AS-LEVEL AQA BIOLOGY NOTES
TOPIC 1: dna, genes and chromosomes
Eukaryotic cells
Prokaryotic cells
Gene = section of DNA bases which codes for the amino acid sequence of one polypeptide or functional RNA molecule
Locus = the location of a specific gene on a chromosome
Triplet = 3 consecutive nucleotide bases on a gene which code for 1 amino acid
Introns and Exons
- DNA contained within a nucleus
- DNA is in very long chains
- DNA is associated with proteins called histones
- DNA + associated histones = chromosome
- Some DNA present in chloroplasts and mitochondria which resembles prokaryotic DNA
Prokaryotic cells
- DNA is short and circular
- DNA is free in cytoplasm
- DNA is not associated with proteins
Gene = section of DNA bases which codes for the amino acid sequence of one polypeptide or functional RNA molecule
Locus = the location of a specific gene on a chromosome
Triplet = 3 consecutive nucleotide bases on a gene which code for 1 amino acid
- No overlapping
- Degenerate, meaning one amino acid can be coded for by several different triplets
- Universal
Introns and Exons
- Post-transcriptional gene regulation
- Regions of DNA that don’t code for genes are called introns - they separate…
- Regions of DNA that are expressed, called exons
- Both are transcribed, but resulting mRNA is modified to remove the introns