The life and death of proteins Flashcards
What is the enzyme attaches an amino acid to a tRNA?
Amino-acyl-tRNA synthetases
True or false: the reaction of amino-acyl-tRNA synthetase is an ATP dependent one
True
Where does protein synthesis occur?
In the cytosol
True or false: mitochondria have their own ribosomes?
True
What are ribosomes composed of?
1-3 rRNA molecules, as well as dozens of proteins.
Why is the fact that bacterial ribosomes differ greatly from human ribosomes important?
Targeting by Abx
What is the structure responsible for rRNA synthesis?
Nucleolus
Where are ribosomal subunits made? How do they get rRNAs that are in the nucleus?
Cytosol
Transported in, then back out of the nucleus when they get their rRNA
Initiation requires what three components?
Ribosomal subunit
an mRNA
a bound tRNA
What is the aminoacid that usually begins every polypeptide?
M
What are the five steps of ribosomal initiation?
- elF2a is activated by binding GTP
- elf2a-GTP binds a Meth-tRNA to form a ternerary complex
- The ternerary complex binds a small ribosomal subunit
- mRNA binds the ternerary complex
- A large ribosomal subunit binds, and elF2a is hydrolyzed.
What is EF-1 used for?
(elongation factor 1) helps the additional tRNA molecules bind to the M-tRNA initially-no longer needed after second tRNA has been added
What is EF-2 used for?
Used to move the ribosome one codon further on the DNA chain
What is selenocysteine? What is its purpose in translation?
A rare aminoacid that will is coded for by stop codons.
How does translation of a protein get terminated (Hint: there are four steps, last one is the separation of the ribosome).
- stop site on mRNA is reached
- eRF binds to the A site
- eRF-bound GTP hydrolyzed and peptide is release
- Ribosome separates
What is the action of streptomycin?
Binds to the small subunit of prokaryotic ribosomes and inhibits initiation.
What is the action of Neomycin and gentamicin?
Bind to prokaryotic ribosomes and cause mistranslation
What is the action of tetracycline?
Blocks prokaryotic, ribosomes’ A site.
What is the action of chloramphenicol?
Prevents prokaryotic peptidyl bond formation
What is the action of Ricin?
it is a glycosidase that removes adenine bases from rRNA
What is the action of diptheria toxin?
inactivates EF-2 to prevent elongation
What are the two ways that translation is regulated?
- Preventing recognition of the start codon by binding earlier in the mRNA
- Phosphorylating initiation factors (e.g. eIF-2)
What are chaparones?
Proteins that aid in the correct folding of other polypeptides
What is Charcot Marie tooth disease?
A protein folding disorder caused by mutations in HSPs (heat shock proteins)
Proteins destined for secretion out of the cell are produced where?
In the ER
What are the steps involved in the synthesis of exported proteins (4)?
- Signal sequence emerges from the ribosome
- A signal recognition protein (SRP) binds the singal sequence and the complex moves to the ER
- SRP dissociates and translation goes through the ER
- Signal peptidase cleaves the signal peptide
When there are too many unfolded proteins in the ER due to excess cholesterol or starvation, the cell has three ways of dealing with this. What are they?
- Inhibit protein translation
- Introduce chaperones
- Apoptosis
Why is the glycosylation of proteins important? (2 reasons)
- Change physical characteristics (Increases solubility, stability, size)
- Recognition sites
Where does glycosylation being and end? What class of enzymes catalze this reaction?
Starts in the ER, ends in the golgi
Glycosyltransferases (SUPER specific)
What is the amino acid involved in N-link glyslyation?
N
What are the three steps involved in the syntesis of N-linked oligosaccahides?
- Synthesis of a dolichol phosphate in the ER
- Transfer of a universal oligosaccharide to the nascent polypeptide chain
- Specific modification of the universal oligosaccharide by the Golgi
The Golgi produces two types of N-link polysaccharides. What are they?
High mannose type Complex type (contain mannose and other carbs)
O-linked glycosylation occurs only on folded or unfolded proteins?
Only on fully folded