Func/dysfunc of protein processing Flashcards
which steps in translation require GTP hydrolysis
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
what are the four categories of mutations
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)
what kind of mutation causes sickle cell anemia
-missense mutation
-Val (hydrophobic) for Glu
(negatively charged and
hydrophillic)
-Deformed erythrocytes have poor
oxygen capacity and tend to clog
capillaries,
what mutation causes DMD
Large in-frame and out-of-frame (OOF) deletions to the
dystrophin gene causes little/no expression of dystrophin
protein
what causes Becker muscular dystrophy
In-frame deletions result in expression of truncated forms
of dystrophin, milder form of DMD
what does eukaryotic mRNA contain?
- Codons (present in coding region)
- 7-methylguanosine cap at the 5′ end
- Poly(A) tail at the 3′ end.
what is the anticodon loop in tRNA
a set of 3
consecutive nucleotides that
pair with a complementary
codon in mRNA.
what is 3’CCA terminal region in tRNA
binds the amino acid that
matches the corresponding
codon.
how are amino acids activated
Catalyzed by enzymes called aminoacyl tRNA
synthetases
**uses ATP
size of prokaryotic ribosome
50S and 30 S
size of eukaryotic ribosome
60s and 40 s
what are 3 steps of translation
- Initiation: formation of mRNA, small ribosomal subunit
and initiator tRNA pre-initiation complex - Elongation: activated AA attached to initiating Met by
forming a peptide bond - Termination: peptide chain is released
From the ribosomal complex
what are polysomes?
• Clusters of ribosomes simultaneously
translating a single mRNA molecule
• Each synthesizing a polypeptide
• Makes protein synthesis more efficient
streptomycin
binds to 30s subunit to disrupt initiation of translation
- interferes with binding of fmet tRNA
- interferes with association between 30s and 50s
shiga toxin and ricin
binds to 60 s subunit to disrupt elongation (eu)
-blocks entry of aminoacyl-tRNA to ribosomal complex
clindamycin and erythromycin
bind to 50s subunit to disrupt translocation of ribosome (prok)
tetracycline
bind to 30 s subunit to disrupt elongation
-blocks entry of aminacyl-tRNA
diphtheria toxin
inactivates eEF2-GTP and inhibits elongation (translocation) (eukaryotic)
chloramphenicol
-inhibits peptidyl transferase (prok./mitochon)
what is commonly used to treat purtussis
erythromycin
cycloheximide
inhibits peptide transferase (euk)
what are post translational modifications?
– Glycosylation
– Phosphorylation
– Disulfide bonds
– Acetylation
what are two major pathways for protein sorting
1) cytoplasmic
2) secretory
cytoplasmic pathway
– 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
secretory pathway
– 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
where does protein with no translocation signal go?
stay in cytoplasm
where does protein with N terminal hydrophobic α-helix go?
mitochondria
where does protein with KKKRK residues go
nucleus
where does protein with SKL signal sequence go?
peroxisomes
where does protein with N terminal +++ amino acids go?
ER target sequence
where does protein with KDEL go?
stays in ER lumen
where does protein with stop trsf (N terminal apolar region) go?
membranes (cell membrane)
where does protein with Mann 6 P go?
lysosomes
where does protein with tryptophan rich domains go
secretory vesicles
I cell disease
- severe lysomal storage disease
- tagging of proteins with mannose 6P= defective
- High plasma levels of lysosomal enzymes
chaperones
– Protect the protein and help fold into proper tertiary
structure
chaperonins
barrel shaped
compartments that admit unfolded proteins and
catalyze their folding in an ATP-dependent manner
Proteolytic Cleavage:
– 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)
post-translational covalent modifications
– Glycosylation
– Phosphorylation
– Disulfide bond formation
– Acetylation
Glycosylation
Covalently linked to sugar residues in the ER lumen
O-glycosidic linkage
formed with hydroxyl groups of Ser or Thr residues
N-glycosidic linkage
are always with Asparagine. Precursor sugar
transferred from phospho Dolichol
Phosphorylation
Formation of an ester bond between
phosphate and OH of an amino acid
through activity of serine/threonine
and tyrosine kinase
Disulfide bond formation
• 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
Acetylation
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
defect in Lysyl hydroxylases
collagen disorder- result in skin, bone and joint disorders
such as Ehlers-Danlos Syndrome, Nevo syndrome, Bruck Syndrome,
Epidermolysis Bullosa Simplex)
Alzheimer’s disease (AD)
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
Parkinson’s disease (PD)
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
Huntington’s disease (HD)
• 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
Creutzfeldt-Jakob disease (HD)
• 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.
