Tag: replication and protein synthesis

Questions Related to replication and protein synthesis

Which enzyme catalyses the synthesis of a new strand for a DNA molecule by linking nucleotides to the developing strand?

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. RNA polymerase

  2. DNA ligase

  3. DNA polymerase

  4. Topoisomerase

Show answer
Correct Option: C
Explanation:

  • RNA polymerase helps in DNA dependent RNA synthesis. This process is known as transcription. DNA strands are used as a template to synthesize RNA molecules.
  • DNA ligase is used to join DNA segments during DNA repair or during replication (to join Okazaki fragments of the lagging strands).
  • DNA polymerase works in the pair to synthesis new strand for DNA molecule from deoxyribonucleotides. In other words, it helps in DNA dependent DNA synthesis.
  • Topoisomerase enzyme participates in overwinding or unwinding of DNA. During DNA replication or transcription, DNA becomes overwound ahead of the replication fork. It binds to DNA and cut the phosphate backbone of either one or both the DNA strands.
So, the correct option is 'DNA polymerase'.

Thermostable enzymes Taq and Pfu isolated from thermophilic bacteria are

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. DNA polymerases

  2. DNA ligases

  3. Restriction endonucleases

  4. RNA polymerases

Show answer
Correct Option: A
Explanation:

Thermophilic bacteria that live in hot springs and hydrothermal vents. Taq polymerase and Pfu polymerase are enzymes isolated from thermophilic bacteria. These enzymes are used in polymerase chain reaction as these enzymes are able to withstand the protein-denaturing conditions (high temperature) required during polymerase chain reaction ( PCR ). 

So, the correct option is 'DNA polymerases'.

Select the correct match of enzyme with its related function

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. DNA polymerase - Synthesis of DNA Strands

  2. Helicase - Unwinding of DNA helix

  3. Ligase - Joins together short DNA segments

  4. All of these

Show answer
Correct Option: D
Explanation:

DNA polymerase is the enzyme required for the addition of nucleotides into a DNA strand being synthesized from an existing strand of DNA. Helicase refers to another enzyme that functions in unwinding of the double helix structure of DNA wound around one another to result in a melted region of DNA strand to begin the replication of DNA. The joining of the short segments of DNA created during replication of the lagging strand (3' to 5') happens due to the enzyme ligase that acts as a molecular glue.

So, the correct option is 'All of these'.

Choose the correct answers from the alternatives given :
RNA polymerase

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. can produce several polypeptide chains at one time through the creation of polysomes

  2. starts transcribing at an AUG triplet on one DNA strand

  3. transcribes both introns and exons

  4. transcribes both DNA strands, but always in a $5' \, \rightarrow \, 3'$ direction

Show answer
Correct Option: C
Explanation:

RNA polymerase transcribes both exons and introns present in DNA which are consecutively present in the RNA too, although, introns are removed by splicing in a mature mRNA. Exons are the segment of the genetic material or DNA/RNA that code for an amino acid but introns do not code for any amino acid sequence or protein. Introns have a regulatory function in both replication and transcription processes.

So, the correct option is 'transcribes both introns and exons'.

Which of the following is known as joining enzyme or repair enzyme of DNA?

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. Transcriptase

  2. Endonucleases

  3. Ligases

  4. Polymerase

Show answer
Correct Option: C
Explanation:

In molecular biology, DNA ligase is a specific type of enzyme that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms. Single-strand breaks are repaired by DNA ligase using the complementary strand of the double helix as a template, with DNA ligase creating the final phosphodiester bond to fully repair the DNA.

Therefore, the correct answer is option C.

DNA polymerase enzyme is required for the synthesis of

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. RNA from DNA

  2. DNA from DNA

  3. RNA from RNA

  4. DNA from RNA

Show answer
Correct Option: B
Explanation:

DNA polymerase enzyme helps in DNA dependent DNA synthesis by addition of deoxyribonucleotides, building blocks of DNA. This enzyme uses DNA as the template and synthesizes DNA. This process is also known as replication.

RNA from DNA is synthesized by RNA polymerase enzyme through the process called transcription. RNA is used as the template and nucleotides are for RNA synthesis. 
DNA from RNA is synthesized by reverse transcriptase enzyme in some retroviruses where RNA acts as the genetic material.
So, the correct option is 'DNA from DNA'.

Which of the following statements are correct?
(i) RNA polymerase I transcribes rRNAs.
(ii) RNA polymerase II transcibes snRNAs.
(iii) RNA polymerase III transcibes hnRNA,
(iv) RNA polymerase II transcribes hnRNA.

