Practice Paper of NEET PG: Important Questions of Biochemistry

The Important Questions of Biochemistry for NEET PG exam:

1. Deficiency of lysyl hydroxylase causes?
A. Alport syndrome
B. Menkes disease
C. Epidermolysis bullosa
D. Osteogenesis imperfecta

Correct answer: B. Menkes disease

Pili torti in Menkes disease – brittle and short hairs which appear twisted and flat during microscopy.

  • Alport syndrome is caused by mutation in the collagen genes COL4A3 and COL4A6.
  • Epidermolysis bullosa dystrophica is due to mutation in the collagen gene COL7A1.
  • Osteogenesis imperfecta is caused by mutations in COL1A1 and COL1A2.

2. The enzyme used for the mapping of hypersensitive sites in recombinant DNA research is?
A. DNA ligase
B. DNA polymerase I
C. DNase I
D. Polynucleotide kinase

Correct answer: C. DNase I (Deoxyribonuclease I)

Production of recombinant DNA

  • DNA ligase is used for joining of DNA molecules.
  • DNA polymerase I is used for synthesis of double stranded cDNA.
  • Polynucleotide kinase is used for T-32 end labeling of DNA or RNA.

3. Deficiency of argininosuccinate synthase causes?
A. Hyperargininemia
B. Hyperammonemia type II
C. Argininosuccinicaciduria
D. Citrullinemia

Correct answer : D. Citrullinemia

  • Argininosuccinicaciduria is caused by metabolic defect in argininosuccinase.
  • Hyperammonemia type II is due to defect in ornithine transcarbamoylase.
  • Hyperargininemia is an autosomal recessive disorder characterised by defect in the gene for arginase.

4. Which of the following is true regarding Okazaki fragment?
A. Are segments of RNA attached to an RNA initiator component
B. Are related to the leading strand
C. Several Okazaki fragments must be sequentially synthesized for each replication fork
D. Helicase acts on the leading strand to unwind dsDNA

Correct answer : C. Several Okazaki fragments must be sequentially synthesized for each replication fork

 

  • Okazaki fragments are segments of DNA attached to an RNA initiator component.
  • They are related to the lagging strand.
  • Helicase acts on the lagging strand to unwind dsDNA.

5. All are disorders due to peroxisomal abnormalities except?
A. Pfeiffer syndrome
B. Zellweger syndrome
C. Hyperoxaluria type 1
D. Acatalasemia

Correct answer : A. Pfeiffer syndrome

Types of craniosynostosis

  • Peroxisome is an organelle involved in the metabolism of many molecules including fatty acids, purines and amino acids.
  • It is bounded by a single membrane and contains more than 50 enzymes.
  • Pfeiffer syndrome is due to mutations in the gene encoding fibroblast growth factor receptor 1 (FGR1).
  • It is a craniosynostosis syndrome.

6. The most widely used method for determining the purity of a protein is?
A. Isoelectric focusing
B. Polyacrylamide gel electrophoresis
C. Ion exchange chromatography
D. High pressure chromatography

Correct answer: B. Polyacrylamide gel electrophoresis

SDS-PAGE

  • The most widely used method for determining the purity of a protein is polyacrylamide gel electrophoresis (PAGE) in the presence of an anionic detergent, sodium dodecyl sulphate (SDS).
  • Electrophoresis separates the charged biomolecules based on the rates at which they migrate in an electrical field.

7. The enzyme catalyzing the production of orotidylic acid is?
A. Dihydro orotase
B. Aspartyl transcarbamoylase
C. Dihydro orotate dehydrogenase
D. Orotate phosphoribosyl transferase

Correct answer : D. Orotate phosphoribosyl transferase

  • In the de novo synthesis of pyrimidines, the enzyme aspartyl transcarbamoylase catalyses the combination of carbamoyl phosphate and aspartate to form carbamoyl aspartate.
  • Dihydro orotase catalyses the production of dihydro orotic acid.
  • Dihydro orotate dehydrogenase catalyses the production of orotic acid from dihydro orotic acid.
  • Orotate phosphoribosyl transferase is the enzyme catalyzing the synthesis of orotidylic acid (Orotidine 5′-monophosphate).

