IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: Sue T on January 13, 2010, 04:17:16 pm

Title: cie bio: subject content
Post by: Sue T on January 13, 2010, 04:17:16 pm

on th 3rd page of the curriculum under genetic control it says:

(d) describe the way in which the nucleotide sequence codes for the amino acid sequence in a
polypeptide with reference to the nucleotide sequence for HbA (normal) and HbS (sickle
cell) alleles of the gene for the ?-haemoglobin polypeptide;

i have nothin like tht in my txt book  :-\
can ny1 temme wat theyre talkin bout?

Title: Re: cie bio: subject content
Post by: mousa on January 13, 2010, 07:05:44 pm

Haemoglobin is a globular protein consisting of four polypeptide chains – 2 alpha chains and 2
beta chains. In normal individuals, in the DNA which codes for each beta chain, the sixth triplet
has a code for glutamic acid.
In individuals with sickle cell anaemia this base triplet changes and codes for valine.In the DNA sequence for sickle cell anaemia, adenine replaces thymine in a CTT triplet, forming
the DNA  triplet CAT. During synthesis of the sickle cell haemoglobin molecule, the amino acid valine is
incorporated instead of glutamic acidand therefore leading to the formation of the ubnormal Haemoglobin, due to the distortion of its primary structure.

hope that helped :)

Title: Re: cie bio: subject content
Post by: Sue T on January 14, 2010, 11:09:51 am

thank u!