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152 Cards in this Set
- Front
- Back
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What are exergonic processes that produce ATP?
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catabolic reactions
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What is the Gibbs free energy of catabolic reactions? Explain.
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Negative. Products are at a lower energy state than reactants. |
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What are endergonic processes?
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anabolic reactions, require ATP
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What does the binding of substrate to enzyme usually occur through? |
weak molecular interactions, such as ionic and hydrogen bonding
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What does the binding of an enzyme cause in its substrate? |
change to allow breakage or formation of bonds
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What are four mechanisms of catalysts?
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Enzyme puts strain on substrate bonds so they break more readily. Enzyme puts substrates in correct orientation for a reaction. Enzyme creates a more favorable microenvironment, such as proper pH. Enzyme forms temporary bonds that aid the conversion from substrate to product. |
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What is the active site hypothesis? |
lock and key
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What gives enzymes the flexibility to bind to substrates with some degree of variation in size and shape? |
induced fit
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What are cofactors? |
nonprotein activators of certain enzymes
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What is an enzyme bound with a required cofactor called?
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holoenzyme
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What is an enzyme without the cofactor it requires? |
nonfunctional apoenzyme
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What are prosthetic groups? |
cofactor molecules permanently bound covalently
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What are coenzymes? |
reversibly bound cofactors
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What transfer organic subunits to enable catalysis? Give three examples. |
coenzymes ATP NAD water-soluble vitamins |
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What are second substrates? |
coenzymes, which are physically altered during the course of a reaction
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Are coenzymes specific or can they assist a wide variety of different enzymes? |
They can assist a wide variety of different enzymes.
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What is the rate at which an enzyme converts substrate to product? |
enzyme activity
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What is enzyme activity determined by? |
saturation kinetics
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What is the Michaelis-Menten constant and its symbol?
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substrate concentration that generates a reaction rate that is 1/2 of Vmax for a particular enzyme Km |
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Does an enzyme with a higher Km have more or less ability to bind its substrate? Explain. |
Less. It requires more substrate to achieve the same reaction rate.
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Why do enzymes have optimal temperature and pH ranges?
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Outside of its range, the enzyme's three-dimensional structure will be disrupted. Ultimately it may be denatured and cease to function.
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What are enzyme regulators that increase the action of an enzyme? |
enzyme activators
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Are enzyme activators more or less common than inhibitors? |
less
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Are enzyme inhibitors reversible or irreversible? |
can be either
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Are most biological enzyme inhibitors reversible or irreversible?
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reversible
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What are inhibitors that are structurally similar to the substrate? |
competitive inhibitors
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Are competitive inhibitors less effective on enzymes with high or low Km? Explain. |
Low. The enzyme's high binding affinity for substrate will outcompete the inhibitor.
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Do competitive inhibitors change Vmax?
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no
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What inhibitors bind to an allosteric site on the enzyme? |
uncompetitive noncompetitive mixed |
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What inhibition occurs only in the presence of substrate and why?
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uncompetitive inhibition, inhibitors bind to enzyme-substrate complex
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Does uncompetitive inhibition affect Vmax? |
Yes, it lowers it. |
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Does uncompetitive inhibition affect Km? |
Yes, it lowers it by increasing the apparent binding affinity of the enzyme which remains attached to the substrate.
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Does uncompetitive inhibition occur more readily at high or low substrate concentrations? |
high
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When does noncompetitive inhibition occur? |
when an inhibitor can bind to an enzyme regardless of whether substrate is present
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What kind of inhibition prevents the enzyme from undergoing the conformational change necessary for conversion of substrate to product? |
noncompetitive inhibition
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What happens if the concentration of a noncompetitive inhibitor is raised to saturation levels?
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Enzyme activity ceases.
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Does noncompetitive inhibition occur more readily at high or low substrate concentrations? |
both
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What kind of inhibition lowers binding affinity (therefore raising Km)? |
mixed
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Does noncompetitive inhibition affect Vmax? |
Yes, it lowers it.
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Does mixed inhibition affect Vmax? |
Yes, it lowers it.
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What enzymes do not follow Michaelis-Menten kinetics?
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allosteric enzymes
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What behaves like an allosteric enzyme? Explain. |
Hemoglobin. It exhibits cooperativity in binding oxygen and has a sigmoidal reaction curve.
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What are two examples of covalent modification that can regulate enzymes? |
phosphorylation/dephosphorylation proteolytic cleavage (breaking of peptide bonds to remove a peptide or amino acid) |
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What amino acids can participate in phosphorylation/dephosphorylation?
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serine tyrosine |
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What is a newly synthesized enzyme in an inactive precursor state?
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zymogen
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What are generally produced as zymogens and why?