8. Azaserine inhibits?
A. Glycinamide ribonucleotide synthetase
B. Glycinamide ribonucleotide transformylase
C. Formyl glycinamide ribonucleotide amidotransferase
D. Inosine monophosphate synthase

Correct answer : C. Formyl glycinamide ribonucleotide amidotransferase

Azaserine

  • In de novo synthesis of purine nucleotides, there are 10 steps.
  • The 4th step (addition of N3) is catalysed by the enzyme Formyl glycinamide ribonucleotide amidotransferase.
  • This enzyme is inhibited by azaserine, an anticancer drug.

9. Deficiency of lysosomal maltase causes?
A. McArdle disease
B. Andersen disease
C. Cori disease
D. Pompe disease

Correct answer : D. Pompe disease

Pompe disease – Muscle biopsy showing large vacuoles

  • In McArdle disease, there is deficiency of muscle phosphorylase.
  • Branching enzyme is deficient in Andersen disease.
  • Debranching enzyme is deficient in Cori disease.

10. All are inhibitors of oxidative phosphorylation except?
A. Carboxin
B. Oligomycin
C. Valinomycin
D. Atractyloside

Correct answer : A. Carboxin

Mitochondrial electron transport chain

  • Carboxin inhibits the transfer of ions from FADH2.
  • Oligomycin, Valinomycin and Atractyloside are inhibitors of oxidative phosphorylation.
  • Oligomycin inhibits flow of protons through Fo.
  • Valinomycin is an ionophore which inhibits oxidative phosphorylation.
  • Atractyloside inhibits translocase.

11. Which of the following is not a protein misfolding disorder?
A. Tuberculosis
B. Creutzfeldt Jakob disease
C. Alzheimer’s disease
D. Cystic fibrosis

Correct answer : A. Tuberculosis

  • Tuberculosis is not a disorder of protein misfolding

A beta amyloid deposits in the cerebral cortex of a patient with Alzheimer’s disease – Immunohistochemistry photomicrograph.

PROTEIN MISFOLDING DISORDERS

  • Protein misfolding disorders, also known as proteopathies are conditions in which some proteins become structurally abnormal and impair the function of cells and tissues.
  • Protein folding is abnormal and they fail to perform normally and may even gain toxic effects.
  • e.g. Alzheimer’s disease (beta amyloid peptide), Creutzfeldt Jakob disease (prion disease), Cystic fibrosis (CFTR).

12. Decreased energy production in thiamine deficiency is due to?
A. It is a cofactor for oxidative reduction
B. It is required for transamination reactions
C. It is a coenzyme for alpha ketoglutarate dehydrogenase and pyruvate dehydrogenase in citric acid cycle
D. It is a coenzyme for transketolase in hexose monophosphate shunt

Correct answer : C. It is a coenzyme for alpha ketoglutarate dehydrogenase and pyruvate dehydrogenase in citric acid cycle

A patient suffering from beriberi

THIAMINE – PROPERTIES, FUNCTIONS AND DEFICIENCY DISORDERS

  • Thiamine (vitamin B1) is a water soluble vitamin
  • Thiamine pyrophosphate acts as a coenzyme in the catabolism of carbohydrates and amino acids
  • It is also required for the biosynthesis of acetylcholine and gamma aminobutyric acid (GABA)
  • Cereals are the important dietary sources of thiamine
  • It is present in yeast extract and pork in very high concentrations
  • It is important for energy production as it is a coenzyme for pyruvate dehydrogenase and alpha ketoglutarate dehydrogenase in citric acid cycle (Krebs cycle / Tricarboxylic acid cycle)
  • It is a also a coenzyme for transketolase in pentose phosphate pathway (involved in the production of NADPH)
  • Deficiency of thiamine leads to Beriberi
  • The major forms of beriberi are:
    • Wet beriberi (cardiovascular disease)
    • Dry beriberi (neurological disease)
    • Infantile beriberi
  • Alcoholics are prone to develop Wernicke’s encephalopathy due to deficiency of thiamine

13. Which of the following enzymes is responsible for the transfer of amino groups from an amino acid to an alpha keto acid?

