AQA A Level Bio 4.1 DNA, Genes and Chromosomes

Describe how a gene is a code for the production of a polypeptide. Do not include information about transcription or translation in your answer. (3)

(Because) base/nucleotide sequence (1)

(in) triplet(s) (1)

(Determines) order/sequence of amino acid sequence/primary structure (in polypeptide (1)

Define the term exon (1)

Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure (1)

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule. (2)

Condensation (reaction)/loss of water (1)

(Between) phosphate and deoxyribose (1)

Complete Table 1 to show three differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell. (3)

Associated with histones (1)

Linear vs circular (1)

Introns vs no introns (1)

Scientists investigated the genetic diversity between several species of sweet potato. They studied non-coding multiple repeats of base sequences.

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome.(2)

DNA that does not code for protein/polypeptides (1)

(Positioned) between genes

The diagram shows a tRNA molecule

Name the structures labelled W and X in the diagram.(1)

W = amino acid binding site and X = anticodon (1)

Not all mutations in the nucleotide sequence of a gene cause a change in

the structure of a polypeptide.

Give two reasons why (2)

Triplets code for the same amino acid (1)

Occurs in introns/non-coding sequence (1)

This question is about the genetic code. Define universal, non-overlapping and degenerate.(3)

(Universal) The same codon/triplet always codes for the same amino acid (1)

(Non-overlapping) Each base is only part of one triplet/codon (1)

(Degenerate) More than one codon/triplet codes for each amino acid; (1)