Exam1 Part 2

Question 1

What is an enzyme?

Answer 1

Large polymers made of amino acids that act as catalysts, speeding up chemical reactions necessary for life

Enzymes change the chemical structure of small organic molecules, known as substrates.

Question 2

What are enzymes made of and how do they work?

Answer 2

Made of amino acids linked by peptide bonds; they lower the activation energy of reactions

This allows reactions to occur at a rate consistent with life.

Question 3

How are enzymes synthesized in the cell?

Answer 3

Through the central dogma: DNA → RNA → Protein

Genes are transcribed into mRNA, which is translated into protein by ribosomes.

Question 4

What is a metabolic pathway?

Answer 4

A series of enzyme-catalyzed reactions that transform a substrate into another compound

Functions include energy production, detoxification, or synthesis of necessary molecules.

Question 5

What is the difference between anabolic and catabolic reactions?

Answer 5

Anabolic reactions build complex molecules; catabolic reactions break down molecules to release energy

Examples include protein synthesis for anabolic and glycolysis for catabolic.

Question 6

What does Gibbs free energy indicate?

Answer 6

Indicates whether a reaction is spontaneous; a negative ΔG signifies a spontaneous process

This is important in determining the direction of metabolic reactions.

Question 7

What is coupling in relation to metabolism?

Answer 7

Energy-releasing reactions are coupled with energy-requiring reactions

This drives biological processes.

Question 8

What is the role of oxygen in human metabolism?

Answer 8

Final electron acceptor in the electron transport chain, essential for ATP production in aerobic respiration

Question 9

What is the primary energy source for most cells?

Answer 9

Glucose

It is absorbed in the intestines and transported through the bloodstream to various tissues.

Question 10

How is glucose transported upon absorption?

Answer 10

Facilitated by GLUT transporters and sodium-dependent glucose transporters (SGLTs)

For example, GLUT4 is insulin-dependent and located in muscle and adipose tissues.

Question 11

What are the consequences of defects in glucose transporters?

Answer 11

GLUT1 deficiency causes developmental delays; GLUT2 deficiency leads to Fanconi-Bickel syndrome

Question 12

What are the basic reactions of glycolysis?

Answer 12

Consists of 10 enzymatic steps converting glucose to pyruvate while producing ATP and NADH

Question 13

What is the net gain of ATP and NADH in glycolysis?

Answer 13

2 ATP and 2 NADH molecules per glucose molecule

Question 14

What is allosteric regulation in glycolysis?

Answer 14

ATP and citrate inhibit, while AMP activates key enzymes like phosphofructokinase (PFK1)

Question 15

How does hormonal regulation affect glycolysis?

Answer 15

Insulin promotes glycolysis, while glucagon inhibits it

Question 16

What happens to pyruvate under limited oxygen conditions?

Answer 16

Converted to lactate to regenerate NAD+ and sustain glycolysis

The Cori cycle transports lactate to the liver, where it is converted back to glucose.

Question 17

What is the difference between glycolysis and gluconeogenesis?

Answer 17

Glycolysis breaks down glucose; gluconeogenesis synthesizes glucose from non-carbohydrate precursors

Irreversible steps in glycolysis are bypassed in gluconeogenesis.

Question 18

What is the overall reaction of the pyruvate dehydrogenase reaction?

Answer 18

Pyruvate + CoA + NAD+ → Acetyl-CoA + CO2 + NADH

Question 19

What inhibits and activates pyruvate dehydrogenase?

Answer 19

Inhibited by acetyl-CoA, NADH, and ATP; activated by ADP and pyruvate

Question 20

What vitamins are required for the pyruvate dehydrogenase reaction?

Answer 20

Requires TPP (B1), FAD (B2), NAD (B3), CoA (B5), and lipoic acid

Question 21

How does pyruvate dehydrogenase relate to the TCA cycle?

Answer 21

Links glycolysis to the TCA cycle by converting pyruvate to acetyl-CoA

Question 22

What are important TCA cycle intermediates?

Answer 22

• Citrate (fatty acid synthesis)
• α-ketoglutarate (amino acid synthesis)
• Succinyl-CoA (heme synthesis)
• Oxaloacetate (gluconeogenesis)

Question 23

How does fructose enter glycolysis?

Answer 23

Via fructose-1-phosphate; galactose enters as glucose-6-phosphate

Question 24

What defects are associated with fructose and galactose metabolism?

Answer 24

• Fructokinase deficiency causes essential fructosuria
• Aldolase B deficiency leads to hereditary fructose intolerance
• Galactokinase or galactose-1-phosphate uridyltransferase deficiencies cause galactosemia

Question 25

What are the major products of the pentose phosphate pathway?

Answer 25

• NADPH
• Ribose 5-Phosphate

Question 26

What is the role of NADPH in the body?

Answer 26

Used in fatty acid synthesis, antioxidant defense, and immune response

Question 27

What is the function of ATP synthase?

Answer 27

Uses the proton gradient to synthesize ATP from ADP and Pi

Question 28

What enzymes are involved in glycogen breakdown?

Answer 28

• Glycogen phosphorylase
• Debranching enzyme
• Phosphoglucomutase

Question 29

What hormones regulate glycogen metabolism?

Answer 29

Glycogen breakdown is promoted by glucagon and epinephrine; insulin stimulates synthesis

Question 30

What condition can high insulin levels in infants lead to?

Answer 30

Neonatal hypoglycemia due to maternal hyperglycemia

Question 31

What is McArdle’s Disease?

Answer 31

A deficiency in muscle glycogen phosphorylase causing exercise intolerance, muscle cramps, and rhabdomyolysis