(3) Functions and Dysfunctions of Protein Processing Flashcards
1
Q
What does AUG code for?
A
Met (M), START codon
2
Q
What are the three STOP codons?
A
UAA, UAG, UGA
3
Q
What is a codon?
A
A group of 3 consecutive nucleotides
4
Q
What are the four different categories of mutations?
A
- Silent mutation
- Missense mutation
- Nonsense mutation
- Frameshift mutation
5
Q
What happens with a silent mutation?
A
Does not change the amino acid
6
Q
What happens with a missense mutation?
A
Changes amino acid in the protein
7
Q
What happens with nonsense mutation?
A
Codon changes into a STOP codon;
protein either degraded or formed as a truncated version
8
Q
What happens with a frameshift mutation?
A
Change in the codon sequence and consequently alteration in the amino acid sequence
*MAJOR EXAMPLE: Duchenne Muscular Dystrophy
9
Q
CLINICAL CORRELATION:
Sickle Cell anemia:
A
MISSENSE mutation
- Substitutes Val (hydrophobic) for Glu (neg., hydrophilic)
- Deforms RBCs
- Deformed erythrocytes have poor oxygen capacity and clog capillaries
10
Q
CLINICAL CORRELATION:
Duchenne Muscular Dystrophy
A
FRAMESHIFT MUTATION
- Deletions in dystrophin gene
- Muscle wasting
- In-frame deletions result in expression of truncated forms of dystrophin: milder form BECKER muscular dystrophy
11
Q
What is the mRNA 5’ cap made of?
A
7 Methyl Guanosine at 5’ end
12
Q
What is the mRNA poly(A)tail?
A
Repeating A’s at the 3’ end
13
Q
What are tRNA?
A
“Transfer” RNAs
- Have binding site for both codons (in mRNA) and amino acid)
- Match amino acids to codons in mRNA
14
Q
What is the structure of tRNA?
A
Cloverleaf Shape:
ONE END=Anticodon loop
OTHER END= 3’ CCA Terminal region, binds amino acid that matches corresponding codon
15
Q
Aminoacyl tRNAs?
A
- complex of tRNA w/ AA
- catalyzed by AMINOACYL tRNA synthetases
- each tRNA charged with the correct AA to maintain fidelity of protein synthesis
16
Q
Ribosomes have ____ subunits
A
2; a large and small subunit
17
Q
What is the difference b/w prokaryotic and eukaryotic ribosomes?
A
Prokaryotic: 70S, large=50S, small=30S
Eukaryotic: 80S, large 60S, small=40S
18
Q
What are the three important sites of the ribosomal complex?
A
- Acceptor site (A) site
- Peptidyl (P) site
- Empty (E) exit site
19
Q
What are the three steps of translation?
A
- Initiation
- Elongation
- Termination
20
Q
Describe INITIATION of translation, elongation and termination via WHITEBOARD GO!
A
Did you do it? Hope so.
21
Q
What are polysomes?
A
- Clusters of ribosomes simultaneously translating a single mRNA molecule
- Makes protein synthesis more efficient
22
Q
What are the two major pathways for protein sorting?
A
- Cytoplasmic pathway
2. Secretory pathwy
23
Q
What is the function of the cytoplasmic pathway?
A
*For proteins destined for CYTOSOL, MITOC., NUCLEUS, and PEROXISOMES
24
Q
What is the function of the secretory pathway?
A
*For proteins destined for ER, LYSOSOMES, PMs, or for FAT SECRETION
25
Proteins that are targeted for the mitochondria have...
N-terminal hydrophobic alpha helix
26
Proteins that are signaled to the nucleus have...
Lots of Lys(K) and Arg(R)
27
Proteins that are signaled to the peroxisome have...
-SKL
28
Secretory pathway:
What is the ER targeting signal?
(+) charged aa sequence at N terminus
29
Secretory pathway:
What signals proteins to stay in RER?
K(Lysine)
D(Aspartic acid)
E(Glutamic Acid)
L(Leucine)
30
Secretory pathway
What signals protein to lysosome?
Mann 6-P
31
Secretory pathway:
What signals protein to secrete protein out into cytosol?
Trp-rich domain
32
Nuclear Import:
How do materials get into the nucleus?
- Imported via nuclear pores
- Small proteins able to pass through specific pores
- Large proteins >40kDa require a NUCLEAR LOCALIZATION SIGNALS
- FOUR continuous basic residues (Lys and Arg)
33
What is Alzheimer's disease?
