Protein Synthesis and sorting

Question 1

What is Translation?

Answer 1

mRNA is decoded in a ribosome to produce a specific amino acid chain, or polypeptide

Question 2

What are the five major components are involved in translation?

Answer 2

Ribosomes, tRNA molecules, Aminoacyl-tRNA syntheses, mRNA molecules and Protein factors

Question 3

attach amino acids to their appropriate tRNA molecules

Answer 3

Aminoacyl-tRNA synthetases

Question 4

encode the amino acid sequence information

Answer 4

mRNA molecules

Question 5

Protein factors function as what?

Answer 5

facilitate some of the steps of translation

Question 6

Made of two dissociable subunits; large subunit and small subunit
Each subunit self-assembles from rRNA and proteins
come together only when binding mRNA

Answer 6

The bacterial Ribosome

Question 7

How many and what are the binding sites of a Ribosome?

Answer 7

3 tRNA (A aminoacytl site, P peptidl site, E Exit site)
mRNA binding site

Question 8

an adaptor that binds both a specific amino acid and the mRNA sequences that specify the amino acid

Answer 8

tRNA

Question 9

Once amino acid is attached to tRNA it is called

Answer 9

amino acyl tRNA

Question 10

Messenger RNA Brings what Information to the Ribosome

Answer 10

Polypeptide Coding

Question 11

mRNA is exported to the cytoplasm via binding to mRNA-binding protein that contains amino acid sequence …

Answer 11

nuclear export signals (NES) for transport through the nuclear pores

Question 12

Start codon where translation starts (N-terminus of polypeptide) and the stop codon is where

Answer 12

where translation ends (C-terminus of polypeptide (UAG, UAA, UGA)

Question 13

Initiation of translation in bacteria: Assembly of the 70S translation initiation complex occurs in ___ steps

Answer 13

3

Question 14

Step 1: initiation of translation

Answer 14

Three initiation factors (IF1, IF2 and IF3) and GTP bind to the small ribosomal subunit

Question 15

Step 2: initiation of translation

Answer 15

The initiator aminoacyl tRNA and mRNA are attached and bind to the small ribosomal unit
initiator tRNA is tRNA that carries an N formylmethionine→ tRNAfMet

Question 16

Step 3: initiation of translation

Answer 16

The large subunit joins the complex resulting 70S initiation complex and GTP is hydrolysed

Question 17

The start codon in eukaryotes and archaea specifies

Answer 17

methionine rather than N-formylmethionine

Question 18

After binding to mRNA, the small ribosomal subunit begins translation at the

Answer 18

first AUG triplet it encounters

Question 19

a common start sequence is ACCAUGG called a

Answer 19

Kozak sequence, the entire thing is a start codon

Question 20

Chain elongation involves what three steps

Answer 20

Aminoacyl tRNA binding
Peptide bond formation and
Translocation

Question 21

Termination: A stop codon goes to the A site and recognized by

Answer 21

Release factors

Question 22

releases the polypeptide

Answer 22

Hydrolysis

Question 23

Post translational processing

Answer 23

Must be chemically modified before they perform their normal functions

Question 24

In bacteria which two groups are removed during Post translational processing

Answer 24

N-formyl group and the Met are removed

Question 25

In eukaryotes which group is removed during Post translational processing

Answer 25

Met at the N-terminis

Question 26

Some enzymes synthesize as

Answer 26

inactive precursors, and must be activated by removal of specific sequences at one end or the other

Question 27

Internal stretches of amino acids are

Answer 27

removed to make an active protien

Question 28

Chemical modifications of individual amino acid groups by what three ways

Answer 28

methylation, phosphorylation or acetylation

Question 29

Ploypeptides may undergoto to prosthetic groups

Answer 29

glycosylation or binding

Question 30

• inteins are removed from a one or more polypeptides
• Resulting segments create a continuous polypeptide chain
• can be intramolecular or intermolecular

Answer 30

Protein Splicing

Question 31

What are the two types of protein targeting and sorting?

Answer 31

Cotranslational and Posttranslational import

Question 32

Posttranslational

Answer 32

after translation is completed, the polypeptides which are destined to cell organelles. Requires presence of special targeting signals

Question 33

movement of the polypeptide across or into the ER membrane is directly coupled to the translational process

Answer 33

Cotranslational import

Question 34

facilitate protein folding and assembly

Answer 34

Molecular chaperones

Question 35

Folding is accompanied with formation of disulfide bonds between

Answer 35

Cys in the pp chain

Question 36

Improperly folded proteins can activate

Answer 36

several types of quality control mechanisms

Question 37

Unfolded protein response (UPR)

Answer 37

detect misfolded proteins and enhance pathways for protein folding

Question 38

recognizes misfolded proteins and exports or ‘retranslocates’ them back to cytosol for degrdation

Answer 38

ER-associated degradation (ERAD)

Question 39

Proteins Released into the ER Lumen Are Routed to the

Answer 39

Golgi Complex, Secretory Vesicles, Lysosomes, or Back to the ER

Question 40

Most proteins synthesized on rough ER are

Answer 40

glycoproteins

Question 41

The initial glycosylation takes place in the __ as the polypeptide is being synthesized

Answer 41

ER

Question 42

Default pathway:

Soluble proteins move from the Golgi complex to

Answer 42

Secretory vesicles

Question 43

The other major group of polypeptides is destined to become

Answer 43

integral membrane proteins

Question 44

The completed polypeptide chain remains embedded in the ER membrane and then

Answer 44

can be targeted to its proper destination

Question 45

Posttranslational import into organelles that are

Answer 45

not part of the endomembrane system

Question 46

Proteins imported into organelles after completion of translation are synthesized on

Answer 46

free ribosomes and released into the cytosol