Biology 1111

1
Lecture 24

• Biology 1111
• Chapter 11 The Control of Gene Expression

2
Learning Objectives

• Contrast
• Alpha beta cells of pancreas
• Define
• Operon
• RNA polymerase
• Promoter, operator, repressor
• Discuss lac operon, cell differentiation

3
Exam Announcement

• Exam 4 will be next week (before the Thanksgiving
  break)
• See course website for coverage
• Todays material will be on the test!

4
Review

• Chapter 9 Patterns of Inheritance
• Genes defined
• Chapter 10 Molecular Biology of the Gene
• Use of viruses to study biochemistry of genetics
• Chapter 11 The Control of Gene Expression
• Turning genes on and off
• What happens when genes arent controlled

5
RNA Viruses (Review)

• Nucleic acid replicated in cytoplasm
• No error checking
• Evolve faster
• Examples
• Hanta virus
• Ebola virus
• Influenza (flu)

Hanta
Ebola
6
DNA viruses (Review)

• Cell error checks
• Slower evolution
• Can integrate into hosts DNA

7
HIV (Review)
White Blood Cell

• An RNA virus
• Can evolve quickly
• Attacks white blood cells
• But has reverse transcriptase
• Can reverse information flow (against central
  dogma of molecular biology)!
• Integrates genetic code into DNA
• The first human retrovirus

Viruses
8
Demo
9
Operon

• Operon a DNA sequence having
• A group of genes
• A promoter
• An operator

10
The lac Operon (Background)

• In the bacterium E. coli
• Lactose sugar
• Bacterium can use it for food
• Needs 3 enzymes to do so
• Inefficient to make enzymes when not needed

11
The lac Operon Described

• The lac operon regulates transcription of enzyme
  genes
• Transcribes enzyme RNA when lactose present
• Shuts down transcription when not needed

12
The lac Operon Components

• RNA polymerase the enzyme which makes RNA
• Promoter a region on the DNA, where RNA
  polymerase can attach
• Operator a region on the DNA, behind the
  promoter
• Repressor a protein molecule
• Binds to operator when lactose absent
• Cannot bind when lactose present

13
The lac Operon Components

• RNA polymerase the enzyme which makes RNA
• Promoter a region on the DNA, where RNA
  polymerase can attach
• Operator a region on the DNA, behind the
  promoter
• Repressor a protein molecule
• Binds to operator when lactose absent
• Cannot bind when lactose present

14
The lac Operon Off
15
The lac Operon On
16
Question

• What does the lac operon make?
• Answer mRNA

17
The trp Operon

• Controls tryptophan production
• E. coli bacteria normally need to make tryptophan
  (an amino acid)
• When its available in environment (milk,
  turkey), they turn it off

18
7th Inning Stretch
19
Cellular Differentiation

• Happens in eukaryotes
• A zygotes cells divide specialize to perform
  functions in tissues
• The proteins that are expressed in cells differ
  from tissue to tissue

20
Specialization via Protein Expression

• Two types of cells in pancreas
• Alpha cells make glucagon to raise blood sugar
  levels
• Beta cells make insulin to lower blood sugar
  levels