Functions and Dysfunctions of protein processing Flashcards
component of Prokaryotic ribosome?
70S large subunit & 30S small subunit
50S
component of Eukaryotic ribosome?
60S large subunit & 40S subunit
80 S total
Three component of ribosomes?
Acceptor (A site)
Peptidyl (P Site)- Aminoacyl tRNA’s attach and add AA here
Empty (Exit Site)
What are Aminoacyl tRNAs? where do they attach to AA?
Complex of tRNA w/ AA
AA esterified to CCA terminal region at 3’ end of tRNA
CCA terminal region binds AAs that match corresponding codon
what is used to activate AA?
Aminoacyl tRNA synthetase, each AA has own
Charged with correct AA to maintain fidelity of protein synthesis
Two steps in AA activation?
Aminoacyl tRNA synTHETASE catalyzes addition of AMP to COOH end of AA
AA transferred to cognate tRNA
Three steps of AA synthesis?
Initiation
Elongation
Termination
Steps in initiation of translation?
In Eukaryotes initiation occurs in the Kozak sequence and an ATP-dependent mRNA scan
- First AA (MET) binds to P site on small ribosomal subunit, eukaryotic initiation factor (eIF2) binds to GTP
- mRNA slides across small subunit until AUG is found
- eIF2 and other initiation factors dissociate
- Large ribosomal subunit binds
- As ribosome complex slides across mRNA, the next Aminoacyl tRNA is recruited
Steps in elongation of translation?
Activated AA attached to initiating MET by
forming a peptide bond
- Loading of an Aminoacyl tRNA onto the ribosomes such that the anticodon bases pairs with codon positioned on “A Site”
- Prior to loading, the Aminoacyl tRNA is attached to a GTP-bound elongation factor
- Loading accompanied by GTP hydrolysis and release of factor from Aminoacyl tRNA
Steps in elongation of termination?
- Termination triggered by stop codons
- Stop codons are recognized by release factors (RFs)
- RFs bind to “A” ste and cleaves the ester bond between C terminus of polypeptide of tRNA
- GTP hydrolysis dissociates ribosomal complex
Streptomycin, what does it do?
binds to 30S subunit to disrupt initiation of translation
in prokaryotes
Clindamycin & Erythromycin, what do they do?
bind to 50S subunit to disrupt translocation of ribosome
in prokaryotes
Shiga Toxin & Ricin
binds to 60S subunit to disrupt elongation in eukaryotes
Diphtheria toxin
inactivates EF2-GTP and inhibits elongation
Tetracyclines?
bind to the 30S subunit to disrupt elongation
Blocks aminoacyl-tRNA to ribosomal complex
Puromycin?
causes premature chain termination in both prok/euks
Forms a puromyclated chain at 3’ end of aminoacylated-tRNAs which leads to premature chain release
Chloramphenicol
inhibits peptidyl transferase in prokaryotes
Cycloheximide
inhibits peptidyl transferase in eukaryotes
Sickle cell anemia, what does it do?
Change in 6th codon of GAG to GTG changing VAL(hydrophobic/ mutant) from GLU(negatively charged and hydrophilic/ wild type)
Deformed RBC have poor oxygen capacity and clog capillaries, restricting blood flow
missense
Duchenne muscular dystrophy, what is it do?
Large out-of-frame deletion that causes a non-functioning dystrophin gene
In-frame deletion results in expression of truncated forms of dystrophin
What are the two protein sorting pathways?
Cytoplasmic
Secretory
Where do proteins in te cytoplasmic sorting pathway go?
have no translocation signals
cytosol, mitochondria, nucleus, and peroxisomes
How does translation in the cytoplasmic pathway work?
Translation begins and ends on free ribosomes
N terminal hydrophobic A-helix signal ? where does it go?
peptide goes to mitochondria
LYS, ARG rich , where does it go?
nucleus
-SKL, where does it go?
peroxisome
How do proteins get to the mitochondria?
TIM and TOM
What are nuclear localization signals?
help large molecules go in nucleus
KKKKRK
Where do proteins in the secretory pathway go?
ER, lysosomes, plasma membrane, or for secretion
where does translation in the secretory pathway happen?
Translation begins on free ribosomes, but ends on ribosomes sent to ER
Whats special about secretory pathway structures?
First 20 AA residues of polypeptide has ER targeting signal sequences
15-60 AA at N terminus of protein
1-2 basic AA near N terminus
Followed by Extremely hydrophobic sequence on C terminus of the basic residues
How do proteins get into ER lumen
Signal recognition particle (SRP) binds to ER-targeting signal and ribosome during translation
Wraps itself around ribosome-mRNA-peptide complex, tethering it to ER membrane halting translation temporarily
Resumes when protein directed into ER lumen trough translocator
Enzymes on luminal side cleave the signal to release the protein
Protein undergoes post-translational modification in ER and/or golgi
KDEL?
ER lumen proteins
Mannose-6-phosphate?
for lysosomal proteins
ICELL DISEASE!!
tryptophan rich domains?
proteins for secretion
N terminal apolar regions?
proteins for membranes
I-cell disease, what is it?
Tagging of proteins with mannose 6P is broken
Severe form of lysosomal storage disease
High plasma levels of lysosomal enzymes
@6mo FTT & developmental delays and physical manifestations
Hepatomegaly, splenomegaly, occasional heart valve damage
Developmental delays, motor function delays, and more pronounced cognitive delays
Chaperonins? what do they do?
have barrel shaped compartments that admit unfolded proteins and catalyze their folding in an ATP-dependent manner
large proteins cant fold on their own
what is Glycosylation? significance?
Addition of sugar residues to proteins
O-linked: occurs through hydroxyl groups of serine / threonine residues
N-linked: occurs through asparagine residues (N-H bonds)
too much=cataracts
what is Phosphorylation ? significance?
Formation of an ester bond b/w phosphate and OH
Via serine/threonine and tyrosine kinase
Regulates enzyme activity and protein function
what is Disulfide bond formation? significance?
S-S bonds between cysteines, allows for tertiary structure for proteins
what is Acetylation ? significance?
Covalent linkage to amine, LYSINE
Use acetly cOa as donor
Catalyzed by HAT
Histone modifications are heritable
what is significance of Post-translational modifications of collagen?
Collagen most abundant structural protein in vertebrates
Lysines in collagen modified to form 5-hydroxylysine, further glycosylated with addition of glucose or galactose
Ascorbic acid essential for activity of lysl and prolyl hydroxylases
Defects in lysyl hydroxylases result in?
Ehlers-Danlos- overly flexible joints, walls of blood vessels, intestines or uterus may rupture
Alzheimers, what is it, how does it happen?
loss of memory, cognitive function
Amyloid beta peptide: plaques formed
Tau is hyperphosphorylated (TANGLES!)
APP and Tau cause familial forms of AD
PArkinsons, what is it , how does it happen?
fine motor control doesnt work
A synuclein undergoes deposition as Lewy bodies
Reduced availability of dopamine
Aging causes sporadic form
Huntington,what is it , how does it happen?
loss of movement, cognitive functions, psychiatric problems
Huntingtin gene mutation: CAG triplet repeats
Polyglutamine repeats
Death of cells in basal ganglia
Creuzfeld, what is it , how does it happen?
transmissable, behavioral changes, lack of coordination, mental deterioration
prions!
