, one class of nucleic acids, makes up our genes. In humans, DNA is found mostly in the nucleus of our cells.
However, there is a little bit of DNA found in the mitochondria of cells. RNA is an intermediate form when decoding DNA into a protein. Now, nucleotides, as I mentioned, consist of a phosphate group, a pentose sugar, which is deoxyribose in DNA and ribose in RNA, and a nitrogen base. Now, there is four bases, the purines, which are double ring, and they consist of adenine, guanine, and the pyrimidines, which are a single ring and consist of cytosine, thymine, uracil, which is found in RNA only.
To assemble a nucleic acid, you must first build many nucleotides. Then you can link the nucleotides together via sugar phosphate bonds to form long chains of nucleotides. And then the strands can form into a helix, a double-stranded helical molecule. DNA is in the cell nucleus and provides the instructions for protein synthesis.
Now, DNA and RNA are both nucleic acids. They again are formed by dehydration synthesis. Same reaction we've talked about previously. And you can see how nucleic acids come together. to form the two different strands of DNA.
So DNA is a double-stranded molecule and RNA is a single-stranded molecule. There's different forms of RNA that you will learn about later on in the course. Messenger RNA, transfer RNA, and ribosomal RNA. These are the three different varieties of RNA that carry out the DNA orders for protein synthesis. And remember RNA is single-stranded and also has uracil as its base instead of thymine.
Now finally the energy currency of our cells is ATP. ATP are adenine containing RNA nucleotides with two additional or up to three additional phosphate groups. So the high energy phosphate bonds in these molecules can be hydrolyzed to release energy. ATP is the energy molecule or currency of our cells. All cells must have an available supply of ATP.
If our cells don't have this supply, they die. So with one phosphate, it is AMP, adenosine monophosphate. With two phosphates, it is ADP, adenosine diphosphate.
And with three, it's adenosine triphosphate. And energy, as you recall, is the capacity to do work. ATP is synthesized in every body cell constantly. And that concludes our overview of chemistry. and the chemical level of organization.