Func/dysfunc of protein processing

Question 1

which steps in translation require GTP hydrolysis

Answer 1

1) adding large su after preintiation complex finds AUG
2) loading second amino acyl tRNA on A site
3) translocating ribosome during elongation
4) termination to dissociate complex

Question 2

what are the four categories of mutations

Answer 2

1)Silent Mutation: does not change the amino acid
2)Missense Mutation: changes amino acid in the protein with
either no effect on protein function or a protein with vastly
different function.
3) Nonsense Mutation: codon changes into a stop codon causing
premature chain termination. Also called null mutation. Protein
either degraded or formed as a truncated version
4) Framesift Mutation: one or more nucleotides are deleted or
inserted into ORF. Out of frame causes change in the codon
sequence and consequently alteration in the amino acid
sequence (E.g., Duchenne Muscular Dystrophy, beta
thalassemia)

Question 3

what kind of mutation causes sickle cell anemia

Answer 3

-missense mutation
-Val (hydrophobic) for Glu
(negatively charged and
hydrophillic)
-Deformed erythrocytes have poor
oxygen capacity and tend to clog
capillaries,

Question 4

what mutation causes DMD

Answer 4

Large in-frame and out-of-frame (OOF) deletions to the
dystrophin gene causes little/no expression of dystrophin
protein

Question 5

what causes Becker muscular dystrophy

Answer 5

In-frame deletions result in expression of truncated forms

of dystrophin, milder form of DMD

Question 6

what does eukaryotic mRNA contain?

Answer 6

• Codons (present in coding region)
• 7-methylguanosine cap at the 5′ end
• Poly(A) tail at the 3′ end.

Question 7

what is the anticodon loop in tRNA

Answer 7

a set of 3
consecutive nucleotides that
pair with a complementary
codon in mRNA.

Question 8

what is 3’CCA terminal region in tRNA

Answer 8

binds the amino acid that
matches the corresponding
codon.

Question 9

how are amino acids activated

Answer 9

Catalyzed by enzymes called aminoacyl tRNA
synthetases
**uses ATP

Question 10

size of prokaryotic ribosome

Answer 10

50S and 30 S

Question 11

size of eukaryotic ribosome

Answer 11

60s and 40 s

Question 12

what are 3 steps of translation

Answer 12

1. Initiation: formation of mRNA, small ribosomal subunit
   and initiator tRNA pre-initiation complex
2. Elongation: activated AA attached to initiating Met by
   forming a peptide bond
3. Termination: peptide chain is released
   From the ribosomal complex

Question 13

what are polysomes?

Answer 13

• Clusters of ribosomes simultaneously
translating a single mRNA molecule
• Each synthesizing a polypeptide
• Makes protein synthesis more efficient

Question 14

streptomycin

Answer 14

binds to 30s subunit to disrupt initiation of translation

• interferes with binding of fmet tRNA
• interferes with association between 30s and 50s

Question 15

shiga toxin and ricin

Answer 15

binds to 60 s subunit to disrupt elongation (eu)

-blocks entry of aminoacyl-tRNA to ribosomal complex

Question 16

clindamycin and erythromycin

Answer 16

bind to 50s subunit to disrupt translocation of ribosome (prok)

Question 17

tetracycline

Answer 17

bind to 30 s subunit to disrupt elongation

-blocks entry of aminacyl-tRNA

Question 18

diphtheria toxin

Answer 18

inactivates eEF2-GTP and inhibits elongation (translocation) (eukaryotic)

Question 19

chloramphenicol

Answer 19

-inhibits peptidyl transferase (prok./mitochon)

Question 20

what is commonly used to treat purtussis

Answer 20

erythromycin

Question 21

cycloheximide

Answer 21

inhibits peptide transferase (euk)

Question 22

what are post translational modifications?

Answer 22

– Glycosylation
– Phosphorylation
– Disulfide bonds
– Acetylation

Question 23

what are two major pathways for protein sorting

Answer 23

1) cytoplasmic

2) secretory

Question 24

cytoplasmic pathway

Answer 24

– for proteins destined for cytosol, mitochondria, nucleus,
and peroxisomes
– Protein synthesis begins and ends on free ribosomes in
cytoplasm
– Absence or presence of certain translocation signals play
role in final targeting

Question 25

secretory pathway

Answer 25

– for proteins destined for ER, lysosomes, plasma membranes, or for secretion. – Translation begins on free ribosomes but terminates on ribosomes sent to ER – First 20 amino acid residues of the polypeptide has ER targeting signal sequences

Question 26

where does protein with no translocation signal go?

