1. Gene Expression and Protein Synthesis
Higher Human Biology
Subtopic 3 (b)

2. Learning Intentions Describe the structure of tRNA
Describe the process of Translation
Discuss alternative splicing and
modification

3. Translation
Translation is the synthesis of a protein in the form of a polypeptide chain.
The strand of mRNA is divided into triplet bases called codons.
Each codon contains the code for one amino acid – the building block of a protein.

4. Transfer RNA - tRNA tRNA is found in the cells cytoplasm
Its function is to pick up a SPECIFIC AMINO ACID and bring it to the mRNA on the ribosome.

5. The Structure of tRNA Singled stranded, folded structure
There is an ANTI-CODON at one end
There is an AMINO ACID BINDING SITE the other

6. Anti-codons
The anticodon is composed of a triplet of bases which are complementary to a codon on the mRNA .

7. THE CODE….. There are 64 combinations of 3 bases.
The mRNA codon AUG is always the start codon in a sequence
There are 3 mRNA codons that don’t code for an amino acid – these are the stop codons.

8. Stage 3 : Tranlsation

9. The Ribosoms
Small structures that contain rRNA and enzymes needed for protein synthesis
A ribosome has 3 sites within it.
P site : holds the tRNA carrying the growing chain
A site : holds the tRNA carrying the next amino acid to join the chain
E site : discharges a tRNA once the amino acid is part of the chain.

10. The Stages………… 1 – mRNA moves to ribosome and binds at 5’ end
2 – AUG codon gets into place at the P site
3 – the tRNA with complimentary anticodon is held in place
by hydrogen bonds
4 – the next complimentary tRNA joins at the A site
5 – strong peptide bonds form between the amino acids

11. The Stages…………
6 – the ribosome moves along opening up the A site so another
complimentary tRNA can join
7 – the polypeptide chain continues to grow and the tRNA discharge
at the E site
8 – a stop codon on the mRNA is reached which signals the end of the
protein chain as there is no matching tRNA anti-codon
9 – a release factor occupies the A site and frees the polypeptide chain
from the ribosome
translation animation

12. Overview of gene expression
Nucleus
A G A G G T T G A C G A
T C T C C A A C T G C T
DNA
Transcription
Overview of gene expression
mRNA
U C U C C A A C U G C
codon
ser
pro
thr
ala
Ribosome
Translation
Protein

13. Polyribosomes
This is where several ribosomes attach to an mRNA strand.

14. Definitions Term Definition Transcription
Copying of the DNA code onto the mRNA
Translation
Converting the information given on the mRNA into a sequence of amino acids
Triplet
Sequence of bases specifying one amino acid
Codon
Triplet of bases on mRNA
Anticodon
Triplet of bases on tRNA

15. One Gene Can Code for Many Proteins
ALTERNATIVE SPLICING +
POST TRANSLATIONAL MODIFICATION
OHow can one gene
How can this be? Hmmm..

16. CRACK THE CODE
CODON: UUU =
CODON: CCA =
CODON: CAU =
CODON: AAU =

17. CRACK THE CODE
What is the CODON for:
Leucine
Tyrosine
Lysine
Stop

18. Alternative Splicing One gene can code for different proteins
When the primary transcript is spliced after transcription, alternative segments of RNS may be treated as introns and exons.
This means that one primary transcript can lead to different mature mRNA strands………………..
……………..This leads to different polypeptide chains.
One gene can code for different proteins

19. Primary transcript
Different proteins are formed

20. Post Translational Modification
After translation the polypeptide chain can be modified to produce many different proteins by:
Cleavage
Molecular addition

21. 1. Cleavage
The polypeptide chain can be cut and combined with other poly peptides.

22. 2. Molecular addition
A PHOSPHATE or CARBOHYDRATE group can be added to the polypeptide chain.

23. Gene Expression
Your PHENOTYPE are determined by the proteins you produce.
The proteins you produce are controlled by the gene being expressed (switched on)
Only a fraction of genes in a cell are expressed.
GENE
EXPRESSED
PROTEIN
PHENOTYPE

24. Gene activity in different specialised cells
Cell type
Activity of genes coding for production of:
antibodies
lysosome enzymes
enzymes for synthesis of urea
pepsin
phagocyte
off on
liver
stomach lining
lymphocyte

25. Gene Expression
Gene expression can be influenced by intra cellular and extra cellular environmental factors.
It is controlled by the regulation of transcription and translation

26. Learning Intentions Describe the structure of tRNA
Describe the process of Translation
Discuss alternative splicing and
modification