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Molecular Biology

Description: GATE: Biotechnology: Molecular Biology & Genetics
Number of Questions: 20
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Tags: Genetics Molecular Biology and Genetics
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In an eukaryote during the transcription holoenzyme, RNA polymerase binds to a DNA sequence and the DNA assumes to have a saddle like structure at that point. What is that region on the DNA called?

  1. AAAT box

  2. Pribnow box

  3. Hogness box

  4. GTTA box

  5. AAGGAGU sequence


Correct Option: C
Explanation:

Hogness box is found in promoter region of DNA of archea and eukaryotes and it provides a saddle-like structure for the attachment of RNA polymerase.

Which of the following statements is true in case of RNA polymerase III enzymes?

  1. They are responsible for synthesis of precursors for large ribosomal RNAs.

  2. They are responsible for the synthesis of precursor mRNA and small nuclear RNAs.

  3. They are responsible for the synthesis of small ribosomal RNAs.

  4. They are responsible for synthesis of tRNA and small ribosomal RNAs.

  5. They are responsible for synthesis of precursor of hetero nuclear RNAs.


Correct Option: D
Explanation:

RNA polymerase III participates in the formation of tRNAs and small ribosomal RNAs during transcription from the template DNA.

E.coli bacteria are placed in a medium, which is inoculated with radioactive guanosine for 5 minutes. Then it was made to replicate in a normal medium. Which of the following is correct for the replication process of DNA?

  1. Each strand will be partly radioactive.

  2. Both the strands of DNA are radioactive.

  3. Only one strand will be radioactive.

  4. Radioactivity is seen only on the leading strand.

  5. None of the strands is radioactive.


Correct Option: C
Explanation:

Only one strand will be radioactive. Replication of DNA is semi-conservative in nature. Hence, a new strand is formed on the template DNA strand. The new strand while replicating use radioactive guanosine from the medium but the template strand would not have the radioactive G. Therefore after 5 minutes, only one strand, i.e. the newly produced strand will have the radioactive guanosine.

Wobble hypothesis was proposed by F.H.C.Crick (1966) from the structure of anticodon loop in tRNA. Which one of the following is established by this hypothesis?

  1. Economy in tRNA molecules

  2. Initiation of peptide chain

  3. Termination of peptide chain

  4. Elongation of peptide chain

  5. Non-ambiguous nature of genetic code


Correct Option: A
Explanation:

A single tRNA type is able to recognise two or more codons by their anticodon loops differing only in the third base, which is known as Wobble position. This kind of Wobbling allows economy of the number of tRNA molecules because several codons meant for the same amino acid are recognised by the same tRNA.

With which of the following does the operator gene in an operon of a prokaryote (E. coli) combine?

  1. Repressor protein (to switch on gene action)

  2. Inducer gene (to switch off structural gene action)

  3. Inducer gene (to switch on structural gene action)

  4. Promoter gene (to start transcription of structural gene)

  5. Regulator or repressor protein (to switch off structural gene action)


Correct Option: E
Explanation:

Regulator or repressor protein (to switch off structural gene action): In Lac operon as it is described by Jacob and Monad in E.coli, the operator gene combines with repressor tetramer produced on translation of mRNA transcripted from inducer or regulatory gene. It inhibits the RNA polymerase from running over the structural genes. This consequently switches off the functioning of the structural genes.

Translation of proteins from mRNA is characterised by formation of specific structures during the process. Which one is correct for polysome formation?

  1. Ribosomes with several subunits bind with Shine Dalgarno sequence.

  2. Several ribosomes are attached to a single mRNA during translation.

  3. Many ribosomes are attached to membrane of rough endoplasmic reticulum.

  4. Several subunits of ribosomes are attached with each other in a linear arrangement.

  5. Several 30S subunits are attached to mRNA.


Correct Option: B
Explanation:

During translation, several ribosomes are arranged in linear manner over a single mRNA. This is known as polysome. It helps in formation of globuler structure of proteins as many polypeptides are formed together.

Which of the following is/are responsible for the prevention of ribosomal association at the end of initiation step?

Different antibiotics affect translation in various ways. Some of them prevent ribosomal association with mRNA or block amino acid binding sites on the ribosome to cause damage in the process of translation.

  1. Erythromycin

  2. Chloramphenicol and tetracycline

  3. Streptomycin

  4. Tobramycin and kanamycin

  5. Neomycin


Correct Option: D
Explanation:

Tobramycin and kanamycin prevent ribosomal association at the end of initiation step and cause misreading of the genetic code.

