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Book notes chapter 2

by: Amanda Windham

Book notes chapter 2 BIOL4100

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Amanda Windham

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Notes from book reading on Chapter 2
Cell Biology
Anthony Moss
Class Notes
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This 13 page Class Notes was uploaded by Amanda Windham on Friday February 12, 2016. The Class Notes belongs to BIOL4100 at Auburn University taught by Anthony Moss in Spring 2016. Since its upload, it has received 36 views. For similar materials see Cell Biology in Biology at Auburn University.


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Date Created: 02/12/16
Cell Biology Spring 2016 Dr. Moss Chapter 2: Chemical Foundations  Understanding the molecular components and elements of a cell is important in understanding the function and structure of cells.  We must understand the properties of water to understand the how water controls the chemistry of life.  Water is the most abundant molecule in biological systems.  Amino acids: the building blocks of proteins  Nucleotides; the building blocks of DNA and RNA  Lipids: the building blocks of biomembranes  Sugars: the building blocks of complex carbohydrates  Hydrophilic molecules: “water loving” molecules that readily dissolve in water; ex sugars  Hydrophobic molecules: ‘water fearing” substances that do not dissolve in water; ex cholesterol, fats, oils.  Amphipathic: “both liking” contain hydrophilic and hydrophobic regions; ex phospholipids  The functioning of cells depends on all of these molecules. The chemical reaction of all of these molecules with water and with one another define the nature of life. 2.1 Covalent Bonds and Noncovalent Interactions  Covalent bond: when two atoms share a sing pair of electrons.  Sharing of multiple pairs of electrons results in multiple covalent bonds (double or triple bonds)  Covalent bonding is relatively strong.  Noncovalent interactions are weaker but just as important: ionic bonds, hydrogen bonds, Van der Waals interactions, and hydrophobic effect  Hydrogen, Oxygen, Carbon, Nitrogen, Phosphorus, and Sulfur are the most abundant elements in biological molecules.  Carbon always forms 4 covalent bonds, but some other molecules can form a variety of covalent bonds.  Carbon is the central building biological building block.  In these organic biomolecules, each carbon usually bonds to three or four other atoms (but can form linear bond with 2 atoms such as O=C=O but these arrangements are not found in biological building blocks.)  Ex: Formaldehyde (CH20): C forms two single bonds with H atoms and one double bond with O atom. o The single bonds can usually rotate freely about the bond axis, but double bonds cannot.  The rigidity of double bonds is important in forming the structure of certain biomolecules.  Methane (CH4): contains one Carbon atom with 4 single covalent bonds to Hydrogen atoms. o When carbon is bonded to 4our other atoms, the angle between any two bonds is 109.5° and the positions of bonded atoms define the four points of a tetrahedron. This geometry defines the structure of many biomolecules.  A carbon atom bonded to four dissimilar atoms or groups in a nonplanar configuration is said to be asymmetric. o The tetrahedral orientation of bonds formed by an asymmetric carbon atom can be arranged in 3D space in 2 different ways, producing molecules that are mirror images of each other, a property called chirality. These molecules are called stereoisomers. o Many molecules in cells contain at least one asymmetric carbon atom, also called a chiral carbon atom.  The different stereoisomers of a molecule usually have very different biological activities because the arrangement of atoms within their structures, and their ability to interact with other molecules is different.  Phosphate groups covalently attached to proteins play a key role in regulating the activity of many proteins, and the central molecule of cell energetics, ATP, contains 3 phosphate groups.  Electronegativity: the ability of an atom to attract an electron  If two atoms have the same electronegativity, the electrons are shared equally and the bonds are non-polar.  Bonds between two atoms with different electronegativities are said to be polar, and have uneven sharing of electrons. o One end of a polar bond has a partial negative charge and the other has a partial positive charge.  Dipole: a positive charge separated from an equal but opposite negative charge. Created when a polar bond is present.  Dipole Moment: a common quantitative measure of the extent of charge separation, or strength, of a dipole. The dipole moment depends on the bonds and the geometry of the molecules.  Covalent bonds are considered to be strong because the energy required to break them are much greater than the thermal energy available at room temperature or body temperature. (So, they are stable at these temperatures)  Double covalent bonds require more energy to break than single covalent bonds.  