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.