Question

Consider the structures that are referred to as ‘ketone bodies’. A. What metabolic states can lead to their formation? B. What organ absolutely requires these structures as an energy source? And why? C. Outline their syntheses starting from acetylCoA. D. The formation of excess levels of ketone bodies (ketosis) is a bad thing for the organism? Why exactly? E. When a person is experiencing ketosis, it is sometimes mistaken for excess alcohol consumption. Why? There are 2 distinct reasons why this mistake may be made. What are they?

Answer 1

The three related compounds acetoacetate, acetone and D-- hydroxybutyrate that are produced during the metabolism of fat are considered as ketone bodies.

A) Ketone bodies are synthesized within mitochondria of liver cells at times of fasting.ie; due to lack blood glucose or during times of vigorous exercise, consumption of fat rich diets or due to some medical conditions.

B) It is the brain that uses these structures as an energy source. It is because, brain cannot metabolize fatty acids directly while, the ketone bodies ( - Hydroxybutyrate and acetoacetate) can easily diffuse through membranes or are transported with the help of transporters. Thus our brain recieves 60 to 70 % ofr equired energy from ketone bodies.

C.     2 Acetyl-CoA

          ↕    Thiolase

Aceto acetyl-Co A

↕    HMG-CoA Synthase

HMG-CoA

(β- Hydroxy β- methylglutaryl-CoA)

↕   HMG-CoA Lyase

Acetoacetate

From Acetoacetate, two other ketone bodies are also formed. They are, Acetone and - Hydroxybutarate ( Major Ketone bodie).

D) Excess generation of ketone bodies results in a condition called Ketoacidosis. It is because both Acetoacetate and - Hydroxybutyrate are acidic and if levels of these compounds become too high, the pH of blood falls and results in Ketoacidosis. Diabetes (Type 1) when left untreated can also result in Ketoacidosis.

E) When a person is experiencing Ketosis, it is sometime mistaken for excess alcohol consumption. It is because, in people who consume alcohol there is a problem of apetite loss. So they try to avoid food. So, when the uptake of carbohydrate decreases, there is a decrease in insulin production and at the same time other hormones like glucagon level shoots up. So, when body is devoid of energy from carbohydrate, it starts breaking down fats to produce ketone bodies which ultimately results in ketoacidosis. So, in people who consume alcohol there is a chance of ketoacidosis because of their low food intake (ie; an indirect relation). Hence persons experiencing ketosis is sometimes mistaken for excess alcohol consumption.