| What is a gene | - Section of DNA
- Contains coded information for making polypeptides + functional RNA
- Determines the nature + development of organisms |
| Locus meaning | - Each gene occupies a specific position, locus, along DNA molecule |
| The genetic code | - 3 bases code for 1 amino acid
- Each one called triplet
- 64 possible triplet + only 20 amino acids
- Some amino acids are coded by more than 1 triplet |
| Why do 3 bases code for 1 amino acid | - 20 different amino acids occur in proteins
- 64 possible triplet + only 20 amino acids, more than enough
- Each amino acid must have its own code of bases on DNA
- Only 4 different bases are present in DNA |
| Further features of the genetic code | - A few amino acids are coded by 1 single triplet
- There are degenerate codes
- Triplet read in 1 direction along DNA strand
- Triplet at start of DNA strand codes for methionine
- Has 'stop-codes'
- The code is non-overlapping
- Its universal |
| Degenerate code | - Most amino acids are coded for by more than one triplet
- Between 2 + 6 triplet codes |
| Methionine (muh-thigh-a-neen) | - Triplet at start of every DNA strand codes for the amino acid methionine
- If first methionine molecule doesn't form part of final polypeptide, it is later removed |
| The genetic code has 'stop-codes' | - Refers to three triplets do not code for 1 amino acids
- These mark the end of polypeptide chain
kinda acts like full stop |
| The genetic code is non-overlapping | - Each base in sequence is only read once
e.g.123456 read 123 + 456 instead of 123,234,543.. |
| Why is the genetic code described as being universal | - All organisms have the same triplet codes for the same amino acid |
| Exons meaning | - The sections of DNA (or RNA) that code for proteins |
| Introns meaning | - Non-coding sections of a gene |