A. Transaminase
B. Transketolase
C. Deaminase
D. Lyase

Correct answer : A. Transaminase

 

Transamination reaction

TRANSFER OF AMINO GROUPS (TRANSAMINATION)

  • Transaminases are responsible for the transfer of an amino group (NH2) from an amino acid to an alpha keto acid.
  • It results in the formation of a new amino acid and alpha keto acid.
  • Transaminases are also known as aminotransferases.
  • Pyridoxal phosphate (derived from Vitamin B6) acts as a coenzyme for transamination reactions.
  • These reactions are reversible.

14. Process used in an expression vector to increase yield of recombinant protein synthesis ?

A. Translation initiation
B. Promoter induction
C. Transcription terminators
D. Multiple cloning sites

Correct answer : B. Promoter induction

EXPRESSION VECTORS AND RECOMBINANT PROTEIN SYNTHESIS

  • Expression vectors are plasmids / viruses designed to regulate protein expression in a target cell
  • They are used to insert a specific gene into the target cell to produce the desired protein
  • They contain regulatory sequences which act as enhancer and promoter regions to bring about efficient transcription of the gene
  • An inducible promoter regulates the gene expression and can increase the yield of the recombinant protein

15. Site of urea cycle is?

A. Liver
B. Kidney
C. GIT
D. Lungs

Correct answer : A. Liver

SITE OF UREA CYCLE

  • Urea cycle (also known as ornithine cycle / Krebs Henseleit cycle) takes place in the liver
  • It is responsible for the conversion of toxic ammonia (produced by amino acid catabolism) to urea for excretion
  • 5 enzymes are involved in the urea cycle are:
    1. Carbamoyl phosphate synthetase I
    2. Ornithine transcarbamylase
    3. Argininosuccinate synthase
    4. Argininosuccinate lyase (also known as argininosuccinase)
    5. Arginase
  • The first 2 enzymes are located in the mitochondria, whereas the other 3 are located in the cytoplasm
  • The rate limiting enzyme is Carbamoyl phosphate synthetase I

16. Rothera’s test is utilised for detection of?

A. Glucose

B. Proteins

C. Urea

D. Ketone bodies

Correct answer : D. Ketones

Tests in biochemistry:

  • Ketone bodies – Rothera’s test
  • Reducing sugars – Benedict’s test, Fehling’s test
  • Proteins – Heller’s nitric acid test, Heat and acetic acid test
  • Bile salts – Hay’s test
  • Bile pigments – Fouchet’s test
  • Blood – Benzidine test

17. Sphingomyelinase deficiency is characteristic of ?

A. Fabry disease

B. Krabbe’s disease

C. Tay Sachs disease

D. Niemann Pick disease

Correct answer : D. Niemann Pick disease

Sphingomyelinase deficiency is seen in Niemann Pick disease. The enzymes deficient in the other disease are:

  • Fabry disease – alpha galactosidase
  • Krabbe’s disease – beta galactosidase
  • Tay Sachs disease – Hexosaminidase A

18. Which among the following is a cardioprotective fatty acid?
A. Palmitic acid
B. Stearic acid
C. Oleic acid
D. Omega-3 fatty acids

Correct answer : Both C and D

Palmitic acid and stearic acid are saturated fatty acids – promote atherogenesis.
Oleic acid is a monounsaturated fatty acid – cardioprotective, reduce LDL.
Omega-3 fatty acids like linolenic acid and docosahexaenoic acid are cardioprotective.

19. Xeroderma pigmentosum is produced as a result of a defect in :
A. DNA polymerase III
B. DNA polymerase I
C. DNA exonuclease
D. DNA ligase

Correct answer : B. DNA polymerase I or D. DNA ligase

Xeroderma pigmentosum is an autosomal recessive disease with defect in DNA repair. It is characterised by extreme sensitivity to sunlight. The enzymes affected in this condition are:
1. UV specific endonuclease (most common)
2. DNA polymerase I
3. DNA ligase

20. A genetic disorder renders fructose 1,6 — biphosphatase in liver less sensitive to regulation by fructose 2,6 — bi-phosphate. All of the following metabolic changes are observed in this disorder except:
A. Level of fructose 1,6—biphosphate is higher than normal
B. Level of fructose 1,6 — biphosphate is lower than normal
C. Less pyruvate is formed
D. Less ATP is generated