Although non-covalent interactions are considerably weaker, they serve important roles. Non-covalent interactions are constantly being broken and formed at room temperature. Though a single non-covalent interaction may be weak, multiple interactions can produce stable molecules and interactions between molecules such as protein-protein interactions or protein-nucleic acid interactions.  Ionic interactions: result from the attraction of a cation (+) and an anion (-). o Do not have fixed or specific geometric orientations. o Energy required to break ionic interactions depends on the distance between the ions and the environment of the ions. o When salts are dissolved in water, the ions separate from one another and are stabilized by ionic interactions with the water molecules. (remember: water is polar and forms a dipole, so the + and – ends of water molecules can arrange themselves around the cations or anions when dissolved in water)  Hydrogen Bond: the interaction of a partially positively charged hydrogen atom in a molecular dipole, such as water, with unpaired electrons from another atom. o The Hydrogen must be in a dipole molecule o The atom to interact with hydrogen must have a free pair of nonbonding electrons to form a hydrogen bond. o Donor atom: the molecule that Hydrogen is covalently bonded with. o Acceptor atom: the atom that forms a hydrogen bond with the Hydrogen atom o The strongest hydrogen bonds are linear. Non-linear hydrogen bonds are weaker.  The solubility of uncharged substances in an aqueous environment depends largely on their ability to form hydrogen bonds with water.  Van der Walls Interaction: when any two atoms approach each other closely, they create a weak, nonspecific attractive force resulting from momentary fluctuations in the distribution of the electrons of any atom. o Occur in both polar and non-polar molecules. o Responsible for the cohesion between nonpolar molecules that cannot form hydrogen bonds or ionic interactions with each other. o Van der Walls interactions only occur if the atoms are close to one another. However, if they are too close, the negative charge of the electrons will repel one another. o 1 kcal/mol, so it requires several interactions to form stable attractions  The hydrophobic effect causes nonpolar molecules to adhere to one another. o Nonpolar molecules do not contain charged groups, do not possess a dipole moment, become hydrated, insoluble in water, and are hydrophobic. o Hydrocarbons: molecules made up of only hydrogen and carbon; are virtually insoluble in water, due to the nonpolar nature of the covalent bonds between two carbon atoms or between carbon and hydrogen atoms. o Hydrophobic effect: the tendency of nonpolar molecules to aggregate in water. o If nonpolar molecules in an aqueous environment aggregate with their hydrophobic surfaces facing each other, the net hydrophobic surface area exposed to water is reduced. Thus, less water is needed to form “cages” around the molecule, entropy is increased and an energetically more favorable state is formed.  Cholesterol: lipid, cannot dissolve in the blood. Must be packaged into hydrophilic carriers to be transported throughout the body. o HDL: high density lipoprotein; “good” cholesterol o LDL: Low density lipoprotein; “bad” cholesterol o HDL and LDL have different effects on cells. LDL contributes to clogging of arteries. HDL protects from clogging of arteries.  Molecular Complementarity: a “lock and key” kind of fit between their shapes, charges, or other physical properties, can form multiple noncovalent interactions at close range causing them to bind together. o Allows proteins to fold into their unique, 3 dimensional shape. o Holds 2 chains of DNA together in double helix. o The higher the affinity of two molecules for each other, the tighter they can bind together. o Kd= binding dissociation constant 2.2 Chemical Building Blocks of Cells  3 main types of biological macromolecules o Proteins o Nucleic Acids o Polysaccharides  All 3 are polymers composed of covalently linked monomers.  Proteins: linear molecules, 10-1000s amino acids, linked by peptide bonds.  Nucleic Acids: hundreds to millions of nucleotides linked by phosphodiester bonds.  Polysaccharides: linear or branched monosaccharides linked by glycosidic bonds (dehydration reactions). o The breakdown of this bond is hydrolysis.  Noncovalent interactions help to form the bilayer structure of membranes.  The building blocks of proteins are 20 Amino Acids o All amino acids have a characteristic structure consisting of a central alpha carbon atom bonded to 4 different chemical groups: an amino acid, carboxyl acid, hydrogen atom, and a variable R group. The alpha carbon in all amino acids (except glycine) is asymmetric. All Amino acids exist in D and L isomers. o L form found in proteins o D form found in bacterial cell walls and microbial products.  Aliphatic amino acids: linear or branched hydrocarbons that do not form a ring and are nonpolar.  