Translation Flashcards
*Creation of protein molecules using mRNA as the template
*To translate the nucleotide sequence of mRNA into the amino acid sequence of protein
Translation
How many substrates are in protein synthesis
20 amino acids
- Enzymes and protein factors:
initiation factor (IF), elongation factor (EF), releasing factors
- is the template for the protein synthesis
mRNA
Prokaryotic mRNA is ______; that is, a single mRNA molecule may code for more than one peptides
polycistron
- Eukaryotic mRNA is ______; that is, each mRNA codes for only one peptide.
monocistron
- Is a sequence of three adjacent nucleotides on mRNA that corresponds with a specific amino acid
Genetic codon
Stop codons
UAA, UAG, UGA
Start codon (methionine)
AUG
- 61 codons for 20 amino acids
- A portion of a DNA sequence that does not include a stop codon
Open reading frame
Properties of genetic code:
- Commaless = genetic codons should be read continuously without spacing or overlapping.
- Degeneracy = More than one codon can specify the same amino acid (degenerated codons differ on the third nucleotide).
- Universal = genetic codons for amino acids is the same in humans, animals, plants and bacteria
Refers to the insertion or deletion of nucleotide bases in numbers that are not multiples of three
Frameshift mutation
Non-Watson-Crick base pairing is permissible between the 3rd nucleotide of the codon on mRNA and the first nucleotide of the anti-codon on tRNA
Wobble
in tRNA, which has the proofreading ability
Aminoacyl-tRNA synthetase
- Prokaryotic Met-tRNA^met can be formylated to fMet-tRNAi^met.
For prokaryotes:
* fMet-tRNAi^met can only be recognized by initiation codon.
*Met-tRNAe^met is used for elongation.
For eukaryotes:
*Met-tRNAi^met is used for initiation.
*Met-tRNAe^met is used for elongation.
*Is the place where protein synthesis takes place
Ribosome
Three sites on ribosomes
- Aminoacyl site (A site) = Composed by large and small subunit; Accepting an aminoacyl-tRNA.
- Peptidyl site (P site) = Composed by large and small subunit; Holds the growing amino acid chain.
- Exit site (E site) = Only on large subunit; Releasing the deacylated tRNA
The direction of the protein synthesized:
N-terminal—C-terminal
Protein synthesis process steps
–Initiation
–Elongation
–Termination
Three initiation factors in prokaryotes: IF-1, IF-2 and IF-3
ribosomal binding site in bacteria
Shine-Dalgarno (SD sequence)
- The IF-1 and IF-3 bind to the 30S subunit, making separation between 50S and 30S subunit.
- The mRNA then binds to 30S subunit.
*The complex of the GTP-bound IF-2 and the fMet-tRNA enters the P site. - The 50S subunit combines with this complex.
- GTP is hydrolyzed to GDP and Pi.
- All three IFs depart from this complex.