Biology

DNA and Genetics

1,095 Questions

DNA and genetics questions explore molecular biology, DNA replication, and genetic engineering techniques. These topics are essential for various competitive exams requiring a strong foundation in life sciences. Practice these questions to understand complex biological processes thoroughly.

DNA replication mechanismsGenetic engineering techniquesGene editing toolsPolymerase chain reactionDNA sequencing methods

DNA and Genetics Questions

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

Enzyme responsible for DNA chain elongation is

  1. DNA polymerase II

  2. DNA ligase

  3. RNA poymerase III

  4. DNA polymerase III
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
DNA polymerase II has 5’ to 3’ polymerization activity and 3’ to 5’ exonuclease activity and is mainly involved in DNA repair which makes option A incorrect. DNA polymerase III is a heteroenzyme with 10 subunits and has both 5’ to 3’ polymerization and 3’ to 5’ exonuclease activity. The gamma and epsilon subunits impart processivity, the ability to remain on the template and not to dissociate and reassociate, which in turn allow it to carry out primer elongation which makes option D correct. DNA ligase enzyme joins two DNA fragments together via phosphodiester bond between 3’ hydroxyl at the end of one fragment and a 5’ phosphate at the end of another fragment; it does not polymerise DNA which makes option B incorrect. RNA polymerase III synthesizes tRNAs, the 5S rRNA, and some other small specialized RNAs which makes option C incorrect.
Multiple choice dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

DNA helicase helps in 

  1. Opening supercoils of DNA

  2. Making DNA helix

  3. Opening two chains of DNA helix

  4. Making hydrogen bonds of nitrogenous bases
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Helicases move along the double-stranded DNA and separate the strands by breaking hydrogen bonds at the expense of energy from ATP. DNA unwinding by helicases creates topological stress/supercoils in the helical DNA structure which is relieved by the action of topoisomerases. These enzymes transiently break both DNA strands of one chromosome thereby making the other chromosome to pass through the break and relieve the stress. DNA polymerase enzyme synthesizes DNA strands by adding deoxyribonucleotides to 3' end of the primer via phosphodiester bonds; it uses parental DNA as template. Hydrogen bonding between base pairs is facilitated by the presence of hydrogen bond donor (primary and secondary amine groups or hydroxyl groups) and complementary hydrogen bond acceptor (carbonyls and tertiary amines) in bases; it is not enzymatic process. The correct option is C.

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

Which of the following help in repairing of DNA?

  1. Ligase

  2. DNA polymerase I

  3. RNA primer

  4. DNA polymerase III
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

DNA polymerase I serve clean-up functions during replication, recombination, and repair. It has 3' --> 5' proofreading exonuclease activity and 5' --> 3' exonuclease activity. The 5' --> 3' exonuclease activity of DNA polymerase I can replace an error containing the segment of DNA/RNA, paired to the template strand which is then simultaneously replaced by polymerase activity of the same enzyme. The process is called as nick translation. DNA polymerase III with its ten types of subunits has 5' --> 3' polymerization and 3' --> 5' proofreading activities in its $\alpha$ and $\epsilon$ subunits, respectively. 

As DNA pol III does not have 5' --> 3' exonuclease activity; it can not remove the erroneous segments of DNA/RNA. RNA primer is an oligonucleotide, synthesized by primase enzyme, that is elongated into long strands of deoxyribonucleotides or ribonucleotides by DNA and RNA polymerase enzymes respectively. Ligase enzyme joins two DNA strands by facilitating phosphodiester bond formation between the adjacent nucleotides; it can not cut and remove the DNA segments and thus, can not repair DNA. The correct option is B.

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

Which is true for DNA helicases?

  1. Separate DNA strands and establish replication forks

  2. ATP requiring unwinding enzymes

  3. Hydrolyse ATP

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

During DNA replication, two hexamers of helicases are loaded onto each DNA strand. Helicases move along the double stranded DNA and separate the strands by breaking hydrogen bonds between base pairs. ATP hydrolysis provides the required energy for breaking of hydrogen bonds; options B and C are correct. Thereby, DNA is unwound bidirectionally and two potential replication forks are created. The point at which two DNA strands are separated to facilitate the replication is called replication fork; option A is correct. Correct answer is D.

