Nucleotide Triplets

NA QUESTION 1982: L. PETERSON/AP BIOLOGY

A portion of a specific DNA molecule consists of the following sequence of

nucleotide triplets:

TAC GAA CTT CGG TCC

This DNA sequence codes for the following short polypeptide:

methionine - leucine - glutamic acid - proline - arginine

Describe the steps in the synthesis of this polypeptide. What would be the

effect of a deleltion or an addition in one of the DNA nucleotides? What would

be the effect of a substitution in one of the nucleotides?

STANDARDS:

In the transcription phase of protein synthesis, students were given a point for a correct

definition of transcription. They were awarded one point for mentioning each of the following:

__ DNA as the template molecule for messenger RNA

__ The proper base pairing (including the uracil substitution)

__ The chemical characteristics of nucleotides

__ A comparison of RNA and DNA (other than uracil substitution)

__ The triplet arrangement of codons and/or anticodons

__ The control of transcription (Operon, etc.)

__ Promoters

__ The role of polymerase

__ Intervening sequences in eukaryotic cells

__ Factors involved in the release of mRNA from DNA

__ 5' - 3' arrangement with attachment at -OH end

A definition of translation was worth an additional point with one point given for

mention of each of the following:

__ Movement of mRNA from nucleus to ribosome

__ Association of mRNA with the ribosome and ribosomal RNA

__ Location of ribosomes

__ Description of ribosome/polyribosome structure

__ Role of transfer RNA in transporting amino acids

__ Specific characteristics of tRNA

__ Amino acid-tRNA complex activation

__ Role of ATP and enzymes

__ tRNA initiator molecules (met or f-met)

__ Initiation factors (GTP, etc.) resulting in union of 30s and 50s

__ Bonding of tRNA to 50s (A site)

__ Role of amino transferase

__ Initiation codons