Correct answer : A. Level of fructose 1,6—biphosphate is higher than normal

Fructose 2,6 – biphosphate acts to decrease the activity of fructose 1,6 – biphosphatase. When the enzyme becomes less sensitive to regulation, the inhibitory effect is lost and the enzyme activity increases. The following effects are observed:
1. Level of fructose 1,6 — biphosphate decreases
2. Pyruvate is used up for glucose synthesis
3. ATP is used up for glucose synthesis

21. Alpha helix and Beta pleated sheet are examples of:
A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure

Correct answer : B. Secondary structure

22. Cytochrome C of the bacteria has 50% identity of amino acid sequence with that of human. Which of the following is the most conserved parameter in these two proteins?
A. Quarternary structure
B. Tertiary structure
C. Amino acid sequence
D. Loop and turn segments

Correct answer : B. Tertiary structure

23. A young man finds that every time he eats dairy products he feels very uncomfortable. His stomach becomes distended. He develops gas and diarrhea frequently. These symptoms do not appears when he eats foods other than dairy products. Which of the following is the most likely enzyme in which this young man is deficient?
A. alpha-amylase
B. B-galactosidase
C. alpha-glucosidase
D. Sucrase

Correct answer : D. Sucrase

The clinical picture is suggestive of lactose intolerance. But lactase is not given in the options. Hence we have to look for an enzyme whose deficiency produces a similar clinical picture. Sucrase-isolamtase deficiency also presents with diarrhoea and bloating (gas) following intake of a diet containing sucrose or glucose polymers.

24. In which of the following conditions the level of creatinine kinase 1 increases ?
A. Myocardial ischemia
B. Brain Ischemia
C. Kidney damage
D. Electrical cardioversion

Correct answer : B. Brain Ischemia

Localisation of CPK isoenzymes
CPK 1 (CPK BB) – Brain
CPK 2 (CPK MB) – Myocardium
CPK 3 (CPK MM) – Skeletal muscle

25. Which of the following elements is known to influence the body’s ability to handle oxidative stress ?
A. Calcium
B. Iron
C. Potassium
D. Selenium

Correct answer : D. Selenium

Selenocysteine is a part of the enzyme glutathione peroxidase which has antioxidant action.

26. A middle aged woman on oral contraceptives for many years, developed neurological symptoms such as depression, irritability, nervousness and mental confusion. Her hemoglobin level was 8g/dl. Biochemical investigations revealed that she was excreting highly elevated concentrations of xanthurenic acid in urine. She also showed high levels of triglycerides and cholesterol in serum. All of the above findings are most probably related to vitamin B6 deficiency caused by prolonged oral contraceptive use except :
A. Increased urinary xanthurenic acid excretion
B. Neurological symptoms by decreased synthesis of biogenic amines
C. Decreased hemoglobin level
D. Increased triglyceride and cholesterol level

Correct answer : D. Increased triglyceride and cholesterol level

Increased triglyceride and cholesterol level are due to metabolic effects of OCP’s and are not secondary to vitamin B6 deficiency.

27. A person on a fat free carbohydrate rich diet continues to grow obese. Which of the following lipoproteins is likely to be elevated in his blood?
A. Chylomicrons
B. VLDL
C. LDL
D. HDL

Correct answer : B. VLDL

High carbohydrate diet increases lipid synthesis. There is increased synthesis of tryglycerides and secretion of VLDL by liver.

28. A small calcium binding protein that modifies the activity of many enzymes and other proteins in response to changes of Ca2+ concentration, is known as:
A. Cycline
B. Calmodulin
C. Collagen
D. Kinesin

Correct answer : B. Calmodulin

Calmodulin is a calcium dependent regulatory protein which activates enzymes and ion channels.

29. Which of the following substances acts to increase the release of Ca2+ from endoplasmic reticulum ?
A. Inositol triphosphate
B. Parathyroid hormone
C. 1,25 dihydroxy cholecalciferol
D. Diacylglycerol

Correct answer : A. Inositol triphosphate

Inositol triphosphate (IP3) and diacylglycerol (DAG) are second messengers for G protein coupled receptors. IP3 stimulates release of calcium from endoplasmic reticulum. DAG activates protein kinase C.

30. Which of the following is a membrane bound enzyme that catalyzes the formation of cyclic AMP from ATP?
A. Tyrosine Kinase
B. Polymerase
C. ATP synthase
D. Adenylate cyclase

Correct answer : D. Adenylate cyclase

 

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