Energy I

Question 1

What two categories can metabolic processes be subdivided into?

Answer 1

Catabolic processes- the breakdown of complex molecules to release energy
Anabolic processes- synthesis of new molecules from less complex components

Question 2

How is major fuels obtained and used?

Answer 2

Major fuels obtained from the diet include carbohydrates, fats and proteins
When oxidised they produce water, CO2 and ATP
Most of catabolism consists of reactions that extract energy from fuel stuffs and convert it to ATP

Question 3

How much ATP do we obtain and how much do we use?

Answer 3

Total amount of energy available from the hydrolysis of ATP is 65Kj/mol
At rest we use 40Kg/24hours
During exercise we use 0.5Kg/minute
The body has 100g of ATP

Question 4

What are the cofactors central to metabolism?

Answer 4

NAD and FAD are activated carriers of electrons used for oxidation/reduction reactions
NAD- nicotinamide adenine dinucleotide
FAD- flavin adenine dinucleotide
NAD+ (oxidised) turns to NADH + H+ (reduced)
FAD+ (oxidised) turns to FADH2 (reduced)

Question 5

What are the major oxidative pathways?

Answer 5

Glycolysis
Citric acid cycle
Electron transport coupled to oxidative phosphorylation
Fatty acid oxidation

Question 6

Recall the steps of glycolysis?

Answer 6

1. The phosphorylation of glucose(C6) to form glucose-6-phosphate (uses ATP) which has two functions:
   maintains glucose gradient
   unable to be transported out of cells
2. G6P turns to fructose 6-phosphate
3. Fructose 6 phosphate is further phosphorylated to form Fructose 1,6-bisphosphate (C6)
   This uses ATP
4. This is then split into2 3-carbon units:
   Dihydroxyacetone phosphate
   Glyceraldehyde 3-phosphate
5. Glyceraldehyde 3-phosphate then goes through a series of reactions resulting in the reduction of NADH from NAD and Pi, the synthesis of ATP from ADP and lastly the formation of Phosphoenolpyruvate
6. Finally the phosphoenolpyruvate is converted to pyruvate (C3)
   Through this reaction ATP is synthesised from ADP

Question 7

What is the balance sheet for glycolyisis like?

Answer 7

Reactant:
1 glucose
2 ATP
2 NAD+
2 ADP
2 Pi 
Products:
2 pyruvate
2 NADH
2 ATP

Question 8

How can enzymes catalysing irreversible reactions in glycolysis be regulated?

Answer 8

Reversible binding of allosteric effectors
Covalent modification
Transcription

Question 9

What are the three points in glycolysis pathway that is regulated?

Answer 9

The first two steps are hexokinase and phosphorylation-fructokinase
Hexokinase regulates the first step in glycolysis
Phosphofructokinase regulates the step of conversion of fructose 6-phosphate to fructose 1,6-bisphosphate
The third step regulates the last reaction, from phosphoenolpyruvate to pyruvate
This is an enzyme that exists in a number of forms; distributed in different tissues
Only regulated in glycolysis in the liver

Question 10

How are the three enzymes in glycolysis regulated (those that can be)?

Answer 10

Hexokinase is regulated by the product of the reaction
G-6-P will inhibit further conversion of glucose to G-6-P
The major site of regulation is phosphofructokinase
It is negatively regulated by ATP, citrate and H+ because they are the end products of glycolysis or pathway which follow after
It’s positively regulated by AMP
Pyruvate kinase in the liver is negatively allosterically regulated by ATP

Question 11

Why is glycolysis in the muscle regulated?

Answer 11

In muscle, glycolysis is regulated to meet the need for ATP
AMP is a good indicator of the energetic state of the cell
ADP+ADP—-> ATP+AMP

Question 12

How does regulation of glycolysis in the liver reflect its diverse functions?

Answer 12

Regulation is more complex
High conc. of ATP inhibits PFK
PFK is inhibited by citrate
PFK is stimulated indirectly by a buildup of F6P
Hexokinase is inhibited by G6P
But the liver also has glucokinase which is not inhibited by G6P

Question 13

Where do galactose and fructose come into the glycolytic pathway?

Answer 13

Glucose gets converted to glucose

Fructose (from adipose tissue) gets converted to fructose 6-phosphate

Question 14

What can happen to pyruvate in exercising muscle?

Answer 14

Pyruvate can either:
Turn to Acetyl CoA which can then go into OXPHOS
Can be converted to lactate oxidising NADH to NAD

Question 15

How does oxygen stimulate the expression of many glycolytic enzymes?

Answer 15

Hypoxia–> HIF-1 activated
—> Blood vessel growth
—> Metabolic adaptation (increase in glycolytic enzymes)
When tumours outgrow their blood supply, oxygen delivery is reduced tumour cell metabolism reverts to glycolysis
A reduction in O2 leads the activation of the TF HIF-1a
HIF-1a regulated the expression of a no. of enzymes in the glycolytic pathway