genes DNA and chromosomes EQ Flashcards
name fixed position occupied by a gene in a dna molecule
loci
describe how a gene is a code for a polypeptide (3)
do not include details about translation and transcription
(1) nucleotide sequence
(2) in triplets
(3) determines order of amino acid sequence/ primary structure of polypeptide
define exon
base/ nucleotide/ triplet which codes for a sequence of amino acids
describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule
(3)
(1) condensation reaction/ loss of water
(2) between phosphate group and deoxyribose
(3) catalysed by DNA polymerase
name the protein associated with DNA in a chromosome
histone
3 differences between DNA in the nucleus of a plant cell and in a prokaryotic cell
plant v prokaryote:
histones v no histones
linear v circular
no plasmids v plasmids
introns v no introns
longer v shorter
define non coding base sequences
DNA that doesn’t code for polypeptide/ sequence of amino acids
where are non-coding base sequences located
positioned between genes
give 3 ways DNA in chloroplast is different t nuclear DNA
in chlroplast:
DNA shorter
Fewer genes
circular not linear
not associated with histones unlike nuclear DNA
Introns absent- present in nuclear DNA
give one structural difference between the structure of RNA and DNA
NOT U swapped for T
deoxyribose in DNA, ribose in RNA
why do not all mutations in nucleotide sequence of gene cause changed structure of polypeptide?
triplets code for the same amino acid as DNA is degenerate
could occur in introns which don’t code for polypeptide
compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells
compare :
- nucleotide structure identical
- nucleotides joined by phosphodiester bonds
- mitochondrial DNA similar
contrast:
- eukaryotic dna longer
- eukaryote contain introns
- eukaryotic DNA is linear
- eukaryotic DNA associated with histones
what is a homologous pair of chromosomes
2 chromosomes which carry the same genes
what is a gene
a section of DNA which contains the coded information for making polypeptides and functional RNA
how many amin acids are there
20
name the bases present in DNA
Thymine, Adenine, Cytosine, Guanine
why is the DNA code degenerate?
most amino acids are coded for by more than one triplet
what are stop codons
the 3 triplets which don’t code for an amino acid so mark the end of the polypeptide
2 features of DNA base code
non-overlapping - each base read once
universal- found in all organisms
how is dna packed into a chromosome
DNA molecule is combined with histone proteins, this complex coils to form loops which pack together to form chromosome
what are homologous pairs
one maternal chromosome and one paternal chromosome, form total diploid number of cells
2 chromosomes carry same genes but not same alleles necessarily
what is an allele
one of a number of alternative forms of a gene
how are new alleles produced
mutation causing a change to base sequence s codes for a new amino acid
