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Molecular Biology- Translation Cheat Sheet (DRAFT) by

Translation steps and ribosome structure and synthesis

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Ribosome Structure & Synthesis

Structure
Synthesis
Large ribonu­cle­opr­otein (RNP) complexes that contain large amounts of RNA
Synthesis is complex and energe­tically demandind
Highly conserved
Ribosomes are produced in abundance to make necessary proteins
Have a large and small subunit. Transl­ation occurs at the interface, where the two subunits meet
Specia­lised proteins for ribosome synthesis are also produced in abundance
Codon anticodon binding occurs on small subunit (decoding centre), peptide bond formation occurs on large subunit (pepti­dyl­tra­nsf­erase centre- PTC)
rRNA transc­ription and processing occur in nucleoli which are found in the nucleus
3 binding sites are found on the interface: A, P, E
Ribosomal subunits are generated and are only functional in the cytoplasm, they do not work in the nucleus
Charged tRNA initially binds to A site, then moves to P site and peptide bond forms, finally tRNA moves to E site, and then leaves the ribosome
 

Peptid­ylt­ransfer and Transl­ation Steps

Peptid­ylt­ransfer
Initiation
Elongation
Termin­ation
Charging enzymes attach amino acid to the 3’ end of the tRNA via a carboxylic ester linkage to a carboxyl group
The start codon must be directed to the P site to start transl­ation
Two tRNAs are bound to the ribosome at one time; A and P sites (pre-t­ran­slo­cation state), or P and E sites (post-­tra­nsl­ocation state, ribosome has moved along the RNA)
Termin­ati­on/­release factors recognise the stop codon
Amino acids are added to the carboxyl end of the polype­ptide chain
Prokar­yotes: a nucleotide sequence close to the start codon pairs with rRNA
Elongation factors are proteins that aid the elongation process. There are different types for specific functions.
Initial binding of RF1 or RF2 (proka­ryo­tes), or eRF1 (eukar­yotes) causes peptide hydrolysis
Peptid­ylt­ransfer reaction is the formation of a peptide bond between two amino acids
Allows initiation to occur on multiple sites along the sequence, useful for polyci­stronic mRNA
EF1A brings the charged tRNA to the ribosome
RF3 (proka­ryote) or eRF1 (eukar­yote) allows release of RF1/RF2 from ribosome
Aminoacyl tRNA- peptide bond is attached to the amino group
Eukary­otes: ribosome is targeted to the start of the transc­ript, the small subunit moves along the sequence until the start codon is recognised
EF2 aids the movement of ribosome along the mRNA chain
RF3 is a GTPase
Peptidyl tRNA- peptide bond is attached to the carboxyl group
Small subunit moves along sequence until it recognises the start codon. Large subunit is recruited to start transl­ation
Both are GTPases, and have the capacity to hydrolyse GTP to GDP. Each time an amino acid is added to the polype­ptide chain GTP is hydrolysed into GDP