8.1 - Genes + the Genetic Code Flashcards
What is a gene?
- a section of DNA containing the coded info for making polypeptides + functional RNA
What do genes determine?
The nature + development of all organisms
Where is a gene located?
- at a locus on a DNA molecule
What do genes code for?
- the amino acid sequence of a polypeptide
- or a functional RNA, (rRNA + tRNA)
How many different triplets are there?
64
What is a triplet?
A sequence of 3 bases
How many triplets are most amino acids coded for by?
- 2 - 6
- only a few are coded by only 1 triplet
What is the genetic code known as?
- a ‘degenerate code’
How is a triplet read?
- in 1 particular direction along the DNA strand
What amino acid does the triplet at the start of a DNA sequence code for for a polypeptide?
- Methionine
How many triplets don’t code for any animo acid?
3
What are the triplets that don’t code for any amino acid called?
- stop codes
What do ‘stop codes’ do?
- mark the end of a polypeptide chain
What does the genetic code being non-overlapping mean?
- each base in the sequence is read only once
What does the genetic code being universal mean?
- each triplet codes for the same amino acid in all organisms (w a few exceptions)
What are the features of the genetic code?
- few AA coded by 1 triplet
- most AA coded by 2-6 triplets
- genetic code knows as a ‘degenerate code’
- triplet always read in 1 direction along DNA strand
- DNA sequence coding for a polypeptide always starts w triplet coding for AA Methionine
- 3 stop codes
- genetic code is non-overlapping + universal
What are exons?
- sequence of bases coding for sequence of AA
What are introns?
- non-coding sequences in genes that separate exons
What is the definition of ‘non-coding base sequences’?
- DNA that doesn’t code for AA
Why don’t all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide?
- triplets code for same AA (as code degenerate)
- mutation occurs in introns (non-coding base sequence)
