Transcription And Translation Flashcards
What enzyme carries out transcription
- RNA polymerases
What are the 4 basic steps of transcription
- promoter recognition
- initiation
- elongation
- termination
E. coli RNA polymerase
- Holoenzyme (consisting of 6 subunits)
- without a subunit is called core enzymes (abbwa)?
What is meant by the -35 and -10 sequences?
- conserved and have consensus sequences
- meaning its consistent, and have similar base sequences (most likely thing to find at that position)
- around 35/10 base sequences away from the promoter region in the opposite direction of elongation
What is another way to analyse conserved sequence
- sequence logos
Steps of Transcription in prokaryotes
- non specific binding of polymerase holoenzyme and migration to the promoter
- formation of a closed promoter complex
- formation of an open promoter complex
- intiation of mRNA synthesis almost always with a purine
- elongation of mRNA by about 8 more nucleotides
- release of sigma as polymerase process down the template
What happens inside the transcription bubble?
- unwind as you head downstream
- rewinding (the DNA strand) as you head upstream
What are the components of RNA polymerase?
A (a’ and a’’), B, B’, omega, needs sigma factors to work. (Mainly sigma 70)
What does the Prokaryotic promoter consist of?
- +1 end (RNA start)
- -10 end (TATAAT base sequence)
- -35 end (TTGACA base sequence)
- UP element
What is the function of the -10 end of the prokaryotic promoter sequence?
What is the function of the -35 end?
- transcription initiation
- transcription rate
What is a sigma factor?
- protein needed for transcription initiation.
What are the 2 types of termination in transcription in prokaryotes?
- rho indépendant, rho dépendant
Rho independant termination
- physical modified RNA structure terminates transcription.
- regions on the RNA transcript that are rich in Gs and Cs pair together in a hair pin loop like structure.
- but there illustrates be regions rich in Ts and As in the DNA template strand, thus transcribing it to Us on the RNA transcript, which pulls out the RNA transcript (weak point)
Rho Dépendant termination
- Rho Helicase binds to RUT site on RNA transcript and starts to move towards the RNA polymerase (ATP DEPENDANT)
- When it reaches the end of the RNA molecule, it encounters a RNA-DNA duplex, and it, being a helicase, unwinds this duplex to release the RNA transcript
What are the 3 major types of RNA
- mRNA
- rRNA
-tRNA
MRNA
- not functional on their own
- carry instructions for making specific proteins
RRNA
- small RNA molecule complexes with ribosomal proteins to make ribosomes, which protein synthesis occurs
TRNA
- small RNA molecules that carry amino acids to the ribosomes where only the amino acid gets incorporated into the growing protein chain
RNA polymerase I
- transcribes rRNA genes
RNA polymerase II
- transcribes mRNA genes and many others
RNA polymerase III
Transcribes tRNA genes, some rRNA
How many types of polymerase in bacteria
- ONE
Holoenzyme
Core enzyme
Includes sigma subunit
No sigma subunit
Important differences between RNA polymerases in eukaryotes and prokaryotes
Prokaryotes:
- only one type of RNA polymerase
Eukaryotes:
- 3 types of RNA polymerase z
Genomic structure of bacteria and eukaryotes
Most DNA in bacteria does code for proteins, rRNA or tRNA, coding sequences proceed without interruption
- length of gene in DNA = length of RNA
In Eukaryotes, most DNA DOES NOT code for proteins, rRNA or tRNA (mostly non coding DNA)
Introns
- non coding DNA within a gene
Spacer DNA
Noncoding DNA is between genes
Exons
- coding regions within a gene
Why do we have to bother with the whole central dogma?
- Amplification: very little template for making proteins - most genes are only present tiny 1 or possible 2 copies.
TATA region
- region on the promoter where the RNA polymerase II one.
TATA region
- region on the promoter where the RNA polymerase II one.
To what end is the amino acid attached to in tRNA
- ACC, 3’ end
- attaches according to anticodon on tRNA
Charged tRNA process
- requires input of energy by ATP hydrolysis to AMP and Pyrophosphate (2 phosphate0
- charging reaction catalyzed by enzymes called aminoacyl tRNA synthetases
- different aminoacyl tRNA synthétase for each amino acids.
- added covalently either on te 3’ or 2’ OH group (endergonic)
Ribosome structure
- complexes of rRNA and ribosomal proteins
Components of ribosome (prokaryotes)
- 70S ribosomes
- 50S and 30S subunits
- 50S: 5S rRNA, 23S rRNA, around 34 proteins
- 30S: 16S rRNA, 21 proteins.
Components of ribsosome (eukaryotes)
- 80S ribosomes - 60S and 40S subunit
- 60S: 5.8S rRNA, 5S rRNA, 28S rRNA, 49 proteins
- 40S subunit: 18S rRNA, around 33 proteins
Translation initiation
- mRNA binds to small unit of ribosome
- initiator aminoacyl tRNA binds to start codon (AUG)
- large subunit of ribosome binds (usually starts with f-methionine in prokaryotes, only met in eukaryotes
- initiator tRNA occupies the P site of ribosome
- all other tRNA enter the A site
- E site is where the tRNAs are ejected from
How does a prokaryote know which AUG is the correct start codon?
- ribosome binding site sequence comes before a start codon
- 16S rRNA binds to this Shine-Dalgarno subunit, and then finds the AUG start codon
Can bacteria have multiple proteins on the same mRNA strand? Why?
- YES!
- because there ca be multiple Shine-Dalgarno sequences and AUGs on the same mRNA
- this means they can be polycistronic
How to eukaryotes know which AUG to start?
- small ribosomal subunit (40S) binds to the cap (the 5’ cap) and finds the nearest AUG
- can only make one protein per mRNA strand.
- monocistronic
Elongation in translation steps
- binding of charged tRNA (in A site)
- peptide bond formation
- translocation
Binding of charged tRNA
- any tRNA molecule comes into the A site to attempt to match its anticodon to the codon on the mRNA
- elongation factor, along with GTP and tRNA molecule join onto the A site of the ribosome.
What end of the amino acid was covalently bound to the tRNA?
Carboxyl group
Peptidyl transferase
- triggers peptide bond formation between amino acids
- active in the largest rRNA subunit in the ribosome
Translocation
- uncharged tRNA is move to the E site, exposing the A site for a new charged tRNA to come in and elonagate chain of amino acids
- ribosome moves a codon along the chain of mRNA
Termination
- elongation continues until one of the 3 stop codons reaches A site
- release factors recognize stop codons and high energy bond between protein and tRNA is broken. (Physically shape similar to a charged tRNA)
- Peptidyl transferase breaks off amino acid form tRNA in P site.
- ribosome subunits dissociate.
Polysome
- assembly line style production of protein on mRNA
Cotranscriptional translation
- simultaneous transcription and translation that is possible in prokaryotic cells.
Cotranscriptional translation
- simultaneous transcription and translation that is possible in prokaryotic cells.
