1. Higher Biology
Unit 1:
1.3 Translation

2. Learning Intentions
To be able to describe the stages involved in translation
To be able to explain the following terms: codon, polypeptide, tRNA, anti codon, attachment site

3. Success Criteria I can identify and explain the stages of translation
I can explain the following terms: codon, polypeptide, tRNA, anti codon, attachment site

4. Translation
Translation is the formation of a polypeptide (protein) using the mature mRNA transcript
The mRNA code is read in series of 3 bases (triplet of bases) known as codons
Each codon is complementary to a triplet of bases on the original DNA strand

5. tRNA
Another RNA molecule known as transfer RNA (tRNA) is found in the cytoplasm and is involved in translation
tRNA is folded into a 3D structure and held together by hydrogen bonds

7. tRNA structure
tRNA is composed of a single chain of nucleotides, an amino acid attachment site and an anticodon region
The anticodon is a triplet of bases complementary to the mRNA codon
Each anticodon corresponds to a specific amino acid on the attachment site

8. tRNA
tRNA picks up amino acids in the cytoplasm and then carries them to the ribosome to match with the mRNA codons

9. Ribosomes
Ribosomes are organelles found in the cytoplasm and attached to other organelles in cells
They contain ribosomal RNA and enzymes required for protein synthesis

10. Ribosome Structure

11. Site P – holds the tRNA carrying the growing polypeptide chain
Site P – holds the tRNA carrying the growing polypeptide chain. Site A – holds the tRNA carrying the next amino acid to be joined to the chain.
Site E – releases the empty tRNA once it has dropped off its amino acid.

12. Ribosome
The function of ribosomes is to bring tRNA into contact with mRNA
This allows the complementary codons and anticodons to form bonds
As the codons and anticodons bond, peptide bonds are formed between amino acids on the tRNA molecules
This forms a chain of bonded amino acids known as a polypeptide

14. The translation process
1. The ribosome binds to the 5’ end of the mRNA so that the start codon (AUG) is in site P. 2. Next a tRNA carrying the amino acid methionine becomes attached to site P.

15. 3. The mRNA codon at site A bonds complementary anticodon on the appropriate tRNA bearing the correct amino acid.
4. A peptide bond then forms between these two amino acids.
5. The ribosome then moves along one codon.
6. The tRNA from Site P is move to Site E and released.
7. Steps 3-6 then repeat until it reaches a stop codon.

16. Professor Dave will explain…

17. Success Criteria I can identify and explain the stages of translation
I can explain the following terms: codon, polypeptide, tRNA, anti codon, attachment site