Chapter 22: Translation Flashcards
What is Translation?
THe process of turning a transcript into a polypeptide chain using ribosomes
Where does protein synthesis occur?
At the Endoplasmic reticulum on ribosomes embedded in the lumen
How is the correct amino acid added to the polypeptide chain?
- tRNA has a complementary sequence to the mRNA
How is it possible there is 64 combinations of three letters but only 20 amino acids?
Some amino acids can be coded for by more than one codon. It is called degeneracy
What happens if a missense mutation occurs?
It is often a silence mutation because of the genetic code
What is the wobble position and what happens if there is a mutation
The wobble position is the third position in a codon and only results in a change of amino acid 25% of the time
What are the following mutations: Transition, silent, frame shift, and nonsense?
Transition: Pur replaced by Pur or Pyr by Pyr
Silent: When a mutation results in the same amino acid
Frame shift: when a nucleotide is added or deleted resulting in a shift of the codon reading
Non-sense: premature end
What is an open reading frame?
A reading frame without a termination codon among 50+ codons
What is a transversion?
- When a purine is replace by a pyrimidine
Ex.
Glu->Val = Sickle cell
If there is 61 possible codons but only 32 tRNAs, How can they be accomidated?
- Third Base of a codon(wobble) can form non-canonical base pair with its complement in tRNA
- Some tRNA contain Inosinate (I) which can bond with U C and A
What is an overlapping codon?
Read the codons in a non-overlapping format
What happens if sequence has an open reading frame?
- A frame without a termination codon 50< codons
- List all three possibilities for the section
- Open reading frame must have stop and start
What is involved in protein synthesis?
- Ribosome (rRNA and proteins)
- mRNA
- Charged tRNAs (aa activated)
- Initiation, Elongation, Release factors
What are the five stages of protein translation?
- **Activation of AA **: tRNA is aminoacetylated
- Initiation of translation: mRNA and aminoacylated tRNA bind to ribosome
- Elongation: cycle continues till stop codon
- Termination and ribosome recycling: mRNA and protein dissociate, ribosome recycled
- Folding and processing: catalyzed by enzymes
What does the tRNA accomplish?
- Activates an amino acid for peptide bond formation
- Ensures appropriate placement of amino acid in a growing chain
(uses Mg 2+ cofactor)
What is the general composition of the ribosome?
A smaller subunit and larger subunit
Which rRNA subunit of the ribosome catalyzes the peptide bond formation?
30S ribosome subunit
What does aminoacylation of tRNA do?
Attaches the correct amino acid to the corresponding tRNA
How do aminoacyl tRNA make sure they have the right amino acid?
Proofreading by aminoacyl-tRNA synthetase
Why is the interaction between amino-acyl tRNA synthetase and tRNA referred to as the second genetic code?
Because aminoacyl-tRNA synthetase are spcific for the amino acid and tRNA
Which amino acid is the first to begin translation in bact, mito, chloro?
- tRNA^fMet
- Different from methionine found in the middle of the polypeptide chain
What is the shiner dalgarno sequence? How does it help alignment of start codon and P site?
- 4-9 purine a few bp upstream of initiation codon
- Guide mRNA to the correct position on the 30s subunit
What are three steps in initiation?
- IF1, IF2-GTP, IF3 binds to 30S ribosomal subunit
- mRNA + fMet bind to shine-Dal aligning sequence, IF3 released
- GTP hydrolyzed helps bind 50S, release of IF1 + IF2 form 70S complex
Which AA is first to start translation in eukaryotes?
Methionine
What is the significance of circularization of euk mRNA in translation?
What are three steps of elongation? (EF-Tu and EF-G)
- Binding of incoming aminoacyl- tRNA: GTP hydrolyzed EF-Tu GDP released
- (EF-Tu recycled)
- Formation of peptide bond: cataylzed by 23S, amino group of tRNA in A attacks carbonyl tRNA in P site
- Translocation: Met moves from P to E causing the rest to follow and continue
- EF-G is GTP carrier that provides energy for codon shift
How do release factors help termination of translation?
- Hydrolyze terminal peptide-tRNA bond
- Release polypeptide and tRNA from ribosome
- Cause subunits of ribosome to dissociate so that initiation can begin again
What are polysomes?
When multiple ribosomes are translating an mRNA
What modifications to proteins undergo after termination?
Folding and
Know how antibiotics inhibit translation. Why don’t they inhibit eukaryotic transcription?
Antibiotics dont inhibit eukaryotic transcription because ribosomes are different shapes and sizes than that of bacteria.
