Genetic code Flashcards
What is the central dogma of molecular genetics
Genetic information moves in one direction
What is the importance of the ATG codon
Is methionine - initiator
Why may mitochondria have once been a bacterium
Has own chromosomes and protein synthesising machinery
What is gene expression
Process by which information stored in gene made into functional product
What is gene regulation
Ability of cell to control expression of each gene
Stages of transcription
Template strand copied by RNA polymerase
RNA created from template/antisense strand (new RNA strand made needs to be the same as coding)
(Coding strand carries codons)
What does RNA polymerase I transcribe
Most ribosomal RNA
What does RNA polymerase II transcribe
Messanger RNA
What does RNA polymerase III transcribe
Transfer RNA and one small rRNA
What must be edited in type II genes in eukaryotes
Introns cut out
Cap and tail added
Where are promoters needed
Where RNA synthesis starts
Where does RNA polymerase bind to in prokayotes
Directly to DNA of promoter
Where does RNA polymerase bind to in eukaryotes
Need transcription factor to bind to promoter DNA first, which RNA polymerase then binds to
What happens if there is no lactose present in the lac operon
No expression of genes/proteins for lactose metabolism as Lac1 repressor binds to promoter - RNA polymerase cannot move along DNA
What is the Lac1 repressor made from
mRNA translated into protein - Lac1 repressor
What is the regulatory gene in lac operon
Lac1 repressor
What happens if lactose is present in the lac operon
Allolactose (rearranged lactose) binds to the Lac1 repressor so RNA can move along the DNA
What message is sent when RNA moves along the DNA
Polycistronic message
What happens when all lactose is metabolised
Lactose bound to repressor is metabolised
New repressors made are active - bind to promoter, stopping process
What must happen for eukaryote transcription initiation to occur
Several transcription factors bind to core promoter TATA box - must be specific combination of TFs for RNA polymerase to bind
Eukaryote TRANSCRIPTION termination
AAUAA cleavage signal, signals RNA ending, specific endonuclease cleaves off and poly(A) tail added
What are the two types of prokaryote transcription termination
Rho-independent
Rho-dependent
What is Rho-independent
RNA forms a hairpin loop due to inverted repeats in DNA, hairpin loop signals RNA polymerase to stop transcribing
Followed by uracil poly tail - only weakly bound to poly A sequence so RNA ‘falls off’ as no strong connection between DNA and RNA
What is Rho-dependent
Rho interacts with elongating RNA transcript, disrupts interaction causes RNA polymerase to ‘fall off’
Why is expression stage in prokaryotes important
As transcription and translation occur in cytoplasm, once read is immediately translated
