Molecular Basis of Inheritance Test

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Molecular Basis of Inheritance Test - 33

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Question 1
1 / -0

One turn of the helix in a B-form DNA is approximately

A
3.4 nm

B
2 nm

C
20 nm

D
0.34 nm
Solution
In a DNA molecule, the two strands are not parallel but intertwined with each other. Each strand looks like a helix.
The two strands form a "double helix" structure, which was first discovered by James D. Watson and Francis Crick in 1953.
In this structure, also known as the B form, the helix makes a turn every 3.4 nm, and the distance between two neighbouring base pairs is 0.34 nm.
So, the correct answer is '3.4 nm'.
Question 2
1 / -0

Histone occupies the major grooves of DNA at an angle of

A
15$$^o$$

B
90$$^o$$

C
45$$^o$$ to the helix axis

D
30$$^o$$ to the helix axis
Solution
- Nucleosomes are the basic structural packing unit of DNA in chromatin built from histone proteins around which DNA is wrapped. Histone occupies the major groove of DNA at an angle of 30 degrees.
So, the correct answer is "30$$^o$$ to the helix axis".
Question 3
1 / -0

Okazaki fragments are synthesised on

A
Leading strands of DNA only

B
Lagging strands of DNA only

C
Both leading and lagging strands of DNA

D
Complementary DNA
Solution
Synthesis of leading strand DNA, as the name indicates occurs in an easier and faster way in 5' $$\rightarrow$$ 3' direction.
Whereas, lagging strand synthesis lags behind and is done with the help of the production of Okazaki fragments in 5' $$\rightarrow$$ 3' direction, which are then joined with the help of ligase. This results in the formation of a continuous strand.
Question 4
1 / -0

The enzyme, DNA polymerase was discovered by

A
Kornberg

B
Okazaki

C
Waston and Crick

D
Jacob and Monod

Solution

A. Kornberg was an American biochemist who discovered DNA polymerase.
B. Okazaki discovered the formation of Okazaki fragments which are the short fragments formed during the replication of lagging strand of DNA.
C. Watson and Crick in 1953 discovered the double helix structure of DNA.
D. Jacob and Monod in 1961 discovered the regulation of bacterial enzyme.
So, the correct answer is 'Kornberg'.
Question 5
1 / -0

DNA replication is aided by

A
DNA polymerase only

B
DNA ligase only

C
Both DNA polymerase and ligase

D
RNA polymerase

Solution

DNA polymerase catalyes the formation of DNA strand. DNA ligase is otherwise called as molecular sutures. 5'---->3' strand synthesis happens with the help of DNA Polymerase I. Synthesis of strand in 3' ---> 5' strand happens by the formation of okazaki fragments. These fragments are further joined together by the action of DNA ligase enzyme.
Question 6
1 / -0

Okazaki segments are formed during

A
Replication

B
Transduction

C
Transcription

D
Translation
Solution
Okazaki segments are formed during DNA replication.
The DNA polymerase on the lagging strand synthesizes discontinuous short DNA segments known as Okazaki fragments in $$5'- 3'$$ direction.
DNA ligase joins the Okazaki fragments and forms the continuous complementary strand.
So, the correct answer is option A.
Question 7
1 / -0

When DNA replication starts

A
The leading strand produces Okazaki fragments.

B
The hydrogen bonds between the nucleotides of two strands break.

C
The phosphodiester bonds between the adjacent nucleotides break.

D
The bonds between the nitrogen base and deoxyribose sugar break.
Solution
A. Correct Option: B

B. Explanation for the correct option:
- DNA replication starts with the unzipping of the DNA helixes which are held together by the hydrogen bonds.
- Helicase enzyme is responsible for the breaking of hydrogen bonds between nucleotides of the DNA strand thus separating two strands of the DNA.
Question 8
1 / -0

The enzyme that breaks Hydrogen bonds between the 2 strands of a DNA molecule is

A
Helicase

B
Topoisomerase

C
Ligase

D
Polymerase

Solution

Helicases are a class of enzymes vital to all living organisms, Their main function is to unpackage an organism's genes. DNA helicases are essential during DNA replication because they separate double - stranded DNA strands into single strands allowing each strand to be copied.
Question 9
1 / -0

During replication of a bacterial chromosome, DNA synthesis starts from a replication origin site and it

A
Moves in one direction of the site

B
Moves in bi-directional way

C
Involves RNA primers

D
Is facilitated by telomerase

Solution

Bacterial chromosomes are circular. DNA replication begins at certain fixed unique points and is called origin. In bacteria, replication occurs in bidirectional way and two separated strands between the two forks appear as a bubble under the microscope.
So, the correct answer is 'Moves in bi-directional way'.
Question 10
1 / -0

The two polynucleotide chains in a DNA are

A
Parallel

B
Discontinuous

C
Antiparallel

D
Semiconservative

Solution

Solution:

Correct answer is option C.
Explanation for correct option:

DNA strands are antiparallel in nature. While one strand of the double-stranded DNA runs the in 5' → 3' direction the other strand is placed parallel to it in the reverse direction i.e. 3' → 5' direction.
So, the correct answer is (C).

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Molecular Basis of Inheritance Test - 33

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Molecular Basis of Inheritance Test - 33

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Question 1

3.4 nm

2 nm

20 nm

0.34 nm

Solution

Question 2

15$$^o$$

90$$^o$$

45$$^o$$ to the helix axis

30$$^o$$ to the helix axis

Solution

Question 3

Leading strands of DNA only

Lagging strands of DNA only

Both leading and lagging strands of DNA

Complementary DNA

Solution

Question 4

Kornberg

Okazaki

Waston and Crick

Jacob and Monod

Solution

Question 5

DNA polymerase only

DNA ligase only

Both DNA polymerase and ligase

RNA polymerase

Solution

Question 6

Replication

Transduction

Transcription

Translation

Solution

Question 7

The leading strand produces Okazaki fragments.

The hydrogen bonds between the nucleotides of two strands break.

The phosphodiester bonds between the adjacent nucleotides break.

The bonds between the nitrogen base and deoxyribose sugar break.

Solution

Question 8

Helicase

Topoisomerase

Ligase

Polymerase

Solution

Question 9

Moves in one direction of the site

Moves in bi-directional way

Involves RNA primers

Is facilitated by telomerase

Solution

Question 10

Parallel

Discontinuous

Antiparallel

Semiconservative

Solution

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