Q: A cell maintains a concentration gradient of potassium ions ($$K^+) $$across its membrane. Which equation would you use to calculate the free energy change ($$\Delta G) $$for transporting $$K^+$$ from outside to inside, considering both concentration and charge gradients?

$$\Delta G = RT \ln \left( \frac{[K^+]_{\text{outside}}}{[K^+]_{\text{inside}}} \right) + zF\Delta \Psi$$

Question 1

Which of the following best explains why cis-unsaturated fatty acids have a lower melting temperature ($$T_m) $$than trans-unsaturated fatty acids?

Accepted Answer

Cis-unsaturated fatty acids introduce kinks in the hydrocarbon chain, preventing tight packing and lowering $$T_m.$$

Question 2

A fatty acid is named 18:2(Δ9,12) according to IUPAC conventions. Which of the following statements is correct?

Accepted Answer

It is a polyunsaturated fatty acid with double bonds at carbons 9 and 12.

Question 3

Which of the following best describes the role of triacylglycerols in human metabolism?

Accepted Answer

They function primarily as energy storage molecules, storing fatty acids in a compact form.

Question 4

Which of the following statements about membrane fluidity is correct?

Accepted Answer

Cholesterol decreases membrane fluidity at high temperatures but increases it at low temperatures.

Question 5

A cell maintains a concentration gradient of potassium ions ($$K^+) $$across its membrane. Which equation would you use to calculate the free energy change ($$\Delta G) $$for transporting $$K^+$$ from outside to inside, considering both concentration and charge gradients?

Accepted Answer

$$\Delta G = RT \ln \left( \frac{[K^+]_{	ext{outside}}}{[K^+]_{	ext{inside}}} ight) + zF\Delta \Psi$$

Question 6

Which of the following best describes the difference between primary and secondary active transport?

Accepted Answer

Primary active transport uses ATP directly, while secondary active transport uses the energy from an ion gradient established by primary transport.

Question 7

Which of the following is a correct example of a symport transport system?

Accepted Answer

Transport of glucose and sodium ions ($$Na^+) $$together into the cell.

Question 8

Which of the following statements about G-protein coupled receptors (GPCRs) is correct?

Accepted Answer

GPCRs activate G-proteins, which act as molecular switches by binding GTP and GDP.

Question 9

Which of the following best describes the principle of feedback inhibition in metabolic pathways?

Accepted Answer

A product of a pathway inhibits an enzyme earlier in the pathway, preventing overproduction.

Question 10

Which of the following statements about NADH and NADPH is correct?

Accepted Answer

NADH is used in catabolic pathways for ATP production, while NADPH is used in anabolic pathways for biosynthesis.

Question 11

Which of the following best explains why the phosphoanhydride bond in ATP is considered 'high energy'?

Accepted Answer

Hydrolysis of the bond releases energy due to increased resonance stabilization and decreased electrostatic repulsion in the products.

Question 12

Which equation correctly relates the standard free energy change ($$\Delta G^\circ') to $$the actual free energy change ($$\Delta G) in a $$metabolic reaction?

Accepted Answer

$$\Delta G = \Delta G^\circ' + RT \ln Q$$

Question 13

During glycolysis, which enzyme catalyzes the committed step and is subject to regulation by fructose-2,6-bisphosphate?

Accepted Answer

Phosphofructokinase-1 (PFK-1)

Question 14

Which of the following best describes the fate of pyruvate under anaerobic conditions in human muscle cells?

Accepted Answer

Pyruvate is converted to lactate, regenerating NAD$$^+$$ for glycolysis.

Question 15

Which of the following is a correct description of the Cori Cycle?

Accepted Answer

It describes the conversion of lactate produced in muscles to glucose in the liver.

Question 16

Which of the following statements about the pentose phosphate pathway is correct?

Accepted Answer

It produces NADPH and ribose-5-phosphate for nucleotide synthesis.

Question 17

Which of the following steps in gluconeogenesis requires a unique enzyme not found in glycolysis?

Accepted Answer

Conversion of pyruvate to phosphoenolpyruvate (PEP) via pyruvate carboxylase and PEP carboxykinase.

Question 18

Which of the following best describes the reciprocal regulation of glycolysis and gluconeogenesis by fructose-2,6-bisphosphate (F2,6BP)?

Accepted Answer

F2,6BP activates phosphofructokinase-1 (PFK-1) and inhibits fructose-1,6-bisphosphatase.

Question 19

Which of the following best explains the effect of insulin on glycogen metabolism in liver cells?

Accepted Answer

Insulin stimulates glycogen synthesis and inhibits glycogen breakdown.

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