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Exam 1 SQ Key Chapter 2: Water and Carbon—The Chemical Basis of Life Lecture 2 PPT Review: 1.) What is electronegativity? Compare and contrast polar covalent vs nonpolar covalent bonds? a. Electronegativity = A measure of the ability of an atom to attract electrons toward itself from an atom to which it is bonded (caused by number of protons in NUC and distance between NUC and valence shell. b. Nonpolar Covalent—electrons are shared equally between atoms of the same or similar electronegativity Polar Covalent—electrons are shared unequally between atoms differing in electronegativity. This results in a the more electronegative atom having a partial negative charge and the other atom having a partial positive charge 2.) Why do partial charges form on molecules? ^^^ 3.) What is an ionic bond? a. Electron is completely transferred from one atom to another so that the atoms remain associated due to their opposite electric charges 4.) Explain the properties of water a. Polar or Nonpolar? i. Polar b. Covalent or noncovalent bonding? i. Covalent c. Partial charges for each atom? i. Partial negative on oxygen and partial positive on H’s 5.) What types of bonds form between water molecules? a. Hydrogen bonds 6.) Why is water an excellent solvent? (p.25) –think about its interaction with an ionic molecule like NaCl. a. Electronegativity causing partial + and partial – charge b. Molecule is bentPartial – charge of O sticks out, away from the partial + charges on H. Makes it so these partial charges can interact with those on other H2O (H-bonding) or other molecules. i. Ions and polar molecules stay in solution bc of their interaction w/ H2O charges 7.) Are nonpolar molecules hydrophilic or hydrophobic? What properties of both the molecule and water cause this? a. HydrophobicUncharged and nonpolar. They have minimal or nonexistent interaction with water. H2O is opposite of this (Polar w/ the partial charges) 8.) What are the two properties of buffers we discussed? 1. Resist changes in pH 2. Have the ability to accept or donate H+ 9.) What is pH? What is the physiological pH? a. pH = the concentration of H+ (proton) in solution b. Physiological pH = 6.5 – 8.0 10.) At a basic pH, what is the relationship between [OH-] and [H+]? What is the relationship at an acidic pH? a. Basic = [OH-] > [H+] b. Acidic = [H+] > [OH-] 11.) What types of bonds can carbon form? How many? a. Covalent bonds b. 4 because Carbon has 4 electrons in outer valence shell so needs 4 more electrons to complete octet. Therefore forms 4 covalent bonds to satisfy this. 12.) Be sure to know the functional groups and family of molecules that Dr. A recommended to know! 13.) Review the examples on the PPT + Bioskills 6 and 8 in Appendix B of textbook. Chapter 3: Protein Structure and Function Lecture 3 “PSF” Review: 1.) What is an amino acid (AA)? What are the structural components of an AA? What is the central carbon denoted as? a. AA = the building blocks of proteins, each containing an amino group, a carboxylic group, and a side chain (R group) attached to the alpha carbon 2.) What is the difference between the non-ionized form of an AA and the ionized form? (Be able to draw both is a good idea!) a. Ionized has carboxylic group deprotonated (COO-) and amino group protonated (NH3+) 3.) Which structural component of an AA distinguishes it from all of the other AAs? a. The side chain (R group) 4.) Classify the AAs according to the following properties of their side chains: a. Nonpolar i. G A P I L V M C F W b. Polar i. S T Y N Q c. Polar (+) charge i. H R K d. Polar (-) charge i. D E 5.) Which AAs are basic? Which are acidic? a. Basic = H R K b. Acidic = D E 6.) What is the name of the covalent bond that links peptides? What reaction joins peptides together? What molecule is released during this reaction? What is the reverse of this reaction? a. Peptide Bond b. Condensation Rxn c. H2O released d. Hydrolysis 7.) Is the directionality of AA arranged CN terminus or NC terminus? a. NC 8.) Describe the flexibility of the peptide backbone. a. Peptide bond has partial double bond character which limits free rotationthe bonds directly adjacent to the alpha carbon have some rotation 9.) Explain the four levels of protein structure. a. 1* = sequence of amino acids b. 2* = Hydrogen bonding between peptide backbone that form alpha helices and beta sheets. H-bonding between C=O on one AA to the Hydrogen on N-H of another AA c. 3* = Interactions between the R groups causes the protein to adopt its folded structure. One of the driving forces here is the hydrophobic effect. Disulfide bridges between Cys, van der waals, h-bonding (polar r groups), ionic. d. 4* = Multiple polypeptides coming together to form a single structure. Can have different functions. Defined by “domains” of the protein 10.) What are the structural differences between alpha helices and beta sheets? 