Chapter 26, Problem 26.67AP

Interpretation Introduction

Interpretation:

The double-stranded DNA sequence code for metenkephalin has to be predicted.

Concept Introduction:

Base pairing in DNA: The two strands of the DNA double helix run in the opposite directions- one in 5’ to 3’ direction and other from 3’ to 5’ direction. The hydrogen bonding between two strands enhances the stability of the DNA; where the alignment of hydrophobic nitrogenous bases in the interior and hydrophilic phosphate and sugar groups on the exterior also enhance the stability. Adenine and thymine gives a pair forming two hydrogen bonds and cytosine and guanine gives rise to another pair forming three hydrogen bonds.

Codon: A sequence of three ribonucleotides in the mRNA chain that codes for a specific amino acid; also a three-nucleotide sequence that is a stop codon and stops translation.

Genetic code: The sequence of nucleotides, coded in triplets (codons) in mRNA that determines the sequence of amino acids in protein synthesis.

Illustrated relationships are:

DNA informational strand: 5’ ATG  CCA   GTA  GGC  CAC   TTG   TCA  3’

DNA Template strand:         3’ TAC  GGT   CAT  CCG  GTG   AAC   AGT  5’

mRNA:                                  5’ AUG  CCA  GUA  GGC  CAC  UUG   UCA  3’

protein:                                       Met    Pro     Val    Gly     His    Leu      Ser

Notice: 5’ end of the mRNA strand codes for the N-terminal amino acid, whereas the 3’ end of the mRNA strand codes for the C-terminal amino acid. Proteins are always written N-terminal to C-terminal, reading left to right.