Learn: exam 3 pt 2

What substrate enters the oxidative PPP?

Glucose-6-phosphate.

What does the oxidative PPP generate?

NADPH and ribulose-5-phosphate, releasing CO₂.

What is the purpose of the nonoxidative PPP?

Reversible sugar-phosphate rearrangements.

Which glycolytic intermediates connect to the PPP?

Fructose-6-phosphate and GAP.

Can the nonoxidative PPP run in reverse?

Yes.

Which pathway produces ribose-5-phosphate?

Pentose phosphate pathway.

Why do muscles convert pyruvate to lactate anaerobically?

Regenerate NAD⁺ for glycolysis.

Why do yeast convert pyruvate to ethanol anaerobically?

Regenerate NAD⁺ for glycolysis.

Does fermentation require oxygen?

No.

What happens if NAD⁺ becomes unavailable to GAPDH?

Glycolysis stalls at GAPDH.

What is the Warburg effect?

High glycolysis rates in cancer cells, even with oxygen present.

What does a radiolabeled hydrogen on GAP C1 become during GAPDH?

Part of NADH.

What does PDH convert pyruvate into?

Acetyl-CoA, CO₂, and NADH.

Where is PDH located?

Mitochondrial matrix.

Is PDH one enzyme or a multienzyme complex?

Multienzyme complex.

What does PDH E1 use?

TPP.

What does PDH E2 use as its swinging arm?

Lipoamide.

What does PDH E3 do?

Reoxidizes reduced lipoamide via FAD and NAD⁺.

What is the net reduced cofactor leaving PDH?

NADH.

What is substrate channeling?

Direct intermediate transfer between active sites.

Why is substrate channeling useful?

Limits intermediate loss and side reactions.

What does alanine scanning test?

Importance of individual amino acid residues.

How do you perform an alanine-scanning experiment?

Mutate a selected residue to alanine and measure enzyme activity.

What does loss of activity after mutation suggest?

Original residue is important for enzyme function.

What does radioactive labeling test?

Where a specific atom travels through a reaction.

What does stereospecificity mean?

Enzyme selectively reacts with or produces a particular stereoisomer.

92. What does ΔG < 0 mean?

Forward reaction is thermodynamically favorable.

93. What does ΔG > 0 mean?

Forward reaction is thermodynamically unfavorable.

94. What does ΔG = 0 mean?

Equilibrium.

95. What does negative ΔG°′ imply about Keq?

Keq > 1.

96. What does positive ΔG°′ imply about Keq?

Keq < 1.

97. What is Q?

Products/reactants, with stoichiometric exponents.

98. What happens when Q < Keq?

Forward reaction is favorable.

99. What happens when Q > Keq?

Reverse reaction is favorable.

100. If actual ΔG is more negative than ΔG°′, what does that imply?

Q < 1; reactants favored in the concentration ratio.

101. When calculating Keq from ΔG°′, what mathematical operation isolates Keq?

Exponentiate after dividing by −RT.

102. What units must temperature use?

Kelvin.

103. What units must match when using R?

ΔG and R must use compatible energy units.

104. How do you identify the electron acceptor?

Species being reduced (gains electrons).

How do you identify the electron donor?

Species being oxidized (loses electrons).

What direction is spontaneous electron transfer?

Lower to higher reduction potential.

107. What does positive ΔE°′ imply?

Negative ΔG°′; favorable standard redox reaction.

108. What does negative ΔE°′ imply?

Positive ΔG°′; unfavorable standard redox reaction.

109. In a redox calculation, what does n represent?

Number of electrons transferred.

110. If [reduced]/[oxidized] increases, what happens to reduction potential?

It decreases.

111. Does a reaction with positive ΔG°′ always have positive actual ΔG?

No; concentrations can make actual ΔG negative.

112. If an enzyme is inhibited, what often happens to its substrate?

It accumulates.

113. If an enzyme is inhibited, what often happens to downstream products?

Their production decreases.

114. Can a favorable reaction drive an unfavorable one?

Yes, through reaction coupling.

115. What is the difference between ΔG and ΔG°′?

Actual cellular conditions vs. biochemical standard conditions.

116. Does a catalyst change Keq or ΔG?

No; it changes reaction rate.

117. What happens when a pathway's final product inhibits its first committed step?

Pathway flux decreases.

118. Does an enzyme's stereospecificity mean it makes equal amounts of stereoisomers?

No; it favors a specific stereoisomer.

119. If the reduced form of a redox cofactor accumulates, what happens to its reduced/oxidized ratio?

It increases.

120. What does a strongly negative ΔG tell you about reaction direction?

Forward direction is favorable under those conditions.

Which polysaccharide is a homopolymer of D-glucose?

Cellulose; β(1→4) bonds.

What is chitin made of?

N-acetylglucosamine; β(1→4) bonds.

Where is chitin commonly found?

Insect exoskeletons.

What are glycosaminoglycans (GAGs) made of?

Repeating disaccharides.

Why are GAGs negatively charged?

Sulfate and carboxylate groups.

What is peptidoglycan made of?

NAG + NAM with peptide crosslinks.

Where is peptidoglycan found?

Bacterial cell walls.

What bonds does amylose contain?

Unbranched α(1→4) glucose bonds.

What bonds does amylopectin contain?

α(1→4) chains and α(1→6) branches.

What makes glycogen different from amylose?

Glycogen is highly branched.

How many electrons does NADH transfer?

2 electrons; water-soluble cosubstrate.

How many electrons does NADPH transfer?

2 electrons; water-soluble cosubstrate.

How many electrons can FAD transfer?

1 or 2 electrons; enzyme-bound prosthetic group.

How many electrons can FMN transfer?

1 or 2 electrons; enzyme-bound prosthetic group.

How many electrons can ubiquinone (Q) transfer?

1 or 2 electrons; lipid-soluble mobile carrier.

How many electrons does cytochrome c transfer?

1 electron; water-soluble mobile protein.

How many electrons do Fe-S centers transfer?

1 electron; protein-bound prosthetic groups.

How many electrons does cytochrome heme transfer?

1 electron at a time; protein-bound prosthetic group.

Which electron carrier moves within the lipid membrane?

Ubiquinone (Q/QH₂).

What is the net mobile reduced product of succinate dehydrogenase?

QH₂; FAD remains enzyme-bound.