Q-81. In oxidative phosphorylation, the ATP production and respiratory chain are linked by
a) Chemical methods
b) Physical methods
c) Chemi-osmotic methods
d) Conformational changes
Answer: Chemi-osmotic methods
Explanation:
Oxidative phosphorylation:
The flow of electrons from NADH or FADH2 to O2 through protein complexes located in the mitochondrial inner membrane leads to the pumping of protons out of the mitochondrial matrix.
The resulting uneven distribution of protons generates a pH gradient and a trans-membrane electrical potential that creates a proton-motive force.
ATP is synthesized when protons flow back to the mitochondrial matrix through an enzyme complex. Thus, the oxidation of fuels and the phosphorylation of ADP are coupled by a proton gradient across the inner mitochondrial membrane.
Important point:
The chemi-osmotic theory proposed by Peter Mitchell, postulates that above two processes are coupled by proton gradient across inner mitochondrial membrane.
Q-82. Thiamin level is best monitored by best monitored by
a) Trans-ketolase level in blood
b) Thiamine level in blood
c) G-6-PD activity
d) Reticulocytosis
Answer: Trans-ketolase level in blood
Explanation:
Thiamin deficiency:
Chronic peripheral neuritis
Beriberi with or without heart failure and edema
Wernicke encephalopathy with Korsakoff psychosis associated specially with alcohol and narcosis
Lactic acidosis in subjects on a relatively high carbohydrate diet
Important point:
The role of thiamin diphosphate in pyruvate dehydrogenase means that in deficiency there is impaired conversion of pyruvate to acetyl Co-A resulting in increased plasma concentration of lactate and pyruvate which may cause life threatening lactic acidosis.
Thiamin nutritional status can be assessed by erythrocyte trans-ketolase activation.
Q-83. Vitamin B12 and folic acid supplementation in megaloblastic anemia leads to the improvement of anemia due to
a) Increased DNA synthesis in bone marrow
b) Increased hemoglobin production
c) Erythroid hyperplasia
d) Increased iron absorption
Answer: Increased DNA synthesis in bone marrow
Explanation:
Impairment of methionine synthase in B12 deficiency results in the accumulation of methyl tetra-hydro-folate- folate trap.
There is therefore functional deficiency of folate secondary to the deficiency of Vitamin B12.
Deficiency of folic acid itself or deficiency of Vitamin B12, which leads to functional deficiency of folate, affects cells that are dividing rapidly because they have a large requirement for thymidine for DNA synthesis.
Clinically, this affects the bone marrow leading to megaloblastic anemia.
Important points:
The most common cause of pernicious anemia is failure of absorption of Vitamin B12 rather than dietary deficiency.
This can be result of failure of intrinsic factor secretion caused by chronic use of proton pump inhibitors and autoimmune disease affecting parietal cells or from the production of anti-intrinsic factor antibodies.
Q-84. Nitric oxide synthase
a) Is inhibited by Ca++
b) Catalyzes a di-oxygenase reaction
c) Accepts electrons from NADH
d) Requires NADPH, FAD, FMN, & Heme iron
Answer: Requires NADPH, FAD, FMN, & Heme iron
Explanation:
NO synthase catalyzes a five electron oxidation of amidine nitrogen of arginine.
NO synthase is a very complex enzyme employing five redox cofactors: NADPH, FAD, FMN, Heme and tetra-hydro-biopterin
Important point:
The electron flow in the NO synthase reaction is: NADPH > FAD > FMN > heme > O2.
Q-85. Phenylalanine is the precursor of all the following EXCEPT
a) Tyrosine
b) Epinephrine
c) Thyroxine
d) Melatonin
Answer: Melatonin
Explanation:
Tryptophan-> Serotonin-> Melatonin
Phenylalanine-> Tyrosine-> Epinephrine, Nor-epinephrine and thyroxin
Q-86. In a well fed state, acetyl Co-A obtained from diet is least used in the synthesis of
a) Palmity CoA
b) Citrate
c) Acetoacetate
d) Oxalo-succinate
Answer: Acetoacetate
Explanation:
Acetoacetate is ketone body formed during starvation and not in well fad state.
