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 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

1. The regulator gene produces the repressor protein
   molecule.
2. The repressor protein binds to the operator
   sequence.

16
Jacob-Monod Hypothesis
When lactose is ABSENT

1. The operator gene switches off the structural
   gene.
2. NO b-galactosidase is produced.

17
Jacob-Monod Hypothesis
When lactose is PRESENT

1. The regulator gene produces the repressor protein
   molecule.
2. The repressor protein binds to lactose.

18
Jacob-Monod Hypothesis
When lactose Is PRESENT

1. The operator gene is switched on.
2. The structural gene is switched on.
3. 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

1. Explain what happens to the metabolism of someone
   suffering from PKU.
2. Describe the effects on a person suffering from
   PKU.
3. 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.