Amino acids with polar side chains are called hydrophilic. o Arginine and Lysine have + charged side chains, referred to as basic amino acids. o Aspartic acid and glutamic acid have – charged side chains, and are called acidic.  The activity of many proteins are modulated by shifts in environmental pH.  Cysteine contains a reactive sulfhydryl group that can release a proton and convert into thiolate anion. Thiolate anions can play important roles in catalysis.  In proteins, each of two adjacent sulfhydryl groups can be oxidized and form a covalent disulfide bond. Disulfide bonds help to “cross-link” regions within a single polypeptide chain or between two separate chains. Disulfide bonds stabilize the folded structure of some proteins.  The smallest amino acid is glycine.  Proline is very rigid and the amino group is not available for typical hydrogen bonding. The presence of proline in a protein creates a fixed kink in the polymer chain, limiting how it can fold in the region of the proline residue.  Leucine, serine, lysine, and glutamic acid are the most abundant amino acids.  Many proteins are regulated by phosphorylation and dephosphorylation. Five different nucleotides are used to build nucleic acids  DNA: deoxyribonucleic acid:  RNA: ribonucleic acid:  Monomers of DNA and RNA are nucleotides: o Phosphate group linked by phosphoester bond to a pentose sugar that is linked to a ring base.  In DNA, the 2’ carbon has a proton rather than hydroxyl group.  The bases of DNA and RNA: o Adenine, Guanine, Cytosine (in both DNA and RNA) o Thymine (DNA only) o Uracil (RNA only)  Purines: Adenine and Guanine; contain 2 fused rings  Pyrimidines: cytosine, thymine, uracil: contain single ring  The 1’ Carbon atom of the sugar is attached to the Nitrogen at position 9 of purines or position 1 of a pyrimidine. The acidic characteristic of nucleotides is due to the phosphate group. o Most nucleic acids in cells are associated with proteins, which form ionic interactions with the negatively charged phosphates.  Nucleoside: base and a sugar w/ out a phosphate; can be found in extracellular fluid and in cells. Monosaccharides Covalently Assemble into linear or branched polysaccharides  Monosaccharides are carbohydrates, which re covalently bonded combinations of carbon and water in a 1:1 ratio. Hexoses and Pentoses are the most common.  Disaccharides are the simplest of polysaccharides. o Lactose: glactose+glucose; major sugar in milk o Sucrose: glucose+fructose; principal product of plant photosynthesis and refined into table sugar.  Large polysaccharadies can function as reservoirs for glucose, structural components, or adhesives that hold cells together in tissues.  Glycogen: most common storage carbohydrate in animal cells, very long, highly branched, glucose polymer.  Starch: the primary storage carbohydrate in plant cells, also a glucose polymer, unbranched form called amylose, and lightly branched form called amylopectin.  Cellulose: major constituent of plant cell walls, unbranched polymer of the β anomer of glucose. o Cannot be broken down by human digestive enzymes, but many plants, bacteria, and molds produce cellulose degrading enzymes. Cows and termites contain cellulose degrading bacteria in their GI tract.  Peptidoglycan: polysaccharide chain cross-linked by peptide cross bridges found in bacterial cell walls. o Human tears and intestinal fluids contain lysozyme, capable of hydrolyzing peptidoglycan. Phospholipids associate noncovalently to form the basic bilayer structure of biomembranes  The primary building blocks of all biomembranes are phospholipids.  Biomembranes can also contain a variety of other moleculesu such as cholesterol, glycolipids, and proteins.  Phospholipids consist of 2 long-chain, non-polar fatty acid groups linked by an ester bond to small, highly polar groups like phosphate or glycerol.  Fatty acids: consist of a hydrocarbon chain attached to a carboxyl group. o Important energy source for cells o Predominant fatty acids in cells have an even number of carbon atoms (usually 14, 16, 18, or 20) o FA’s containing 12 or more carbon atoms are nearly insoluble in aqueous solutions because of their long hydrophobic hydrocarbon chains. o Saturated fatty acids: fatty acids that have all single carbon-carbon bonds. o Unsaturated fatty acids: fatty acids that have one or more carbon- carbon double bond. (polyunsaturated fatty acids if more than one)  In phospholipids, fatty acids are covalently attached to another molecule by a type of dehydration reaction called esterification, in which the OH from the carboxyl group of the FA and the H from the hydroxyl group on the other molecule are lost.  Phospholipids are not only membrane building blocks, but are also important signaling molecules.  Phospholipids that have both hydrophobic and hydrophilic regions are called amphipathic.  Triglycerides include fatty acyl groups covalently linked into other fatty molecules.  Triglycerides and cholesteryl esters are extremely water insoluble molecules in which fatty acids and cholesterol are stored and transported. Triglycerides are the storage form of FAs in adipose tissue (fat tissue) and are the principle components of dietary fats. o Cholesteryl esters and triglycerides are transported through the blood stream in specialized carriers called lipoproteins.  