Molecules and Their Interactions part-1

The following reactions are part of the citric acid cycle. The numbers in parenthesis indicate the number of carbon atoms in each molecule.

Which of the following sequences of the reaction systems A → D is correct?
(1) NAD⁺ → NADH+H⁺, → NAD⁺,CO₂ → NADH+H⁺, GDP, CO₂ → GTP, FAD, iP → FADH₂
(2) NAD⁺ → NADH+H⁺, NAD⁺, CO₂ → NADH+H⁺, ADP, CO₂ → ATP, FAD, iP → FADH₂
(3) NAD⁺ → NADH+H⁺, FAD⁺, CO₂ → FADH₂, ADP → ATP, NAD⁺, iP → NADH+H⁺ ,CO₂
(4) NAD⁺ → NADH+H⁺, FAD⁺, CO₂ → FADH₂, GDP → GTP, NAD⁺,iP → NADH+H⁺ ,CO₂

29. The following statements are made regarding conversion of pyruvate to acetyl- CoA going from glycolysis to citric acid cycle:
    A. Oxidation of pyruvate to acetyl-CoA is reversible.
    B. Pyruvate is transported into the mitochondrion by a transporter.
    C. Pyruvate is carboxylated by pyruvate dehydrogenase.
    D. Acetyl lipoamide reacts with coenzyme A to form acetyl-CoA.
    E. The flavoprotein, dihydrolipoyl dehydrogenase, containing flavin adenine dinucleotide (FAD), is involved in conversion of pyruvate to acetyl-CoA.

Which one of the following options represents the combination of all correct statements?
(1) A, B and C                                           (2) B, C and D
(3) C, D and E                                           (4) B, D and E

Question

Which statement is FALSE about glycolysis?
(1) 2 molecules of NADH+H is formed per glucose
(2) 1 molecule of FADH₂ is formed per glucose
(3) Electron are released during oxidation of 3-phoshoglyceraldehyde
(4) Pyruvic acid is formed at last step

The glycolysis and citric acid cycles are important pathways o generate energy in the cell. Given below are statements regarding the production of ATP.
A. Electrons released during the oxidative steps of glycolysis and citric acid cycle produce 10 molecules of NADH and 2 molecules of, FADH2 per molecule of glucose.
B. Electrons released during the oxidative steps of glycolysis and citric acid cycle produce 20 molecules of NADH and 4 molecules of F ADH₂ per molecule of glucose.
C. The coenzymes produced are oxidized by electron transfer chain.
D. The conversion of ADP and Pi to ATP takes place in the intermembrane space of mitochondria.
Which one of the following combinations of above statements is correct?
(1) A and B (2) B and C
(3) C and D (4) A and C

The gradient of oxygen available to cells at inner regions of a tumour tissue environment is typically low that creates a hypoxic micro-environment. If enough oxygen is supplied to the cancer cells residing in hypoxic micro-environment, which one of the following processes may NOT occur?
(1) HlF-1α stable in the cells under hypoxic conditions, may undergo oxygen-dependent hydroxylation, targeting it for ubiquitination and proteolysis by tumour-suppressor protein VHL.
(2) Warburg effect will be reversed and conversion of glucose to lactate will not take place as
sufficient oxygen will be available for oxidative phosphorylation.
(3) Expression of HlF-1α dependent genes will be lowered
(4) Lactate generation in the tumour microenvironment, which contributed to M2 polarization of tissue-associated macrophages, will continue.

In yeast, under anaerobic conditions, pyruvate is fermented to ethanol through two steps:
decarboxylation of pyruvate to acetaldehyde and NADH-mediated reduction of acetaldehyde to ethanol. The mammalian liver also expresses alcohol dehydrogenase (Liver ADH: L-ADH).
From the options given below, choose the one that best explains the physiological significance of L-ADH in the absence of fermentation in the liver.
(1) The direction of L-ADH reaction varies with the relative concentrations of acetaldehyde and ethanol.
In addition, the enzyme metabolizes the alcohols produced by intestinal microflora anaerobically.
(2) NAD⁺ produced by L-ADH drives glycolysis in the liver.
(3) Mammalian L-ADH converts pyruvate to lactate and the NAD thus generated drives
glycolysis.
(4) Mammalian L-ADH has non-metabolic moonlighting functions.

