Higher Biology
Genetic Control of Growth
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.
2
Introduction

1.
2.
3.
4.
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.
3
Genes and differentiation

1.
2.
3.
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.
4
Genes and differentiation

4.
5.
6.
7.
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.
5
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.
6
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.
7
Jacob-Monod Hypothesis

1.
2.
3.
4.
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.
8
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.
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Jacob-Monod Hypothesis



E coli only produces b-galactosidase when
lactose is present.
Somehow the gene which codes for bgalactosidase is only switched on when
lactose is present.
No lactose = gene switched off.
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Jacob-Monod Hypothesis
OPERON
An operon is a section of DNA found in E coli.
The operon contains the operator gene and
structural gene.
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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.
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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.
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Jacob-Monod Hypothesis
OPERON
Lactose acts as an inducer by preventing the
repressor protein molecule from binding to the
operator gene.
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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.
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Jacob-Monod Hypothesis
When lactose is ABSENT:
3. The operator gene switches off the
structural gene.
4. NO b-galactosidase is produced.
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Jacob-Monod Hypothesis
When lactose
is PRESENT:
1. The regulator gene produces the repressor
protein molecule.
2. The repressor protein binds to lactose.
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Jacob-Monod Hypothesis
When lactose
Is PRESENT:
3. The operator gene is switched on.
4. The structural gene is switched on.
5. b-galactosidase is produced.
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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.
19
Jacob-Monod Hypothesis
Advantages of enzyme induction:
Since the enzyme is only produced when it
is required, then the cells save:
1. Amino acids
2. Nucleotides
3. ATP
Animation- lac operon- no lactose
Animation- lac operon- with lactose
20
Jacob-Monod Hypothesis

Insert and complete the “Jacob-Monod
Hypothesis” summary diagram into your
notes.
21
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.
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Control of Metabolic Pathways


1.
2.
3.
4.
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?
23
Control of Metabolic Pathways
5.
6.
7.
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.
24
Practice Questions

1.
2.
Torrance
TYK page 239 Q1-3
TKY page 240 Q2 and 3
25
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.
26