Translation

Question 1

How are amino acids encoded?

Answer 1

Three nucleotides (codon) encode amino acid

Question 2

What are some aspects of the codon?

Answer 2

1. Three nucleotides (“codon”) encode an amino acid.
2. The code is non-overlapping
3. The code has no “punctuation”, it is read sequentially & continuously.
4. The code has directionality; read 5’ –> 3’.
5. The code is degenerate. Amino acids are encoded by more than one codon.

Question 3

Describe tRNA general structure and its function

Answer 3

Function: serves as the adapter molecule between the codon (on
the mRNA) and its specified amino acid.

Structure:
1. 73-93 ribonucleotides
2. “L-shaped” (3-D), “Cloverleaf” pattern (2-D, as shown below)
3. Contain many “unusual” bases such as derivatives (methylated,
dimethylated, deaminated) of A, U, C, and G.
4. 5’ terminus is phosphorylated.
5. 3’-CCA terminus; “acceptor stem”, the site of amino acid attachment
6. Anticodon loop

Question 4

Describe tRNA attachment of amino acids

Answer 4

Catalyzed by aminoacyl-tRNA synthetases, which are specific for a given amino acid / tRNA.
a. Formation of aminoacyl-adenylate by the attachment of high-energy bond from ATP to the amino acid.
b. Transfer of aminoacyl group to specific tRNA matching the correct
amino acid to the correct tRNA (anti-codon).

Question 5

Steps of translation (after tRNA has anticodon)

Answer 5

1) tRNA with amino acid (usually Met) attaches to 30s ribosome subunit (21 proteins + 1 RNA); ribosome subunit is ribonucleoprotein (21 proteins + 1 RNA)
2) bind to 5’ of mRNA, proceed toward 3’ until start codon reached
3) 50s subunit (34 proteins + 2RNA) joins to form initiation complex
4) 4. Translation occurs in a 5’ –> 3’ on the mRNA.
5. Proteins are synthesized in an amino-to-carboxyl
terminus direction.