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

Which of the enzyme joins the broken strands of DNA?

  1. Nuclease

  2. Kinase

  3. Ligase

  4. Endonuclease
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Two classes of enzymes are most important in generating recombinant DNA molecule. First, restriction endonucleases (also called restriction enzymes) recognize and cleave DNA at specific DNA sequences (recognition sequences or restriction sites) to generate a set of smaller fragments. Second, the DNA fragment to be cloned can be joined to a suitable cloning vector by using DNA ligases to link the DNA molecules together. DNA ligase catalyzes the formation of new phosphodiester bonds in a reaction that uses ATP or a similar cofactor.

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

Which of the following does not describe a correct function of DNA polymerase?

  1. It helps to replace RNA primers with DNA nucleotides.

  2. It adds complementary DNA base pairs in a 5 to 3 direction along the DNA leading and lagging strands.

  3. It proofreads the replicated DNA and replaces mismatched DNA nucleotides.

  4. It adds RNA nucleotides along the DNA template in transcription.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

DNA polymerase is an enzyme used in the replication of DNA. It ads the DNA primers to the parent chain. This enzyme acts in the 5'-3 direction and thus forms lading stand on the chain that has 3'5' direction.

There are 3 DNA polymerases in use from which only the DNA polymerase II helps in replication and rest of the two are used in the DNA proofreading.

So, the correct option is 'It adds RNA nucleotides along the DNA template in transcription.'

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

DNA replication requires

  1. DNA polymerase

  2. DNA ligase

  3. RNA polymerase

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

RNA polymerase serves as primase during DNA replication and synthesizes RNA/DNA primer which is a stranded segment (complementary to the template) and has a free 3’ hydroxyl group to facilitate the addition of deoxyribonucleotides by DNA polymerase enzyme. DNA polymerase is polymerizing enzyme that has 5’ to 3’ polymerization and 3’ to 5’ exonuclease proofreading activities; it adds deoxyribonucleotides to free 3’ hydroxyl group of primer to synthesize new DNA strands. DNA ligase enzyme joins two Okazaki fragments together via phosphodiester bond between 3' hydroxyl at the end of one fragment and a 5' phosphate at the end of another fragment. Thus, option D is the correct answer. 

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

The helicase enzyme breaks

I. Covalent bonds

II. Hydrogen bonds

III. Ionic bonds

  1. II only

  2. I and II

  3. I and III

  4. II and III

  5. I, II and III
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
 Helicase is the enzyme that binds to DNA and remodels the nucleic acid i.e DNA. During DNA replication, the double helix unwinds as the preliminary step. The unwinding of DNA strand is catalysed by helicase enzyme. DNA polymerase is the enzyme responsible for the ongoing of the replication process, which was initiated by RNA primer. It breaks the hydrogen bonds between the nucleotides and thus helps in unzipping the DNA strands. Thus, the correct answer is option A.
Multiple choice dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

DNA ligase helps in                           

  1. Joining bits of DNA

  2. Splitting or separation of two strands of DNA

  3. Renaturation

  4. Denaturation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In molecular biology, DNA ligase is a specific type of enzyme, a ligase, that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond.

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

The enzyme which can cut molecules of DNA into segments is known as

  1. DNA polymerase

  2. DNA ligase

  3. Restriction enzyme

  4. DNA gyrase
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Restriction enzymes are nick named as 'molecular scissors' due to their ability to cut DNA fragments. Thus, restriction enzymes are of great use in genetic engineering for restricting desired genes for incorporation
So, the correct answer is 'Restriction enzyme'
Multiple choice dna replication replication and protein synthesis nucleic acids and protein synthesis heredity biology

DNA replication occurs in 5' 3' direction because 

  1. DNA polymerase III can polymerise nucleotides in 5 3 direction

  2. DNA polymerase I carries out editing

  3. DNA polymerase I carries out polymerisation

  4. DNA polymerase II can link up only in 5 3 direction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

DNA polymerase III is the primary enzyme for DNA replication and is structurally constrained to add nucleotides only in the 5' to 3' direction.