11.) Are peptide bonds broken when proteins denature? What two ways (that we discussed) can a protein be denatured? a. Peptide bond stays intact b. Heat and surface denaturation Chapter 4: Nucleic Acids and the RNA World Lecture 4 PPT Review: 1.) What are the structural components of nucleic acids? Nucleic acids are also called what type of molecule? a. 5-carbon sugar, nitrogenous base, and phosphate group b. Nucleotide 2.) What structural feature distinguishes ribose from deoxyribose? a. Ribose has OH on C2 while deoxyribose has H on C2 3.) What are the names of all the nitrogenous bases? Which are purines and which are pyrimidines? What general structural characteristic distinguishes purines from pyrimidines? a. Adenine, Guanine, Cytosine, Thymine, Uracil b. A and G = purines, C, T, U = pyrimidines c. A and G are larger—they have the extra 5C cyclic ring attached. 4.) How do DNA and RNA differ in: a. Function i. DNA stores genetic info ii. RNA has potential for multiple fxns and structures b. Composition i. Deoxyribose vs ribose 5.) What reaction joins nucleotides in a DNA and RNA chain? What is the name of the bond that forms? What molecule is released from this reaction? What components of the nucleotide are interacting in this reaction? a. Polymerization (condensation) rxn. b. Phosphodiester linkage (bond) c. H2O released (condensation) d. Phosphate OH on one nucleotide with OH attached to C3 of nitrogenous base of another nucleotide 6.) What two interactions are occurring in the DNA double helix? Explain each. Together, both yield what structural benefit for the helix? a. Complementary base pairing and Base stacking by hydrophobic interactions b. Provides stability 7.) The directionality of the nucleotide sequence is read in what direction? a. 5’ 3’ (because of phosphodiester linkage between 5’C of one nuc with 3’C of another nuc. one end of the sugar-phosphate backbone has an unlinked 5’ phosphate while the other end has an unlinked hydroxyl 8.) How many bonds form between Guanine and cytosine versus adenine and thymine? How does heat denaturation affect these bonds? Therefore, how would you expect the composition of G’s and C’s vs A’s to T’s to differ in the DNA of an organism that lives in very high temperatures versus low temperatures? a. 3 H bonds between G---C | 2 H bonds between A and T b. Heat denaturation breaks H bonds c. A higher concentration of G---C would provide the most stability against heat denaturation 9.) What are the general steps in DNA synthesis? What catalyzes polymerization in cells? a. Strand separation b. Base-pairing c. Polymerization---Catalyzed by DNA polymerase 10.) How does the secondary structure of RNA differ from that of DNA? What about tertiary structure? a. RNA has hairpin loop + helices. DNA has beta sheets and alpha helices b. RNA can form tertiary. DNA has no tertiary structure 11.) What are the major types of RNA? a. Ribosomal b. Messenger c. Transfer d. Small nuclear e. Micro 12.) What protein enzyme catalyzes splicing of introns in “precursor” rRNA? What did this discovery indicate? a. RNA is catalytic—ribozyme 13.) What is the function of most ribozymes? What do rRNA catalyze during translation? a. Most catalyze the breaking of phosphodiester bonds 14.) What are the components of the RNA World Hypothesis? a. RNA replicates itself b. Self-replicating RNA also catalyzes protein synthesis c. DNA becomes the genetic material and codes for RNA Chapter 5: Introduction to Carbohydrates Lecture 5 PPT Review: 1.) What is a monosaccharide? What is the general formula for a monosaccharide? What structure allows monosaccharides to form polysaccharides? a. Monosaccharide = molecule that has molecular formula (CH2O)n and cannot be hydrolyzed to form any smaller carbs b. Forms polysaccharides via glycosidic linkages 2.) What do the functional groups tell you about the properties of monosaccharides? (3 discussed in lecture) a. Polar b. Hydrophilic c. Forms Hydrogen bonds 3.) What is the structural difference between a. Aldose and ketose i. Aldose has carbonyl at end of chain/Ketose has carbonyl in middle of chain b. Glucose and galactose i. Differ only by positioning of one hydroxyl OH on C4 4.) Review ring structure conformation of sugar using α- and β-glucose example. Why can sugars form the ring structure? a. Ring structures are more stable in ring structures—which is favorabletherefore occurs spontaneously 5.) How are disaccharides formed? How does the structure of fructose differ from glucose? a. Condensation Rxn b. Fructose is 5C ring 6.) Complete the following reaction: a. Gives you fructose and glucose 7.) What is the role of glycoproteins in cell identity? a. Each cell in your body has glycoproteins on its surface that identify it as part of your body (important for immune system!)