Fatty acids can be either saturated or unsaturated: o The double bond in unsaturated fatty acid creates two stereoisomers of the molecule; cis and trans. o A cis double bond introduces a rigid kink in the otherwise straight chain acyl chain. o Unsaturated fatty acids in biological systems contain only cis double bonds. o Fatty acids with trans bonds can pack together tightly and have higher melting points than unsaturated FAs. o Unsaturated FAs with cis double bond kink cannot pack as closely together as saturated FA chains. o The trans fatty acids have similar properties as saturated FAs, but are not natural. Trans fatty acids can be associated with increased plasma cholesterol levels and lead to heart disease. 2.3 Chemical reactions and chemical equilibrium  The extent and the rate at which reactions take place determine the chemical composition of cells.  Chemical reaction is in equilibrium when the rates of the forward and the reverse reactions are equal.  The ability of a reaction to go backward is called microscopic reversibility.  Initially, the rate of the forward reaction is determined in part by their initial concentrations and likelihood of the reactants bumping into one another.  As more products are formed, the concentration of reactants decreases and so does the forward reaction rate.  Once products accumulate, some of them will start participating in the reverse reaction.  Eventually, the rates of the forward and reverse reactions become equal, so that the concentrations of reactants and products stop changing, and the system is said to be in chemical equilibrium.  The ratio of the concentration of products to reactants when they reach equilibrium is called the equilibrium constant K , eq a fixed value. Keq provides a measure of the extent to which a reaction occurs by the time it reaches equilibrium. A catalyst can change the rate of a reaction but does not change Keq.  Keq depends on the nature of the reactants and products, the temperature, and pressure. o Standard physical conditions (25°C and 1 atm), Keq is always the same for a given reaction, wheter or not a catalyst is present or not. o aA + bB + cC  zZ + yY + xX x y z a b c o Keq= [X] [Y] [Z] /[A] aB] [b] c o Rate forward= kf [A] [B] [C] o Rate reverse= kr [X] [Y] [Z] z  At equilibrium, the forward and reverse rates are equal; so Rate forward/Rate reverse=1  Reactions within cells usually never reach equilibrium. Instead, they are said to be in a steady state. Steady state refers to the concept that some products of one reaction may be the reactants for a different reaction. o If the products are being consumed by another reaction, they are not available for a reverse reaction to achieve equilibrium. So equilibrium is not achieved in these situations. o Instead, the system of linked reactions, the rate of formation of a substance can be equal to the rate of its consumption. This is referred to as steady state.  These linked reactions help protect cells from excess, harmful intermediates that may be created.  Steady state reactions often help achieve homeostasis in biological systems by preventing drastic changes within the systems.  Equilibrium also refers to binding reactions of some molecules involving noncovalent interactions. o Ex: a ligand (insulin or adrenaline) binding to its receptor which triggers an intracellular pathway. o Ex: binding of a protein to a specific sequence of base pairs in a DNA molecule, which causes the expression of a nearby gene to increase or decrease.  Binding reactions are described in terms of the dissociation constant Kd. o P + D   PD o Kd= [P] [D]/[PD] o The lower Kd, the tighter the binding (higher affinity) o For protein-protein or protein-DNA binding,  Tight binding: Kd= < 10 -9 -6  Modestly tight: Kd= 10 -3  Relatively weak: Kd= 10  Large molecules such as proteins, can have multiple binding surfaces. o In some cases, binding reactions are independent with their own distinct Kd values that are constant. o In some cases, binding of a molecule at one site can change the 3D shape of a distant site, thus altering the binding interactions at the distant site. o This is an important mechanism by which one molecule can alter, and thus regulate, the binding of another. Biological Fluids have characteristic pH values  The solvent inside cells and in all extracellular fluids is water.  H+ (proton) and OH- are the dissociation products of water, constituents of all living systems, and necessary for many reactions that take place between organic molecules within cells.  The concentration of hydrogen ions is expressed as its pH; negative log of the hydrogen ion concentration.  pH of pure water at 25°C is 7. o A 1 unit difference in pH represents a 10 fold difference in the concentration of protons. o 7.0= neutral o 0= acidic o 14= basic  Cytosol of cells normally has a pH of 7.2  The interior of some organelles can be much lower. o Lysosomes: 4.5 pH; many of the enzymes function well at a lower pH and their actions are inhibited by higher pH.  