Gene Products and Protein Synthesis Flashcards
How many codons exist for the 20 different AA’s?
X64
How many of the X64 AA codons are stop codons?
X3
What triplet of bases is the start of every protein?
Which AA does this codon code for?
What is the name given to this codon?
AUG
Methionine
The initiation codon
What is a frameshift mutation?
The addition or deletion of a base pair/s which alters the reading frame of the base pair sequences
What is a point mutation?
The alteration (addition or removal) of a single base pair
What are the x3 different types of point mutation?
1) silent
= the alteration in base pairs still codes for the same amino acid
2) missense
= the alteration in base pairs codes for a different amino acid
3) nonsense
= the new codon produced by altering the base pairs is a stop codon
What is the point mutation in sickle cell anaemia?
An A goes to a T in the 6th AA
GAG —> GTG
GLUTAMINE —> VALINE
POLAR —> NON-POLAR
This occurs on the beta chains and creates hydrophobic regions on their outsides
What is the shape or tRNA?
Clover leaf due to internal base pairings
What is the name for the site on the middle tRNA loop that is specific for each AA?
The anticodon
What is the sequence at the end of the 3 prime end of tRNA?
CCA-OH
What is the name of the process whereby the last base on the anticodon loop can form non-Watson/crick base pairs?
Wobble base pairing
Does amino acid attachment to tRNA require energy?
Yes - ATP
How does the tRNA bind amino acids and where?
It binds them to the terminal adenosine from then CCA-OH complex at the 3-prime end of the tRNA.
It does this via aminoacyl-tRNA-synthetases
What are the X2 safety mechanisms the tRNA-synthetases have when loading AA’s into tRNA?
1) the amino acid fits
2) the tRNA fits
What is the name of the X3 binding sites of ribosomes?
1) A site = acceptor site
2) P site = polymerisation site
3) E site = exit site
What is the first set of binding in initiation of translation?
What other factors need to bind?
The smaller subunit binds mRNA and the first tRNA in the central (P) position and then the larger subunit binds on top
The first tRNA is fmet-tRNA
(Fmet in prokaryotes = met in eukaryotes)
The initiation actors IF1, 2 and 3 also bind (2 requires GTP)
Where do IF1 and 3 bind in initiation?
The small ribosomal subunit
Where does IF2-GTP bind during initiation?
To the met-tRNA
In the elongation phase of translation, what is an aminoacyl-tRNA?
tRNA with an amino acid bound
How does elongation occur?
Elongation factor (EF) binds to GTP and aminoacyl-tRNA and enters the A site of the ribosome
GTP is hydrolysed as proof reading occurs
Which enzyme links the amino acids in the elongation process?
Where is this enzyme found?
Peptidyl transferase
In the large ribosomal subunit
How does the A site become free again to carry on elongation?
EF-G binds to the complex causing the ribosome to translocate.
The existing AA chain is added to the newest tRNA in the P-site, and the A site is free again for a new aminoacyl-tRNA complex to join
How does termination occur within translation?
When the top codon on the mRNA reaches the A-site of the ribosome release factors 1 and 2 (RF 1 and 2) bind to the A-site why hydrolyses the newly formed protein.
The ribosome complex then disassembles
What does monocistronic mean?
For eukaryotes, it means mRNA can code for only a single protein
What happens to hnRNA to mature it into mature RNA in eukaryotes?
Capping and splicing
What is the shine-dalgarno sequence
A sequence of base pairs upstream of the start codon which acts to re riot ribosomes to align in the correct place
How does actinomycin work?
Binds to DNA at the transcription initiation complex to prevent transcription and rRNA elongation via RNA polymerase
What type of RNA polymerase does mRNA use?
2
What type of RNA polymerase does tRNA use?
1
What type of RNA polymerase does rRNA use?
3
How does rifamycin work?
It inhibits transcription by binding to prokaryotic RNA polymerase
How does streptomycin work?
It affects the 30s subunit
How does erythromycin work?
Affects the 50s subunit by preventing translocation
How does chloramphenicol work?
It affects the 50s subunit by inhibiting peptidyl transferase
How does tetracycline work?
Inhibits binding of aminoacyl-tRNA’s to the A-site of ribosomes
How does puromycin work?
It prematurely terminates the chain
How does alpha-aminitin work?
It inhibits RNA polymerase 2
How does cyclohexamide work?
It interferes with translocation to prevent protein biosynthesis
How does diphtheria toxin work?
It inactivates EF-2