What would happen if in a gene encoding a polypeptide of 100 amino acids, the 83rd codon (UAC) is mutated to UAG?

  1. A polypeptide of 99 amino acids will form.

  2. A polypeptide of 83 amino acids will form.

  3. A polypeptide of 82 amino acid will form.

  4. A polypeptide of 17 amino acids will form.

  5. Two polypeptides of 83 and 17 amino acids respectively will form.


Correct Option: C
Explanation:

A polypeptide of 82 amino acid will form. As UAG is a stop codon, it will not attach with any anticodon loop of tRNAbecause polypeptide elongation will be stopped at the 83rd position. Therefore, polypeptide chain with 82 amino acids will form.

Splicing is a post transcriptional modification in which newly transcribed hetero nuclear RNA is modified into mRNA. Faulty splicing can cause diseases in any organism. Identify the way by which faulty splicing can cause thalasemia in humans.

  1. Malformation of α chain of haemoglobin leads to α thalassemia.

  2. Malformation of β chain of haemoglobin leads to β thalassemia.

  3. Malformation of one α and one β chains of haemoglobin causes α β major thalassemia.

  4. Malformation of both α and β chains of haemoglobin causes α β major thalassemia.

  5. α chains have less amino acids.


Correct Option: B
Explanation:

This is due to the mutation that results in a nucleotide change at an exon-intron junction, which leads to lack of synthesis of β chain of haemoglobin and consequently the disease β thalassemia occurs to the human being.

How does chloramphenicol affect bacterial translation?

Different antibiotics affect translation in various ways. Some of them prevent ribosomal association with mRNA or block amino acid binding sites on the ribosome to cause damage in the process of translation.

  1. Chloramphenicol causes misreading of the genetic code.

  2. Chloramphenicol inhibits translocation of mRNA along ribosome.

  3. Chloramphenicol blocks peptidyl transferase and formation of peptide bond on the 50S ribosomal subunit.

  4. Chloramphenicol blocks A-site of 50S subunit.

  5. Chloramphenicol inhibits interaction with tRNA and mRNA.


Correct Option: C
Explanation:

It is an antibiotic, which causes inhibition of bacterial translation process by blocking synthesis of peptide bond.

Proteins involved in Hsp70 system are ___________.

Chaperons are heat shock proteins, which facilitate the interactions on the polypeptide surface to finally give the specifc conformation of proteins. They are categorised into two major groups; Hsp70 system and chaperonine system.

  1. Hsp 70 and Hsp 30

  2. Hsp 40 and Hsp 100

  3. Hsp 70 and Hsp 20

  4. Hsp 70 and Hsp 40

  5. Hsp 50 and Hsp 30


Correct Option: D
Explanation:

Hsp 70 and Hsp 40: 70 KD is a heat shock protein and 40 KD is a heat shock protein that can bind individually to the substrate, and help in the correct formation of protein folding.

Which of the following is a short lived RNA having molecular weight ranging from 500000 to 1000000?

On the basis of life span, molecular weight, function, etc. RNAs are classified into various types like mRNA, rRNA, tRNA smRNA, scRNA, etc.

  1. rRNA

  2. mRNA

  3. tRNA

  4. smRNA

  5. scRNA


Correct Option: B
Explanation:

It is 5% to 10% of total RNA having molecular weight ranging from 500000 to 1000000, which is short lived in nature. It carries genetic information from DNA to protein.

Match the following:

 
Column A Column B
P. Translation i. Production of ribosomes
Q. Nucleolus ii. Ribosomes
R. Crick iii. DNA polymerase
S. Replication iv. Central dogma
  1. P - iv, Q - ii, R - i, S - iii

  2. P - ii, Q - iv, R - i, S - iii

  3. P - iv, Q - iii, R - ii, S - i

  4. P - ii, Q - i, R - iv, S - iii

  5. P - iii, Q - iv, R - i, S - ii


Correct Option: D
Explanation:

Ribosome is the organelle where translation occurs. Ribosomes are produced in the nucleolus. Francis Crick discovered Central dogma. Replication of DNA is brought about by DNA polymerase.

Proof reading and DNA repair are the characteristic functions of DNA polymerase I in prokaryotic replication. Identify the enzyme having the same function in eukaryotes.

In eukaryotic replication,  5 different kinds of polymerases have been demonstrated. They perform different functions.

  1. DNA polymerase α

  2. DNA polymerase β and DNA polymerase γ

  3. DNA polymerase γ

  4. DNA polymerase δ, DNA polymerase β and DNA polymerase ε

  5. DNA polymerase ε


Correct Option: D
Explanation:

DNA polymerase β is involved in the repair of DNA, and proof reading is done by DNA polymerase δ. DNA polymerase ε is involved in DNA synthesis on the lagging strand and the proof reading function.