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digestive enzymes, to prevent tissue damage
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What are pepsin and trypsin?
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enzymes that break down protein in the digestive tract
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What is renin?
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protease and hormonal regulator in the kidneys
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What type of reaction do oxidoreductases catalyze? |
oxidation/reduction reactions via transfer of electrons or H and O atoms |
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What type of reaction do transferases catalyze? |
transfer of a functional group between substrates |
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What type of reaction do hydrolases catalyze? |
cleavage of a substrate by the addition of water (hydrolysis) |
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What type of reaction do lyases catalyze?
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non-hydrolytic bond formation or cleavage of functional groups, particularly of C-C, C-O, C-N, or C-S bonds |
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What type of reaction do isomerases catalyze? |
rearrangement of a molecule from one isomer to another |
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What type of reaction do ligases catalyze? |
ATP-fueled joining of substrates by formation of C-C, C-O, C-S, or C-N bonds |
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What is the principal metabolic pathway for generating energy for the cell?
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cellular respiration
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What is the overall reaction for cellular respiration in the presence of oxygen?
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C6H12O6 + 6O2 -> 6CO2 + 6H2O + chemical energy + heat
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What is essentially the reverse of aerobic respiration?
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photosynthesis
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Where is the chemical energy (energy not lost as heat) generated in aerobic respiration?
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in the bonds of a variety of transition molecules (ultimately ATP)
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What is ATP composed of? |
nitrogenous base adenine linked to a ribose sugar with three phosphate groups attached
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What are the three end products of glycolysis?
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2 3-carbon pyruvate molecules 2 ATP 2 NADH |
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Where does glycolysis occur?
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cytoplasm
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Does glycolysis require oxygen? |
no
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What prepares the way for either aerobic or anaerobic respiration?
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glycolysis
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What is the first step of glycolysis? What enzyme catalyzes this reaction?
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phosphorylation of glucose to glucose-6-phosphate hexokinase |
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What is the second step of glycolysis? What enzyme catalyzes this reaction?
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conversion of glucose-6-phosphate to fructose-6 phosphate isomerase |
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What is the third step of glycolysis? What enzyme catalyzes this reaction?
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phosphorylation of fructose-6-phosphate to fructose-1,6,-bisphosphate phosphofructokinase |
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What is the fourth step of glycolysis? What enzyme catalyzes this reaction? |
splitting of fructose-1,6-bisphosphate into two 3-carbon sugars: glyceraldehyde 3-phosphate (GADP) and dihydroxyacetone phosphate (DHAP), which is immediately converted into GADP aldolase splits fructose-1,6-bisphosphate, triose isomerase (TPI) converts DHAP into GADP |
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What is the fifth step of glycolysis? What enzyme catalyzes this reaction?
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dehydrogenation and phosphorylation of GADP to convert it into 1,3-bisphosphoglycerate glyceraldehyde 3-phosphate dehydrogenase |
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What is the sixth step of glycolysis?
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transfer of phosphate to create ATP, 1,3-bisphosphoglycerate molecules are converted to 3-phosphoglycerate
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What is the seventh step of glycolysis? |
shift of phosphate group, 3-phosphoglycerate is rearranged to 2-phosphoglycerate
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What is the eighth step of glycolysis?
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production of phosphoenolpyruvate (PEP) by removing a molecule of water from 2-phosphoglycerate
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What is the ninth step of glycolysis? What enzyme catalyzes this reaction?
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transfer of phosphate group from PEP molecule to ADP, forming two pyruvate molecules and 2 ATP molecules
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What is the overall reaction for glycolysis?
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glucose + 2ADP + 2Pi + 2NAD+ -> 2pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
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What steps of glycolysis require ATP?
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glucose -> glucose-6-phosphate fructose 6-phosphate -> fructose-1,6-bisphosphate |
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What steps of glycolysis produce ATP and how?
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1,3-bisphosphoglycerate -> 3-phosphoglycerate phosphoenolpyruvate -> pyruvate substrate-level phosphorylation |
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Is NAD+ or NADH the reduced form?
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NADH
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What step of glycolysis produces NADH and what is produced with it? |
glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate H+ (oxidized) |
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What step of glycolysis produces H2O?
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2-phosphoglycerate to phosphoenolpyruvate
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After what step of glycolysis do intermediates double up?
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Fructose-1,6-bisphosphate splits into GADP and DHAP, which is converted into GADP. Two GADP molecules then go on to eventually produce two pyruvate molecules.
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What are the intermediates of glycolysis from glucose to pyruvate?
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Glucose Glu-6-P Fru-6-P Fru-1,6-bP GADP & DHAP(-> GADP) 1,3-bPG 3-PG 2-PG PEP Pyruvate |
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What is phosphofructokinase subject to feedback inhibition by?
