50 Questions
What is the function of NADH and FADH2 in the cell?
They act as energy carriers through redox reactions
Why are NADH and FADH2 considered energetic molecules?
Because they have low reduction potential and carry high-energy electrons
In glycolysis, how many ATP molecules are invested initially for each molecule of glucose?
2 ATP molecules
During the 'pay off phase' of glycolysis, how many ATP molecules are released per glyceraldehyde molecule?
2 ATP molecules
What is the net gain of ATP molecules per molecule of glucose that follows the glycolytic pathway?
2 ATP molecules
Why is the priming phase of glycolysis named as such?
Because it requires an input of energy in the form of ATP
What is the primary function of the coenzyme FAD in cellular metabolism?
Acting as an electron acceptor in catabolic processes
In response to the need for ribose-5-phosphate, how does the flux through the pentose phosphate pathway change?
The flux is diverted towards the non-oxidative phase
What is the advantage of glycogen's branched structure?
Facilitates rapid and efficient breakdown and synthesis of glycogen
Which enzymes are involved in glycogen degradation?
Glycogen phosphorylase, glycogen debranching enzyme, phosphoglucomutase
What activates glycogen phosphorylase?
AMP
How does phosphorylation affect the activity of glycogen phosphorylase?
It converts it to the more active form
What is the primary purpose of the dehydration of 2-phosphoglycerate in glycolysis?
To form a high-energy enol intermediate, phosphoenolpyruvate (PEP)
How does glycolysis utilize the chemical coupling of endergonic and exergonic reactions to generate ATP?
By generating high-energy compounds that undergo substrate-level phosphorylation
Which products of glycolysis are reduced molecules that the cell can oxidize to recover free energy?
NADH and pyruvate
What are the three possible fates of pyruvate?
Conversion to acetyl-CoA, conversion to lactate, and conversion to CO2
In which type of fermentation is pyruvate converted into lactate?
Homolactic fermentation
What is the role of TPP in glycolysis?
To catalyze the decarboxylation of pyruvate
What is the net ATP yield per glucose molecule in anaerobic degradation?
2 ATP
Which process has a higher production rate, anaerobic or aerobic degradation of glucose?
Aerobic degradation
What are the potential control points in glycolysis?
Hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase
What are the allosteric inhibitors of PFK-1?
High levels of ATP and citrate
How is PFK-1 activity regulated by phosphorylation?
Phosphorylation decreases enzyme activity
Why is ATP not an effective allosteric regulator of enzyme activity?
It is too abundant in cells to have a regulatory effect
What is the metabolic advantage of a substrate cycle?
It provides a means of fine-tuning metabolic intermediates
How does fructose enter the glycolytic pathway?
Through the action of fructokinase
What is the net equation for the pentose phosphate pathway?
Glucose-6-phosphate + 2NADP+ + H2O → ribulose-5-phosphate + CO2 + 2NADPH + 2H+
Summarize the reactions of each stage of the pentose phosphate pathway.
The oxidative phase involves reversible interconversions of sugar phosphate intermediates.
How do the transketolase and transaldolase reactions differ?
The transketolase reaction transfers a two-carbon fragment, while the transaldolase reaction transfers a three-carbon fragment.
What is the free energy source for glycogen synthesis?
Uridine triphosphate (UTP)
Describe the role of glycogenin.
It catalyzes the formation of initial glucose residues for glycogen synthesis.
Summarize the effects of AMP and G6P on glycogen phosphorylase and glycogen synthase.
AMP activates glycogen phosphorylase and inhibits glycogen synthase.
Summarize the effects of phosphorylation and dephosphorylation on glycogen phosphorylase and glycogen synthase.
Phosphorylation activates glycogen phosphorylase and inhibits glycogen synthase.
Why does a phosphorylation/dephosphorylation system allow more sensitive regulation of a metabolic process than a simple allosteric system?
It allows for fine-tuned control and rapid response to changes in cellular conditions.
How does regulation of glycogen metabolism differ between liver and muscle?
It is regulated by hormones in the liver and by exercise in muscle.
Summarize the effects of insulin, glucagon, and epinephrine on glycogen metabolism.
Insulin stimulates glycogen synthesis and inhibits glycogen breakdown, while glucagon and epinephrine stimulate glycogen breakdown.
What are the intracellular effects of cAMP and Ca2+?
cAMP activates protein kinase A (PKA), while Ca2+ can have various intracellular effects depending on the target proteins involved.
What are the substrates for gluconeogenesis?
Lactate, glycerol, amino acids, and citric acid cycle intermediates
What role do fatty acids play in gluconeogenesis?
Provide a source of acetyl-CoA for gluconeogenesis
Which reactions are not shared with glycolysis?
Pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose-1,6-bisphosphatase
Why is the malate–aspartate shuttle system important for gluconeogenesis?
It allows for the recycling of NADH between cytoplasm and mitochondria to generate ATP for gluconeogenesis.
Which enzyme catalyzes the conversion of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate in glycolysis?
Aldolase
During glycolysis, what is the role of phosphoglycerate kinase?
Catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate
Why does triose phosphate isomerase achieve the designation of being catalytically perfect?
It proceeds through the transition state with a rate enhancement near the diffusion limit
What type of catalytic mechanism involves the transfer of a proton between an enzyme and the substrate, altering the substrate's reactivity?
Acid-base catalysis
Which compound with high phosphate group-transfer potential is synthesized during glycolysis and yields ATP through substrate-level phosphorylation?
Phosphoenolpyruvate
What is the role of NADH generation during glycolysis?
To conserve energy and reducing power in the form of NADH
Which enzyme requires the cofactor NAD+ for its oxidation reaction in glycolysis?
Glyceraldehyde-3-phosphate dehydrogenase
What is the chemical logic behind converting glucose to fructose before aldolase splits the sugar in two during glycolysis?
To ensure precise and controlled cleavage by aldolase
What is the role of metal-ion catalysis in glycolytic enzymes?
Assists in substrate binding or participates in the reaction mechanism
Learn about the differences in ATP yields and production rates during anaerobic and aerobic degradation of glucose. Understand the ATP production through glycolysis and the variations in production rates between anaerobic and aerobic processes.
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