Q-87. Substrate level phosphorylation is seen in the conversion of
a) Acetoacetate to a-keto glutarate
b) Succinyl Co-A to succinate
c) Fumarate to malate
d) Succinate to Fumarate
Answer: Succinyl Co-A to succinate
Explanation:
Substrate level phosphorylation:
Substrate-level phosphorylation results in the formation of ATP or GTP by the direct transfer and donation of a phosphoryl (PO3) group to ADP or GDP.
There is a net direct capture of two high energy phosphate groups in glycolytic reactions catalyzed by phosphoglycerate kinase and pyruvate kinase.
Two ore high energy phosphate per mole of glucose are captured in citric acid cycle during the conversion of succinyl Co-A to succinate reaction catalyzed by succinate thiokinase.
Important points:
Glycolysis: ATP per mole of glucose under aerobic condition
Substrate level phosphorylation= 4
Respiratory chain oxidation of 2 NADH (Malate shuttle) =5
Consumption of ATP for reactions of hexokinase and Phospho-Fructokinase= – 2
Total per mole glucose under aerobic condition= 7
Glycolysis: ATP per mole of glucose under anaerobic condition
Substrate level phosphorylation= 4
Consumption of ATP for reactions of hexokinase and Phospho-Fructokinase= – 2
Total per mole glucose under anaerobic condition= 2
Important points:
Respiratory chain oxidation of 2 NADH formed during glycolysis (Glycero-phosphate shuttle) = 3
There is a considerable advantage in using glycogen rather than glucose for anaerobic glycolysis in muscle, since the product of glycogen phosphorylase is G-1-P, which is inter-convertible with G-6-P. This saves the ATP that would otherwise be used by hexokinase, increasing the net yield of ATP from 2 to 3 per glucose.
Citric acid cycle: ATP per mole of glucose
Total net ATP= 25
Q-88. Apo B-48 and B-100 are expressed as two different apo-proteins because of difference in
a) RAN editing
b) RNA Splicing
c) Chromosomal loci
d) Apo-B gene
Answer: RAN editing
Explanation:
RAN editing:
The central dogma states that for a given gene and gene product there is a linear relationship between the coding sequence in DNA, m-RNA sequence and protein sequence.
Exception to this dogma is RNA editing. Coding information can be changed at the m-RNA level by RNA editing. In such cases, the coding sequence of the m-RNA differs from that in the cognate DNA. An example is the apo-lipoprotein B gene and m-RNA.
In liver, the single Apo-B gene is transcribed into m-RNA that directs the synthesis of Apo B-100.
In intestine, the same gene directs the synthesis of the primary transcript; however, a Cytidine deaminase converts a CAA codon in m-RNA to UAA at a single specific site. Rather than encoding glutamine, this codon becomes a termination signal and Apo B-48 is result. Apo B-100 and Apo B-48 have different functions in two organs.
Q-89. All the following can be used to detect mutation except
a) Single strand conformational polymorphism
b) Ligase chain reaction
c) Polymerase chain reaction
d) DNA sequencing
Answer: Ligase chain reaction
Explanation:
Mutation Detection techniques:
Cytogenetics and Molecular Cytogenetics:
Conventional Karyotyping
Fluorescence in situ hybridization (FISH)
Comparative genomic hybridization (CGH)
Molecular Diagnostics:
Polymerase chain reaction (PCR) and its versions
DNA microarray
DNA Sequencing
Multiplex ligation-dependent probe amplification (MLPA)
Single Strand Conformational Polymorphism (SSCP)
Denaturing Gradient Gel Electrophoresis (DGGE)
Hetero-duplex analysis
Restriction fragment length polymorphism (RFLP)
Next Generation Sequencing:
DNA sequencing in a massive scale
Q-90. Which of the following is true regarding hydroxyl ethyl starch?
a) It is an anesthetic agent
b) It is a plasma expander
c) It is a crystalloid
d) Used as a nutritional agent
Answer: It is a plasma expander
Explanation:
Plasma expanders:
Dextran
Degraded gelatin polymer
Hydroxyl ethyl starch
Human albumin