6.1.1 Cellular control Flashcards
substitution mutation features
also known as point mutation
one base pair replaces another
same number of amino acids results
types of mutation and effects
silent mutations (no effect on protein) missense mutations (usually has effect on protein) nonsense mutations (usually had a large effect on protein)
silent mutations
change in base pair will still code for same amino acid = same protein = no effect
(most AA coded for by more than one DNA codon)
why genetic code is non-overlapping
makes sure genes are read “in-frame” by start and stop codons
no codon codes for more than one amino acid
why genetic code is redundant / degenerate
more than one codon codes for the same amino acid
missense mutation features
change in base pair causes change in amino acid
= change in primary and tertiary structure of protein
= change in shape and function
e.g. sickle cell anaemia
nonsense mutation features
change in base pair causes it to become a stop codon
= early termination of polypeptide chain
= change in shape/function of protein
e.g. cystic fibrosis
insertion and deletion mutation features
indel mutations
extra base pairs inserted / some deleted
results in number of base pairs not being in multiples of 3
causes frameshift
alters all subsequent DNA codons
= large change in primary and tertiary structure of protein
= large change in shape and function
if 3 bases are inserted/deleted no frame shift occurs (only 1 less/more amino acid)
lac operon in prokaryotes
lacI transcripted and translated to synthesise lacI repressor protein
lacI repressor protein binds to operator region on bacterial DNA, preventing expression of lacZ and lacY genes
when all glucose used up and lactose present
lactose binds to repressor protein
alters its shape and prevents it binding to operator
allows RNA polymerase to bind to promoter region
lacZ and lacY genes undergo transcription
beta-galactosidase and lactose permease are synthesised
thus, lactose induces the enzymes needed to break it down
what gene expresses beta-galactosidase
lacZ
what gene expresses lactose permease
lacY
lactose permease function
embedded into plasma membrane
acts as channel protein for lactose
greater rate of lactose entering the cell
beta-galactosidase function
breaks down lactose into glucose and galactose
control of gene expression at transcriptional level in eukaryotes method
certain genes only expressed in certain cells
transcription factors (proteins) control which genes are switched on or off
transcription factors bind to specific promoter regions of DNA for gene they control
helps or prevents RNA polymerase from binding and transcribing gene
how primary mRNA is spliced method
both intron and exons are transcribed to produce primary mRNA
primary mRNA binds to endonuclease enzyme (forms spliceosome)
primary mRNA spliced by endonuclease enzyme to remove introns
exons join together to produce mature mRNA, leaves cell and translated
why introns exist
some primary mRNA spliced in different ways - allows it to code for more than 1 protein