Answer 26

stay in cytoplasm

Question 27

where does protein with N terminal hydrophobic α-helix go?

Answer 27

mitochondria

Question 28

where does protein with KKKRK residues go

Answer 28

nucleus

Question 29

where does protein with SKL signal sequence go?

Answer 29

peroxisomes

Question 30

where does protein with N terminal +++ amino acids go?

Answer 30

ER target sequence

Question 31

where does protein with KDEL go?

Answer 31

stays in ER lumen

Question 32

where does protein with stop trsf (N terminal apolar region) go?

Answer 32

membranes (cell membrane)

Question 33

where does protein with Mann 6 P go?

Answer 33

lysosomes

Question 34

where does protein with tryptophan rich domains go

Answer 34

secretory vesicles

Question 35

I cell disease

Answer 35

- severe lysomal storage disease - tagging of proteins with mannose 6P= defective - High plasma levels of lysosomal enzymes

Question 36

chaperones

Answer 36

– Protect the protein and help fold into proper tertiary | structure

Question 37

chaperonins

Answer 37

barrel shaped compartments that admit unfolded proteins and catalyze their folding in an ATP-dependent manner

Question 38

Proteolytic Cleavage:

Answer 38

– converts inactive forms to active enzymes by unmasking active site (e.g., trypsinogen and chymotrypsinogen to trypsin and chymotrypsin, respectively) – Converts nascent precursor proteins to mature ones (e.g., proinsulin to insulin)

Question 39

post-translational covalent modifications

Answer 39

– Glycosylation – Phosphorylation – Disulfide bond formation – Acetylation

Question 40

Glycosylation

Answer 40

Covalently linked to sugar residues in the ER lumen

Question 41

O-glycosidic linkage

Answer 41

formed with hydroxyl groups of Ser or Thr residues

Question 42

N-glycosidic linkage

Answer 42

are always with Asparagine. Precursor sugar | transferred from phospho Dolichol

Question 43

Phosphorylation

Answer 43

Formation of an ester bond between phosphate and OH of an amino acid through activity of serine/threonine and tyrosine kinase

Question 44

Disulfide bond formation

Answer 44

• These binds form between thiol (SH) group of 2 cysteine residues • Formation and reorganization of these bonds occur in ER lumen • Facilitated by protein disulfide isomerases

Question 45

Acetylation

Answer 45

Proteins are typically acetylated on lysine residues. • Use Acetyl CoA as the acetyl group donor. • Histones are acetylated and deacetylated on their N terminal lysines – critical for gene regulation. • Reactions catalyzed by Histone acetyltransferase (HAT) or histone deacetylase (HDAC) enzymes. **ARE HERITABLE

Question 46

defect in Lysyl hydroxylases

Answer 46

collagen disorder- result in skin, bone and joint disorders such as Ehlers-Danlos Syndrome, Nevo syndrome, Bruck Syndrome, Epidermolysis Bullosa Simplex)

Question 47

Alzheimer’s disease (AD)

Answer 47

Amyloid precursor protein (APP) breaks down to form amyloid beta peptide (Aβ) • Misfolding/Aggregation of Aβ forms plaques in brain (extracellular) • Hyperphosphorylation of Tau (neurofibrillary tangles) (intracellular) • Mutations in APP and Tau cause Familial forms of AD. Brain aging is the common denominator for Sporadic form

Question 48

Parkinson’s disease (PD)

Answer 48

Aggregation of α-synuclein (AS) protein forms insoluble fibrils which deposit as Lewy bodies in dopaminergic neurons in substantia nigra • Results in selective death of these neurons • Symptoms due to reduced availability of dopamine. • Mutations in AS cause Familial forms of PD. Brain aging is the common denominator for the Sporadic form

Question 49

Huntington’s disease (HD)

Answer 49

• Mutation in Huntingtin gene results in expansion of CAG triplet repeats • Results in Polyglutamine repeats in abnormal HTT protein. Forms intramolecular H-bonds, which eventually misfold and aggregate. • Selective death of cells in basal ganglia cause the symptoms

Question 50

Creutzfeldt-Jakob disease (HD)

Answer 50

• Caused by misfolding of prion proteins • Transmissible – infection by misfolded proteins converts normal proteins to misfolded form • Belongs to Transmissible spongiform encephalopathies (TSEs). • Spongiform - appearance of infected brains, filled with holes and resemble sponges under a microscope.