Lecture 5

Question 1

Monocistronic

Answer 1

An mRNA which encodes just one polypeptide

Question 2

Polycistronic

Answer 2

An mRNA which encodes multiple polypeptides, not in eukarya

Question 3

Operons

Answer 3

Polycistronic transcription units

Question 4

Ribosome

Answer 4

Complexes of RNA and protein, have large and small subunits, can be found in the cytoplasm or bound to the rough ER

Question 5

tRNA

Answer 5

Transfer RNA, an adaptor that link a codons to a specific amino acid

Question 6

Aminoacyl tRNA

Answer 6

‘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’

Question 7

Aminoacyl-tRNA Synthetase

Answer 7

Attaches amino acids to tRNA molecules through the breakdown of ATP and displacement of AMP

Question 8

Initiation

Answer 8

First stage of translation, the components of the translational apparatus assemble

Question 9

Elongation

Answer 9

Second stage of translation, amino acids are brought to the mRNA by tRNAs and are added to a growing polypeptide chain

Question 10

Termination

Answer 10

Final stage of translation, a stop codon in the mRNA is recognized by a protein release factor and the translational apparatus comes apart

Question 11

Initiation Factors

Answer 11

Called eIFs, they bind to the initiator tRNA and then bind to the small ribosomal subunit

Question 12

Kozak Sequence

Answer 12

ACCAUGG, start sequence recognized by rRNA in the small ribosomal subunit

Question 13

Elongation Factors

Answer 13

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

Question 14

Translocation

Answer 14

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

Question 15

Protein Release Factors

Answer 15

Proteins that look like tRNA and can interact with the codon on the mRNA

Question 16

Molecular Chaperones

Answer 16

Proteins which assist other proteins folding, can bind polypeptide chains in the early stages of folding or rescue misfolded proteins and refold them

Question 17

Posttranslational Import

Answer 17

Proteins which fully fold in the cytoplasm and are then directed to the proper compartment using special targeting signals

Question 18

Cotranslational Import

Answer 18

Proteins destined for the endomembrane system and export from the cell are transferred across the ER membrane as synthesis takes place

Question 19

Signal Recognition Particles

Answer 19

SRPs bind an ER signal sequence on a newly forming polypeptide and mediate cotranslational import into the ER

Question 20

Protein Disulfide Isomerase

Answer 20

Facilitate the formation of disulfide bonds to strengthen protein structure

Question 21

Unfolded Protein Response

Answer 21

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

Question 22

ERAD

Answer 22

ER-associated degradation, a mechanism which recognizes misfolded or unassembled proteins and exports them to the cytosol where they are degraded by proteasomes

Question 23

KDEL Sequence

Answer 23

A sequence (Lys-Asp-Glu-Leu) of a protein that is recognized by the Golgi which delivers the protein to the ER

Question 24

Electrophoresis

Answer 24

A group of techniques that use an electric field to separate charged molecules based on charge and size

Question 25

Western Blot

Answer 25

Immunoblot, technique used for the detection of specific proteins in a complex mixture