MDS PREP
A vitamin B12 deficiency may affect heme synthesis by reducing the concentration of which of the following? Choose the one best answer.
1) Acetyl-CoA
2) Succinyl-CoA
3) Glycine
4) Alanine
Biochemistry Answer: 2
Vitamin B12 participates in two reactions in the body-conversion of homocysteine to methionine and conversion ofmethylmalonyl-CoA to succinyl-CoA.
Methylmalonyl-CoA is produced via various amino acid degradation pathways, and from oddcarbon chain fatty acid oxidation. In the absence of B12, succinyl-CoA would only be produced as an intermediate of the TCA cycle, and if it were removed from the cycle for heme synthesis, energy production may suffer.
Glycine is usually obtained from the diet, although in a B12 deficiency a functional folate deficiency may also develop, leading to an inhibition of serine hydroxymethyltransferase, the enzyme that converts serine to glycine, and requires free tetrahydrofolate.
Succinyl-CoA and glycine are the precursors for heme synthesis. A B12 deficiency would not inhibit the production of acetyl-CoA, succinate, or alanine.
Which of the following enzymes is active in adipocytes following a heavy meal?
1) Glycogen phosphorylase
2) Glycerol kinase
3) Hormone-sensitive triacylglyceride lipase
4) Phosphatidate phosphatase
Biochemistry Answer: 4
The enzyme phosphatidate phosphatase converts phosphatidic acid to diacylglycerol during synthesis of triacylglycerides.
The function of adipose tissue is the storage of fatty acids as triacylglycerols in times of plenty and the release of fatty acids during times of fasting or starvation.
Fatty acids taken in by adipocytes are stored by esterification to glycerol-3-phosphate. Glycerol-3-phosphate is derived almost entirely from the glycolytic intermediate dihydroxyacetone phosphate through the action of glycerol-3-phosphate dehydrogenase. Glycolytic enzymes are active in adipocytes during triglyceride synthesis, but those of glycogen degradation (low levels in adipocytes) and gluconeogenesis (ie, glucose-6-phosphatase) are not.
Glycerol kinase is not present to any great extent in adipocytes, so that glycerol freed during lipolysis is not used to reesterify the fatty acids being released.
The enzyme triacylglyceride lipase is turned on by phosphorylation by a cyclic AMP-dependent protein kinase following epinephrine stimulation.
Glutamate-pyruvate trans-aminase is predominantly present In:
1. Skeletal muscle
2. Cardiac muscle
3. Brain
4. Liver
Biochemistry
Answer: 4
Glutamate-pyruvate trans-aminase is predominantly present In Liver
The rate limiting step in glycolysis is catalyzed by:
1. Hexokinase
2. Phosphofructokinase
3. Enolase
4. Pyruvate kinase
Biochemistry
Answer: 2
The rate limiting step in glycolysis is catalyzed by Phosphofructokinase
The reaction used for estimating free amino, groups in proteins is:
1. Ninhydrin test
2. Deamination with HNO2
3. Biuret test
4. Formol titration
Biochemistry
Answer: 2
The reaction used for estimating free amino, groups in proteins is Deamination with HNO2
Features of Vitamin C deficiency is due to defect of which enzyme
1. Lysyl hydroxylase
2. Lysyl oxidase
3. Procollagen peptidase
4. None of the above
Biochemistry
Answer: 1
Vitamin C deficiency is due to defect of Lysyl hydroxylase
If a biochemical test gives the same reading for a sample on repeated testing, it is inferred that the measurement is:
1. Precise.
2. Accurate.
3. Specific.
4. Sensitive.
repeatablity of test is precision and getting results within reference range is accuracy
Iodine is a characteristic component of
1. Cysteine
2. Tyrosine
3. Thyroxine
4. Thiamin
Biochemistry
Answer: 3
odine is a characteristic component of Thyroxine