MDS PREP
The biochemical defect in Osteogenesis Imperfecta, type II is:
1. a mutation in the alpha 1 chain of Type I collagen.
2. a deficiency in collagenase.
3. a deficiency in lysyl oxidase.
4. a deficiency in lysyl hydroxylase.
Biochemistry
Answer: 4
The biochemical defect in Osteogenesis Imperfecta, type II is a deficiency in lysyl hydroxylase.
Which of the following dental tissues is most likely to be effected by Vit-A
deficiency
1. enamel
2. dentin
3. cementum
4. pulp
Biochemistry Answer: 1
Enamel most likely effected by deficiency of vitamin A
A component of the coenzyme required in a transamination process is
1. Thiamine
2 Folic acid
3 Pyridoxine
4 Riboflavin
Biochemistry
Answer: 3
A component of the coenzyme required in a transamination process is Pyridoxine
The principal role of Vitamin E in the prevention of oxidative damage is to
1. oxidize metals to their less reactive state.
2. potentiate the action of superoxide dismutase.
3. reduce Vitamin C to its active oxidation state.
4. terminate free radical chain reactions in lipid bilayers.
Biochemistry
Answer: 2
The principal role of Vitamin E in the prevention of oxidative damage is to potentiate the action of superoxide dismutase
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
Which of the following amino acids is a
precursor for epinephrine?
1. Valine
2. Leucine
3. Tyrosine
4. Cysteine
Biochemistry
Answer: 3
Epinephrine, also known as adrenaline, is a hormone and neurotransmitter that
is synthesized in the body from the amino acid tyrosine. Tyrosine is a
non-essential amino acid, which means that it can be synthesized in the body
from phenylalanine, another essential amino acid. The synthesis of epinephrine
occurs in two main steps:
1. Hydroxylation of tyrosine: Tyrosine is converted into dihydroxyphenylalanine
(DOPA) by the enzyme tyrosine hydroxylase. This is the rate-limiting step in the
synthesis of epinephrine.
2. Decarboxylation and further hydroxylation: DOPA is then decarboxylated to
form dopamine, which is further hydroxylated to produce norepinephrine.
Norepinephrine is the immediate precursor of epinephrine.
3. Formation of epinephrine: Norepinephrine is methylated by the enzyme
phenylethanolamine N-methyltransferase (PNMT) and converted into epinephrine.
The other amino acids listed are not directly involved in the synthesis of
epinephrine:
1. Valine and Leucine are branched-chain amino acids that are primarily involved
in the metabolism of muscles and energy production.
2. Cysteine is a sulfur-containing amino acid that is important for the
synthesis of proteins with disulfide bridges and is a precursor for other
molecules like glutathione and taurine, but not directly involved in the
synthesis of epinephrine.
An enzyme increases the rate of a biochemical reaction by
1. decreasing substrate concentration.
2. decreasing activation energy.
3. increasing Km.
4. increasing Keq.
Biochemistry
Answer: 2
Enzymes are biological catalysts that increase the rate of chemical reactions
by lowering the activation energy required for the reaction to occur.
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.