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ATP citrate |
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What controls the rate of glycolysis?
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phosphofructokinase
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What is substrate-level phosphorylation?
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transfer of an inorganic phosphate group from an intermediate molecule to ADP to form ATP
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Why is the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate a rate-limiting step? What other step is regulated in the same way?
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It depends on the availability of ADP for substrate-level phosphorylation. PEP -> pyruvate |
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What are the two components of aerobic respiration?
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citric acid cycle and oxidative phosphorylation
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What happens to pyruvate produced by glycolysis when there is oxygen present in the cell?
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It's converted into carbon dioxide and water via the citric acid cycle and oxidative phosphorylation.
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Where do the citric acid cycle and oxidative phosphorylation take place in prokaryotes?
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cytoplasm
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Where do the citric acid cycle and oxidative phosphorylation take place in eukaryotes?
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mitochondria
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How does pyruvate get from the cytoplasm to the mitochondria and what happens next?
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It is actively transported across both mitochondrial membranes into the inner matrix, where it is decarboxylated to acetyl coenzyme A by a complex of pyruvate dehydrogenase enzymes.
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What is the reaction for the conversion of pyruvate to acetyl CoA from one glucose molecule?
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2pyruvate +2coenzyme A + 2NAD+ -> 2 acetyl CoA + 2CO2 + 2 NADH + 2H+
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How many carbons are in acetyl CoA?
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2
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What is the citric acid cycle also known as? (2)
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tricarboxylic acid cycle (TCA) Krebs cycle |
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What is acetyl CoA combined with in the citric acid cycle? What exits the cycle at this stage?
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oxaloacetate to form 6-carbon citrate coenzyme A |
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What happens to citrate in the citric acid cycle?
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It's broken down in a series of steps, releasing 2 molecules of CO2 and transferring electrons to the electron carries NAD+ and FADH+.
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How many NADH carriers are formed per citric acid cycle? FADH2?
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3 1 |
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What provides ions for NAD+ and FADH+ in the citric acid cycle?
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water
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What is phosphorylated in the citric acid cycle in some animals and can be used to synthesize 1 ATP via substrate-level phosphorylation?
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GDP -> GTP
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What is regenerated in the "last" step of the citric acid cycle?
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oxaloacetate, which perpetuates the cycle to start anew
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What is the reaction equation for two turns of the citric acid cycle (made possible by one molecule of glucose)?
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2acetyl CoA + 6NAD+ 2FADH+ + 2GDP +2Pi + 2H2O -> 4CO2 + 6NADH + 6H+ + 2FADH2 + 2GTP + 2coenzyme A
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What proteins incorporate an iron-containing heme group as both a prosthetic group and an electron acceptor?
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cytochrome
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What happens to each electron acceptor in the electron transport chain?
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Each is alternately reduced and then oxidized as it accepts and then donates electrons.
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How does energy relate to the electron transport chain?
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Electrons travel down a free-energy gradient, passing from a less electronegative receptor to a more electronegative receptor. The change in free energy is coupled with the pumping of H+ ions across the inner mitochondrial membrane into the inner membrane space.
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Why can't H+ ions actively transported into the inner membrane space of mitochondria go back into the matrix? What does this form?
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They are charged and cannot cross the membrane, resulting in a positive charge buildup in the intermembrane space, creating a region of low pH. This forms an electrochemical gradient across the membrane that can be coupled with ATP synthesis in a process called chemiosmosis. |
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What occurs in chemiosmosis?
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The high concentration of H+ ions in the intermembrane space generates a proton-motive force to do molecular work in the cell. The return of H+ ions down a concentration gradient through a transmembrane channel protein (ATP synthase) drives the phosphorylation of ADP to ATP.
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What acts as a molecular motor and is a multiunit enzyme composed of 4 subunits?
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ATP synthase
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How are ADP and inorganic phosphate converted to ATP in oxidative phosphorylation?
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Hydrogen ions bind to each subunit of ATP synthase, triggering rotational movement and allowing H+ to be pumped back into the matrix. The turning of the rotor activates catalytic regions in the matrix that make the conversion.
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What is ATP synthesis that involves the phosphorylation of ADP along with the redox reactions of the electron transport chain?
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oxidative phosphorylation
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What happens to ATP once it is synthesized in the matrix?
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ATP-ADP translocase exports it across both mitochondrial membranes to the cytoplasm by coupling it with the transport of ADP into the matrix. This results in positive feedback if there is little ADP outside of the cell (and thus little need for ATP).
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How many ATP molecules are formed from every NADH entering the electron transport chain?
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2-3
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How many ATP molecules are formed from every FADH2 entering the electron transport chain?
