GENETIC CODE-
Q1.Peptide sequence-Phe-Tyr-Met-Pro-His.
a.Why more than one nucleotide sequence is possible?ans. due to degeneracy of codon.
b.Calculate the no.of possible nut.sequence?
ans.Its 32 (Phe ,Tyr &His have 2 codons,pro has 4 and Met only 1.So, 2*2*2*4*1)
Q2. How many different codons are possible?
Ans. (64) as the 4 nucleotides that constitute the DNA :A,T,C,G. With triplet codon (3 nuclotides)per word can produce = 43
3.Which one is the initiation codon -AUG
4.Stop codons are-UAA,UAG,UGA
5.Degeneracy of genetic code was identified by
A.Watson
B.Crick
C.Lagervis
D.Darwin
- Genetc code is a triplet code called a codon.
- Certain codons contain start codon and stop signals to initiate and terminate translation .The initiation codon is usally AUG which codes for amino acid methionine.In few m-rna GUG,UUG also acts as a initiation codon.The stop or termination codons(UAA,UAG &UGA).
- The code is ambiguous meaning that each triplet specifies only a single amino acid.
- No interal punctuation (commas) is used in the code.Thus, the code is said to be commaless.Once the translation of m-rna begins,the codons are read one after the other with no breaks between them.
- The code is degenerate i.e a given amino acid can be specified by more than one triplet codon.(synonymous) .For example-UUU and UUC are synosymous for phenylalanine where as serine is encoded by the synonyms UCU,UCC,UCA,UCG,AGU & AGC.
- T he codon is non overlapping .After translation commences any single ribonuclotide at a specific location within the m -rna is part of only one triplet.
- It is usual to describe the genetic code as a universal code.(The same code is used throughout all life forms.)with some exceptions .
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| Triplet codon |
imagesource:http://www.sparknotes.com/biology/molecular/geneticcode/section1.rhtml
Q1.Peptide sequence-Phe-Tyr-Met-Pro-His.
a.Why more than one nucleotide sequence is possible?ans. due to degeneracy of codon.
b.Calculate the no.of possible nut.sequence?
ans.Its 32 (Phe ,Tyr &His have 2 codons,pro has 4 and Met only 1.So, 2*2*2*4*1)
Q2. How many different codons are possible?
Ans. (64) as the 4 nucleotides that constitute the DNA :A,T,C,G. With triplet codon (3 nuclotides)per word can produce = 43
3.Which one is the initiation codon -AUG
4.Stop codons are-UAA,UAG,UGA
5.Degeneracy of genetic code was identified by
A.Watson
B.Crick
C.Lagervis
D.Darwin
Ans. c
6.To describe the genetic code as degenerate indicates that
A. mRNA is rapidly degraded
B. The code is not universal among organisms
C. Some amino acids have more than one codon
D. Frameshift mutations are tolerated
Ans. C
6.To describe the genetic code as degenerate indicates that
A. mRNA is rapidly degraded
B. The code is not universal among organisms
C. Some amino acids have more than one codon
D. Frameshift mutations are tolerated
Ans. C
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