—Keep in mind that there are huge potential for oligosaccharides to be unique, therefore each cell type and species can display a unique identity 8.) What are two of the major roles of polysaccharides discussed in class? a. Energy storage depots b. Structural scaffolds 9.) Compare/contrast the types of polysaccharides by each of the following: a. Roles/Uses b. Glycosidic Linkage/Chemical Structure c. 3D structure d. Use table 5.1 in book to review this 10.) Difference between Amylose and Amylopectin? a. Amylose has unbranched helices while amylopectin has branched helices 11.) Explain the role of carbohydrates in chemical energy storage. a. Starch and glycogen can convert glucose to ATP 12.) What feature makes cellulose, chitin, and peptidoglycan advantageous for organismal structures? Explain why. a. The beta1,4 glycosidic linkages are 1.) Difficult to hydrolyze and 2.) very few enzymes have activate sites that accommodate their geometry Chapter 6: Lipids and Getting Across Cell Membranes Lecture 6 PPT Review: 1.) Describe the solubility of lipids. a. Insoluble or only slightly soluble in H2O 2.) What are the general structural components that form fats and oils? Draw the general structure of a triglyceride. a. Glycerol w/ ester linkages attaching fatty acids (hydrocarbon chains) 3.) What attributes determine the properties of fats? Compare and contrast saturated vs unsaturated fats at room temperature (that we discussed in lecture—think back to video). a. SaturatedNo double bonds, linear structure, high melting point, solid at RT, “fat” b. Unsaturated double bonds, kink in structure, low melting point, liquid at RT, “oil” 4.) Why are phospholipids structurally important for eukaryotes? What are the structural components? Describe the hydrophobicity of these components. a. Essential for cell membrane—serving as barrier to outside world b. Amphipathichas polar, charged, hydrophilic head (interacts with surrounding H2O), and hydrophilic tail 5.) What is selective permeability? What two characteristics of a molecule is permeability dependent on? Arrange the following in terms of highest to lowest permeability: CO2 Na+ Sucrose N2 ClO2 Glycerol H2O K+ Glucose - O2, CO2, N2 > H2O, Glycerol > Glucose, Sucrose > Cl-, K+, Na+ - Permeability is dependent on temperature and fluidity 6.) What is the net water movement via osmosis under the following conditions? Describe the outcome/appearance for a RBC under these conditions, as well. a. Isotonic – concentration is at equilibrium b. Hypertonic – high solute concentration outside of cell, so H2O moves out of cell to balance c. Hypotonic – high solute concentration inside the cell, so H2O moves from outside the cell to inside to balance concentrations 7.) What is facilitated diffusion? How are ions passing through the membrane? (think concentration gradient) Does this transport require energy? What are allosteric proteins? What example was used in class to supplement this? a. Specific molecule binds to carrier protein in the membranewhich causes CCcausing molecule to travel down concentration gradient (so no energy required). Going from high concentration to low concentration** b. Allosteric proteins undergo shape change caused by binding (or other interaction) with another molecule/protein c. GLUT1 protein example 8.) What is active transport? How are ions passing through the membrane? (think concentration gradient) Does this transport require energy? What example was used in class to supplement this? a. Transporting molecules from low concentration to high concentration (against concentration gradient) therefore ATP input is required. ATP causes carrier protein to change shape and then allows transport. 9.) Permeability is a function of what two parameters? How does the structure of the bilayer influence these? a. Temperature and fluidity b. Short and unsaturated lipid bilayer = higher permeability and fluidity c. Long and saturated lipid bilayer = lower permeability and fluidity 10.) What structural component of steroids distinguishes these lipids from others? What example from lecture did we discuss? What 2 functions did we discuss this example as having? a. The four cyclic rings b. Cholesterol—cell membrane component and precursor of vitamin D and sex steroid hormones 11.) Review the Question box from Chapter 6 included in the lecture. 