Lecture 5 Flashcards
Monocistronic
An mRNA which encodes just one polypeptide
Polycistronic
An mRNA which encodes multiple polypeptides, not in eukarya
Operons
Polycistronic transcription units
Ribosome
Complexes of RNA and protein, have large and small subunits, can be found in the cytoplasm or bound to the rough ER
tRNA
Transfer RNA, an adaptor that link a codons to a specific amino acid
Aminoacyl tRNA
‘Charged’ tRNA, tRNA that is attached to an amino acid by an ester bond at the 3’ end of the molecule, attached amino acid is ‘activated’
Aminoacyl-tRNA Synthetase
Attaches amino acids to tRNA molecules through the breakdown of ATP and displacement of AMP
Initiation
First stage of translation, the components of the translational apparatus assemble
Elongation
Second stage of translation, amino acids are brought to the mRNA by tRNAs and are added to a growing polypeptide chain
Termination
Final stage of translation, a stop codon in the mRNA is recognized by a protein release factor and the translational apparatus comes apart
Initiation Factors
Called eIFs, they bind to the initiator tRNA and then bind to the small ribosomal subunit
Kozak Sequence
ACCAUGG, start sequence recognized by rRNA in the small ribosomal subunit
Elongation Factors
In prokaryotes:
EF-Tu and Ef-Ts, EF-Tu with GTP attached escorts an aminoacyl tRNA to the A site where it hydrolyses the GTP and is released, EF-Ts helps recycle EF-Tu
In eukaryotes:
eEF1 does both jobs
Translocation
The mRNA advances by 3 nucleotides, the peptidyl tRNA moves from the A site to the P site and the empty tRNA moves from the P site to the E site accompanied by the hydrolysis of GTP bound to EF-G
Protein Release Factors
Proteins that look like tRNA and can interact with the codon on the mRNA
Molecular Chaperones
Proteins which assist other proteins folding, can bind polypeptide chains in the early stages of folding or rescue misfolded proteins and refold them
Posttranslational Import
Proteins which fully fold in the cytoplasm and are then directed to the proper compartment using special targeting signals
Cotranslational Import
Proteins destined for the endomembrane system and export from the cell are transferred across the ER membrane as synthesis takes place
Signal Recognition Particles
SRPs bind an ER signal sequence on a newly forming polypeptide and mediate cotranslational import into the ER
Protein Disulfide Isomerase
Facilitate the formation of disulfide bonds to strengthen protein structure
Unfolded Protein Response
A mechanism in which sensor molecules in the ER lumen detect misfolded proteins and activate signalling pathways that enhance production of proteins needed for folding and degradation
ERAD
ER-associated degradation, a mechanism which recognizes misfolded or unassembled proteins and exports them to the cytosol where they are degraded by proteasomes
KDEL Sequence
A sequence (Lys-Asp-Glu-Leu) of a protein that is recognized by the Golgi which delivers the protein to the ER
Electrophoresis
A group of techniques that use an electric field to separate charged molecules based on charge and size
Western Blot
Immunoblot, technique used for the detection of specific proteins in a complex mixture
