Question

Explain the meaning of genetic code, and describe how the genetic code functions.
a. Explain the one gene-one polypeptide theory.
b. The DNA sequence of a gene determines the sequence of amino acids in a polypeptide chain. What studies have demonstrated this relationship?
c. In what molecule are codons found? How many nucleotides are in each codon? How many nucleotides are available to make up each codon? How many different types of codons are possible? How many amino acids are specified by one codon? Theoretically, how many different amino acids could be coded? How many different amino acids are available? Given this information, is it possible that each amino acid is coded by more than one codon?
d. Would a mutation involving deletion of one nucleotide affect the amino acid sequence of the corresponding peptide? Would deletion of a sequence of three nucleotides have a similar effect? What does this fact say about the nature of the genetic code?

(please answer all the questions above thank you!)

Answer 1

The genetic code is a set of rules that govern an organisms DNA, RNA and finally protein sequence. It was deciphered by Hargovind Khorana for which he received the Nobel prize in 1959. Here, a specific set of RNA sequence codes for specific AMINO ACID. This is called the triplet codon where 3 bases are for 1 amino acid. Each organism has predecided set of codons and any deviation leads to mutation. Some amino acids have more than one combination of nucleotide tripet to code for an amino acid. For example, alanine is coded by GCU, GCC, GCA and GCG in humans.

A.. One gene one polypeptide hypothesis says that each gene is responsible for encoding a particular polypeptide chain. These polypeptides can code for enzymes or non-enzyme protein also.

C. Codons are found in mRNA molecules. A group of 3 nucleotides make a codon. 4 nucleotides are available to make a codon. There are 4 available nucleotides but each codon needs only three nucleotides. So the possibility is 4³. Which is equal to 64 possible codons.

In reality there are 61 codons. Yes there are more than one codon for some amino acids. There are a total of 20 amino acids and 61 codons. There are also 3 codons which are stop codons and are not associated with protein amino acids what bring water to end the polypeptide chain.

D. Deletion of one nucleotide leads to a frameshift mutation. In this type of mutation the whole sequence of the protein changes as the codon is read in a different way than before. The ribosome takes 3 nucleotides at a time and calls a tRNA carrying specific amino acid for that codon. But if one nucleotide is deleted the sequence of 3 codon one after the other changes completely. So the new protein forms will have no similarity with the original protein.

If there is deletion of a codon this will lead to deletion of an amino acid from the full length protein. This wouldn't cause much difference in the protein structure as long as it is not a part of the functional site of the protein.