The following are the statements about pyruvate kinase (PK).
A. ATP is an allosteric inhibitor of PK
B. Fructose 1,6 bisphosphate is an activator of PK
C. ADP is an allosteric inhibitor of PK
D. Alanine is an allosteric modulator of PK
Which of the above statement(s) are true?
(1) A, B, C                                    (2) A, B, D
(3) B, C, D                                  (4) only A

Phosopho fructokinase-l (PFK-1) is allosterically inhibited by
(1) ATP              (2) ADP
(3) AMP           (4) Fructose-6-P

Given below are statements that may or may not be correct.
A. Fructose 2, 6- biphosphate is an allosteric inhibitor of phosphofructokinase-l.
B. The TCA cycle intermediates, succinate and oxaloacetate can both be derived from amino acids.
C. A diet rich in cysteine can compensate for a methionine deficient diet in humans.
D. dTTP for DNA synthesis can be obtained from UTP.
E. In the fatty acid biosynthetic pathway, the carbon atom from HCO₃– in the synthesis of malonyl CoA is not incorporated into palmitic acid.
Choose the option that represents the combination of all the CORRECT statements
(1) A, B, C and E                                      (2) B, D and E
(3) A, D and E                                     (4) Only B and C

Phosphofructokinase catalyses one of the regulatory steps in glycolysis. Which one of the following metabolic changes leads to the activation of phosphofructokinase?
(1) Increased ATP concentration
(2) Decreased AMP concentration
(3) High citrate levels
(4) Increased fructose 2, 6, bisphosphate concentration

A major functional difference between the succinyl CoA-synthetase of plant and animal cell mitochondria is that it
(1) Does not produce ATP in plant cell.
(2) Produce UTP in plant cell.
(3) Produces ATP in plants and GTP in animal.
(4) Produces GTP in plants and ATP in animals.

Following statements are made regarding glycogen phosphorylase and glycogen synthase activities in relation to their phosphorylation status:
A. Phosphorylation of glycogen phosphorylase increases its activity
B. Phosphorylation of glycogen phosphorylase decreases its activity
C. Phosphorylation of glycogen synthase increases its activity
D. Phosphorylation of glycogen synthase decreases its activity
Which one of the following is a combination of correct statements?
(1) A and C                                        (B) B and C
(3) B and D                                        (4) A and D

Formation of glucose from acetyl Co A is called-
(1) Glycogenesis                            (2) Gluconeogenesis
(3) TCA cycle                                (4) Glycolysis

The organelle responsible for conversion of glucose from fatty acids in plants is
(1) Lysosome (2) Plastids
(3) Glyoxisomes    (4) Peroxisomes

Excess oxygen consumed after a vigorous exercise is
(1) to pump out lactic acid from muscle
(2) to increase the concentration of lactic acid in muscle
(3) to reduce dissolved carbon dioxide in blood
(4) to make ATP for gluconeogenesis

Which of the following ii NOT true for cholesterol metabolism?
(1) HMG-CoA reductase is the key regulator of cholesterol biosynthesis.
(2) Biosynthesis takes place in the cytoplasm.
(3) Reduction reactions use NADH as cofactor.
(4) Cholesterol is transported by LDL in plasma.

Which is true for β-oxidation of fatty acids
(1) Formation of Malonyl CoA is committed and regulatory step
(2) Formation of acetoacetyl ACP occurs in mitochondria
(3) Cytosolic acyl CoA is transported into mitochondria
(4) Use of NADH+H⁺ as reducing equivalent

Some metabolic aspects of the Red Blood Cell (RBC) are proposed in the following
statements:
A. Synthesis of fatty acids does not occur in the RBC
B. The pentose phosphate pathway is operative in the RBC
C. RBC cannot synthesize reduced glutathione (GSH)
D. RBC does not contain enzymes like adenosine deaminase and pyrimidine nucleotidase
E. NADH-dependent methemoglobin reductase system is present in RBC

Which one of the following combinations is NOT correct?
(1) A and B (2) B and C
(3) C and D (4) D and E

In eukaryotes there is single multifunctional fatty acyl synthase complex sufficient for complete fatty acid synthesis where as in prokaryotes there seven different enzymes involved for the same task. The probable explanation for this difference is
(1) fatty acid synthesis is more stringent in eukaryotes
(2) Synthesis of fatty acid is by different mechanism in eukaryotes as compare to prokaryotes
(3) For better regulation and fast fatty acid synthesis in eukaryotes
(4) Fatty acids of eukaryotes are different from the prokaryotes

Common metabolites in nucleotide biosynthesis derived from pentose phosphate pathway is
(1) PRPP (2) Glycerladehyde-3-P
(3) DHAP (4) Sedoheptulose 7-P

Number of cycles required to completely hydrolyze Arachidonic acid into acetyl CoA is
(1) 9 (2) 8 
(3) 10 (4) 11

Major regulatory step in cholesterol biosynthesis is
(1) HMG coA reductase (2) HMG CoA synthase
(3) Thiokinase (4) Mevalonate kinase

