regulation of transcription Flashcards
what is the process of polypeptide synthesis?
polypeptides are chains of aa linked together by peptide bonds. the order of aa is specified by the genetic information in DNA. DNA doesnt code for protein directly but acts through RNA intermediates
describe transcription?
- the hydrogen bonds break between bases on opposite DNA strands to allow localised strand separation
- ONE of the strands becomes a template for the synthesis of the mRNA strand
- the template strand determines the sequence of bases in the mRNA using complimentary base pairing rules
does an entire strand of a chromosome get copied into mRNA during transcription?
NO-its usually one gene at a time thats copied into mRNA and only when its needed
[transcription is different to DNA replication, which replicates the entire genome all at once]
where does transcription take place?
eukaryotes- in the nucleus,
where does transcription take place?
eukaryotes- in the nucleus, RNA is copied from the DNA in the nucleus then RNA travels to the cytosol where ribosomes translate it
prokaryotes- no nuclear membrane, RNA can be translated as soon as its made. translation and transcription are coupled
what is the enzyme that carries out transcription? what does it do?
RNA polymerase
it catalyses the formation of phosphodiester bonds between the new nucleotide and the RNA chain at its 3’ end
what are the three stages of transcription?
- initiation- the most important and complex
- elongation- RNA polymerase continues to add nucleotides to the growing chain
- termination- RNA polymerase reaches the end of the gene and reads a signal to stop transcribing
how does transcription start?
RNA ploymerase initiates transcription at specific sites near the start of the gene. these sequences are called promoters
during transcription, where does bacterial RNA polymerase bind first?
the TATA box
what other factors may be needed for transcription?
- transcription factors TF are proteins that affect transcription
- some are required for the initiation of transcription
- some bind to DNA- but some work indirectly
- some activate transcription=activators
- some repress transcription= repressors
how can gene expression be regulated?
- most efficient control is to regulate transcription
- gene “switches”
- gene expression can be switched “on and off”
what is the lac promoter?
- It’s a gene switch in bacteria.
- it codes 3 proteins/enzymes required to break down sugar lactose
- it can be switched on by the presence of lactose in the growth medium
- this means the enzymes are only made when required to break down lactose
what does the lac repressor do?
[no lactose] it binds to a part of the promoter region, this stops RNA polymerase from binding = no transcription
[lactose present] lactose binds to the lac repressor which makes the repressor change shape and it can no longer bind to the promoter region, this frees up the promoter so that RNA polymerase can transcribe the lac genes
what are enhancers and control elements of transcription?
enhancers- DNA sequences upstream or downstream of the basal promoter
transcription factors- they bing to these enhancer elements to regulate transcription
the DNA can loop over to allow the transcription factors to interact with RNA polymerase
why do we need mRNA?
amplification of expression- you can get many mRNA molecules from a single DNA template
DNA is stable whereas mRNA is short-lived and unstable
information is processed at the RNA level which increases diversity (tissue-specific expression and antibodi diversity)
RNA was likely the original information store
RNA primers are still needed to replicate DNA and in ribosomes
