Structure Of Dna

STRUCTURE OF DNA

Q. 1

Supercoiled DNA is separated by relaxed DNA by:

 A

ELISA

 B

Gel electrophoresis

 C

DNA footprinting

 D

DNA fingerprinting

Q. 1

Supercoiled DNA is separated by relaxed DNA by:

 A

ELISA

 B

Gel electrophoresis

 C

DNA footprinting

 D

DNA fingerprinting

Ans. B

Explanation:

Q. 2

Watson’s DNA model is :  

 A

Right handed, parallel

 B

Left handed, anti parallel

 C

Left handed, parallel

 D

Right handed, anti parallel

Q. 2

Watson’s DNA model is :  

 A

Right handed, parallel

 B

Left handed, anti parallel

 C

Left handed, parallel

 D

Right handed, anti parallel

Ans. D

Explanation:

 

Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds.

This common form of DNA is said to be right handed because as one looks down the double helix, the base residues form a spiral in a clockwise direction.

These two strands run in opposite directions to each other and are therefore anti-parallel.


Q. 3

Which is seen in RNA but not seen in DNA?

 A

Adenosine

 B

Guanine

 C

Uracil

 D

Thymine

Q. 3

Which is seen in RNA but not seen in DNA?

 A

Adenosine

 B

Guanine

 C

Uracil

 D

Thymine

Ans. C

Explanation:

 

In the Watson-Crick base pairing, adenine (A) forms a base pair with thymine (T), as does guanine (G) with cytosine (C) in DNA.

In RNA, thymine is replaced by uracil (U).

Alternate hydrogen bonding patterns also occur — particularly in RNA — giving rise to complex and functional tertiary structures.


Q. 4

DNA has:         

 A

Ribose sugar

 B

Deoxyribose sugar

 C

Both

 D

None

Q. 4

DNA has:         

 A

Ribose sugar

 B

Deoxyribose sugar

 C

Both

 D

None

Ans. B

Explanation:

 

Ribose sugar moiety is found in RNA

Deoxyribose sugar moiety is found in DNA


Q. 5

In DNA structure, maximum number of bonds are seen amongst which of the following pair:

 A

A-T

 B

G-C

 C

A-G

 D

C-T

Q. 5

In DNA structure, maximum number of bonds are seen amongst which of the following pair:

 A

A-T

 B

G-C

 C

A-G

 D

C-T

Ans. B

Explanation:

 

DNA is a double-stranded molecule twisted into a helix (think of a spiral staircase).

Each spiraling strand, comprised of a sugar-phosphate backbone and attached bases, is connected to a complementary strand by non-covalent hydrogen bonding between paired bases.

The bases are adenine (A), thymine (T), cytosine (C) and guanine (G).

A and T are connected by two hydrogen bonds. G and C are connected by three hydrogen bonds.


Q. 6

DNA double helix is maintained by:  

 A

Hydrogen bond

 B

Vanderwaal forces

 C

Disulfide linkage

 D

Covalent bond

Q. 6

DNA double helix is maintained by:  

 A

Hydrogen bond

 B

Vanderwaal forces

 C

Disulfide linkage

 D

Covalent bond

Ans. A

Explanation:

 

In a DNA double helix, two polynucleotide strands come together through complementary pairing of the bases, which occurs by hydrogen bonding.

Each base forms hydrogen bonds readily to only one other — A to T and C to G — so that the identity of the base on one strand dictates what base must face it on the opposing strand.

Thus the entire nucleotide sequence of each strand is complementary to that of the other, and when separated, each may act as a template with which to replicate the other.


Q. 7

In DNA, Adenine pairs with

 A

Guanine

 B

Thymine

 C

Cytosine

 D

Uracil

Q. 7

In DNA, Adenine pairs with

 A

Guanine

 B

Thymine

 C

Cytosine

 D

Uracil

Ans. B

Explanation:

 

Adenine is always paired with thymine by formation of two hydrogen bonds. Guanine is always paired with cytosine by formation of three hydrogen bonds.


