The next chapter we're going to cover is the chemical level of organization. The first thing we're going to talk about is matter. Matter is anything that has mass and occupies space. There are three states of matter that we will examine. Mass is the quantity of matter in an object. Mass is basically the amount of material. And 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 and 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. An 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 atoms interact or bond with one another. Each element has a unique chemical symbol and there is 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 are others like calcium, phosphorus, potassium, sodium, and chlorine, to give you a few examples. Here's the periodic table of elements. You will not be responsible for memorizing the periodic table of elements but you should recognize the major elements and recognize them by their chemical symbol. The symbol for example: oxygen is O, carbon is C, calcium is Ca, potassium is K. If you look at the elements of the human body, we can see that oxygen, carbon, hydrogen, and 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. 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 also composed of subatomic particles. The nucleus of an atom consists of neutrons and protons. A neutron has no charge while a proton has a positive charge. The electrons orbit the nucleus. They are equal in number to the protons in an atom if the atom 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 are two models representing atomic structure. We have the planetary model and the electron cloud model. 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 in the way they interact. So some terms that we need to identify are the atomic number and mass number. An element the atomic number is the number of protons in 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 Radio isotopes can also cause damage to living tissue however Radio isotopes and medicine are very useful against localized cancer the atomic weight the actual mass of an atom is expressed in Dalton's 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 1 but it's atomic weight is slightly more than 1 which represents or reflects the different proportion of 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 the 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 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 our 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 ten electrons now ions are charged atoms and cations are atoms that have gained or lost an electron and so this would be a I own 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 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 so 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 are 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 electric 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 reactants 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 and 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 eat 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 pot particles and bonding them together to form larger more complex molecules so in the example shown here note in plus book equals notebook a plus B yields a B 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 bookworm so you can see that we're both breaking and 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 end 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 our 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 molecule or 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 but 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 zero to just before 7 which is neutral and anything above 7 up to 14 is considered to be basic acids are 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 are tend to be known as proton acceptors as the hydroxide ion concentration increases the 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 assault 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 stager source of our cells fuel in the form of glucose they also conform 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 carbons sugar and a hexose is a six carbon sugar which is actually the most common in nature and glucose would be an example of that fructose is a hexose in fruits other examples of monosaccharides 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 c6 h-12 o-6 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 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 a party 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 8 or more monosaccharides join 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 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 and 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 plants 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 in soluble in water the main chemical difference between lipids and sugars is that lipids do not follow the two-two-one hydrogen ratio that we saw in sugars and carbohydrates they are much less 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 ourselves and outside ourselves 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 theory now fatty acids can be saturated or unsaturated rated a saturated fatty acid has no double bonds between the carbons of the fatty acid this means the acid has the maximum number of hydrogen's 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 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 our modified triglycerides they contain two fatty acid chains and a phosphorous containing group attached to a glycerol backbone 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 hydrophone 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 Luca Tron's and prostaglandins we won't focus so much on these types of lipids they're derived from arachidonic acid Luca Tron's are produced by cells in response to some form of injury or disease and an A&P to 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 sidechain 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 a hundred Nino 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 cordon Airy 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 acid it's our 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 cordon Airi structure is shown here with the complete hemoglobin which contains four polypeptide subunits the coronary structure of a polypeptide is 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 there's strand like water insoluble very stable or you can have globular functional proteins which are compact sphere 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 and structure and so you have irreversibly damaged the shape and proteins acids also denature proteins through a change in pH and these physical and chemical changes destroy the proteins 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 catalysts that will only work for that reaction due to its unique primary secondary or 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 eat whit 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 so 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 is an active site as shown here that maybe 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 which 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 ourselves however there is a little bit of DNA found in the mitochondria cells RNA is an intermediate form when decoding DNA into a protein now nucleotides as I mentioned consists of a phosphate group a pentose sugar which is deoxyribose in DNA and ribose and RNA and a nitrogen base now there is four bases the purines which are double ring and they consist of adenine guanine and the perimeters which are a single ring and consist of cytosine thymine and 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 ourselves all cells must have available and available supply of ATP if our cells don't have this supply they die so with one phosphate is a MP adenosine monophosphate with two phosphates it is adp adenosine diphosphate and with 3 its adenosine triphosphate an 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