Gene Products and Protein Synthesis Flashcards
Definition of wobble mechanism
Last base on codon loop forms non Watson Crick base pairs
Definition of initiation
Formation of initiation complex comprising of ribosomes, mRNA, initiator, tRNA, IF1, IF2, IF3, GTP nucleotide
Definition of the Shine-Dalgarno sequence
Upstream of start AUG, binds to 16s RNA sequence, ensures inframe translation
Definition of elongation
Activated AA binds to elongation factor, enters A site of ribosome
Energy for proof reading provided by GTP hydrolysis to GDP
Peptide bonds formed between AA in P and A site
EF-G binds and ribosome translocates so A site is free again
Definition of termination
Stop codon of mRNA presented to A site Release factor 1, 2 binds Hydrolysis of protein from tRNA Ribosome complex disassembled Needs IF3, ribosomal recycling factor, GTP hydrolysis
How many combinations of codon triplets are there?
4 to the 3 = 64 combinations
How many stop codons are there
3
UAA
UAG
UGA
How many start codons are there
1 AUG
Important components to translation and their roles
mRNA,
carries sequence info to make protein at ribosome
tRNA,
bring inidivual AA to protein synthesis sites
Ribosomes,
contain rRNA and ribosomal proteins
Machinery of protein synthesis bind mRNA, tRNA
Describe the structure of tRNA
5' D loop Anticodon loop T loop Acceptor stem Attached AA at 3'
Extensive internal base pairing
Contains unusual modified base pairing
Describe the tRNA anticodon
Triplet of complementary bases to codon
3 unpaired bases, available for HB
tRNA can recognize more than 1 codon due to wobble pairing
What is the wobble mechanism
Last base on codon loop forms non Watson Crick base pairs
Does not alter AA sequence of protein
Allows single tRNA species to recognize more than 1 codon
How do AA attach to the 3’ end of tRNA
Specific aminoacyl - tRNA - synthetases load tRNA with specific AA
Each tRNA can accept only 1 AA appropriate for the anticodon sequence
Equation for activated AA
AA + tRNA + ATP => PPi + AMP + aminoacyl - tRNA
What bond forms between the AA and the tRNA
High energy ester linkage
Structure of the ribosome
70S complex
Large subunit 50S, 23S rRNA, 5S rRNA, 34 proteins
Small subunit 30S, 16S rRNA, 21 proteins
Internal structure of ribosomes
E= exit site
P= polymérisation site
A= acceptor site
mRNA binding site
Steps in translation
Initiation
Elongation
Termination
Steps in initiation
30S binds to Initiation Factor 1, 3
mRNA, fMet (start codon) and IF2 - GTP enter P site
fMet - tRNA anticodon loop lines up with start codon
50S binds to 30S, GDP and Pi released
What precedes the start codon?
Shine Dalgarno sequence in prokaryotes
What is elongation
Activated AA binds to elongation factor (EF - Tu GTP), enters A site of ribosome
Energy for proof reading provided by GTP hydrolysis to GDP
Peptide bonds formed between AA in P and A site (no additional energy needed)
EF-G binds, ribosome translocates (GTP hydrolysis) so A site is free
Steps of elongation
fMet in P site
EF-Tu GTP binds to AA, both enter A site
Pause for proof reading via GTP hydrolysis, EF-Tu GTP leaves AA
Peptide transferase catalyses the formation of peptide bonds so fMet AA2 is a dipeptidyl- tRNA
Another EF-G-GTP is hydrolyses to EF-G-GDP + Pi, so ribosome translocates, A site is free
tRNA is released and discharged and leaves via exit site
Delivery of AA starts meet round of peptide bond synthesis
What is termination
Stop codon of mRNA presented to A site Release factor RF1/RF2 binds Hydrolysis of protein from tRNA Ribosome complex diseases,bled Requires IF3, ribosomal recycling factor and GTP hydrlysis
Steps in termination
Binding of release factor to A site
Termination of AA chain by hydrolysis, release factor and tRNA move up one position so A site is free
Ribosome complex disassembled, needs IF3, ribosomal recycling factor and GTP hydrolysis
