The genetic material contained in DNA consists of a linear sequence of coding un

Question

The genetic material contained in DNA consists of a linear sequence of coding units, known as codons. Each codon is a specific sequence of three deoxyribonucleotides (three deoxyribonucleotide pairs in double stranded DNA), and each codon codes for a single amino acid unit in a protein. The molecular weight of an E. coli DNA molecule is about 3.1 times 10^9 g/mol. The average molecular weight of a nucleotide pair is 660 g/mol, and each nucleotide pair contributes 0.34 nm to the length of DNA. (a) Calculate the length of an E. coli DNA molecule. Compare the length of the DNA molecule with the cell dimensions (see problem 7). How does the DNA molecule fit into the cell? (b) Assume that the average protein in E. coli consists of a chain of 400 amino acids. What is the maximum number of proteins that can be coded by an E. coli DNA molecule?

Explanation / Answer

a.} Number of nucleotides= 3.1×10(raised to 9)/660 ~ 4700000

Lenght of DNA = 4700000×0.34nm = 1600000nm ~ 1.6mm

However approx length of e.coli cell is 0.002mm. The DNA fit into cell as it is highly packed with the basic proteins present in the cell.

b.} An amino acid is coded by 3 nucleotides. So for a protein with 400 AA, 1200 base pairs are occupied. So 4700000 will code for = 4700000/1200 ~ 3917 proteins.

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