gene regulation & transcription factors Flashcards
what is gene regulation?
the control of gene expression
how can the rate of transcription be changed?
turn it on / slow it down until turned off
what is an operon?
- usually in prokaryotic cell
- group of simultaneously controlled genes which are either all expressed or not
what is a promoter?
- signal to start transcription
- sequence of DNA
- where RNA polymerase binds
what is an operator?
set of structural genes
define gene expression
- conversion of the information encoded in a gene into a functional gene product
- (usually a protein but sometimes just RNA)
describe the transcriptional level of regulation
- transcription regulatory factors
- regulation of gene expression during mRNA production
describe the post translational level of regulation
regulation of gene expression after protein synthesis
- addition of non protein groups
- folding/shortening of proteins
- modification of cAMP
describe the post transcriptional level of regulation
regulation of gene expression after mRNA production
what are transcription factors?
proteins which bind to DNA and increase/decrease transcription of genes
state and describe the two transcription factors
- activators: speed up transcription
- repressors: slow down transcription
how do transcription factors affect hormones/sugars?
- they bind to the TF
- increase or decrease binding to DNA
- so the molecules present in a cell’s environment can control protein synthesis by TF binding
what is a transcription factor?
a protein molecule which binds to complementary base sequences, initiating or inhibiting transcription to control protein synthesis
summarise the process by which transcription factors initiate transcription
- DNA binding site binds to complementary base sequence
- this allows RNA polymerase to bind
- transcription begins and creates the mRNA molecule for the gene, which can then be translated
why will a gene not bound to a transcription factor be inactive?
RNA polymerase cannot bind so transcription is inhibited
describe the movement of transcription factors
move from cytoplasm to nucleus
what is lac operon?
- an operon present in e coli
- sequence of 3 genes: lacZ, lacY and lacA
- collectively aid digestion of lactose
why is lac operon only needed if glucose isn’t present?
- glucose requires less energy to be digested by bacteria so is the favourable respiratory substrate
- if glucose isn’t present, lactose is digested
- lac operon proteins are only needed if glucose is absent
- this regulates transcription
what is a repressor protein?
a protein that inhibits transcription
what is lacL?
a regulatory gene near the operon which codes for a repressor protein
how does lacL control transcription?
- when lactose is absent, repressor is constantly produced
- repressor binds to operator to prevent RNA polymerase binding at promoter
- this inhibits transcription
- when lactose is present, it binds to the repressor to change its shape
- this prevents repressor binding to operator
- allows RNA polymerase to bind to promoter
- this initiates transcription
what is the role of cyclic AMP (cAMP)?
- increases rate of transcription for lac operon
- because when transcription is initiated by repressor removal, it is still too slow to create required amount of enzymes
what is the role of cAMP receptor protein (CRP)?
- binds to lac operon to produce lacZ lacY and lacA
- CRP only binds once bound to cAMP
what are introns?
non coding regions
what are exons?
coding regions
all DNA of a gene, including introns and exons are transcribed to forma strand called ….
primary mRNA
primary mRNA is edited during a process called ….. where the …. are removed, leaving only …. which are complementary to original ….
splicing
introns
RNA exons
DNA exons
what is meant by epigenetics?
a heritable change in gene function without changing the DNA base sequence
- caused by the environment
- can inhibit transcription
what two types of epigenetics prevent transcription?
increased methylation
decreased acetylation of histones
how does increased methylation inhibit transcription?
- methyl groups attach to cytosine bases
- prevents transcription factors binding
- attracts proteins that condense the DNA histone complex
how does decreased acetylation inhibit transcription?
- removal of acetyl groups increases positivity of histones
- they are attracted to phosphate on DNA
- DNA and histones strongly associate
- makes it hard for transcription factors to bind
what is splicing?
the removal of introns
what is alternative splicing?
the concept that splicing occurs in many ways and allows a single gene to result in many proteins being created
describe how genes are regulated after transcription
- primary mRNA modified
- introns removed
- alternative splicing results in different versions of mRNA
- binding of cAMP
what makes a suitable respiratory substrate?
- bonds that contain energy so can be broken
- soluble so can move
- H/OH groups that can bond with water molecules
- for lactose to enter cytoplasm, a protein is required
- why are young mammals more likely to contain this protein in E coli than old mammals?
- diet is high in milk - high lactose concentration
- gene for the protein channel is switched on
state 3 reasons fruit flies are chosen for genetic research
- easy to obtain and keep a large sample
- simple genetics
- rapidly reproduce
state 2 reasons mice are chosen for genetic research
- similar to humans
- easy to keep
explain why some regions of DNA are described as non coding
- introns removed
- not present in mature mRNA
- not translated
suggest why non coding regions of DNA show more variation
doesn’t affect survival
