EXAM2_L17_TRANSLATION Flashcards
What 4 tools needed for translation?
- mRNA- coded instructions
- tRNA- decodes triple codons
- Aminoacyl-tRNA synthetases- attach AA’s to tRNAs w/ anti-codons
- Ribosomes- welder
What are the START and STOP codons?
What terminus does synthesis begin?
START- AUG (methionine)
STOP- [UGA,UAA,UAG]
-begins at Amino terminus (NH2)-
-first codon is ALWAYS methionine
What does degenerate mean talking about codons?
Redundant
- several codons can be used to code for the same AA.
What are the 4 mutations?
- Missense- base change= AA change
- Nonsense- base change= STOP
- Silent- base change= SAME AA
- Frameshift- insertion/deletion- can induce missense/nonsense/ REALLY BAD
Synthetases vs synthase
Synthetases- Require ATP for energy
Aminoacyl-tRNA synthetases
2 steps:
Adds AA’s to correct tRNAs
- link AA to tRNA w/ ATP
- tRNA bind to codon on RNA
Polysome or Polyribosome
mRNA can have multiple ribosomes translating it at any given time
2 Ribosomal subunits:
3 binding sites:
Where is peptide bond formed?
LARGE- forms peptide bonds
SMALL- binds mRNA & tRNA; initiation; decoding center
“APE”
A- aminoacyl-tRNA site (PEPTIDE BOND FORMS HERE)
P-peptidyl-tRNA site
E-exit site
3 types of Translation factors
how do you determine eukaryote/prokaryote TF?
- initiation factors (IFs)
- Elongation factors (EFs)
- Release factors (RFs)
eIF= eukaryotes (“e”- prefix)
IF=prokaryotes
INITIATION/PROKARYOTES:
What sequence used?
Where located?
Where does it bind?
Shine-Delgarno (SD) Sequence
-6-10 bp upstream of START
rRNA of small ribosome unit binds START codon in the P Site
INITIATION/EUKARYOTES-
How does mRNA find/attach ribosome?
What proteins used?
What is NOT found
5’ cap binds two eIF-4’s (cap binding proteins)
— (positions small ribosomal unit @ mRNA)
NO SD SEQUENCE
7 steps of eukaryotic initiation
- Charged initiator tRNA binds eIF2/GTP
- tRNA/eIF2/GTP binds to SMALL ribosomal subunit
- EIF4s bind 5’ end of mRNA
- small subunit binds to 5’ end of mRNA
- Small RS scans/finds AUG
- GTP hydrolyzed
- EIF2/GDP dissociates & Large RS joins
Remember eIF2 must release____ and bind new _____ before it can recruit another _______ to the _______.
Where is Met-tRNA deposited in both eukaryotic and prokaryotic translation?
eIF2 must release GDP,bind new GTP,before recruit another initiator tRNA to the small subunit
Met-tRNA binds P SITE and next AA’s bind A site
What is conserved between prokaryotes and eukaryotes?
elongation process
Eukaryotic Translation Elongation
3 Steps:
- Charged tRNA escorted by eEF1a/GTP to “A”SITE
- GTP hydrolyzed>eEF1a releases tRNA. eEF1a/GDP leaves.
- peptidyl transferase forms peptide bond between meth at Psite with incoming aminoacyl-tRNA at Asite.
4-step cycle of adding additional polypeptides
- translocation “TL” of large subunit
- TL of small subunit
- binding charged tRNA at A site
- Forming peptide bond
Eukaryotic Translation Termination: How is it initiated? is tRNA used? Where is stop codon bound? What bond is broken and where?
UGA, UAA, UAG= STOP CODONS
-Cell use eRF’s (release factors) that terminate synthesis
NO tRNA w/ STOP codons!!!
–> RF binds STOP codon at A site & hydrolyzes
tRNA:::polypeptide bond at the P Site.
-tRNA released, subunits and mRNA dissociate
How do antibiotics affect bacteria and not humans?
Prokaryotic and eukaryotic ribosomes and translation mechanisms are different and can be targets for inhibiting bacterial protein synthesis (killing bacteria not humans).
What drug inhibits initiation of protein synthesis?
What 4 drugs inhibit elongation?
-Streptomycin (inhibits initiation)
Inhibits Elongation:
- Tetracycline
- Chloramphenicol
- Erythromycin
- Puromycin
What are 3 types of post translational modifications?
Where and when can PTM’s happen?
- folding
- covalent modification
- binding
Nucleus, RER lumen, Cytosol
Anytime during proteins life
Alters side chains of AA’s after incorporated into protein
Laundry list of Modifications:
- protein folding
- proteolysis (zymogen)
- Covalent addition of functional groups/proteins:
- phosphorylation,
glycosylation
, methylation
, acetylation,
hydroxylation,
y-carboxylation,
ubiquitination
, add lipids
Glycosylation (2 types)
add sugar to protein> Glycoprotein
- N-linked glycosylation
- O-linked glycosylation
Methylation- What mediated by?
-add CH3
methyltransferases
demethylases
Acetylation
What added?
What 2 mediators?
reversible?
Adding acetyl COCH3 group
-Histone acetyltransferase (HAT)
-Histone deacetylases (HDAC)
REVERSIBLE!
Hydroxylation
adding OH (ie hydroxylation of collagen) vitC> scurvy
y-Carboxylation
What used? what made? What is an example that uses this?
PTM of glutamate to generate y-carboxyglutamate
-Uses y-glutamyl carboxylase and vitK as cofactor
ex: proteins involved in blood clotting cascade
Ubiquitination
What added? What mediated by? What used for?
Adding ubiquitin (Ub)
- 76-amino acid polypeptide to lysine residues of target protein
- mediated by ubiquitin ligase
- Ubiquitin is a tag for protein degredation
