22: Protein Processing

Question 1

Cap and tail on mRNA

Answer 1

5’ cap: 7-methylguanosine

3’ Poly-A tail

Question 2

Structure of tRNA

Answer 2

Cloverleaf with two regions of unpaired nts - the anticodon loop + 3’ CCA terminal region

Question 3

Anticodon loop vs 3’ CCA terminal region

Answer 3

Anticodon loop: 3 nts that pair with a complementary codon in mRNA
3’ CCA terminal region: binds AA that matches the corresponding codonQ

Question 4

Aminoacyl tRNA

Answer 4

TRNA + its respective AA

Question 5

What enzyme activates AAs by adding them to tRNAs?

Answer 5

Aminoacyl tRNA synthetase

Question 6

Two steps in AA activation

Answer 6

1. Aminoacyl tRNA synthetase adds AMP to COOH end of AA

2. AA transferred to cognate tRNA

Question 7

Eukaryotic vs prokaryotic ribosome subunits

Answer 7

Euk: 40S + 66S
Pro: 30S + 50S

Question 8

Three sites on a ribosome

Answer 8

A: Acceptor: mRNA receives aminoacyl tRNA
P: Peptidyl: aminoacyl tRNA is attached
E: Exit: location occupied by empty tRNA before exiting ribosome

Question 9

Polysomes

Answer 9

Clusters of ribosomes simultaneously translating a single mRNA molecule

Question 10

In initiation, which part is assembled first?

Answer 10

Pre-initiation complex

Question 11

Where does the initiator tRNA attach to?

Answer 11

P site of small subunit

Question 12

What is bound to the initiator tRNA?

Answer 12

GTP

Question 13

What is the initiator tRNA?

Answer 13

Met-tRNA

Question 14

When does the large subunit add to the small one?

Answer 14

After tRNA-Met is already bound to P site

Question 15

Initiation codon

Answer 15

AUG (Met)

Question 16

Peptidyl transferase

Answer 16

Adds peptide bonds between AA in A and P sites

Question 17

Three stop codons

Answer 17

UAA, UAG, UGA

Question 18

RFs

Answer 18

Release factors; bind A site with stop codon and cleave ester bond stop the chain - forms COOH at the end of the polypeptide using water

Question 19

How does the ribosomal complex dissociate after use?

Answer 19

GTP hydrolysis

Question 20

Five prokaryotic translation inhibitors and what they bind to

Answer 20

1. Streptomycin: 30S
2. Clindamycin, erythromycin: 50S
3. Tetracycline: 30S
4. Chloramphenicol: peptidyl transferase

Question 21

Three functions of streptomycin

Answer 21

1. Intereferes with fMet-tRNA binding
2. Impairs initiation
3. 30S + 50S cant bind

Question 22

Tetracycline function

Answer 22

Blocks entry of aminoacyl-tRNA into ribosomal complex

Question 23

Four eukaryotic translation inhibitors and what they bind

Answer 23

1. Shiga toxin, Ricin: 60S
2. Diphtheria toxin: GTP-bound EF-2
3. Cyclohexamine: peptidyl transferase

Question 24

Shiga toxin and Ricin function

Answer 24

Block entry of aminoacyl-tRNA into ribosome

Question 25

One elongation inhibitor + function + eukaryotic or prokaryotic?

Answer 25

Puromycin: premature chain termination (in prokaryotes and eukaryotes)

Question 26

How does Puromycin work?

Answer 26

Resembles 3’ end of aminoacyl-tRNA -> enters A site and adds to growing chain, causing premature chain release

Question 27

What binds proteins on the way to mito to inhibit degradation?

Answer 27

HSP70

Question 28

Large vs small proteins going to the nucleus

Answer 28

Large need localization code, small ones can just pass through the nuclear envelope

Question 29

SRP

Answer 29

Signal recognition particle - wraps itself around ribosome/mRNA/peptide and connects it to ER - halts translation until part of peptide is inserted into the ER

Question 30

Only non-peptide protein localization code and for what location?

Answer 30

M6P for the lysosome

Question 31

Inclusion cell disease

Answer 31

Defective GlcNAc phosphotransferase -> no M6P added to proteins destined for the lysosomes

Question 32

Clinical symptoms of inclusion cell disease

Answer 32

Lysosomal enzymes secreted into blood -> failure to thrive and developmental delays by 6months, death usually by 7 years

Question 33

Chaperones vs chaperonins and examples of each

Answer 33

Chaperones: HSP70: help fold and protect proteins Chaperonins: HSP60: barrel where proteins can fold in an ATP-dependent manner

Question 34

Proteolytic cleavage

Answer 34

Turning inactive or nascent proteins into their active or mature forms

Question 35

Four common post-translational modifications

Answer 35

1. Phosphorylation 2. Disulfide bonds 3. Glycosylation 4. Acetylation

Question 36

What proteins get glycosylated vs acetylate?

Answer 36

Glycosylation: extracellular proteins Acetylation: histones

Question 37

Four residues affected by glycosylation

Answer 37

Ser, Thr, Asn, Gln

Question 38

Residue affected by acetylation

Answer 38

Lys

Question 39

Two mechanisms of glycosylation and on which residues they occur

Answer 39

O-linked: on hydroxyl groups of Ser or Thr | N-linked: on Asn or Gln

Question 40

Clinical issue with glycosylated proteins

Answer 40

Role in cataract formation

Question 41

How acetylation occurs

Answer 41

Uses acetyl coA as the acetyl donor group

Question 42

enzymes that add and remove acetyl groups

Answer 42

HAT: histone acetyltransferase: acetylate HDAC: histone deacylase: deacytlate

Question 43

Are genes active or inactive when acetylate?

Answer 43

Active