12.) Review transport animations Chapter 7: Inside the Cell Lecture 8 PPT Review “Inside the Cell: The Dynamic Cell—Intracellular Transport” 1.) What is the central dogma in biology? (will be discussed in more detail in later lectures) a. DNARNAProtein 2.) How do proteins get targeted to their correct destination in the cell? a. Localization signal/sequence 3.) Where does protein synthesis occur in the cell? How do mRNAs get out of the nucleus? How do nuclear proteins get into the nucleus? a. Ribosomes b. mRNAs exit through NPCs c. Nuclear proteins would need NLS to get into nucleus 4.) Outline as many components of the nucleus as you can—think about nuclear import, export, anatomy of nucleus, nucleic acid synthesis. 5.) What structures serve as a passageway into and out of the nucleus? a. Nuclear Pore Complex 6.) What is the name of the amino acid sequence present in all nuclear proteins? What is its function? What family of proteins interacts with these amino acid sequences? a. Nuclear Localization signal b. Localizes proteins to the nucleus—allows entry into nucleus c. Importins 7.) Outline the steps in the endomembrane system using RNA that has just been synthesized/transcribed. a. Ribosome b. RER c. Transport to cis golgi d. Cis to trans golgi e. Golgi packages to be released to destination 8.) What is the signal hypothesis? How does it explain the differences between the “signals” present within the AA sequence of an ER protein versus a nuclear protein? Include the modification to the ER protein that we discussed in class. a. Difference is that ER signal sequence is cleaved whereas nuclear localization signal remains intact. Caused by post translational modification 9.) What is glycosylation? What type of modification is this an example of? Be sure you can identify what the macromolecules are on this slide and any other example. a. Addition of a carbohydrate (sugar) to a molecule 10.) Why would a protein travel from the ER to the golgi? What is the protein transported in? a. Proteins getting different places in the cell need to be “packaged” into vesicles to get to other places 11.) A protein designated for the lysosome would have what unique signal/tag/sequence within its amino acid sequence? a. Mannose-6-phosphate Lecture 9 PPT Review “Inside the Cell: The Dynamic Cytoskeleton” 1.) Why would the cytoskeleton be characterized as dynamic? a. Expands and contracts over time 2.) What are the three major elements of the cytoskeleton? Arrange them in order of greatest to smallest size. a. Microfilaments b. Intermediate Filaments c. Microtubules 3.) What is the globular protein that forms microfilaments? Describe subunits of this protein. Describe polarity for this protein? a. Actin—the microfilament is composed of polymerizing and depolymerizing actin subunits b. Has positive and negative end 4.) What is treadmilling? a. Filaments polymerize and depolymerize 5.) What is myosin classified as? How does it perform its function? What reaction is involved? a. Motor Protein b. Converts chemical energy in ATP into mechanical work—Converts ATP to ADP which causes a shape change that extends the head region, attaches it to actin, and then contracts to pull itself along the actin filament---this shape change causes the actin and myosin to slide past each other. c. ATP hydrolysis 6.) What are 3 different types of movement that can occur through actin-myosin interactions? a. Cell crawling b. Cell division c. Cytoplasmic streaming in plants 7.) What is the primary protein that form intermediate filaments (that we discussed)? What are two functions of this protein? a. Keratin b. Functions = maintain cell shape by resisiting tension and anchor nucleus and some other organelles 8.) Describe polarity and “treadmilling” in intermediate filaments. a. Each end is identicaldoes not treadmill 9.) What are the proteins that make up the composition of microtubules? a. Tubulin—Has alpha and beta tubulin dimers 10.) List a few functions of microtubules? (There are two that were outlined in the PPT). Describe the polarity and “treadmilling” of microtubules. a. Functions = move organelles and provide tracks for intracellular transport b. Each end has distinct polaritytreadmilling can occur 11.) How are microtubules linked with the following: (Also list the motor proteins involved in each) a. Vesicle movement i. Kinesin w/ ATP moves cells along microtubule tracks (Watch video) b. Whole cell movement (think cilia + flagella) i. Dynein w/ ATP—flagella are made of microtubules that whip back and forth 12.) What is an axenome? a. 9 doublets + 2 central microtubules 13.) Watch “The Inner Life of the Cell” and work on understanding each aspect of the video—always good to have a visual memory to refer back to when you get stuck on questions! Chapter 12: The Cell Cycle Lecture 