DNA, RNA and protein synthesis

a gene is a section of dna that contains a code (specific sequence of bases) for making a polypeptide and functional rna polypeptides make proteins so genes determine the proteins of an organism

the location of a particular gene on a chromosome

one of a number of forms of the same gene/ alternatives of the same gene most genes occur in two or more different forms

23 pairs- 46 chromosomes

matching pairs of chromosomes are called homologous pairs- they are exactly the same size with exactly the same genes but may have different alleles

dna is stored as chromosomes inside the nucleus chromosomes are linear in shape to tightly coil dna to fit in the nucleus as chromosomes, dna is tightly wound around proteins called histones the complex of dna being wrapped around a histone is called a nucleosome

dna is also stored as chromosomes but dna is shorter and circular dna is not associated with histones- instead it supercoils to fit in the cell

although these are organelles found in prokaryotes, the dna structure is similar to prokaryotic dna it is short and circular it is not bound to histones

to associate with dna to assist in the tight coiling of dna to fit chromosomes into the nucleus

the first triplet of bases on the dna and mrna start codons initiate translation

the last triplet that does not code for an amino acid (therefore there is no anticodon on a trna molecule to fit it) they mark the end of a polypeptide chain, causing ribosomes to detach so therefore stop translation

• degenerate • universal • non overlapping

there are 64 base combinations which is more than enough to code for 20 amino acids- therefore each amino acid can be coded for by more than one triplet of bases

4^3=64 4 bases 3 bases in each triplet

if a mutation occurred, even though the triplet of bases would be different, it may still code for the same amino acid and therefore have no effect- silent mutation

the same triplet of bases codes for the same amino acid in all organisms

it means genetic engineering is possible e.g inserting the human gene for insulin into bacteria

each base in a gene is part of only one triplet of bases that codes for an amino acid

if a mutation occurs it will only affect one codon, so one amino acid

sections of dna that do not code for amino acids and therefore polypeptide chains

found in eukaryotic dna but not prokaryotic dna

they get spliced out of mrna molecules

sections of dna that code for amino acids

an organisms complete set of dna in one cell- this never changes