Loss of memory, cognitive function, language
34
What is Parkinson's disease?
Impairment of fine motor control
35
What is Huntington's disease?
Loss of movement and cognitive functions and psychiatric problems
36
What is Crutzfeldt-Jacob disease?
Failing memory, behavioral changes, lack of coordination and visual disturbances. Late stages involve mental deterioration blindness, weakness of extremities and coma
37
What is the manifestation of Alzheimer's disease?
- Amyloid beta peptide (ABeta)
- Amyloid beta plaques in brain
- Hyperphosphorylation of Tau (neurofibrillary tangles
38
What is the manifestation of Parkinson's disease (PD)?
- Aggregation of alpha-synuclein (AS) --> deposit as LEWY bodies in dopaminergic neurons in substantia nigra
- Sx. due to reduced availability of dopamine
39
What is the manifestation of Huntington's disease (HD)?
- Mutation in Hungingtin gene; results in expansion of CAG triplet repeats
- Results in Polyglutamine repeats
- Selective death of cells in basal ganglia cause the sxs
40
What is the manifestation of Creutzfeldt-Jakob disease (HD)?
- Caused by misfolding of PRION proteins
- ****Transmissible
- Belongs to Transmissible spongiform encephalopathies (TSEs)
- SPONGIFORM
41
What is the central dogma of molecular biology?
Replication - Transcription - Translation
42
How are tRNAs activated?
AMINOACYL tRNA SYNTHETASE catalyzes the addition of AMP to COOH at the end of AA
43
Ribosome structures differ between prokaryotes and eukaryotes. How is this medically relevant?
Use antibiotics to target prokaryotic translational machinery
44
Translation occurs in the ___' to ____' direction
5' --> 3'
45
Translation initiation:
Where does it occur in prokaryotes?
Shine-Delgarno (SDG) sequence (AGGAGG)
46
Translation initiation:
Where does it occur in eukaryotes?
5' cap, 3' poly-A tail
47
Translation initiation:
All known mRNA molecules contain ...
signals that define the beginning of each encoded polypeptide chain
48
Translation initiation:
Where does the MET add?
Small SU of ribosomes on the P site
49
Translation initiation:
What initiation factors are included in prokaryotes vs eukaryotes?
Proks: IF
Euks: eLFs
50
Translation begins with the initiation codon _____
AUG (Methionine)
51
WHITEBOARD: Explain ELONGATION
GOOOOoooOOOoo
52
Elongation:
Activated aa attached to initiating methionine via a ______ bond
peptide
53
Elongation:
How is the polypeptide chain extended?
Loading of aminoacyl tRNA onto the ribosome so that the anticodon base pairs with codon positioned on A site
54
Elongation:
Prior to loading, the aminoacyl tRNA is attached to a ____ bound elongation factor
GTP
55
Elongation:
Loading accompanied by ____ and _____ from aminoacyl tRNA
GTP hydrolysis; release of factor
56
Elongation:
What is the peptide formation between aa in the A and P site catalyzed by?
Peptidyl transferase
57
Termination:
What is termination triggered by?
STOP CODONS
UAA, UAG, UGA
*Release factor binds to the A site
58
Termination:
Stop codons are recognized by:
Release factors (RFs)
59
Termination:
RFs bind to the _____ of the ribosome containing the stop codon and cleaves the ______
A site; ester bond b/w the C terminus of the polypeptide and the tRNA
60
Termination:
______ dissociates ribosomal complex
GTP Hydrolysis
61
What are the ribosome subunits for prokaryotes?
30S, 50S [70S]
62
What are the ribosome subunits for eukaryotes?
40S, 60S [80S]
63
Ribosome key components to remember:
What binds to the 30S subunit to disrupt initiation of translation?
Streptomycin
64
Ribosome key components to remember:
What binds to the 60S subunit to disrupt elongation?
Shiga Toxin
65
Ribosome key components to remember:
What does Streptomycin do?
Binds to the 30S subunit to disrupt initiation of translation
66
Ribosome key components to remember:
What does Shiga toxin do?
Binds to the 60S subunit to disrupt elongation
67
Ribosome key components to remember:
What two medications bind to the 50S subunit to disrupt translocation of the ribosome?
Clindamycin and erythomycin
68
Ribosome key components to remember:
What to Clindamycin and erythomycin do?
