Questions regardingSthe Watson and Crick article from Nature, April 25 1953 (ple

Question

Questions regardingSthe Watson and Crick article from Nature, April 25 1953

(please answer the 7 questions this is the second time I sent it )

1.What was the purpose of this paper?

2.Contrast the features of the Watson/Crick model to the three features of the Pauling/Corey model.



3.Using your own words, tell how the two chains are held together as explained in the paper.



4.According to Watson and Crick, which specific pairs of bases can bond together?


5.What do they say about the sequence of the bases?


6.Why doesn’t the model work if ribose is used in place of deoxyribose?


7.What do they say the specific pairing of bases suggests?

Explanation / Answer

Ans. 1. The purpose of the paper was to understand the structure of D.N.A. with novel features like position of bases, position of phosphates, size and shape, angle and length etc. (keeping in mind that molecule is present in the natural state) which was not clerified in the previous model proposed by Paulling and Corey.

Ans. 2. Three features of the Watson and Crick model in comparision of Paulling and Corey model are:

(a) No. of chain: In watson and crick model two no. of chains are present whereas in previous model it was three.

(b) Position of Phosphate: Phosphate group is present near to the axis in Paulling and Corey model whereas in Watson and Crick model it is present outside.

(c) Position of bases: bases are present inside in Watson and Crick model where in other model it is present outside.

Ans. 3. Acc. to the Watson and Crick model chains are made up of phophodiester groups and contain purines and pyrimidines which run in the opposite direction. Model suggests that two chains are related by a dyad perpendicular to the fibre axis and are right handed.(means make a twist in right had side). As a result of this bases comes inside of the helix and phosphate comes outside of the helix. bases present on the phosphate chain are joined together by the hydrogen bond so that the two lie side by side with identical z co-ordinates.

Ans.4. for specific pairs bonding occur between purines and pyrimidines only means one must be purine and another most be pyrimidine. Specific pairs are: Adenine(Purine) binds with Thymine(Pyrimidine). Another one is Guanine (Purine) with Cytosine (Pyrimidine). Shortly 'A' binds with 'T' and 'G' binds with 'C'.

Ans. 5. They say about the sequence of the bases on the single chain dose not appear to be restricted in any way.

Ans. 6. If we look into the structure of the ribose(C5H10O5) and deoxyribose consist of (C5H10O4). celary suggests that ribose has one extra molecule of ribose which would make a ‘too close van der Waals contact’.

Ans. 7 Since 'A' binds with 'T' and 'G' binds with 'C' so if we know the sequence of bases of one chain then sequence of bases of another chain can easily be determined.

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