Gene Products And Protein Synthesis Flashcards
Why is the genetic code considered degenerate?
64 combinations of nucleotides in a codon possible yet only codes for 20 amino acid - some amino acids are coded for by more than one triplet
What is the start codon
AUG, methionine
What are the stop codons
UAA, UAG, UGA
What are the types of point mutation?
Nonsense: amino acid to stop
Missense: amino acid to a different amino acid
Silent: amino acid doesn’t change (degenerate code)
What is the mutation that causes sickle cell anaemia?
Mutation in B-globin gene; amino acid coded for at 6th position changed from glutamate to valine
What is the mutation that causes cystic fibrosis?
A mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene
What is tRNAs shape and why?
Single stranded RNA molecule with intramolecular double stranded regions which fold it up into a clover leaf shape.
Where on a tRNA molecule will the amino acid attach?
To the 3’ end at the - CAA-OH group
What is wobble pairing?
The last base on the codon loop can form non-Watson-Crick pairs; this does not change the amino acid sequence, just means that a single tRNA molecule can recognise more than one codon - good for degenerate code when last base in codon won’t effect the the acid called for
What is the enzyme that produces aminoacyl-tRNA
Aminoacyl-tRNA-syntheases
What is an aminoacyl-tRNA?
What forms when an amino acid bonds to a tRNA molecule
Amino acid + tRNA + ATP (via aminoacyl-tRNA) =
= aminoacyl-tRNA + PPi + AMP
What are the subunits (and their compositions) in prokaryotic ribosome?
70s complex, made up of a large 50s and a small 30s subunit.
The 50s subunit is made up of 23s RNA + 5s RNA + 34 proteins
The 30s subunit is made up of 16s RNA and 21 proteins
What is a 50s subunit in a prokaryotic ribosome made up of?
23s RNA + 5s RNA + 34 proteins
What is a 30s subunit in a prokaryotic ribosome made up of?
16s RNA + 21 proteins
What are the three sites in the 30s subunit of a ribosome?
E, P, and A
Describe the initiation step of translation in prokaryotes.
30s subunit binds initiation factors IF1 and IF3
Then the mRNA binds to the 30s subunit; with the AUG start codon binding near the P site (in the middle of E and A). The Shine-Dalgarno Sequence will bind upstream of the start codon to 16s RNA which ensures in-frame translation.
fmet-tRNA^fmet binds IF2-GTP which then enters P site and lines up with start codon.
Then the 50s subunit binds to 30s ribosome, this removes the initiation factors IF1,2,3 and hydrolyses GTP to GDP + Pi - releasing energy.
Describe the elongation step of translation in prokaryotes
Aminoactyl-tRNA bound to EF-Tu-GTP (EF = elongation factor) binds to A site. Tu is a G-protein so factor complex can be called EF-G-GTP as below.
Pause for proof reading + GTP hydrolysis
Peptidyl transferase moves second amino acid on top of first, fMet will stay in same place as it was at P site. The 3’ end of tRNA hydrolysed to -OH group and moves over to E site at top while staying attached to P site (sitting diagonally) then tRNA to which fMet-AA is attached has top move over to P site while attached to A site (also sitting diagonally).
Then translocation occurs where bottom of tRNA lines up with top so top+bottom of tRNA at A and top+bottom of tRNA at P; leaving A site free. EF-G-GTP hydrolysed to EF-G-GDP + Pi
Then tRNA at E site released
repeats
Describe the termination step of translation in prokaryotes
When a stop codon (UAA, UAG, UGA) presented to A site it causes the binding of the release factor and then the protein is released and everything dissociates
Classes of antibiotics:
Chloramphenicol
Actinomycin
Puromycin
Tetracyclines
Alpha-amanitin
Rifomycin
Streptomycin
Erythromycin
Cyclohexamide
Diptheria toxin
Chloramphenicol
Inhibits peptidyl transferase by binding on 50s subunit
Actinomycin
Binding DNA at the transcription initiation complex - preventing elongation by RNA polymerase
Puromycin
Causes premature chain termination during translocation (for both pro- and eukaryotes)
Tetracyclines
Inhibits binding of aminoacyl-tRNAs to the ribosome
