Introduction to Metabolism

Question 1

1) Define metabolism

Answer 1

All chemical reactions and physical changes that can occur in living organisms (incl. anabolism and catabolism)

Question 2

2) Define catabolism and give two examples

Answer 2

Metabolic breakdown of substances into smaller products (glycolysis, lipolysis)

Question 3

3) Define anabolism and give two examples

Answer 3

Simpler substances are transformed into more complex ones, requiring energy (gluconeogenesis, lipogenesis)

Question 4

4) Why do metabolic pathways have stepwise breakdown?

Answer 4

So energy is released in small, usable packages rather than released in one go (none is stored)

Question 5

5) Advantage to different forward and reverse pathways?

Answer 5

Separate regulation prevents a futile cycle

Question 6

6) Where is the energy released at each step stored?

Answer 6

Activated carrier molecules (a.c ATP)

Question 7

7) How can an energetically unfavorable reaction occur?

Answer 7

Using a coupled reaction where an energetically favorable reaction drives and energetically unfavorable reaction (e.g. oxidation of a food molecule producing an activated carrier molecule that provides energy to the unfavorable reaction)

Question 8

8) give examples of activated carrier molecules (6)

Answer 8

ATP
NADH, NADPH, FADH2
Acetyl CoA
Carboxylated biotin
S-adenosylmethionine
Uridine diphosphate glucose

Question 9

9) for each activated carrier molecule, which group is carried in the high energy linkage?

Answer 9

ATP - phosphate
NADH/NADPH/FADH2 - electrons and H+
Acetyl CoA - acetyl group
Carboxylated biotin - carboxyl group
S-adenosylmethionine - methyl group
Uridine diphosphate glucose - glucose

Question 10

10) Why is ATP hydrolysis so energetically favorable?

Answer 10

Relieves electrostatic repulsion between phosphate groups and the released phosphate ion’s resonance is stabilised (increase in entropy means positive delta S value)

Question 11

11) Which ATP hydrolysis produces the most energy?

Answer 11

ATP –> AMP + 2Pi

Question 12

12) 2 examples of when ATP –> AMP + 2Pi occurs?

Answer 12

In DNA replication and when tRNA binds to an amino acid during translation

Question 13

13) Explain the function of ATP as ‘the energy currency of living cells’ (4)

Answer 13

• Used directly in cell motility and muscle contraction
  (Motor proteins dynein and myosin carry cargoes)
• Used in active transport systems (e.g. moving charged particles against the concentration gradient)
• Used in metabolic control - regulation of enzyme activity
• Used in metabolism to add Pi to metabolic intermediates (glucose + ATP –> G-6-P + ADP)

Question 14

14) Explain the significance of the thioester linkage in Acteyl CoA

Answer 14

Thioester linkage is a ‘high energy bond’

Coenzyme A forms a thioester linkage with carboxylic acids to form acetyl CoA

Question 15

15) State subcellular locations for each of the processes: glycolysis, link reaction, TCA cycle, oxidative phosphorylation

Answer 15

Glycolysis - cytosol/cytoplasm
Link reaction - mitochondria matrix
TCA - mitochondria matrix
Oxidative phosphorylation - inner membrane of mitochondria

Question 16

16) State 3 ways in which metabolic pathways can be regulated

Answer 16

1. Changes in amount of enzyme - controlled via enzyme synthesis (gene expression) and whether long term or not (lasts for hrs or days)
2. Changes in enzyme activity –> allosteric regulation:
   Instantaneous and local (within a cell)
3. Changes in enzyme activity –> phosphorylation/ dephosphorylation:
   Rapid, not instantaneous and whole body due to hormonal control
   (e.g. levels of kinase and phosphatase are often activated and regulated by hormones)