Metabolism Of Fat Flashcards
The substance essential for transfer of fatty acids across mitochondrial membrane A. Creatine B. Creatinine C. Carnitine D. Coenzyme A
Answer - C. Carnitine
Long chain activated fatty acid penetrate the inner mitochondrial membrane only in combination with carnitine.
Regarding synthesis of triacyl glycerol in adipose tissue, all of the following are true except
A. Synthesis from dihydroxyacetone phosphate
B. Enzyme glycerol kinase plays an important role
C. Enzyme glycerol 3 phosphate dehydrogenase plays an important role
D. Phosphatidate is hydrolyzed
Answer- B. Enzyme glycerol kinase plays an important role.
Triacyl glycerol is synthesised from acyl CoA and glycerol 3 phosphate.
Glycerol kinase catalyzes the activation of glycerol to sn- glycerol 3 phosphate.
Because the enzyme glycerol kinase is not expressed in adipose tissue or muscle, glycerol cannot be utilised for provision of glycerol 3 phosphate, which must be supplied by glucose via glycolysis.
So in muscle or adipose tissue, most of glycerol 3 phosphate is formed from dihydroxyacetone phosphate by glycerol 3 phosphate dehydrogenase.
In which organelle(s) of hepatocyte, the elongation of long chain fatty acid takes place: A. Endoplasmic reticulum B. Golgi body C. Mitochondria D. Lysosomes E. Ribosomes
Answer- A. Endoplasmic reticulum and C. Mitochondria
Lipogenesis occurs in cytosol.
Palmitate, 16 C, fully saturated long chain fatty acid is the principal end product of fatty acid synthase system in animal cells. It is the precursor of other long chain fatty acids and may be elongated by addition of 2 C unit acetyl groups through the action of fatty acid elongation system present in smooth ER and mitochondria.
Mitochondrial FA chain elongation is not a common pathway. It operates under anaerobic conditions and is favoured by high NADH/NAD+ ratio and pyridoxal phosphate (coenzyme)
Which of the following enzymes is common to the synthesis of cholesterol and ketone bodies A. HMG-CoA reductase B. HMG- CoA lyase C. HMG - CoA synthase D. Thiokinase
Answer- C. HMG-CoA synthase
Both cholesterol and ketone bodies are synthesised from (3)beta hydroxyl (3) beta methyl glutarylCoA (HMG-CoA).
So enzymes, thiolase and HMG CoA synthase involved in conversion of acetyl CoA to HMG CoA are common to synthesis of cholesterol and ketone bodies both.
However cytoplasmic HMG CoA synthase is involved in cholesterol synthesis whereas mitochondrial HMG CoA synthase is involved in Ketone body synthesis.
Cholesterol synthesis is controlled by regulation of HMG CoA reductase which is a rate limiting enzyme.
Cholesterol, the major sterol in animal tissue has steroid nucleus. Of the cholesterol absorbed. 80-90 % is esterified with long chain fatty acids (mainly saturated) such as palmitic and stearic acids.
