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Introduction to DNA MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET
Quick Facts
-
33 Questions around this concept.
Solve by difficulty
A nucleotide is composed of:
1) nitrogenous base
2) pentose sugar
3) phosphate group
DNA fragments are :
Deoxyribonucleic acid lacks
NEET 2025: Syllabus | Most Scoring concepts | NEET PYQ's (2015-24)
Backbone in a polynucleotide chain of DNA is
Concepts Covered - 2
Introduction
- Mendel gave us a basic understanding of inheritance patterns and the genetic basis of such patterns.
- However, at the time of Mendel, the nature of those ‘factors’ regulating the pattern of inheritance was not clear.
- Over the next hundred years, the nature of the putative genetic material was investigated culminating in the realisation that DNA – deoxyribonucleic acid – is the genetic material, at least for the majority of organisms.
- Mendel’s ‘factors’ are called genes. They come in alternating pairs of dominant and recessive alleles.
- Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two types of nucleic acids found in living systems.
- DNA acts as the genetic material in most of the organisms.
- RNA though it also acts as genetic material in some viruses, mostly functions as a messenger.
- RNA has additional roles as well. It functions as an adapter, structural, and in some cases as a catalytic molecule.
Structure of DNA
- DNA as an acidic substance present in the nucleus was first identified by Friedrich Meischer in 1869. He named it ‘Nuclein’.
- In 1953, James Watson and Francis Crick, based on the X-ray diffraction data produced by Maurice Wilkins and Rosalind Franklin, proposed a very simple but famous Double Helix model for the structure of DNA.
- DNA is a long polymer of deoxyribonucleotides.
- The length of DNA is usually defined as the number of nucleotides (or a pair of nucleotide referred to as base pairs) present in it.
- This also is the characteristic of an organism.
- For example, a bacteriophage known as φ 174 has 5386 nucleotides,
- Bacteriophage lambda has 48502 base pairs (bp), Escherichia coli has 4.6 × 106 bp, and haploid content of human DNA is 3.3 × 109 bp.
- A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group.
- There are two types of nitrogenous bases – Purine (Adenine and Guanine), and Pyrimidines (Cytosine, Uracil and Thymine).
- Uracil is present in RNA at the place of Thymine.
- A nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine.
- A phosphate group is linked to 5' -OH of a nucleoside through phosphoester linkage
- Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.
- More nucleotides can be joined in such a manner to form a polynucleotide chain.
- A polymer thus formed has at one end a free phosphate moiety at 5' -end of a ribose sugar, which is referred to as 5’-end of a polynucleotide chain.
- Similarly, at the other end of the polymer, the ribose has a free 3' -OH group which is referred to as 3'-end of the polynucleotide chain.
- The backbone in a polynucleotide chain is formed due to sugar and phosphates.
- The nitrogenous bases linked to the sugar moiety project from the backbone.
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