Shifts in pH may play an important role in controlling cellular activity.  Acids tend to release hydrogen  A base is a molecule, ion, or chemical group that ready combines with H+  Many biological molecules contain both acidic and basic groups.  A molecule that contains equal number of positive and negative ions, having no net charge, and is neutral is called a zwitterion.  Henderson Hasselbalch equation: pKa. pH= pKa + log [A-]/[HA] o HAH+ + A- o pKa of any acid is equal to the pH at which half of the molecules are dissociated and half are neutral. o We can used the Henderson Hasselbalch equation to calculate the degree of dissociation of an acid if both the pH of the solution and the pKa of the acid are known.  A living cell must maintain a constant pH of 7.2-7.4 o Metabolism produces many acids such as lactic acid and carbon dioxide. o Cells has reservoir of weak bases and weak acids, called buffers which ensure that the cells cytoplasmic pH remains relatively constant despite fluctuations in the amounts of H+ and OH-. o Buffers work by “soaking up” excess H+ or OH-  The ability of a buffer to minimize changes in pH is its buffering capacity. The buffering capacity depends on the concentration of the buffer and the relationship between its pKa value and the pH.  Common buffers in biological systems o Phosphate ions, ionized forms of phosphoric acid 2.4 Biochemical Energetics  2 principle forms of energy: o Kinetic: the energy of movement: the motion of molecules o Potential: stored energy: the energy stored in covalent bonds.  Thermal energy: a form of kinetic energy: must flow from high temperature to low temperature. o The thermal energy in warm-blooded animals is used chiefly to maintain constant body temperatures; this is important homeostatic function because rate of cellular activities are temperature dependent.  Radiant energy: the kinetic energy of photons, or waves of light. o Radiant energy can be converted to thermal energy (ex: when light is absorbed by molecules and the energy is converted to molecular motion) o Radiant energy can also change the electronic structure of the molecules, moving electrons into higher-energy orbitals, whence it can later be recovered to perform work. (photosynthesis)  Mechanical energy: form of kinetic energy; usually results from conversion of store chemical energy.  Electric energy: o The energy of moving electrons or other charged particles: form of kinetic energy; important to membrane function and electrically active neurons.  Chemical Potential Energy: the energy stored in the bonds connecting atoms in molecules. Ex: the high potential energy in the covalent bonds of glucose can be released by controlled enzymatic combustion in cells. This energy is used by the cell to do many kinds of work.  Concentration gradient: form of potential energy. All cells form concentration gradients between their interior and exterior fluids by selectively exchanging nutrients waste products, and ions with their surroundings.  Electric Potential energy: the energy of charge separation. Ex: Gradient of =200,000 volts/cm electrical charge across the plasma membrane of most cells.  1 law of thermodynamics: energy is neither created nor destroyed but can be converted from one form to another. o In photosynthesis, the radiant energy of light is transformed into chemical potential energy of the covalent bonds between the atoms in a sucrose or starch molecule. o In muscles and nerves, chemical potential energy stored in covalent bonds is transformed into kinetic energy of muscle contraction and electrical energy in nerve transmission.  In cells, potential energy is used to generate potential energy in the form of concentration and electrical potential gradients.  Potential stored in gradients is used to synthesize chemical bonds or to transport molecules from one side of a membrane to another to generate a concentration gradient.  1 joule=0.239 calorie  A calorie is the amount of energy required to raise the temperature of one gram of water by 1C o 1 kcal=1000 cal  Exergonic reaction: energy releasing: products contain less energy than the reactants. Take place spontaneously, usually release heat and generally result in a raise of temperature.  Endergonic reaction: energy absorbing: products contain more energy than the reactants and energy is absorbed during the reaction. Requires external energy source to drive the reaction.  Free energy: A chemical reaction occurs spontaneously when the free energy of the products is lower than the free energy of the reactants. o J. W. Gibbs “all systems change in such a way that free energy is minimized.” o ΔG = ΔGproducts – ΔGreactants  If ΔG is negative, the forward reaction will tend to occur spontaneously and energy will be released as the reaction takes place; thermodynamically favorable.  If ΔG is positive, the forward reaction will nto occur spontaneously; energy will have ot be added to the system in order to force the reactants to become products; endergonic reaction.  