Sting of a bee causes pain, redness and swelling. Melittin is a major peptide in bee venom. Melittin is a membrane binding peptide that is involved in activating phospholipases in the membrane. The possible target phospholipase that is activated by melittin is
(1) Phospholipase C to generate inositol phosphates.
(2) Phospholipase A₂ to generate arichidonic acid.
(3) Phospholipase D to generate 1′, 3′- inisitol.
(4) Phospholipase A₁ to generate palmitic acid

Biosynthesis of tyrosine is detailed below:
Shikimic acid – A → shikimic acid-5-phosphate -B → C → chorismic acid → prephenic acid → D
→ transaminase → tyrosine.
Identify A, B, C and D
(1) ATP, phosphoenolpyruvic acid, 3-enolpyruyl shikimic acid-5-phosphate, p- hydroxyphenylpyruvic acid
(2) GTP, pyridoxal phosphate, 3-enolpyruvyl shikimic acid-5phosphate, phenylpyruvic acid
(3) NADP, 3-phosphohydroxypyruvic acid, 3-enolpyruvic shikimic acid-5-phosphate, p-
hydroxyphenylpyruvic acid
(4) ATP, 3-phosphohydroxypyruvic acid, 3-enolpyruvyl shikimic acid-5-phosphate, pyridoxylphosphate

Choose the correct answer from the following statements on biosynthesis.
(1) In the biosynthesis of palmitate, all the carbon atoms are derived from activated malonate.
(2) The amino acids Met, Thr, Lys, lle, Val and Leu are biosynthesized from oxaloacetate and pyruvate in most bacteria.
(3) Alanine is a major precursor for the biosynthesis of porphyrin.
(4) Tryptophan is converted to L-DOPA in the biosynthesis of epinephrine.

The inborn error of amino acid metabolism, alkaptonuria. is due to the lack of one of the
following enzymes:
(1) Fumaryl acetoacetate hydrolase
(2) α-keto acid decarboxylase
(3) Hornogentisate oxidase
(4) p-hydroxyphertylpyruvate dehydroxylase

The first step in the biosynthesis of valine begines with enzyme catalyzed condensation of two molecules of pyruvic acid. If an equimolar mixture of ¹³CH₃COCOOH and ¹²CH₃COCOOH are used as substrates for the reaction, which one of the following would represent the correct isotope incorporation pattern of the pro-R and pro-S diastereotopic methyl group in valine?
(1) 50% ¹³CH₃ (pro-R), ¹²CH₃ (pro-S)
50% ¹²CH₃ (pro-R), ¹³CH₃ (pro-S)
(2) 75% ¹³CH₃ (pro-R), ¹²CH₃ (pro-S)
25% ¹²CH₃ (pro-R), ¹³CH₃ (pro-S)
(3) 25% ¹³CH₃ (pro-R), ¹²CH₃ (pro-S)
25% ¹²CH₃ (pro-R), ¹³CH₃ (pro-S)
25% ¹³CH₃ (pro-R), ¹³CH₃ (pro-S)
25% ¹²CH₃ (pro-R), ¹²CH₃ (pro-S)
(4) 75% ¹²CH3 (pro-R), ¹³CH₃ (pro-S)
25% ¹³CH₃ (pro-R), ¹³CH₃ (pro-S)

Question

A cell line deficient in salvage pathway for nucleotide biosynthesis was fed with medium containing ¹⁵N labelled amino acids. Purines were then extracted. Treatment with which one of the following amino acids is NOT likely to produce ¹⁵N labelled purines?
(1) Aspartic acid (2) Glycine
(3) Glutamine (4) Aspartamine

Purine and pyrimidine nucleotides serve as monomeric units of the nucleic acid polymers DNA and RNA. Mentioned below are some of the statements with respect to the de novo synthesis of nucleotides. Which one of the following statements is INCORRECT?
(1) Biosynthesis of both purine and pyrimidine nucleotides begin with ribose-5-phosphate and
purine or pyrimidine rings are built on it.
(2) The first purine nucleotide biosynthesized by de novo pathway is inosinic acid or inosine-monophosphate.
(3) The first pyrimidine nucleotide biosynthesized by de novo pathway is orotidylic acid or orotidine monophosphate.
(4) Thymidylate or TMP is synthesized as deoxy-TMP from deoxy-UMP by thymidylate synthetase.

Question

Catabolic end product of purines is
(1) Xyloric acid (2) Allantoin
(3) Urea (4) Uric acid

Aspartate (Asp) is an amino acid with the structure NH2 – CH(CH₂ — COOH) — COOH. Given below are biosynthetic processes occurring in cells:
A. protein synthesis
B. de novo synthesis of inosine monophosphate and orotic acid
C. synthesis of adenosine monophosphate from inosine monophosphate
D. glutathione synthesis
Which one of the following correctly represents all the biosynthetic process(es) wherein Asp
is involved as a precursor?
(1) A only (2) A, Cand D
(3) A and C only (4) A, B and C