3.4.1 DNA, Genes + Chromosomes

prokaryotic DNA

shorter, circular, not associated with proteins, no introns

eukaryotic DNA

longer, linear, associated with proteins called histones, contains introns

eukaryotic DNA - MITOCHONDRIA + CHLOROPLASTS

-is like prokaryotic DNA

-is short, circular, no histones

SIMILARITIES between eukaryotic DNA + prokaryotic DNA

-nucleotide structure is identical

-nucleotides joined by phosphodiester bond

-DNA in mitochondria + chloroplasts is the same as prokaryotic

histones

-DNA in a chromosome is held by proteins called histones as it is very long

-the double helix is tightly wounded around histones which fix DNA in position

-DNA-helix complex is coiled and looped to form a single chromosome

gene

a sequence of DNA bases that codes for a polypeptide or functional RNA

-the base sequences are in triplets which determines the sequence of amino acids in primary structure

locus

the fixed position occupied by a gene on a DNA molecule

triplet

sequence of 3 DNA bases codes for 1 specific amino acid

genetic code

order of bases on DNA

-universal = the same triplet always codes for the same amino acid

-non-overlapping = each base is only part of one triplet

-degenerative = more than one triplet codes for each amino acid

reading genetic code

-triplets are read in one direction

-start codon = start of a sequence always has the same triplet

-stop codon = three triplets that mark the end of a sequence

types of DNA

-introns = DNA base sequence that does not code for a polypeptide - found between genes

-exons = DNA base sequence that codes for a polypeptide

alleles

alternative forms of the same gene

-found at the same locus and chromosome

-any change in a base sequence of a gene results in a new allele

homologous pairs

-two chromosomes that carry the same genes at the same loci

-but may carry different alleles

-have pairs of matching chromosomes

‘Explain how a change in a sequence of DNA bases could results in a non-functional enzyme’

-change in base sequence

-change in sequence of amino acids

-change in hydrogen bonds resulting in change of tertiary structure

-change in polypeptide so substrate cannot bind