Metabolism Overview

Question 1

Define metabolism

Answer 1

The totality of the chemical reactions and physical changes which occur in living organisms, comprising anabolism and catabolism.

Question 2

What is the definition of catabolism and anabolism?

Answer 2

Catabolism = the metabolic breakdown of complex substances into smaller products 
Anabolism = the energy requiring part where simple substances are transformed into more complex ones

Question 3

What are reasons as to why metabolic pathways are so complex?

Answer 3

1. Stepwise breakdown relates energy in small ‘packages’. Same overall energy consumed, multiple steps where it is used
2. Pathways can be regulated by regulation of specific enzymes
3. Different forward and reverse pathways allow separate regulation of reactions
4. Energy released at each step is stored in activated carrier molecules

Question 4

What 3 things make the hydrolysis of ATP so favourable?

Answer 4

1. Relieves electrostatic repulsion between phosphate groups
2. The released phosphate ion is stabilised: increased entropy
3. Concept of high energy bond or high energy phosphate group releases a lot of energy

Question 5

What are the functions of ATP?

Answer 5

• used directly in cell motility and muscle contraction
• used in active transport systems
• used in metabolism control (regulates enzyme activity)
• used in metabolism to add phosphate to metabolic intermediates

Question 6

What are 2 examples of high energy nucleotides?

Answer 6

UTP (drives the synthesis of complex sugars)

GTP (drives the synthesis of protein)

Question 7

What are examples of energy carrier molecules?

Answer 7

Role of NAD as H atom acceptor.
NADP replaces NAD in anabolic reactions e.g lipid synthesis
Flavin adenine dinucleotide (need to recognise these structures)
Flavins act as H acceptors
Coenzyme A forms a thioester linkage with carboxylic acids (ethanoic acid and coenzyme A (an alcohol) react to form an ester.

Question 8

What are the 2 things which are used to form acetyl CoA?

Answer 8

pyruvate and fatty acids

Question 9

What is the structure of pyruvate?

Answer 9

CH3COCOO-

3 carbons, carboxylic acid group

Question 10

In anaerobic metabolism, pyruvate is reduced to …?

What enzyme is used?

Answer 10

Lactate

Lactate dehydrogenase

Question 11

What is the acetyl group of acetyl CoA structure?

Answer 11

CH3CO

Question 12

What are the two ways in which regulation of metabolic pathways can be achieved?

Answer 12

1) Changes in amount of enzyme (enzyme synthesis is long term - hours or days)
2) Changes in enzyme activity (allosteric regulation, phosphorylation = rapid but not instantaneous

Question 13

What is the difference between allosteric regulation and non-competitive inhibitors?

Answer 13

Allosteric is reversible

Non-competitive is irreversible