Translation Flashcards
(1) Describe the structure of the ribosome in eukaryotic cells. (2) Where does the catalytic
activity reside? (3) What is this catalytic activity? (4) Where would you find ribosomes in
eukaryotic cells? (5) In prokaryotic cells?
(1)
- Complex made from ribosomal proteins and ribosomal RNAs (rRNAs)
-Large subunit and small subunit
(2) Large subunit
(3) Pepetidyl transferase (catalyzes formation of peptide bonds that link amino acids together)
(4) 1. Cytosol 2. ER
(5) Cytosol
(1) How many tRNAs are possible? (2) Codons? (3) Anti-codons? (4) What is the ‘wobble base’?
- 61
- 64
- 64
4.
(1) What is the role of aminoacyl-tRNA synthetases in translation? (2) How many are there?
(1) Enzymes that attache correct each amino acid to tRNA molecule
(2) 20 (one for each amino acid)
What are some major differences among translational initiation, elongation and
termination? Hint: describe interactions at the A, P, E sites in each case.
Initiation:
- Initiator tRNA carries methionine and is loaded into P site of small subunit
- Small subunit bind mRNA on 5’ cap
- large subunit binds assembly (initiation complex complete)
Elongation:
1. Translocation happens in large subunit then to small subunit
2. Carboxyl end of polypeptide chain is uncoupled from tRNA at P site and joined to amino group of amino acid linked to tRNA at A site
3.
4. Empt tRNA ejected (E site)
Termination:
- Release factors bind to stop codon that reaches A site
- Peptidyl transferase catalyzes addition of a water molecules instead of an amino acid
- Ribosome dissociates
Which end of a protein is made first? Each cycle of translation adds an amino acid to which end of the polypeptide chain?
(1) N-terminus
(2) C-terminus
(1) What is the proteosome? (2) Where can it be found it the cell? (3) How does it function?
(1) Proteasome - protein machine that degrades proteins
(2) Cytosol and nucleus
(3)
- Stopper of proteasome recognize proteins marked by polyubiquitin chain
- Central cylinder formed from proteases chop protein to pieces
- Only accept things polyubiquinated (act on protein marked by covalent attachment of ubiquitin)
In general, what are the four major steps in translation?
- tRNA binding
- Peptide bond formation
- Large subunit translocation
- Small subunit translocation
In detail, describe the events that occur in the four major steps of translation.
- 2.
3.
4.
(1) What are proteases? (2) Where are they located and why?
(1) break down proteins no longer needed (for regulatory reasons or because of age/damage)
(2) Contained in proteasome (keeps them away from “healthy” proteins in cell)
What is translation?
Conversion of information from RNA into protein
What is a codon?
group of three nucleotides
What determines the proper open reading frame?
- Start codon
- No interrupting STOP codons
(1) What are the functions of tRNAs? (2) What are the two ends?
(1)
Adaptors that recognize and bind to codon and amino acid
(2)
1. 3’ end (where amino acid attaches)
- Anticodon - set of three nucleotides that pairs with complementary codon in mRNA (reverse complement of codon)
What is the codon of the following anticodon: GAA?
UUC
mRNA message is decoded on __________.
Ribosomes
What is charging?
Process in which each synthetase couples a particular amino acid to proper tRNA
What are ribozymes? Give an example.
RNA molecules that posses catalytic activity (e.g., ribosomes)
What are polyribosomes?
Large assemblies made up of ribosomes along a single mRNA molecule (multiple ribosomes working simultaneously on a single mRNA)
Why is protein production so much more rapid in bacteria compared to eukaryotes?
Can polyribosomes exist in both eukaryotes and prokaryotes? Why or why not?
No - no cap or poly A in prokaryotes
What are the functions of the large subunit and small subunit of the ribosome?
Large subunit - catalyzes formation of peptide bonds that covalently link amino acids together
Small subunit - where mRNA binds; matches tRNAs to codons of mRNA
The large subunit and small subunit only come together when?
Small subunit has bound an mRNA
What are the three binding sites of the ribosome? Explain what happens during each.
- A site - tRNA adds an amino acid to growing peptide chain
- P site - amino acid is linked to growing peptide chain
- E site - where empty tRNA is moved to before being ejected
What is translocation?
Movement from small to large subunit
Why is the rate of translation faster in prokaryotes than in eukaryotes?
Coupling
Which part(s) of the codon are most important. Which one(s) are not?
First 2 nucleotides most important
Third nucleotide is irrelevant in some case
