Biochemistry-12
Basic Principles Of Biochemistry with Any at University of Pennsylvania School of Veterinary Medicine
About this deck
By: Sharon Williams
Created: 2011-09-16
Size: 18 flashcards
Views: 13
Created: 2011-09-16
Size: 18 flashcards
Views: 13
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translation
conversion of nucelic acid language into protein language
(5' --> 3' of RNA.... amino to carboxy terminal end of protein)
protein escapes thru pore in ribosome surface
takes place in ribosomes (large structures) composed of
over 100 proteins and numerous RNA molecules
codons
genetic code is in triplet
3 nucleotides code for one aa
the genetic code is degenerate (ie. multiple codons encode for the same aa)
64 codons in teh genetic code
3 codons for termination
61 codons for amino acids
t-RNA properties
-single stranded RNA of 73-93 nucs
-many unusual or modified bases (7-15 per molecule)
-5' end is phosphorylated and is usually G
-3' end is usually CCA with a 3'OH
-1/2 of the nucleotides in tRNA are intramolecularly base paired
-all can be drawn as 2-d clover leaves
-actual 3D structure is L-shaped
-5 regions are not base paired
*3' CCA
*TYC (pseudo-uridine) loop
*extra arm of variable size
*anticodon loop
*dihydrouridine loop
-anticodone loop has 7 nucleotides
-each tRNA is covalently att
attachment of amino acids to tRNA
amino acids are attached to the hydroxyl (OH) of tRNA's ribose on the 3' end
- aa tRNA synthetases take a specific aa and covalently attach it to the appropriate tRNA with specific recognition
aa + ATP --> AA-pRibose-Adenine + Ppi
AA-pRibose-Adenine + tRNA --> aminoacyl-tRNA + AMP
tRNA
translator/interpreter molecule that reads both genetic lang. of nucleotides and the lang of aa
how do the amino acids get on the right tRNA molecule?
amino aceyl tRNA synthases
Synthase binds ATP and the appropriate aa to form aminoacyl-adenylate (release pyrophosphate Ppi)
The newly formed complex binds to the corresponding tRNA molecule, and the aa is transferred from the aa-AMP to 3’ OH of tRNA
-some mediate a proofreading reaction also… if the tRNA is found to be improperly charged, the aminoacyl-tRNA bond is hydrolyzed
Stop Codons
3 codons are stop codons, which terminate translation by binding to release factors tather than to tRNA molecules.
wobble base pair hypothesis
Each codon requires a tRNA molecule with a complemetary anticodon. There are 61 available mRNA codons but only 45 species of tRNA (usually). Wobble Base Pairs hypothesizes that the 5’ base on the anticodon (which binds to the 3’ base on the mRNA) is not as spatially confined as the other two bases and thus could have non-standard base pairing.
guanine uracil
inosine uracil
inosine adenine
inosine cytosine
stability is comprable to a normal base pair
difference btwn bacterial and eukaryotic ribosomes
Eukaryotic ribosomes are either free in the cytoplasm or attached to the outer membrane of the endoplasmic reticulum
In prokaryotes (bacteria) the ribosomes are only free forms in the cytoplams.
Eukaryotic ribosomes are much larger then prokaryotic ribosomes.
(while euk has transcription in nucleus and translation in cytosol, prok have both in cytosol, no nucleus)
3 step plan for translation
initiaion
elongation
termination
initiation in bacteria
1. mRNA must attacht to ribosome: shine dalgarno seq (10 nucs) in mRNA hybridizes with the rRNA, positioning mRNA for translation
2. IF1, IF2 and IF3 complex with the 30s Ribosomal subunit
3. first tRNA has a methionine grp with a formylated Nterminal(fMet)
4. IF2 binds GTP: inducing confomrational change allowing mRNA and initiator tRNA to join complex... IF3 is displaced
5. release of IF3 allows the 50s Sununit to bind... GTP bound to IF2 is hydrolyzed-- resulting in release of IF1 and IF2
elongation in bacteria
Et Tu Bruta or EF-Tu
On Ribosome:
P(peptidyl) site
A (aminoacyl) site
(there is also an E [exit] site)
EF-Tu delivers Aminoacyl-tRNA to the ribosome (GTP-->GDP +Pi)
-takes any RNA until it finds the one that fits (1st is AUG- methionine)
EF-Tu delivers next aa-tRNA
Peptide-bond formation btwn the amino acids is catalyzed by Peptidyl Transferase
-uncharged first tRNA is released
translocation: EF-G shifts mRNA over 3 spaces/one codon (GTP--> GDP+Pi)
termination
termination codons: UAA, UGA, UAG
no codon sequence in tRNA is complementary
release factors (proteins) recognize and bind to the termination codons
factors activate peptidyl transferase to hydrolize the peptide from the tRNA at the Psite
protein product leaves ribosome followed by tRNA and mRNA
quality control
nonsense mediated decay (NMD) and Non-stop mRNA decay
Eukaryotic translation differences
ribosomes are larger in euaryotes (more proteins and rna)
initiator aa is Met, not N-Formyl Met
mechanism of ribosome binding is different
-mRNA cap is recognized by euk IF and attaches small ribosomal subunit to RNA
mechanism of finding initiation codon is different
-no shine dalgarno sequence
-ribosome moves up and down mRNA until it finds the AUG
consensus AUG is GCCA/GCCAUGG
euks are usually moncistronic (in prokaryotes you can have 2 diff protein encoding portions of same mRNA)
viral strategies of translation
ciruses try to take over translation machinery to preferentially express own RNA
1. internal ribosome entry sites: do not need cap or initiation factors to bind to ribosome
2. proteolysis of elF4G: some viruses will degrade cellular/host initiation factors
3. removal of 5'cap from mRNA
protein processing and post translational modifications
- phosphrylatin
- glycosylation
- farnesylation
- proteolytic cleavage
- protein folding (chaperones)
- multimeric complexes (monomer, heteromers, dimers, etc.)
protein sorting and trafficking
- signal sequence and insertion into ER
- signals for export from ER
- mitochondrial import signals
- nuclear import signals
- sequestration in the cytoplasm
About this deck
By: Sharon Williams
Created: 2011-09-16
Size: 18 flashcards
Views: 13
Created: 2011-09-16
Size: 18 flashcards
Views: 13
About StudyBlue
STUDYBLUE makes things that make you better at school.
Things like online flashcards with photos and audio.
Things like personalized quizzes and friendly reminders about when (and what) to study next.
Think of it as a digital backpack™: access to all of your study materials online and on your phone.
STUDYBLUE exists to make studying efficient and effective for every student, for free. Join us.
“I have used this website for three exams, and I see a huge difference in my test results.”
Naj
Naj