CELLULAR CONTROL Flashcards
define mutation
a random or spontaneous change to the nucleotides in the base sequence of DNA
missense
change to a single nucleotide
nonsense
stops translation prematurely
frameshift
- insertion or deletion of a nucleotide
- sequence is read in codons of 3 nucleotides so the subsequent codons are read incorrectly as translation machinery cannot identify error
- wrong amino acids coded for so different protein produced
insertion
nucleotide incorporated into base sequence during DNA replication
deletion
nucleotide missed or absent during replication
substitution
nuceleotide incorrectly swapped during replication
- can be silent as code is degenerate
- but could swap with stop codon
what is a transcription factor?
proteins that control transcription by regulating gene expression, binding to DNA and controlling protein synthesis
why is controlling transcription important?
- prevents tumour growth
- conserves energy
describe the regulatory mechanism at transcriptional level
- during mRNA production
- cell division
- lac operon
describe the regulatory mechanisms at post transcriptional level
- after mRNA production
- editing of primary mRNA
- removal or introns to produce mature mRNA in a process called splicing
describe the regulatory mechanisms at post translational level
- after protein synthesis
- addition of non protein groups
- folding & shortening of proteins
- binding of cAMP to activate proteins
- adrenaline binds to receptors on surface cell membranes to form a hormone receptor complex which activates adenylate cyclase which converts ATP to cAMP
define operon
a set of simultaneously controlled genes which are either all expressed or not
define repressor
protein that inhibits transcription by binding to a promoter so that RNA polymerase cannot bind
define promoter
region on operon which is a sequence of DNA where RNA polymerase binds to signal the start of transcription
define operator
a protein that inhibits transcription
what is lac operon?
a set of 3 genes (Y,Z,A) which collectively aid lactose digestion in e coli
when is lac operon used?
when lactose is present
why is glucose a favourable respiratory substrate?
- requires less energy to be broken down by bacteria
- due to the OH/H bonds which contain energy
describe what happens when lactose is absent
- lacL produces lots of repressor
- repressor binds to operator on lac operon and blocks promoter
- this prevents RNA polymerase binding
- so transcription is inhibited as structural genes are switched off
describe what happens when lactose is present
- lactose binds to the repressor and changes its shape
- RNA polymerase binds to promotor
- transcription is initiated
what is the role of cAMP?
increases rate of transcription as it is too slow to produce sufficient enzymes
- CRP must bind to it first
homeobox genes
- sequences of genes which code for transcription factors & regulate gene expression
- arranged into hox clusters
- responsible for body feature development in the early embryo
- similar and highly conserved
hox genes
- set of homeobox genes
- produce proteins involved in body feature position
- affected by internal and external stimuli
