Translation Flashcards
1
Q
2 Important components for translation
A
- mRNA
2. tRNA (transferRNA)
2
Q
tRNA (transferRNA)
Two key roles:
A
- reads mRNA codons correctly
2. transfers amino acids to the growing peptide chain
3
Q
Codons
A
- Series of three nucleotides in mRNA that code for an amino acid
4
Q
Ribosomes
2 points
A
- site of translation.
- After tRNA has read mRNA codons and delivered amino acids, the ribosome catalyzes the formation of “peptide bonds” between amino acids
5
Q
3 stages of translation
A
Initiation
Elongation
Termination
6
Q
Initiation
3 points
A
- Ribosome small subunit attaches to mRNA. moves along mRNA until it reaches the start codon (AUG: methionine)
- Methione charged tRNA binds to the start codon.
- Ribosome large subunit joins = initiation complex
7
Q
Initiation
What is the recognition sequence for binding of ribosome small subunit
2 points
A
- Prokaryotes: AGGAGG
2. Eukaryotes GTP cap
8
Q
Initiation
ribosome large subunit 3 sites
3 points
A
- A (Anticodon)
- P (Polypeptide)
- E (exit)
9
Q
Elongation
peptide bond formation
Step 1
A
- Peptidyl transferase
- breaks bonds between amino acid and tRNA.
- makes peptide bonds between amino acids
10
Q
Elongation
step 2
2 points
A
- peptidyl transferase Breaks bond between amino acid and tRNA in P (polypeptide) site
- Form bond between released amino acid and amino acid attached to tRNA in A (anticodon) site
- Free tRNA (with amino acid released) is moved to E site and released as the ribosome moves along to the next codon
- Free A site attracts complementary charged anticodon for the codon in the A site - process repeats
11
Q
Termination
A
- release factor disconnects the polypeptide from the tRNA in the P site
- The remaining components (mRNA, ribosome subunits) separate
12
Q
Start and Stop signals (Signals that start and stop translation)
A
1. Initiation Start codon (AUG) in the mRNA
2. Termination Stop codon (UAA, UAG, or UGA) in the mRNA
13
Q
After translation: Post translational modifications
A
- Most proteins are not identical to the polypeptide chains
- Polypeptide chains are usually modified in any of several ways
- This is essential to the final function of the protein
14
Q
Post-translational modifications
Proteolysis:
5 points
A
- cutting the polypeptide allowing the fragments to fold into different shapes
- E.g. Cutting the signal sequence from the growing polypeptide chain in the ER… Protein might move back out of the ER (through the membrane channel) if signal sequence not cut off.
- Some proteins made from polypeptides – that are cut into final products (active proteins) by proteases
- Proteases are essential to some viruses (HIV) – large viral polypeptides can’t fold properly without the cut
- Some drugs for AIDS work by inhibiting HIV protease, preventing formation of proteins needed for viral reproduction
15
Q
Post-translational modifications
Glycosylation:
5 points
A
- addition of sugars to polypeptide, important for targeting and recognition
- Addition of sugars to proteins, forming glycoproteins
- Catalyzed by enzymes in the ER and Golgi apparatus
- E.g. Essential for directing proteins to lysosomes
- E.g. Important in the conformation of proteins and their recognition functions at the cell surface
