Enzymes and Metabolism Flashcards
Enzymes have specific functions based on their structure. What happens if the structure of an enzyme is changed/mutated? What are two ways in which enzyme structure can be altered?
Change in structure = change in function
extreme temperature and pH
How do enzymes lower the activation energy of a reaction?
Lower the energy of the transition state intermediate
Do enzymes have an effect on kinetics and/or thermodynamics?
Enzymes only affect the kinetics of a reaction. The rate constant (k) changes, but NOT Keq
Why doesn’t enzymes change Keq
Lowers activation energy for both forward and reverse reactions
Describe the two models that determine enzyme specificity. How does each differ in their interpretation of the nature of the active?
- Lock and key - rigid active site
2. Induced fit - flexible active site
Can enzymes can be what two molecules?
RNA or protein
What are the four levels of enzyme structure?
- Primary - AA or mRNA sequence
- Secondary - hydrogen bonding between AA backbone
- Tertiary - side chain (R group) interaction
- Quaternary - multiple subunit interaction
What are three modes of controlling enzyme activity and their mechanisms? Where does the inhibitor bind on the enzyme?
- Feedback inhibition - downstream product of pathway inhibits pathway
- Competitive inhibition - inhibitor competes substrate for active site; same Vmax, different Km; over come by adding more substrate
- Noncompetitive inhibition - inhibitor binds to allosteric site; different Vmax, same Km; cannot be overcome
Compare and contrast the steps to aerobic and anaerobic metabolism?
- Both undergo glycolysis
- Aerobic: oxidative decarboxylation–>Krebs Cycle–>Electron transport
- Anaerobic: alcohol or lactic acid fermentation
Glucose + O2 –> 6CO2 + 6H2O
Trace the atoms
Carbon and oxygen atoms in carbon dioxide come from glucose
Oxygen atom in water comes from oxygen we breathe in
What is the difference in NET ATP from aerobic metabolism and anaerobic metabolism of glucose?
aerobic - 36 ATP
anaerobic - 2 ATP
What is the purpose of anaerobic fermentation?
Regeneration of NAD+ which is required for the first step in the pay-off phase
How many NADH are produced in one glucose molecule during glycolysis?
2 NADH
What enzyme is primarily responsible for regulating glycolysis?
Phosphofructokinase-1 (PFK-1)
What two hormones regulate PFK-1? What are their effects on PFK-1?
Insulin - activates PFK-1
Glucagon - inhibits PFK-1
What are three modes of regulating glycolysis? What enzyme gets regulated?
Regulation occurs on PFK-1
- Hormones - insulin/glucagon
- ATP/AMP - AMP activates/ATP inhibits
- Fructose-6-P/Fructose-1,6-BP - F6P activates; F1,6,BP inhibits
What are the primary and secondary locations of gluconeogenesis?
- Primary - liver
2. Secondary - kidneys
How is glycogen metabolism regulated?
- Insulin - activates glycogenesis
2. Glucagon/Epinephrine - activates glycogenolysis
What tissues store glycogen?
- Liver
2. Muscles
What is the name of the cycle that restores lactic acid to glucose? Where does this occur?
Cori Cycle - liver
What is the energy yield per glucose in terms of ATP, GTP, NADH, and FADH2?
- 2ATP (glycolysis)
- 10 NADH - 2 NADH (glycolysis) + 2 NADH (pyruvate decarboxylation) + 6 NADH (Krebs)
- 2 FADH2
What two molecules inhibit Krebs Cycle?
ATP and NADH
What are the two locations of fat metabolism?
Ester hydrolysis - cytoplasm
Beta-oxidation - matrix
What are the products of beta-oxidation?
Acetyl-CoA + NADH + FADH2
Conversion of triacylglycerides to free fatty acids and glycerol is performed by what enzyme? How is this enzyme regulated?
Hormone-sensitive lipase converts TAG–>FFA + Glycerol. Glucagon and epinephrine activate hormone sensitive lipase in response to stress, fasting, exercise
What are the fates of the FFAs and glycerol? Where are they transported to?
FFAs - transported to other tissues (primarily heart and muscles) for beta-oxidation
Glycerol - transported to liver for glycolysis or gluconeogenesis
What is the mechanism that FFAs undergo to be transported into the mitochondrial matrix to undergo beta-oxidation? What is the enzyme and ATP involved?
ATP–>AMP + PPi (-2ATP)
Acyl-CoA synthetase “activates” FFA and covalently bonds it to CoA-SH
Acylcarnitine is the intermediate that gets transported across the inner mitochondrial membrane into the matrix to undergo beta oxidation? What enzyme is responsible for the synthesis of this molecule and reconversion?
Carnitine acyl transferase I converts activated FFA into acylcarnitine. Acylcarnitine is reconverted back to its activated form (with CoA-S) by same enzyme
How many rounds of beta-oxidation are there for a 18-C fatty acid?
9 acetyl-CoA produced
8 rounds of beta-oxidation –>8 NADH + 8 FADH2
