L8: Protein Synthesis I Flashcards
What does the central dogma states?
Genetic information only flows from DNA to RNA
3 key differences between DNA & RNA
1) DNA is double stranded, RNA is single stranded
2) RNA sugar is ribose, and has OH group at 2’ position
3) DNA bases: ACGT
RNA bases: ACGU
Function of mRNA
Encodes proteins
Function of rRNA
Structural component of the ribosome
Function of tRNA
Delivers amino acids to ribosome
Which RNA is produced from a DNA template?
mRNA
What molecule does the polymerisation of ribonucleoside triphosphate into RNA?
RNA polymerase
3 parts of the mechanism of transcription
1) Initiation
2) Elongation
3) Termination
What is transcription initiated by?
RNA polymerase holoenzyme
First stage of transcription in prokaryotes; INITIATION
Short recognition sequences in the promotor region align RNA polymerase at the transcription start site
What happens in transcription in prokaryotes after RNA polymerase is aligned?
Instead of RNA polymerase, a ‘sigma factor’ binds & recruits RNA polymerase
First stage in elongation in transcription of prokaryotes?
1) RNA polymerase unwinds DNA
2) RNA polymerase reads DNA template, synthesising mRNA by adding nucleotides
3) After 1st few nucleotides completed, sigma factor dissociates
What happens after the sigma factor dissociates in elongation stage of transcription in prokaryotes?
Addition of nucleotides in the 5’ to 3’ direction, joined by covalent phosphodiester bonds
What is another name given to the termination of transcription in prokaryotes?
Rho Independent Termination
What is termination of transcription controlled by?
GC rich-stop sequences in DNA
What is a GC-rich sequence?
DNA segment that is rich in guanine & cytosine bases
How is termination of transcription controlled?
BY GC-rich stop sequences in DNA
How does mRNA transcript reduce binding of mRNA to DNA template?
mRNA transcript forms a stem loop
Which pairings help detachment from DNA template?
A-U pairings
What is the role of Rho in termination?
Rho unwinds DNA-RNA duplex, separating growing RNA from DNA
How can transcription in prokaryotes be terminated?
Rho independent/Rho dependent mechanism
Why does RNA pol II have a C-terminal domain (CTD) tail?
Recruits eukaryotic mRNA
How many RNA polymerases in eukaryotes?
3
What are the 3 RNA polymerases in eukaryotes?
1) RNA Pol I
2) RNA Pol II
3) RNA Pol III
Name given to RNA before they are fully processed?
Heterogenous nuclear RNA (hnRNA) or pre-mRNA
Where does eukaryotic transcription take place?
Inside the nucleus
Where does prokaryotic transcription take place?
Cytoplasm
What is polyadenylation?
Process of adding adenosine nucleotides (A) to the 3’ end of mRNA
What is capping?
7-methylguanosine cap formed at the 5’ end of mRNA
What is the primary transcript called prior to processing?
Heterogenous nuclear RNA (hnRNA)
or
pre-mRNA
Define exons
Regions of DNA that are coding regions & found in mature mRNA
Define introns
Regions of DNA that are non-coding & not found in mature mRNA
Define splicing
Complex of proteins that removes introns
Define alternative splicing
Exons from the same gene are joined in different combinations
Define co-transcriptional
Splicing & capping of eukaryotic mRNA’s happening whilst transcription is ongoing
Function of 5’ capping
Essential for mRNA stability