If ΔG is zero, both forward and reverse reactiosn occur at equal rates and there will be no spontaneous net conversion of reactants to products. The system is in equilibrium.  Enthalpy: bond energy  Entropy: measure of randomness or disorder  2 ndlaw of thermodynamics: the natural tendency of any system is to become more disordered, or an increase in entropy.  A reaction can occur spontaneously only if the combined effects of changes in enthalpy and entropy lead to a lower ΔG.  Exothermic reaction: heat releasing  Endothermic reaction: heat absorbing  Reactions that decrease entropy, such as building proteins, are often coupled with independent reactions that increase entropy and have a highly negative ΔG value.  The actual change in free energy during a reaction is influenced by temperature, pressure, and initial concentration of reactants and products. The actual energy change usually differs from the standard free-energy change. o Biological reactions can also be influenced by the pH of the solution/environment.  The rates of reactions in biological systems are usually determined by the activity of enzymes; protein catalysis that accelerate the formation of products from reactants without altering the value of ΔG.  Transition state: the state during a chemical reaction at which the system is at its highest energy level.  Transition state intermediate: the collection of reactants at the transition state.  Activation energy: the energy needed to excite the reactants to this higher energy state.  From the transition state, the collection of atoms can either release energy as the reaction products are formed or release energy as the atoms go backward and re-from reactants.  The velocity t which products are generated from the reactants during the reaction under a given set of conditions will depend on the concentration of material in the transition sate, which in turn will depend on the activation energy of the characteristic rate constant at which the transition state is converted to products.  The higher the activation energy, the lower the fraction of reactants that reach the transition state and the slower the overall rate of reaction.  Many processes in cells are energetically unfavorable and will not proceed spontaneously. o Ex: synthesis of DNA, transport of substances across a membrane from low concentration to high concentration.  Cells can carry out an endergonic reaction by coupling it to an exergonic reaction if the sum of the two reactions has an overall net negative ΔG.  Energetically unfavorable reactions in cells are often coupled with the hydrolysis of ATP.  ATP: responsible for capturing, transiently storing, and transferring energy to perform work. o Cell’s “energy currency” o Discovered in 1929 by Kurt Lohmann, Cyrus Fiske, and Yellagaprada SubbaRow.  The proposal that ATP is the main intermediary for the transfer of energy in cells is credited to Fritz Lipmann 1941.  The useful energy of ATP is contained in phosphoanhydride bonds, covalent bonds formed from the condensation of two phosphates and loss of water. o Forming these bonds requires energy. When these bonds are hydrolyzed by the addition of water, that energy is released.  Photosynthesis: process by which plants, algae, and photosynthetic bacteria trap the energy of sunlight to use it to synthesize ATP from ADP and Pi. o Much of the ATP produced in photosynthesis is hydrolyzed to provide energy for the conversion of carbon dioxide to six-carbon sugars by carbon fixation. o The sugars made during photosynthesis are a source of food and energy for the photosynthetic organism and the non-photosynthetic organism that consume the plants.  The free energy in sugars and other molecules derived from food is released in the process of glycolysis and cellular respiration. o During cellular respiration, glucose is oxidized to carbon dioxide and water.  The oxygen dependent aerobic catabolism of glucose is the major pathway for generating AP in all animal cells non-photosynthetic plant cells, and many bacterial cells.  Oxidation: the loss of electrons from an atom o Ex: removal of electrons from the sulfhydryl groups of two cysteines to form a disulfide bond.  Reduction: the gain of electrons by an atom  If one atom in a reaction is oxidized, the other must be reduced; redox reactions.  NAD+ is an electron carrier (coenzyme) that aids in the transfer of electrons during a redox reaction. NAD+ is reduced to NADH. o FAD is another carrier that is reduced to FADH2 to transfer protons and electrons to other molecules  Reduction potential: the readiness with which an atom or molecule gains an electron; E.  Oxidation potential: the tendency to lose electrons  In a redox reaction, electrons move spontaneously toward atoms or molecules having more positive reduction potentials. A molecule having a more negative reduction potential can transfer electrons spontaneously to a molecule with a more positive reduction potential.


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