Higher Biology

1. 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 241-243 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 241-243 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 236-7 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 colionly 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 proteinmolecule. • 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 operatorgene.

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 geneswitches off thestructural 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 geneis switched on. Thestructural 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 239-240, 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.