Q. 8

Most common physiological form of DNA

 A

A-form

 B

B-form

 C

Z-form

 D

C-form

Q. 8

Most common physiological form of DNA

 A

A-form

 B

B-form

 C

Z-form

 D

C-form

Ans. B

Explanation:

 

DNA can exist in at least six forms, i.e. A, B, C, D, E and Z.

The B-form of DNA is the most common form of DNA and is right-handed helix.

It is the strandard DNA structure with 10 base pairs per turn.

Watson and Crick model describes the B-form of DNA.

Other forms of DNA are A-form (contains 11 base pairs per turn and is right handed helix) and Z-form (contains 12 base pairs per turn and is left handed helix).

Z-form is favored by alternating G-C sequences in alcohol and high salt solution; and is inhibited by alternating A-T sequnces (Note-B form has minimum base pairs per turn, i.e. 10).


Q. 9

Chargaff’s rule state that, in DNA ‑

 A

Purines to pyrimidines ratio is 2

 B

A+T=G+C

 C

Purines = Pyrimidines

 D

All of the above

Q. 9

Chargaff’s rule state that, in DNA ‑

 A

Purines to pyrimidines ratio is 2

 B

A+T=G+C

 C

Purines = Pyrimidines

 D

All of the above

Ans. C

Explanation:

Q. 10

Both DNA and RNA are present in:

 A

Bacteria

 B

Prions

 C

Virioids

 D

Plasmid

Q. 10

Both DNA and RNA are present in:

 A

Bacteria

 B

Prions

 C

Virioids

 D

Plasmid

Ans. A

Explanation:

Ans. a. Bacteria

Both DNA and RNA are pre sent in Bacteria

Micro-organism Genetic Material
Bacteria Contain both DNA and RNA, as well as extra-chromosomal DNA material (plasmids)Q
Plasmid

Extra-choromosomal circular DNA present in cytoplasm of bacteria and capable of autonomous

Viroids Contain low molecular weight RNA (No DNA)Q
Prions

Are misfolded proteinsQ

Devoid of both DNA and RNA

 

Q. 11

Mitochondiral DNA is ‑

 A

Closed circular

 B

Nicked circular

 C

Linear

 D

Open circular

Q. 11

Mitochondiral DNA is ‑

 A

Closed circular

 B

Nicked circular

 C

Linear

 D

Open circular

Ans. A

Explanation:

Ans. is ‘a’ i.e., Closed circular

  • Human mitochondria contain two to ten copies of a small circular double-stranded DNA molecule that makes up approximately 1% of total cellular DNA. The majority of the peptides in mitochondria (about 54 out of 67) are coded by nuclear genes. The rest are coded by genes found in mitochondrial (mt) DNA.This mtDNA codes for mt ribosomal and transfer RNAs and for 13 proteins that play key roles in the respiratory chain.

Some Major Features of the Structure and Function of Human Mitochonrial DNA

  • Is circular, double-stranded, and composed of heavy (H) and light (L) chains or strands.
  • Contains 16,569 bp.
  • Encodes 13 protein subunits of the respiratory chain (of a total of about 67) –
  • Seven subunits of NADH dehydrogenase (complex I)
  • Cytochrome b of complex III
  • Three subunits of cytochrome oxidase (complex IV)
  • Two subunits of ATP synthase
  • Encodes large (16S) and small (12S) mt ribosomal RNAs 
  • Encodes 22 mt tRNA molecules
  • Genetic code differs slightly from the standard code – a UGA (standard stop codon) is read as Trp.
  • AGP and AGG (standard codons for Arg) are read as stop codons. 
  • Contains very few untranslated sequences.
  • High mutation rate (5 to 10 times that of nuclear DNA).
  • Comparisons of mtDNA sequences provide evidence about evolutionary origins of primates and other species.

