Protein Synthesis and sorting Flashcards Preview

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Flashcards in Protein Synthesis and sorting Deck (46):
1

What is Translation?

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

2

What are the five major components are involved in translation?

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

3

attach amino acids to their appropriate tRNA molecules

Aminoacyl-tRNA synthetases

4

encode the amino acid sequence information

mRNA molecules

5

Protein factors function as what?

facilitate some of the steps of translation

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

The bacterial Ribosome

7

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

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

8

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

tRNA

9

Once amino acid is attached to tRNA it is called

amino acyl tRNA

10

Messenger RNA Brings what Information to the Ribosome

Polypeptide Coding

11

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

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

12

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

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

13

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

3

14

Step 1: initiation of translation

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

15

Step 2: initiation of translation

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

16

Step 3: initiation of translation

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

17

The start codon in eukaryotes and archaea specifies

methionine rather than N-formylmethionine

18

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

first AUG triplet it encounters

19

a common start sequence is ACCAUGG called a

Kozak sequence, the entire thing is a start codon

20

Chain elongation involves what three steps

Aminoacyl tRNA binding
Peptide bond formation and
Translocation

21

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

Release factors

22

releases the polypeptide

Hydrolysis

23

Post translational processing

Must be chemically modified before they perform their normal functions

24

In bacteria which two groups are removed during Post translational processing

N-formyl group and the Met are removed

25

In eukaryotes which group is removed during Post translational processing

Met at the N-terminis

26

Some enzymes synthesize as

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

27

Internal stretches of amino acids are

removed to make an active protien

28

Chemical modifications of individual amino acid groups by what three ways

methylation, phosphorylation or acetylation

29

Ploypeptides may undergoto to prosthetic groups

glycosylation or binding

30

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

Protein Splicing

31

What are the two types of protein targeting and sorting?

Cotranslational and Posttranslational import

32

Posttranslational

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

33

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

Cotranslational import

34

facilitate protein folding and assembly

Molecular chaperones

35

Folding is accompanied with formation of disulfide bonds between

Cys in the pp chain

36

Improperly folded proteins can activate

several types of quality control mechanisms

37

Unfolded protein response (UPR)

detect misfolded proteins and enhance pathways for protein folding

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

ER-associated degradation (ERAD)

39

Proteins Released into the ER Lumen Are Routed to the

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

40

Most proteins synthesized on rough ER are

glycoproteins

41

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

ER

42

Default pathway:
Soluble proteins move from the Golgi complex to

Secretory vesicles

43

The other major group of polypeptides is destined to become

integral membrane proteins

44

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

can be targeted to its proper destination

45

Posttranslational import into organelles that are

not part of the endomembrane system

46

Proteins imported into organelles after completion of translation are synthesized on

free ribosomes and released into the cytosol