MDS PREP
Gout is a disease of purine overproduction. In this disease, joints develop crystals of
1. urea.
2. sodium urate.
3. guanine.
4. hypoxanthine.
Biochemistry
Answer: 2
Gout is a form of arthritis caused by the accumulation of uric acid crystals,
specifically sodium urate crystals, in the joints. The body produces uric acid
as a waste product during the metabolism of purines, which are substances found
in certain foods and also synthesized by the body. High levels of uric acid can
lead to the formation of these crystals, which cause inflammation and pain in
the affected joints. Urea (Answer 1) is a waste product formed from the
metabolism of proteins and amino acids, while guanine (Answer 3) and
hypoxanthine (Answer 4) are purine bases involved in nucleotide metabolism, but
they do not directly form the crystals seen in gout.
In addition to the influence of the oxygen concentration, the formation of oxyhemoglobin is influenced by
1. pH
2. CO2 concentration
3. Temperature
4. All of the above
Biochemistry
Answer: 4
The formation of oxyhemoglobin is influenced by
1. pH
2. CO2 concentration
3. Temperature
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.
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.
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
Epinephrine causes increased blood glucose level due to:
1. Increased glycogenolysis in liver and muscle
2. Activation of phosphorylase
3. Inhibition of glycogen synthesis in liver
4. All of the above
Biochemistry
Answer: 4
Epinephrine causes increased blood glucose level due to:
1. Increased glycogenolysis in liver and muscle
2. Activation of phosphorylase
3. Inhibition of glycogen synthesis in liver
.Glucose can be synthesised from all of the following except
1. amino acids 2.Glycerol
3. Acetoacetate 4.Lactic acid
Biochemistry
Answer: 1
Glucose can be synthesised from Glyerol, Acetoacetate, Lactic acid
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.