Genes (AQA A Level Biology): Revision Note
Exam code: 7402
The definition of a gene
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
Functional RNA molecules are required for protein synthesis
mRNA - the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains
tRNA - amino acids are carried to the ribosome by transfer RNA molecules
rRNA - ribosomal RNA molecules form part of the structure of ribosomes
The shape and behaviour of a protein molecule depend on the exact sequence of these amino acids
The genes in DNA molecules, therefore, control protein structure and as a result, protein function as they determine the exact sequence in which the amino acids join together during protein synthesis
Examiner Tips and Tricks
One gene codes for one mRNA, which codes for one polypeptide — this is the central dogma of molecular biology. Each chromosome contains one long DNA molecule made up of many genes (specific nucleotide sequences that code for proteins). Cells can identify where each gene starts and ends, ensuring the correct proteins are produced as needed.
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