1. Genetic Control of Growth
Higher Biology
Genetic Control of Growth

2. Genetic Control of Growth
By the end of this lesson you should be able to:
Describe the Jacob-Monod hypothesis of gene action
in bacteria.
Explain lactose metabolism in Escherichia coli.
Describe the role played by genes in the control of
metabolic pathways.
Know what PKU is and how it is caused.
Describe how cell differentiation is controlled by
switching genes on and off.

3. Introduction Remember:
Genes determine the structure and function of every cell in an organism.
DNA is made up of a series of genes.
Genes code for proteins which perform all the functions required by the body.
Mutations in a gene means that the “wrong” protein is made.

4. Genes and differentiation
Read pages in Torrance and then answer the following questions:
Describe the sets of genes present in a cell arising from a zygote.
Describe what happens to cells arising from the zygote- mention differentiation and specialised in your answer.
Describe the role of genes in the process of differentiation.

5. Genes and differentiation
Read pages in Torrance and then answer the following questions:
Describe the 2 categories of genes found in all cells and give 1 example of each.
Describe what happens when a gene is switched on.
Explain why some genes must be switched on in all cells.
Describe what happens to genes which are not required by a cell.

6. Genes and differentiation
Insert and complete the “Genetic Control of Blood Cells” diagram from your pack.
Insert and complete the “Genetic Control of Plant Cells” diagram from your pack.

7. Jacob-Monod Hypothesis
When an enzyme is needed by a cell, a gene has to be switched on to make the enzyme.
The process of switching on a gene is known as enzyme induction.

8. Jacob-Monod Hypothesis
Read pages of Torrance and then answer the following questions:
What is the name of the sugar found in milk?
What 2 molecules is this sugar made from?
What is the name of the enzyme which breaks down this sugar?
Describe what this enzyme does to the sugar by writing a word equation.

9. Jacob-Monod Hypothesis
The Jacob-Monod hypothesis was proposed by two French scientists who won the Nobel Prize in the 1950s, for their work.
Escherichia coli (E. coli) is the name of the bacteria they worked with.
E coli can only use glucose as a sugar for respiration to release energy. (& no other type of sugar)
E coli normally lives in an environment rich in glucose, but not lactose.

10. Jacob-Monod Hypothesis
E coli only produces b-galactosidase when lactose is present.
Somehow the gene which codes for b-galactosidase is only switched on when lactose is present.
No lactose = gene switched off.

11. Jacob-Monod Hypothesis
OPERON
An operon is a section of DNA found in E coli.
The operon contains the operator gene and structural gene.

12. Jacob-Monod Hypothesis
OPERON
The structural gene codes for the protein- in this case b-galactosidase
The operator gene controls the expression of the structural gene.

13. Jacob-Monod Hypothesis
OPERON
The regulator gene codes for a repressor protein molecule.
The repressor protein molecule interacts with the operator gene preventing the structural gene from being expressed.

14. Jacob-Monod Hypothesis
OPERON
Lactose acts as an inducer by preventing the repressor protein molecule from binding to the operator gene.

15. Jacob-Monod Hypothesis
When lactose is ABSENT:
The regulator gene produces the repressor protein molecule.
The repressor protein binds to the operator sequence.

16. Jacob-Monod Hypothesis
When lactose is ABSENT:
The operator gene switches off the structural gene.
NO b-galactosidase is produced.

17. Jacob-Monod Hypothesis
When lactose
is PRESENT:
The regulator gene produces the repressor protein molecule.
The repressor protein binds to lactose.

18. Jacob-Monod Hypothesis
When lactose
Is PRESENT:
The operator gene is switched on.
The structural gene is switched on.
b-galactosidase is produced.

19. Jacob-Monod Hypothesis
As the lactose is used up then there is less to bind to the repressor molecules.
The repressor molecule is then free to bind to the operator sequence.
This switches the structural gene off and b-galactosidase production stops.

20. Jacob-Monod Hypothesis
Advantages of enzyme induction:
Since the enzyme is only produced when it is required, then the cells save:
Amino acids
Nucleotides
ATP
Animation- lac operon- no lactose
Animation- lac operon- with lactose

21. Jacob-Monod Hypothesis
Insert and complete the “Jacob-Monod Hypothesis” summary diagram into your notes.

22. Control of Metabolic Pathways
All the reactions that keep an organism alive are collectively called the metabolism.
A metabolic pathway is a series of reactions, each controlled by enzymes, which either synthesises or breaks down substances.
Each enzyme is a protein coded for by a particular gene.
If there is a fault in the gene (mutation) there could be a fault in the enzyme.

23. Control of Metabolic Pathways
Copy Fig 29.6 from p239 of Torrance.
Read about Phenylketonuria (PKU) on pages , and then answer the following questions:
What is phenylalanine?
What is the source of phenylalanine for humans?
What normally happens to phenylalanine in the body?
What type of disorder is PKU?

24. Control of Metabolic Pathways
Explain what happens to the metabolism of someone suffering from PKU.
Describe the effects on a person suffering from PKU.
Insert and complete the “PKU” diagram from your diagram pack.

25. Practice Questions
Torrance
TYK page 239 Q1-3
TKY page 240 Q2 and 3

26. Genetic Control of Growth
Can you do it?
Describe the Jacob-Monod hypothesis of gene action
in bacteria.
Explain lactose metabolism in Escherichia coli.
Describe the role played by genes in the control of
metabolic pathways.
Know what PKU is and how it is caused.
Describe how cell differentiation is controlled by
switching genes on and off.