Match the following: Column A Column B P. PCNA i. Single strand binding protein Q. RPA ii. Prevent continuous DNA loss at the end of Chromosome R. Telomeres iii. Fragmented DNA produced on the lagging strand S. Okazaki fragments iv. Leading strand synthesis

  1. P - ii, Q - i, R - iii, S - iv

  2. P - iii, Q - i, R - iv, S - ii

  3. P - iv, Q - i, R - ii, S - iii

  4. P - ii, Q - iv, R - iii, S - i

  5. P - iii, Q - iv, R - i, S - ii


Correct Option: C
Explanation:

Proliferating cell nuclear antigen (PCNA) along with DNA polymerase δ helps in leading strand synthesis. Replication protein A (RPA) is a single strand binding protein. Telomeres are the special structures that prevent continuous DNA loss at the end of chromosome. The fragmented DNA produced during the lagging strand synthesis is Okazaki fragment.

If a sudden mutation occurs to the gene responsible for coding DNA polymerase α in a unicellular organism, which function will be stopped in that cell?

In eukaryotic replication,  5 different kinds of polymerases have been demonstrated. They perform different functions.

  1. Initiation of leading strand synthesis

  2. Initiation of replication in both leading and lagging strands

  3. Mitochondrial replication

  4. DNA proof reading in lagging strand

  5. Lagging strand synthesis


Correct Option: B
Explanation:

Initiation of replication in both leading and lagging strands. As DNA polymerase α is responsible for synthesis of RNA primer on both the strands, initiation of replication is stopped in both leading and lagging strands. RNA primer provides free –OH at the 3’ end for the attachment of deoxyribonucleotides on both the strands and if it is unable to form, then replication will be stopped.

“Inhibition of the prokaryotic transcription is caused by rifampin, an antibiotic.” Which of the following options is correct for rifampin action?

  1. Binds with the β-subunit of prokaryotic RNA polymerase.

  2. Binds with RNA polymerase II.

  3. Binds with DNA template and blocks movement of RNA polymerase.

  4. Binds with promoter region.

  5. None of the above


Correct Option: A
Explanation:

Rifampin is an antibiotic that is widely used for the treatment of tuberculosis and leprosy. It binds with the β-subunit of prokaryotic RNA polymerase and inhibits the movement of the enzyme and its activity.

Match the following: Column A Column B P. Repressor protein i. Fine structure of gene of R II locus in T4 phage Q. Puromycin ii. Produced from inducer R. eEF1βγ iii. Premature termination of polypeptide S. Benzer iv. Eukaryotic translation

  1. P - ii, Q - iv, R - i, S - iii

  2. P - iv, Q - ii, R - i, S - iii

  3. P - iv, Q - iii, R - ii, S - i

  4. P - iii, Q - iv, R - ii, S - i

  5. P - ii, Q - iii, R - iv, S - i


Correct Option: E
Explanation:

In operon system, repressor protein is produced from inducer gene. Puromycin produced from Streptomyces alboniger responsible for premature termination of polypeptide.  eEF1βγ is the elongation factor in eukaryotic translation. Seymour Benzer discovered fine structure of gene of R II locus in T4 phage.

Who brings about the mRNA and rRNA processing?

On the basis of life span, molecular weight, function, etc. RNAs are classified into various types like mRNA, rRNA, tRNA smRNA, scRNA, etc.

  1. mRNA

  2. tRNA

  3. smRNA

  4. scRNA

  5. rRNA


Correct Option: C
Explanation:

smRNA takes part in splicing, and rRNA and mRNA processing.

Which of the following statements is not true for chaperonin?

Chaperons are heat shock proteins, which facilitate the interactions on the polypeptide surface to finally give the specifc conformation of proteins. They are categorised into two major groups; Hsp70 system and chaperonine system.

  1. This system contains 60 KDa Hsp.

  2. This system contains 10 KDa Hsp.

  3. It works in association with Hsp 70 system.

  4. It is an oligomeric assembly into which the folded proteins are inserted.

  5. It binds individually to the substrate and helps in the correct formation of protein folding.


Correct Option: E
Explanation:

It is true for Hsp 70 system but not for chaperonin. Chaperonin is an oligomeric assembly, which forms a structure into which the folded protein is inserted. This system mainly has Hsp 60 and Hsp10 and is required at later part of the protein folding process and often work in association with Hsp 70 system.

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