Translation is the process by which the genetic code carried by mRNA is used to direct the assembly of amino acids into proteins. It involves tRNA molecules that recognize codons on mRNA and bind specific amino acids. Ribosomes, composed of RNA and proteins, provide the site for protein synthesis and contain binding sites for mRNA and tRNA. Translation occurs in three stages - initiation, elongation, and termination - and proceeds from the 5' to 3' end of mRNA.

1. 7.4 Translation
Topic 7 Nucleic Acids & Proteins

2. Translation
 7.4.1 Explain that each tRNA molecule is recognized by a
tRNA-activating enzyme that binds a specific amino acid
to the tRNA, using ATP for energy.
 Each amino acid has a specific tRNA-activating enzyme
(the name aminoacyl-tRNA synthetase is not required).
The shape of tRNA and CCA at the 3’ end should be
included.
 7.4.2 Outline the structure of ribosomes, including protein
and RNA composition, large and small subunits, three
tRNA binding sites and mRNA binding sites.

3. Translation
 7.4.3 State that translation consists of initiation,
elongation, translocation and termination.
 7.4.4 State that translation occurs in a 5’→ 3’ direction.
 During translation, the ribosome moves along the mRNA
towards the 3’ end. The start codon is nearer to the 5’ end.
 7.4.5 Draw and label a diagram showing the structure of a
peptide bond between two amino acids.

4. Translation
 7.4.6 Explain the process of translation, including
ribosomes, polysomes, start codons and stop codons.
 Use of methionine for initiation, details of the T factor
and recall of actual stop codons are not required.
 7.4.7 State that free ribosomes synthesize proteins for use
primarily within the cell, and that bound ribosomes
synthesize proteins primarily for secretion or for
lysosomes.

5. The Structure of tRNA
 Translation involves reading the mRNA in sets of 3
nucleotides called codons.
 There are 61 codons (excluding 3 stop codons) for the 20
amino acids.
 This also means there are 61 anticodons and hence 61
different types of tRNA
 This is called the triplet code.
 Since there are only 20 amino acids, the triplet code
allows for degeneracy. (more than one tRNA per amino
acid.

6. The Structure of tRNA
 Transfer RNA (tRNA) has a
vital role in translating the
genetic code:
 All tRNA molecules have:
 A triplet of bases called the
anticodon,in a loop of 7
nucleotides.
 Two side loops.
 The base sequence CCA at the
3’ terminal, which forms a site
for attaching an amino acid.
 Sections that become double
stranded by complementary
base pairing.
These features allow all
tRNA molecules to bind to
sites on the ribosome and
mRNA.
Ref: Biology for the IB Diploma, Allott

7. tRNA Activating Enzymes
 The variable features of each tRNA molecule give them a distinctive 3
dimensional shape.
 This allows the correct amino acid to be attached to the 3’ terminal by an
enzyme called the tRNA activating enzyme.
 There are 20 different tRNA activating enzymes (one for each of the 20
amino acids).
 Each enzyme attaches one particular amino acids to all of the tRNA
molecules that have an anticodon corresponding to that amino acid.
 Energy from ATP is needed for the attachment of amino acids.
 The reaction of joining an amino acid to the tRNA is a condensation
reaction, producing water.

8. tRNA Activating Enzymes
Ref: IB Biology HL, OSC

9. Ribosome Structure
 Ribosomes have a complex
structure;
 Proteins and ribosomal RNA
molecules both form part of the
structure.
 There are 2 subunits, one large and
one small.
 There are binding sites for tRNA
on the surface of the ribosome
allow 2 tRNA molecules to bind at
the same time.
 There is a binding site for mRNA
on the surface of the ribosome
Ref: Biology for the IB Diploma, Allott

10. Translation
 Messenger RNA carries the information needed for making
polypeptides.
 The information is in a code form, which is decoded during
the the process of translation.
 Ribosomes, tRNA molecules and tRNA activating enzymes
are needed to carry out this decoding.
 There are 3 main stages in Translation:
 Initiation
 Elongation
 Termination
 Like DNA replication, translation occurs in a 5’  3’
direction.

11. Translation
- Initiation

12. Translation
- Elongation

13. Translation
-Termination

14. Polysomes
 Many polypeptides are needed in
large quantities
 eg: enzymes, antibodies, hormones.
 It would be energetically
inefficient for one mRNA to
synthesise a single polypeptide.
 Thus as a ribosome moves along
the mRNA another one can join
on behind it and so on like beads
on a string.
 Multiple copies of the polypeptide
can be synthesised rapidly.

15. Ribosomes
 The distribution of ribosomes within the cell depends
upon the function of the protein they make.
 Some ribosomes are found bound to the endoplasmic
reticulum while other float free within the cytoplasm.
 Bound ribosomes produce proteins which are to be
secreted out of the cell or for use in lysosomes.
 Free ribosomes synthesise proteins for use primarily
within the cell.

16. Translation
 7.4.1 Explain that each tRNA molecule is recognized by a
tRNA-activating enzyme that binds a specific amino acid
to the tRNA, using ATP for energy.
 Each amino acid has a specific tRNA-activating enzyme
(the name aminoacyl-tRNA synthetase is not required).
The shape of tRNA and CCA at the 3’ end should be
included.
 7.4.2 Outline the structure of ribosomes, including protein
and RNA composition, large and small subunits, three
tRNA binding sites and mRNA binding sites.

17. Translation
 7.4.3 State that translation consists of initiation,
elongation, translocation and termination.
 7.4.4 State that translation occurs in a 5’→ 3’ direction.
 During translation, the ribosome moves along the mRNA
towards the 3’ end. The start codon is nearer to the 5’ end.
 7.4.5 Draw and label a diagram showing the structure of a
peptide bond between two amino acids.

18. Translation
 7.4.6 Explain the process of translation, including
ribosomes, polysomes, start codons and stop codons.
 Use of methionine for initiation, details of the T factor
and recall of actual stop codons are not required.
 7.4.7 State that free ribosomes synthesize proteins for use
primarily within the cell, and that bound ribosomes
synthesize proteins primarily for secretion or for
lysosomes.