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. (i) and (ii)

  2. (i) and (iii)

  3. (i), (ii) and (iv)

  4. (i) and (iv)

Show answer
Correct Option: A
Explanation:

RNA polymerase 1 (also known as Pol I) is, in higher eukaryotes, the polymerase that only transcribes ribosomal RNA (but not 5S rRNA, which is synthesized by RNA polymerase III), a type of RNA that accounts for over 50% of the total RNA synthesized in a cell. Pol I is a 590 kDa enzyme that consists of 14 protein subunits (polypeptides). Twelve of its subunits have identical or related counterparts in RNA polymerase II (Pol II) and RNA polymerase III (Pol III). The other two subunits are related to Pol II initiation factors and have structural homologues in Pol III. Ribosomal DNA transcription is confined to the nucleolus, where about 400 copies of the 42.9-kb rDNA gene are present, arranged as tandem repeats in nucleolus organizer regions. Each copy contains a 13.3 kb sequence encoding the 18S, the 5.8S, and the 28S RNA molecules, interlaced with two internal transcribed spacers, ITS1 and ITS2, and flanked upstream by a 5' external transcribed spacer and a downstream 3' external transcribed spacer. Because of the simplicity of Pol I transcription, it is the fastest-acting polymerase and contributes up to 60% of cellular transcription levels in exponentially growing cells.

RNA polymerase II (RNAP II and Pol II) is a multiprotein complex. It is one of the three RNAP enzymes found in the nucleus of eukaryotic cells. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription. It catalyzes the transcription of DNA to synthesize precursors of mRNA and most snRNA and microRNA. A 550 kDa complex of 12 subunits, RNAP II is the most studied type of RNA polymerase. A wide range of transcription factors are required for it to bind to upstream gene promoters and begin transcription.
So the correct option is ' (i) and (ii)'.

Select the correct option that correctly fill the blanks i - iv
I. Less than (i) of genome represents structural genes that code for proteins.
II. Chemical substance that binds with repressor and convert it into a non-DNA binding State is (ii).
III. In prokaryotes, during replication RNA primer is removed by (iii) whereas in eukaryotes it is removed by (iv).

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. (i) - 5%, (ii) regulator, (iii) - DNA polymerase II, (iv) - DNA polymerase $\beta$

  2. (i) - 10%, (ii) - regulator, (iii) - DNA polymerase I, (iv) - DNA polymerase $\alpha$

  3. (i) - 2%, (ii) inducer, (iii) - DNA polymerase I, (iv) - DNA polymerase $\beta$

  4. (i) - 50%, (ii) inducer, (iii) - DNA polymerase III, (iv) - DNA polymerase $\alpha$

Show answer
Correct Option: C
Explanation:

The human genome is made of 3 billion DNA base pairs and out of them 2% only are responsible for coding for proteins and the rest may have regulatory functions. In an inducible operon such as the Lac Operon the inducer binds to the repressor to inactivate it such that the repressor can no longer bind to the operator and the gene expression can take place. DNA polymerase I (or Pol I) is an enzyme that participates in the process of prokaryotic DNA replication. This is responsible for proof reading and excising or removing off the RNA primers required for initiation of replication. DNA polymerase, beta, also known as POLB, is an enzyme present in eukaryotes involved in base excision and repair, also called gap-filling DNA synthesis.

So, the correct option is '(i) - 2%, (ii) inducer, (iii) - DNA polymerase I, (iv) - DNA polymerase  β '.

DNA replication takes place at ________ phase of the cell cycle

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. G$ _1$

  2. S

  3. G$ _2$

  4. M

Show answer
Correct Option: B
Explanation:

In eukaryotes, the replication of DNA takes place at S-phase of the cell cycle. The replication of DNA and cell division cycle should be coordinated. A failure in cell division after DNA replication results into chromosomal anomaly.

Choose the correct answer from the alternatives given :
The enzyme DNA dependent RNA polymerase catalyses the polymerisation reaction in ________ direction.

dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

  1. Only 5 $\rightarrow$ 3

  2. Only 3 $\rightarrow$ 5

  3. Both (a) and (b)

  4. None of these

Show answer
Correct Option: A
Explanation:

The two strands have opposite polarity and the DNA-dependent RNA polymerase also catalyze the polymerization in only one direction, that is, 5 →→ 3, the strand that has the polarity 3 →→ 5 acts as a template, and is also referred to as template strand. The other strand which has the polarity 5 →→ 3 and the sequence same as RNA (except thymine at the place of uracil) is displaced during transcription. This strand (which does not code for anything) is referred to as coding strand.

So, the correct answer is 'Only 5 → 3'.