GS Metabolic pathways

Question 1

a. Define metabolism, anabolism and catabolism

Answer 1

Metabolism: Substance breakdown and build up for energy transfer/storage

Anabolism: Synthetic/ build up

Catabolic: Degradative, tearing down

Question 2

b. Define oxidation and reduction and know the importance of these reactions in metabolism

Answer 2

Oxidation: Oxygen gain, or hydrogen loss. This is the substance that losses energy in redox reaction and ATP is produced

Reduction: Oxygen loss, or hydrogen gain. This is the substance that gains energy in redox reaction

Electron (i.e. bond/energy) movement with H movement.

Question 3

c. Describe the oxidation of glucose in body cells

Answer 3

Glucose is the pivotal fuel molecule in the oxidative (ATP-producing) pathways.

Catabolism of glucose produces:

• Water
• CO2
• LOTS of ATP
• Heat

3 step process (so lots of ATP production):

1. Glycolysis
2. The Krebs cycle
3. The electron transport chain and oxidative phosphorylation

Question 4

d. Summarize important events and products of glycolysis, the Krebs cycle and electron transport

Answer 4

1. Glycolysis
   Glucose –>2 x Pyruvic acid
   Location: Cytosol of cells
   Reversible anaerobic proces

2.  The Krebs cycle 
Location: Mitochondrial matrix
Aerobic proces
Pyruvic acid and FFAs fuelled process. Broken down to Acetyl CoA which then is broken down further to produce..... 
-NADH 
- H+
-ATP
-FADH2
-CoA
-CO2

3. The electron transport chain/ Oxidative phosphorylation
   Location: Mitochondrial cristae
   O2 use*
   Uses the reduced co-enzymes from Kreb’s cycle for electron transport.
   Combines H+ released from food oxidation with O2, energy released form ATP and then H20 is formed.

Question 5

e. Define glycogenesis, glycogenolysis and gluconeogenesis

Answer 5

Glycogenesis: When glycolysis is turned off due to high ATP levels, glucose molecules are combined to glycogen

Glycogenolysis: When glucose levels drop, glycogen chains breaks down by enzyme glucose-6-phosphatase

Gluconeogenesis: Gluconeogenesis, the process of forming new (neo) glucose from noncarbohydrate molecules, occurs in the liver. It takes place when dietary sources and glucose reserves have been depleted and blood glucose levels are beginning to drop. Gluconeogenesis protects the body, the nervous system in particular, from the damaging effects of low blood sugar (hypoglycemia) by ensuring that ATP synthesis can continue.
Glucose made from glycerol and amino acids

Question 6

f. Describe the process by which fatty acids are oxidised for energy

Answer 6

Fats –> Glycerol and fatty acid chain via oxidation. “Lipolysis”

Glycerol breakdown products enters Kreb’s cycle

Fatty acid: Undergo beta oxidation in the mitochondria, so are broken down into two acetic acid fragments. Each acetic group fuses with CoA to form acetyl CoA. Enters the aerobic pathways to be oxidised to CO2 and H2O.

Question 7

g. Define ketone bodies and indicate when they would be formed

Answer 7

Fat oxidation relies on the ability of acetyl CoA to enter the Krebs cycle depends on the availability of oxaloacetic acid to act as the pickup molecule. When carbohydrates are deficient, oxaloacetic acid is converted to glucose (to fuel the brain). Without oxaloacetic acid, fat oxidation is incomplete, acetyl CoA accumulates

So KETOGENESIS occurs…

The liver converts acetyl CoA molecules to ketone bodies.

Question 8

h. Describe how amino-acids are metabolised for energy and indicate when they would be used for this

Answer 8

How?
AA are deaminated then oxidized. The resulting molecule is converted to pyruvic acid or a keto acid intermediate, for entry into Krebs cycle.

Tissue proteins become the major source of blood glucose when fasting is prolonged and glycogen and fat stores are nearly exhausted.

Question 9

i. Know the major events and principal metabolic pathways of the absorptive state

Answer 9

Absorptive state:
Anabolism> Catabolism
Glucose is the major energy fuel.
Dietary AAs and fats are used to remake degraded body protein or fat, and small amounts are oxidized to provide ATP.
Excess metabolites are transformed to fat if not used for anabolism.

Carbohydrates:
Glucose released from the liver is released to blood to form glycogen and fat. Fat is stored in adipose tissue, glucose form glycogen to be stored in liver. Bloodborne glucose, however, is used as energy source

Triglycerides:
Nearly all products of fat digestion enter the lymph to be hydrolyzed to fatty acids and glycerol before they can pass through the capillary walls. Lipoprotein lipase catalyzes fat hydrolysis. Adipose cells, skeletal muscle cells, and liver cells use triglycerides as their primary energy source.
Although some fatty acids and glycerol are used for anabolic purposes by tissue cells, most enter adipose tissue to be reconverted to triglycerides and stored.

Amino acids:
Absorbed amino acids are delivered to the liver, which deaminates some of them to keto acids. The keto acids may flow into the Krebs cycle to be used for ATP synthesis, or they may be converted to liver fat stores. The liver also uses some of the amino acids to synthesize plasma proteins, including albumin, clotting proteins, and transport proteins. However, most amino acids flushing through the liver sinusoids remain in the blood for uptake by other body cells, where they are used for protein synthesis.

Question 10

j. Describe the carbohydrate /fat and amino acid pools and know why they are important

Answer 10

Carbohydrates:
Glycogen at the liver and skeletal muscles

Fat:
Adipose and liver cells produce glycerol for lipolysis.

Amino acid:
Tissue proteins become the major source of blood glucose when fasting is prolonged and glycogen and fat stores are nearly exhausted.