Fatty Acids And Ketones

Question 1

What is a fatty acid?

Answer 1

It is a carbon chain with a carboxyl is head and an aliphatic tail.
It can be saturated or unsaturated.
Most are derived from phospholipids and triglycerides.

Question 2

How are lipids digested?

Answer 2

1. Bile emulsifies fat
2. Lipases in the ileum breakdown triglycerides
3. They are absorbed in the ileum and once absorbed reform triglycerides
4. They are added to cholesterol and apoproteins to form chylomicrons
5. Chylomicrons move via the lymphatic system
6. Fatty acids and glycerol are released at the cell
7. They are absorbed and then stored or oxidised

Question 3

What is fatty acid oxidation?

Answer 3

It is when a fatty acid is converted into ACYL-CoA
It takes place in the cytoplasm
It uses the enzyme Acyl Adenylate and an ATP — PPi
If the acyl-CoA has more than 13 carbons it is taken through the mitochondrial membrane using the carnitine shutter, if not it can use through the membrane.

Question 4

What is fatty acid B-Oxidation?

Answer 4

It is the cycle in which Acyl-CoA is converted into Acetyl-CoA. The cycle includes an oxidation, then hydration then oxidation and finally an thiolysis reaction.
It takes place in the mitochondria and keeps going round into all the carbons on the acyl-CoA are used.

Question 5

Utilisation of Acetyl-CoA?

Answer 5

It is used in the Krebs cycle where it is reacted with Oxaloacetate to produce citrate.
However some of it will also be converted into ketones, especially if you have too much. This process is called ketogenesis.

Question 6

What is a ketone?

Answer 6

They are a carbonyl where the carbon is attached to no hydrogens. In the body they are produced by the liver.

E.g. Acetone and beta-hydroxybutyrate.

Question 7

Explain the process of ketogenesis?

Answer 7

…

Question 8

What regulates the rate of ketogenesis?

Answer 8

1. The amount of fatty acids available
2. If there’s a high conc of glycerol-3-phosphate in the liver
3. If there are low ATP requirements hence excess Acetyl-CoA
4. Glucagon will lead to an increase of fat oxidation and hence an increase in ketone production
5. Insulin leads to a reduction of fat oxidation and hence a decrease in ketone production.

Question 9

What is ketoacidosis?

And who is it present in?

Answer 9

Ketones are acidic and hence an increase in the amount of ketones in the blood will lead to a lower pH.
This often occurs in type 1 diabetics as if they are injected with too little insulin, more fatty acids will be oxidised and hence there will be an increase in Acetyl-CoA and hence an increase of ketones in the blood.
Often present in type 1 diabetics before they are diagnosed.
Also present in chronic alcohol abuse patients.

Ketones also impair the ability of Hb to bind to O2, which may lead to increased ventilation to increase O2 and due to the acidic nature of ketones a increased ventilation to remove CO2.

Question 10

How do diabetic ketoacidosis work?

Answer 10

1. There is an insulin deficiency - no glycogen produced.
2. Glucagon - stimulates the breakdown of glycogen
3. There is also increased lipolysis

Hence they patient has hyperglycaemia and more ketones in their blood.

Question 11

How does alcoholic ketoacidosis work?

Answer 11

1. The patient has a high blood ethanol concentration
2. This impairs gluconeogenisis
3. Also decreases insulin production and increases glucagon production.
4. Leading to an increased lipolysis

Hence increased ketone production.