Topic 4 Flashcards
Gene
a section of DNA that contains a code for making a polypeptide and functional RNA
Locus
the location of a particular gene on a chromosome
Allele
a different version of the same gene
Chromosome
Threadlike structure
composed of tightly coiled DNA wrapped around histones (if it is a eukaryotic cell)
Homologous chromosome
a pair of chromosomes - maternal and paternal
Have the same gene loci, however they can have alleles
therefore, they are the same size
Eukaryotic DNA
DNA is stored as chromosomes inside the nucleus
linear chromosomes
DNA is tightly coiled and wrapped around proteins called histones
Prokaryotic DNA
DNA molecules are shorter and circular
Circular chromosome
DNA is not wound around histones. Instead, it supercoils to fit in the cell
Codon
3 bases on mRNA that code for an amino acid
Start codon
3 bases at the start of an mRNA sequence which help to initiate translation
Stop codon
3 bases at the end of every mRNA or gene that doesn’t code for an amino acid
this causes ribosomes to detach
and therefore stops translation
Genetic code
an amino acid is coded for by 3 DNA bases which are described as the “triplet code”
What is meant by ‘the genetic code is degenerate?
each amino acid is coded for by more than one triplet of bases
What is the advantage of the genetic code being degenerate?
If a substitution mutation occurs, the new triplet of bases may still code for the same amino acid
Therefore the mutation will have no impact on the final protein produced
What is the advantage of the genetic code being universal?
genetic engineering is possible
a human gene can be inserted into another organism
e.g human gene for insulin inserted into bacteria to make insulin
Also the protein synthesis mechanism or machinery is universal
What is the advantage of the genetic code being non-overlapping?
if a point mutation(substitution)occurs, it will only affect one codon and therefore one amino acid
Triplet code
An amino acid is coded for by 3
Mutation
a change in the base sequence of DNA
can be a gene or chromosome mutation
Frequency can be increased by mutagenic agents
What is meant by ‘the genetic code is universal?
the same triplet of bases codes for the same amino acid in all organisms
What is meant by ‘the genetic code is non-overlapping?
Each base in a gene is only part of one triplet of bases that codes for one amino acid
Therefore each codon is read as a discrete unit
Or each base is only read once
Introns
Non-coding sequence of DNA
Exons
sequences of DNA that code for amino acids
What is splicing?
post-transcription modification
removing introns
Pre mRNA to mRNA
Genome
the complete set of genes in a cell
Proteome
The full range of proteins that a cell is able to produce