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2
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How many ATP molecules does oxidative phosphorylation produce?
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32-34
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What is the total energy produced by aerobic respiration, including glycolysis?
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36-38
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How can bacteria generate ATP in an anaerobic environment?
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by using a final electron acceptor other than oxygen, although oxygen is the most efficient
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What are the sources of NADH?
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2 from glycolysis 2 from oxidation of two pyruvates (pyruvate decarboxylation, forming two acetyl CoA) 6 from citric acid cycle (3 from each acetyl CoA) |
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What are the sources of FADH2?
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2 from citric acid cycle (1 from each acetyl CoA)
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How can cells continue to generate ATP in the absence of oxygen?
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via glycolysis using the process of fermentation
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How does fermentation differ from anaerobic respiration?
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It doesn't use the citric acid cycle or the electron transport chain.
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What are the two main fermentation pathways?
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alcohol fermentation lactic acid fermentation |
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What does fermentation use and how many ATP are produced?
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terminal electron receptor other than oxygen only the 2 from glycolysis |
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What is alcohol fermentation carried out by and what do they do?
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Bacteria and yeast convert the pyruvate generated by glycolysis into ethanol and carbon dioxide.
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What is the mechanism of alcohol fermentation?
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Pyruvate is converted into acetaldehyde by the removal of CO2. Acetaldehyde is then reduced to ethanol by NADH.
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What is the terminal electron receptor in alcohol fermentation?
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acetaldehyde
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What provides the bubbles in beer and enables bread to rise?
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CO2 produced by alcohol fermentation
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What is the terminal electron receptor in lactic acid fermentation?
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pyruvate
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What is the mechanism of lactic acid fermentation?
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NADH reduces pyruvate to lactate (the ionized form of lactic acid). NADH is oxidized to NAD+, which is needed for glycolysis.
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Where does lactic acid fermentation occur?
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In some bacteria and fungi and in human muscle cells in high-performance situations when the supply of oxygen is insufficient to meet metabolic demand.
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What are the primary metabolic energy source?
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carbohydrates
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What is the primary carbohydrate energy source?
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glucose, which makes up 90% of blood sugar
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What is the plant equivalent of glycogen in animals?
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starch
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What happens to monosaccharides other than glucose?
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converted to glucose or other substances that can be used in glycolysis
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What are fat molecules broken down into? Which can be used as an energy source?
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glycerol and fatty acid chains both |
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How can glycerol be used as an energy source?
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It can be converted into GADP.
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How can fatty acids be used as an energy source?
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They can be transported to the mitochondrial matrix where they undergo beta oxidation.
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What is the mechanism of beta oxidation?
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Oxidation of the carbon backbone of the fatty acid followed by dehydrogenation and hydration reactions and ultimately the cleavage of 2-carbon acetyl CoA molecules from the end of each fatty acid chain. The dehydrogenation reactions produce 1 NADH and 1 FADH2 and acetyl CoA enters the citric acid cycle.
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What are a major source of energy for skeletal muscle engaged in sustained aerobic activity?
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fatty acids
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How are dietary proteins broken down?
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They are hydrolyzed by digestive enzymes that break the peptide bonds linking amino acids. Amino acids then undergo deamination, during which the amino group is removed and converted to urea (excreted by the urinary tract). The remaining carbon backbone is then modified and ultimately converted into an intermediate of the citric acid cycle.
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Can structural proteins be used as an energy source?
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In cases of severe malnutrition, resulting in emaciation and wasting of muscle tissue.
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What happens if a glucose molecule is transported into a cell that has sufficient ATP?
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It may be converted to an energy storage molecule such as glycogen or starch.
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How are intermediates in glycolysis used in anabolic biosynthesis? (3)
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Half of the required amino acids can be made in the citric acid cycle. Pyruvate can be converted to glucose via gluconeogenesis. Acetyl CoA can be converted to fatty acids for lipid synthesis. |
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What category of enzymes do oxidases belong to?
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oxidoreductases
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What category of enzymes do dehydrogenases belong to?
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oxidoreductases
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What category of enzymes do kinases belong to?
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transferases
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What category of enzymes do polymerases belong to?
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transferases
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What category of enzymes do phosphorylases belong to?
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transferases
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What category of enzymes do nucleases belong to?
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hydrolases
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What category of enzymes do proteases belong to?
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hydrolases
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What category of enzymes do lipases belong to?
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hydrolases
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What category of enzymes do phosphatases belong to?
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hydrolases
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What category of enzymes do decarboxylases belong to?
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lyases
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What category of enzymes do synthases belong to?
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lyases
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What category of enzymes do aldolases belong to?
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lyases
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What category of enzymes do synthetases belong to?
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ligases
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