10 “Control of Cell Cycle” PPT review: 1.) Watch the Mitosis video from lecture. What are the different phases of mitosis? What happens at each phase? a. Interphase—after chromosome replication, each chromosome is composed of two sister chromatids. Centrosomes have replicated b. Prophase—Chromosome condense and spindle apparatus begins to form c. Prometaphase—Nuclear envelope breaks down. Microtubules contact chromosomes at kinetochores. d. Metaphase—Chromosomes complete migration to middle of cell e. Anaphase—Sister chromatids separate into daughter chromosomes and are pulled to opposite poles by spindle apparatus f. Telophase—The nuclear envelope re-forms, and chromosomes de-condense 2.) What are the phases of the cell cycle? What occurs during Gap phases? Explain the G0 phase. a. G1 growth to accommodate new genetic info—organelle replication (and in G2) etc b. S phase—DNA synthesis c. G2—constructs microtubules, prepares mitotic proteins, cytoplasm growth etc 3.) Define the following: a. MPF—M-phase promoting factor = a complex of a cyclin and CDK that when activated will phosphorylate a number of proteins needed to initiate mitosis in eukaryotic cells b. Cdk—cycling dependent kinase = protein kinase that is functional only when bound to a cyclin and are activated by other modifications. c. Cyclin = regulatory protein whose concentrations fluctuate cyclically throughout the cell cycle. Involved in control of cell cycle via cdk. 4.) How are Cdks activated? Explain the accumulation and degradation of cyclin in cells. a. Has to bind to cyclin 5.) 6.) 7.) 8.) b. Cyclin concentration increases during interphase and peaks in M phase, where it is then destroyed What is the relationship between concentrations of cyclin and activity of MPF? a. When cyclin concentrations are high, more MPF is active What is the function of Cdk? (include the reaction it’s involved in) a. Cdk is a protein kinase. It phosphorylates protein targets. There are 3 cell cycle checkpoints we discussed in lecture: a. What occurs at each checkpoint/What is being “checked”? i. G2—Checking if the DNA is both replicated and undamaged ii. M-Phase—Checking if chromosomes have attached to the spindle apparatus and that the chromosomes have segregated properly iii. G1—Checking if the cell is large enough, has enough nutrition to proceed through the rest of the CC, and that the DNA is undamaged b. State whether MPF is present or absent. i. G2—MPF present ii. M-phase—MPF absent Explain how the G1 checkpoint is subject to social control using the slides from lecture or book. What is acting as the “social control” in this? (p. 234 in text) 1. Growth factors arriving from other cells and stimulate the production of E2F and G1 cyclins 2. Rb binds to E2F, inactivating it. G1 cyclins form cyclin-Cdk dimers. The dimers are phosphorylated which inactivates them 3. The inactivating phosphate on the cyclin-Cdk dimer is removed 4. Active Cdk phosphorylates Rb 5. Phosphorylated Rb releases E2F 6. E2F stimulates production of S-phase proteins a. The growth factors (keep in mind these are from other cells though) are acting as social signals triggering the Rb protein to be overridden—allowing E2F to help progress the cell to S-phase 9.) What characterizes cancer on a cellular level? a. Uncontrolled cell growth, accumulation of genetic changes 10.) If a cancer cell divides without growth factors, which checkpoint does it bypass? Explain why cancer cells passing through this checkpoint is a problem—think about what occurs at the phase following G1. a. G1 phase b. Problem because G1 checkpoints are checking for DNA damage (among other things). Therefore, if these checkpoints are not operating properly and the cell passes through unchecked, DNA damage will be present in the DNA when replicated. 11.) During what phases in the cell cycle would you expect there to be large changes in the polymerization or depolymerization of microtubules? a. Polymerization—while the mitotic spindle is forming—prophase b. Depolymerization--Anaphase 12.) When actively growing cells are treated with Taxol, they often are unable to complete the cell cycle. Based on what you have learned about cell-cycle checkpoints, which checkpoint likely causes these cells to arrest? a. Taxol inhibits cell cycle at Metaphase of M-phase Chapter 8: Energy and Enzymes: An Introduction to Metabolic Pathways Lecture 11 “Energy and Enzymes” PPT Review: 1.) What is the 1st law of thermodynamics? a. States that energy can be transferred and converted into different forms, but it cannot be destroyed 2.) Explain potential and kinetic energy—using one of the examples from class may be a good way to practice this. a. Potential energy is energy associated with