3.4.2 Protein synthesis Flashcards
where does transcription occur
in the nucleus of the cell
what is the process of transcription
- a gene unwinds and unzips
- each gene codes for one polypeptide
- one strand acts as the template strand
- the free RNA nucleotides complementary base pair with the exposed DNA bases on this template strand
- a length of RNA is created by RNA polymerase which is a copy of the sense strand
where does the mRNA leave the nucleus once it has been replicated
nuclear pore
what is the strand of DNA called that isn’t copied
anti sense strand
what happens during processing of the DNA
sections of it are removed - splicing
what are introns
part of the gene that are non-coding
what does it mean if something is non-coding
don’t encode a polypeptide sequence so are spliced out of the mRNA
what is the first copy of mRNA called
pre-mRNA which still contains introns before they are spliced out in processing
what are exons
coding sections of a gene
what is a genome
all the genes in a cell
what is a proteome
all the proteins seen in an organism
why do we use triplets in a codon
4^3 = 64 so we have more possible combinations than we do amino acids as 64>20
how many possible amino acids are there
20
where does translation occur
cytoplasm of a cell - on ribosome
how many codons of mRNA are exposed at a time during translation
2
process of translation
- transfer RNA brings amino acids to the ribosome
- the tRNA has a binding site made up of three bases specific to a particular amino acid
- the tRNA also has an anti-codon which is complementary to the codon on the mRNA strand
- temporary hydrogen bonds form between codon and anti codon as 2 amino acids are bought close together by another tRNA molecule
- a peptide bond forms between them which require ATP
- eventually a STOP codon is reached
what happens when a STOP codon is reached during translation
- signals the end of the polypeptide which is then released so the polypeptide can fold into its 3D shape with the help of chaperone proteins
- tRNA molecules are released as the ribosome moves along the mRNA strand and are free to pick up another amino acid from the cytoplasm
what is the difference between mRNA and tRNA
mRNA: single stranded, has a codon, doesn’t have a binding site for amino acid
tRNA: folded-> clover shaped, held in place by hydrogen bonds, binding site for amino acids, has anti-codon
why do prokaryotes not have introns
as they don’t have pre-mRNA so don’t need to splice them out
what is a universal code
used by evrey cell-on earth as far as we know
what is a degenerate code
a code that has multiple codes for the same protein
what is a non-overlapping code
all triplets are completely separate and discrete to its neighbours
what is a mutation
a random DNA copying error
what are the different types of mutations
- substitution
- addition
- deletion
- inversion
what is substitution
when a single nucleotide base is swapped for another
what is addition
another base is added in
in what scenario is a substitution neutral
if a code is degenerate resulting in the same amino acid
what is a deletion
a base is removed
what do both an addition an deletion cause
a frame shift so it effects all the amino acids in the sequence
what is an inversion
where bases swap round -> effects at most 2 amino acids
