Competitive Exams Botany Notes: Genetics: Translation
Translation: Synthesis of a linear polymer of amino acids from a linear polymer of nucleotides
Where does it occur?
- On the ribosome, a rRNA-protein complex that provides:
- a scaffold for mRNA
- sites for the docking of tRNA charged with a specific amino acid
- an enzyme for peptide bond synthesis between amino acids
- an enzyme for translocation of the mRNA through the ribosome
What is the function of tRNA?
Carrier of a specific amino acid during translation
What is the structure of tRNA?
- secondary structure has some base-pairing → cloverleaf
- information transfer at the anti-codon loop, complementary to the codon
- note the importance of H-bonds in the genetic code
- tertiary structure is L-shaped which places the amino acid far from the codon-anticodon site
- degeneracy of the code produces wobble
What is the genetic code?
- A sequence of 3 nucleotides forms a codon
- unambiguous, each codon specifies an amino acid, or start, or stop
- degenerate, some amino acids have multiple codons
- 2-letters often sufficient, specifiy hydrophobic and hydrophillic amino acids
What is the enzyme that charges tRNA with an amino acid?
- An aminoacyl-tRNA synthetase
- it has proof reading capabilities through the precise fit of amino acid and tRNA
- energy provided by ATP: Energy for the formation of aminoacyl-tRNA and for proof reading
- there are at least 20 synthetases, isoaccepting for the tRNA's coding for a single amino acid
What is the mechanism of translation?
- mRNA forms a large complex with the ribosome and protein factors
- together they guide in the correct aminoacyl-tRNA
- correct amino acid specified by codon-anticodon base pairing (H-bonds)
- protein factors have proof reading capability--energy provided by GTP
- an enzyme catalyzes polymerization of two amino acids, peptide (amide) bond formation between two amino acids
- an enzyme catalyzes movement of mRNA through the polymerization site: Energy provided by GTP
- mRNA translated from 5 ‘→ 3’ same direction as it is synthesized
- Reprise: Flow of information: Central dogma
- DNA → RNA → linear amino acid sequence → 3D-conformation of protein
- But some viruses have only RNA as their genome: No DNA.
How do they carry out information transfer? How do they get around the unidirectional flow of information in the central dogma?
- Use an enzyme called reverse transcriptase to transcribe RNA into DNA.
- Example: HIV, a retrovirus
- Then, use central dogma.
- For HIV:
- RNA → DNA → mRNA → linear amino acid sequence → 3D-conformation of protein.