Q. 12

Not present in DNA ‑

 A

Uracil

 B

Thymine

 C

Cytosine

 D

Adenine

Q. 12

Not present in DNA ‑

 A

Uracil

 B

Thymine

 C

Cytosine

 D

Adenine

Ans. A

Explanation:

Ans. is ‘a’ i.e., Uracil 

Two types of bases are found in nucleotides : (i) purines and (ii) pyrimidines.

  1. Purines : Two major purine bases found both in DNAs as well as RNAs are (i) adenine (A) and (ii) guanine (G).
  2. Pyrimidines : Three major pyrimidine bases are (i) cytosine (C), (ii) Uracil (U) and (iii) Thymine (T). Cytosine and uracil are found in RNAs and cytosine and thymine are found in DNAs. Uracil is not found in DNAs e and thymine is not found in RNAs.

Different major bases with their corresponding nucleosides and nucleotides

Base

Ribonucleoside Ribonucleotide
Adenine (A)  Adenosine  Adenosine monophosphate (AMP) 
Guanine (G)  Guanosine  Guanosine monophosphate (GMP) 
Uracil (U) 

Uridine

Uridine monophosphate (UMP)

Cytosine (C)

Cytidine

Cytidine (Monophosphate) (CMP)

Base

Deoxyribonucleoside

Deoxyribonucleotide

Adenine  Deoxyadenosine Deoxyadenosine monophosphate (dAMP) 
Guanine  Deoxyguanosine Deoxyguanosine monphosphate (dGMP) 
Cytosine  Deoxycytidine  Deoxycytidine monophosphate (dCMP) 

Thymine

Deoxythymidine

Deoxythymidine monophosphate (dCMP)



Q. 13

Adenine in DNA binds with ‑

 A

Thymine

 B

Guanine

 C

Cytosine

 D

Uracil

Q. 13

Adenine in DNA binds with ‑

 A

Thymine

 B

Guanine

 C

Cytosine

 D

Uracil

Ans. A

Explanation:

Ans. is ‘a’ i.e., Thymine 

  • Adenine is always paired with thymine by formation of two hydrogen bonds. Guanine is always paired with cytosine by formation of three hydrogen bonds.

Q. 14

At physiological pH DNA is ‑

 A

Acidic

 B

Negatively charged

 C

Amphipathic

 D

All of the above

Q. 14

At physiological pH DNA is ‑

 A

Acidic

 B

Negatively charged

 C

Amphipathic

 D

All of the above

Ans. D

Explanation:

Ans. is ‘d’ i.e., All of the above 

DNA is amphipathic

  • Amphipathic molecule is one which contains both polar (hydrophilic) and nonpolar (hydrophobic) regions in its structure, i.e. the part of molecule is water soluble and part is water insoluble.
  • In DNA helix
  • Hydrophilic (polar) deoxyribose-phosphate of each chain is on outside of molecule.
  • Hydrophobic (nonpolar) bases are stacked in. 
  • Thus DNA is regarded as amphipathic in nature.

DNA is negatively charged and acidic

  • Phosphate group lies on outside of molecule of DNA.
  • Each phosphate group has a negative charge at physiological pH, making DNA a negatively charge (anion) at physilogical pH.
  • Histones are strongly cationic and can bind non-specifically to strongly aniomic DNA” Harper “At physiological pH DNA is negatively charged, and is associated with positively charged (basic) histones” Ronald Hofmann. o Anionic molecules are acidic in nature.

Q. 15

Molecular interaction, found in the structure ofDNA –

 A

Hydrogen bond

 B

Glycosidic bond

 C

Covalent interactions 

 D

All of the above

Q. 15

Molecular interaction, found in the structure ofDNA –

 A

Hydrogen bond

 B

Glycosidic bond

 C

Covalent interactions 

 D

All of the above

Ans. D

Explanation:

Ans. is’d’ i.e., All of the above



Leave a Reply

Free Mini Course on Stomach

Mini Course – Stomach

22 High Yield Topics in Stomach

in Just 2 Hours

Submission received, thank you!

Close Window
%d bloggers like this:
Malcare WordPress Security