ICSE Class 10 Answered
Sir plZz send me link for video lesson of DNA replication and structure of dna
Asked by nandinidwivedi062002 | 24 Mar, 2018, 01:33: AM
Expert Answer
We do not have the video for DNA replication and DNA structure. For infromation, the below answers will be helpful:
DNA Replication
DNA is a double stranded helical macromolecule. The two strands of DNA are complementary to each other. For replication, the DNA double helix opens at one end, making the two strands free to which new strands begin to form and the process continues in a sequence for the whole length of the DNA.
DNA Structure
- Deoxyribonucleic acid (DNA) is composed of two polynucleotide strands which form a ladder.
- The nitrogenous bases in DNA store the information for the synthesis of polypeptide chains, essentially coding for every feature of the entire organism.
- The two polynucleotide strands run 'antiparallel' (in opposite directions, parallel to one another) to each other, with nitrogenous bases projecting inwards.
- The antiparallel strands twist in a complete DNA structure, forming a double helix.
- The strands are held together by hydrogen bonds between the nitrogenous bases which lie opposite to each other.
- Bases bonded together are termed 'paired' and are very specific as to which base they will join.
- A purine will only pair with a pyrimidine. The purine adenine will always pair with the pyrimidine thymine (A–T). The purine guanine will only pair with the pyrimidine cytosine (G–C). These base pairings are termed complementary base pairings.
- Purines will always bond with pyrimidines because purines are larger molecules composed of a double ring structure. So, in order to ensure that the polynucleotide strands are equally spaced apart, the larger bases must pair with the smaller bases.
- The root for specific complementary base pairings is the number of hydrogen bonding sites available. Adenine and thymine have two sites each, whereas guanine and cytosine have three sites each.
Answered by Sivanand Patnaik | 24 Mar, 2018, 12:16: PM
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