position or configuration—stored energy b. Kinetic energy is energy of motion c. In the waterfall example from class: A water molecule at the top of a molecule has high potential energythen as it falls the energy is converted to kinetic energyonce it strikes the rocks at the bottom, the kinetic-motion energy is converted to other kinds of energy (included mechanical, heat, sound) 3.) What is the second law of thermodynamics? Where is potential energy stored in a molecule? a. Second law states that entropy will always increase in an isolated system b. Potential energy is stored in the chemical bonds of a molecule 4.) If a reaction is favorable in the direction of reactantsproducts: a. Which would have the highest potential energy? i. Reactants b. Would the entropy be high or low in the High PE component?\ i. Low entropy (More ordered) 5.) What is a redox reaction? What is oxidation? What is reduction? Is oxygen usually an e- acceptor or donor? a. Redox rxn = a chemical reaction that involves the loss or gain of one or more electrons b. Oxidation is the loss of electrons c. Reduction is the gain of electrons d. Oxygen is usually the electron acceptor 6.) Compare and contrast Reduced molecules and Oxidized molecules by expressing: a. Bonds that are in high quantity i. Reduced = C-H ii. Oxidized = C-O b. Level of potential energy (high or low) i. Reduced = many C-H with high PE ii. Oxidized = many C-O with low PE 7.) Define: a. Exothermic reaction i. A chemical reaction that can occur spontaneously, releasing heat and/or increasing entropy, and for which the Gibbs free energy is less than zero b. Endothermic reaction i. Chemical reaction that requires an input of energy to occur and for which the Gibbs free energy is greater than zero. 8.) Why are endergonic reactions linked to exergonic reactions in cells? –> So why is ATP hydrolysis an important reaction in cellular energetics? a. Endergonic reactions require an input of energy—Exergonic reactions release energy. Therefore, the energy released by the exergonic reaction can be used to drive the endergonic reaction forward b. ATP hydrolysis releases high amount of energy and can initiate many of the cell’s endergonic reactions 9.) What structural component of ATP causes it to have potential energy stored within the molecule? a. The triphosphate component has the (-) charges of each phosphate in close proximity. Since like charges repel each other, this makes hydrolysis very favorable (exergonic) to relieve the repulsion between the (-) charges 10.) What is the activation energy of a reaction? How do molecules deal with this? a. The amount of energy required to initiate a chemical reaction; specifically the energy required to reach the transition state b. Energy molecules must collide in precise oritentation and overcome mutual repulsion—enzymes help to lower the activation energy 11.) Define: a. Enzyme i. A globular protein that is specialized to serve as a catalyst b. Catalyst i. A substance that lowers the energy of activation for a reaction by forming a temporary association with the reacting molecule 12.) Draw the generic energy profile that we looked at in lecture. Include: a. Reactants b. Transition State c. Products d. Label the x and y axis e. State whether your rxn is exergonic or endergonic f. Ea g. ΔG h. Figure 8.11 and 8.12 in text shows energy diagrams from class 13.) Explain induced fit using the reaction above. Would the cell be able to utilize an enzyme after it undergoes the reaction we examined in lecture? Why? a. Induced fit is a change in the shape of an enzyme’s active site in response to the initial binding with a substrate. In the example from class, the substrate binds to the active site of the enzyme which causes a shape change in the active site. The shape change allows the active site to bind to the substrate more tightly which lowers Act. Energy b. Yes, the enzyme is not consumed during the reaction. The reason that it isn’t bound anything in the final step is because the products of the reaction bind with lower affinity and therefore release. However, the same substrates would be able to bind and initiate the reaction again. 14.) What is allosteric activation? What is allosteric inhibition? What is competitive inhibition? a. Allosteric activation and inhibition involve a substrate binding to a site on the enzyme other than the active site which causes a conformational change that makes the active site available (allosteric activation) or unavailable (allosteric inhibition) b. Competitive inhibition occurs when the active site of the enzyme is occupied by a molecule that isn’t the enzymes normal substrate. Hence, the alternate molecule is competing with the normal substrate.