Bind to the 50S subunit to disrupt translocation of the ribosome
69
Ribosome key components to remember:
________ bind to the 30S subunit to disrupt elongation
Tetracyclines
70
Ribosome key components to remember:
What does Tetracycline do?
Binds to the 30S subunit to disrupt elongation
71
Ribosome key components to remember:
_________ is housed in the large subunits
Peptidyl transferase activity
72
Initiation requires hydrolysis of:
ONE GTP
73
Elongation requires hydrolysis of:
TWO GTP per amino acid added
74
Termination requires hydrolysis of:
ONE GTP
75
What does Diphtheria do?
Inactivates EF2-GTP and inhibits elongation
76
What are the (4) prokaryotic elongation inhibitors?
- Tetracycline
- Chloramphenicol
- Clindamycin/Erythromycin
- Streptomycin
77
What does Chloraphenicol do?
Inhibits peptidyl transferase
*Prok
78
What does Clindamycin/Erythromycin do?
Binds to large 50S SU blocking translocation of the ribosome
*Prok
79
What does Streptomycin do?
Binds to 30S subunit, interferes with the binding fmet-tRNA. Interferes with 30S subunit association with 50S subunit
*Prok
80
What are the four eukaryotic elongation inhibitors?
- Cycloheximide
- Diptheria toxin
- Shiga Toxin
81
What does Cycloheximide do?
Inhibits peptidyl transferase
*Euk
82
What does Diphtheria toxin do?
Inactivates GTP bound- eEF-2 interfering with ribosomal translocation
*Euk
83
What does Shiga toxin/Ricin do?
Binds to large 60S SU, blocking entry of aminoacyl tRNA to ribosomal complex
84
What does Puromycin do?
Causes premature chain termination
*elongation inhibitor
85
Cytoplasmic Pathway:
Proteins synthesized in this pathway have _________. Stay in cytoplasm
NO TRANSLOCATION SIGNALS
86
What are TIM and TOM?
Transporters in the mitochondrial membrane
TOM: Transporter in Outer membrane
TIM: Transporter in Inner membrane
87
Unfolded proteins are protected by binding to chaperones, in particular _______
Heat Shock Proteins 70 (HSP70)
88
What is the fx of signal recognition particle (SRP)?
Binds to the ER-targeting signal and the ribosome during translation;
SRP wraps itself around the ribosome-mRNA-peptide complex, halts translation temporarily
89
What are HSP60 and HSP70 examples of?
Chaperone proteins
90
Post-translational processing:
What is proteolytic cleavage?
Converts inactive forms to active enzymes by unmasking active site
Converts nascent precursor proteins to mature ones
91
What are the 4 post translational covalent modifications?
1. Glycosylation
2. Phosphorylation
3. Disulfide bond formation
4. Acetylation
92
Post Translational Modifications:
Acetylation:
What? Functional Group? Residue Affected?
Covalent linkage to amine
Amine (-NH3)
Lys
93
Post Translational Modifications:
Glycosylation
What? Functional Group? Residue Affected?
O-glycosylation(hydroxyl -OH) ; Ser, Thr
N-glycosylation (Acid Amide (-CONH2) ; Asn (Asparagine)
94
Post Translational Modifications:
Phosphorylation
What? Functional Group? Residue Affected?
Phosphate linked via esterification
Hydroxyl (OH)
Ser, Thr & Tyrosine Kinase
*regulated enzyme activity and protein function
95
Post Translational Modifications:
Disulfide bonds
What? Functional Group? Residue Affected?
Oxidation to achieve covalent linkage of cysteine residues
Sulfhydryl (-SH)
Cys
96
Phosphate removed by:
Phosphatases
97
Post Translational Modifications:
How are acetylation reactions catalyzed?
Histone acetyltransferases (HAT)
of
Histone deacetylase (HDAC)
98
CORRELATION BOX:
Sickle cell anemia
MISSENSE MUTATION THAT....
changes HYDROPHOBIC (VAL) to HYDROPHILIC (GLU)
- Aggregate and form rigid, rod-like structures
- Deforms RBCs
- Poor oxygen capacity, clog capillaries
99
CORRELATION BOX:
Duchenne muscular dystrophy (DMD)
- Large in-frame and out of frame deletions to the DYSTROPHIN GENE
- Muscle wasting
100
Initiation requires hydrolysis of _______
One GTP
101
Elongation requires hydrolysis of _______
2 GTP per amino acid added
102
Termination requires hydrolysis of _____
1 GTP
