Gene Expression Flashcards
In which direction is mRNA produced?
In the 5’—->3’ direction
In which direction are proteins made?
From the n terminus end to the c terminus end
A gene is not a direct code for a protein, part of it is…
Introns (spliced out)
Initiation and termination signals
Making a polypeptide/polynucleotide/dna replication follows which 3 stage process?
Initiation
Elongation
Termination
How is dna replication initiated?
Recognition of origin of replication
Initiation proteins recruit DNA polymerase
In both DNA replication and transcription, what happens in the elongation stages?
There is 5’—>3’ chain growth
When is DNA replication terminated?
When replication forks meet
How is transcription initiated?
Recognition of the promoter region
Transcription initiation factors recruit rna polymerase
How is transcription terminated?
Dependent on the sequence
What are the promoter regions?
Signals that tell the transcription where to start
What is the transcription unit?
The promoter region + the gene coding for the protein
What does every promoter region contain?
A TATAAA box sequence in the 5’—>3’ direction
How is transcription initiated?
Binding of transcription initiation factors to TATAAAA box of the promoter region —> recruitment of rna polymerase
When does transcription begin?
The +1 point after RNA polymerase binds
What does rna polymerase do during the elongation phase of transcription?
Unwinds 2 dna strands, reads template strand in 3’–>5 direction —> produces mRNA in the 5’—>3’ direction
What are the two dna strands called in transcription?
Coding strand
Template strand
What is the purpose of RNA processing? When does it happen?
To protect the mRNA
Happens immediately while mRNA is being made
What are 3 different ways in which mRNA is processed?
Capping
Tailing (polyadenylation)
Splicing
What is capping?
Cap created at the 5’ end to prevent against degradation - 5’-5’ linkage is created
What is tailing/polyadenylation?
At the 3’ end, a polyA (200+ bases long) tail added to protect against degradation
Which enzyme adds the polyA tail to mRNA?
PolyA polymerase
What is splicing of an mRNA molecule?
Introns that do not code for the protein are spliced out by endocnucleases
Ribosomes which exist freely in the cytoplasm usually form which shape? What is the structure called?
A spiral shape
Polysome
What is the length of a prokaryotic ribosome? What type of ribosome exist in prokaryotes?
20nm
70S
What is the length of a eukaryotic ribosome? What type of ribosomes exist in eukaryotes?
32nm
80S
What does a 70S prokaryotic ribosome consist of?
2 sub units; 50S and 30S
3rRNAs + 56 proteins
What does an 80S ribosome consist of?
2 sub units; 60S and 40S
4rRNAs + 82 proteins
What are the majority of the proteins found in 70s and 80s ribosomes?
Enzymes for translation
What are the three main types of RNA? By which enzyme are each of them produced?
Ribosomal RNA (rRNA) - RNA polymerase I Messenger RNA (mRNA) - RNA polymerase II Transfer RNA (tRNA) - RNA polymerase III
The majority of RNA found in our cells is…
Ribosomal RNA
There are around _____ different kinds of tRNA
~100 different kinds
The genetic code is degenerate, what does this mean?
There are 20 amino acids and 64 different codons, this means that 1 amino acid can be coded for by more than 1 codon.
What is the structure of a tRNA molecule?
Single stranded
Clover model
What property of RNA allows tRNA to form this clover shape?
RNA is able to make stem loops, where hydrogen bonds are formed between anti-parallel complementary sequences
Where does the amino acid bind to on a tRNA molecule?
At the 3’ (-OH) end
Proteins always begin with which amino acid?
AUG - methionine
Translation is terminated by stop codons, what are the stop codons?
UAG, UGA, UAA
Each tRNA contains a __________ anticodon to the amino acid it recruits
Complementary
What bases exist at tRNA anticodons to allow the degeneracy/flexibility of the genetic code? What are bases at this position called?
I bases
Wobble bases
Which bases occupy the wobble base position on the codon and anticodon?
The 5’ base of the anticodon
And the 3’ base of the codon
What happens at initiation during translation?
Methionine connected to tRNA binds to 5’ cap of mRNA with the 40S sub unit of the ribosome
Sub unit moves along until AUG codon found (energy required)
Fully functional ribosome formed (energy required)
A ribosome can recognise how many codons at one time? What two sites does a ribosome have?
2
A site and a P site
Which enzyme helps with the formation of peptide bonds at ribosomes?
Peptidyl transferase
What happens during the elongation stage of translation?
Binding of the complementary amino-acyl tRNA
Peptide bond formed at the A site
Uncharged tRNA at P site released from ribosome
Translocation (using ATP), growing chain at P site, A site empty
Process continues….
When does termination occur in translation?
When a stop codon appears at A site
What happens during termination in translation?
Stop codon appears at A site
Bond between peptide and tRNA broken with H2O
Leaves uncharged tRNA molecule and peptide
Peptide released leaving empty ribosome
What is the complex of proteins that splices out the introns in a pre-RNA molecule called?
Spliceosome
In any mRNA molecule there are two UTR (untranslatable regions) - where are these found? What is the sequence between these two points called?
Before the initiation codon
After the stop codon
Open reading frame
What are some features of translation in bacteria?
It is coupled with transcription
Only one type of rna polymerase
No post transcriptional modification
Give an example of a drug affecting bacterial translation by affecting prokaryotic ribosomes?
Erythromycin - binds to the 50S ribosomal subunit
Prevents translocation
