Question 1

Which amino acid in the chymotrypsin catalytic triad acts as a nucleophile during peptide bond cleavage?

Accepted Answer

Ser195

Question 2

A patient is exposed to DFP (diisopropyl fluorophosphate), an irreversible inhibitor of chymotrypsin. What is the most likely molecular consequence?

Accepted Answer

DFP covalently modifies Ser195, permanently inactivating the enzyme.

Question 3

Which kinetic equation correctly describes competitive inhibition?

Accepted Answer

$V_0 = \frac{V_{max}[S]}{\alpha K_m + [S]}$, \quad \alpha = 1 + \frac{[I]}{K_I}$

Question 4

Which statement best describes the effect of uncompetitive inhibition on enzyme kinetics?

Accepted Answer

Vmax and Km both decrease.

Question 5

During the acylation phase of chymotrypsin's catalytic mechanism, which event occurs immediately after substrate binding?

Accepted Answer

His57 deprotonates Ser195, enabling nucleophilic attack.

Question 6

Which feature distinguishes sphingolipids from glycerophospholipids?

Accepted Answer

Sphingolipids have a sphingosine backbone, while glycerophospholipids have a glycerol backbone.

Question 7

A mutation in the GLUT1 transporter impairs glucose uptake in erythrocytes. Which structural feature of GLUT1 is most directly involved in its function?

Accepted Answer

12 amphipathic alpha-helical segments spanning the membrane

Question 8

Which process is catalyzed by lipases in adipocytes and germinating seeds?

Accepted Answer

Hydrolysis of stored triacylglycerols to release fatty acids for energy

Question 9

Which statement about membrane dynamics is correct?

Accepted Answer

Flippases catalyze movement of phospholipids from the outer to inner leaflet and require ATP.

Question 10

Which carbohydrate structure is formed by the reaction of an alcohol with an aldehyde or ketone?

Accepted Answer

Hemiacetal or hemiketal

Question 11

Which statement best explains why glycogen is more soluble than starch?

Accepted Answer

Glycogen has more frequent branching (every 8-12 residues), increasing solubility.

Question 12

Which of the following is true regarding the effect of competitive inhibition on enzyme kinetics?

Accepted Answer

Vmax remains unchanged, Km increases.

Question 13

A researcher observes that an enzyme's Lineweaver-Burk plot shows parallel lines in the presence of an inhibitor. What type of inhibition is most likely occurring?

Accepted Answer

Uncompetitive

Question 14

Which of the following best describes the amphipathic nature of cholesterol?

Accepted Answer

It has a polar OH head and a hydrophobic tail.

Question 15

Which enzyme is responsible for removing one fatty acid from a phospholipid during lipid breakdown in lysosomes?

Accepted Answer

Phospholipase A

Question 16

Which of the following correctly describes the role of Mg	extsuperscript{2+} in ATP-dependent reactions?

Accepted Answer

Mg	extsuperscript{2+} binds ATP/ADP to neutralize charge, forming the true substrate MgATP	extsuperscript{2-}.

Question 17

Which statement about polysaccharides is correct?

Accepted Answer

Amylopectin is a branched form of starch with both $\alpha$-1,4 and $\alpha$-1,6 linkages.

Question 18

Which of the following is a function of membrane protein ion channels?

Accepted Answer

Provide aqueous pores for ions and conduct electrical impulses.

Question 19

Which of the following best describes the difference between aldoses and ketoses?

Accepted Answer

Aldoses have a carbonyl group at the chain end; ketoses have a carbonyl group internal to the chain.

Question 20

Which statement about catabolic and anabolic pathways is correct?

Accepted Answer

Catabolic pathways release energy and converge to central intermediates.

Biochemistry Study Notes: Enzyme Mechanisms, Lipids, Membranes, Carbohydrates, and Metabolism

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