Metabolism (Module 2 Lecture 7)

Question 1

What is an isozyme (isoenzyme)?

Answer 1

Related enzymes that have similar catalytic activity.

Question 2

Name two coenzymes and their functions.

Answer 2

1. NAD+ accepts hydrogens.

2. Pyridoxal phosphate is used by many enzymes that digest amino acids.

Question 3

Contrast the metabolic turnover to DNA stability.

Answer 3

1. Membrane lipids are broken down and resynthesized continuously.
2. Many enzymes have very short half-lives.
3. Structural proteins and receptors also show metabolic turnover.
4. mRNA have often rapid turnover.

Question 4

Contrast between dietary and cellular sources of energy.

Answer 4

1. Dietary (carbohydrates, fats, protein, ethanol?)

2. Cellular (glucose, fatty acids, amino acids, and metabolic intermediates like pyruvate)

Question 5

Why is the Kreb’s cycle considered an amphibolic pathway?

Answer 5

It has both catabolic components, like breaking down acetyl CoA, and anabolic components, like phosphorylating ADP.

Question 6

Describe the stages of catabolism for glycogen, triglycerides, and proteins.

Answer 6

1. Hydrolysis of macromolecules (during digestion).
2. Conversion via oxidation into acetyl-CoA (by glycolysis, beta-oxidation, or deamination oxidation).
3. Further oxidation of acetyl-CoA into CO2 and H2O (common pathway for all and localized in mitochondria).

Question 7

What are the two primary ways cells obtain fuels?

Answer 7

Oxidation of glucose and/or fatty acids.

Question 8

Describe the oxidation of fatty acids in the cell.

Answer 8

1. Fatty acids –> 2acetyl CoA –> CO2 + H2O

Question 9

What happens when proteins are catabolised?

Answer 9

1. Proteins –> L-amino acids
2. Amino acids –> NH4+ + alpha-keto acids + pyruvate
3. (NH4+ –> urea via the urea cycle, and alpha-keto acids –> Krebs cycle and pyruvate –> acetyl CoA –> Krebs cycle

Question 10

ATP Provides energy for what four main things?

Answer 10

1. Biosynthesis (anabolic rxns)
2. Active transport
3. Cellular motion (flagellar activity)
4. Phosphorylation of signaling molecules

Question 11

What molecules besides ATP also possess high-energy phosphate groups?

Answer 11

1. Metabolic intermediates like phosphoenolpyruvate and 1,3-biphosphoglycerate are intermediates in the catabolism of glucose)
2. Creatine phosphate is a high energy store that is particularly important in muscle and heart cells.
3. Phosphodiester bonds of other nucleotides (CTP, UTP, GTP) are sometimes used instead of ATP to drive metabolic processes.

Question 12

What hydrogen/electron carrier is used for anabolic reactions?

Answer 12

NADPH (generated by specialized oxidation reactions, it’s used in the synthesis of things like fatty acids and cholesterol)

Question 13

Give examples of in vivo pathways that are irreversible.

Answer 13

1. Glucose synthesis from fatty acid carbons in humans

2. All fatty acids and amino acids can be oxidized in humans although not all can be synthesized.

Question 14

Where does fatty acid synthesis occur?

Answer 14

In the cytosol.

Question 15

List the four nutritional requirements of humans.

Answer 15

1. Energy (from fatty acids & glucose)
2. Amino acids (for energy, protein synthesis, and synthesis of amino-containing compounds like nucleic acids and heme groups)
3. Essential organic molecules (essential amino acids, essential polyunsaturated fatty acids, and vitamins, which are small preformed molecules which are converted to enzymatic cofactors such as niacin (NAD+) and pantothenic acid (CoA)).
4. Minerals (major minerals like Na+, K+, Ca2+, and Mg2+ as well as trace elements like Fe3+, Zn+, Cu2+, and I-)