Controls Over Genes

1
Controls Over Genes

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life

2
Key Concepts

• A variety of controls govern how genes are
  expressed
• Control is exerted by regulatory proteins
• Prokaryotes depend on rapid control over
  short-term shifts in environmental conditions
• Eukaryotes depend on controls over short-term
  shifts in diet and levels activity, growth and
  development
• Different allele types activate or suppress
  genes in different ways in multicellular
  organisms

3
Overview of Gene Controls

• Regulatory proteins
• Internal and external control
• Negative Control Systems
• Positive Control Systems

4
Negative Control of the Lac Operon

• Three genes in transcription
• Promoter
• Operator
• Repressor
• Escherichia coli

5
Negative Control of the Lac Operon

• Lactose-degrading enzymes are not built when they
  are not required
• Lactose binds to repressor
• Operator is no longer blocked

6
Positive Control of the Lac Operon

• Lactose-Operon isnt used much unless glucose is
  absent
• Regulatory proteins like CAP exert rapid on/off
  control
• http//www.youtube.com/watch?voBwtxdI1zvk

7
Controls in Eukaryotic Cells

• Cell differentiation
• Specialized in
• Composition, structure, and function
• Gene amplification
• DNA rearrangement
• Chemical modification

8
Controls in Eukaryotic Cells
9
Lampbrush Chromosomes

• DNA loops profusely in Prophase I

10
Lampbrush Chromosomes

• Histones loosen their grip on DNA
• Transcription proceeds in regions where
  chromosome packaging has relaxed
• Lampbrush chromosomes occur in a limited phase of
  meiosis during oogenesis

11
Examples of Signaling Mechanisms

• Hormonal
• Growth Hormone
• Prolactin
• Sunlight
• Phytochrome detect light conditions

12
X Chromosome Inactivation

• In female mammals, one of the two X chromosomes
  is completely inactivated
• Inactivation is random
• Inactivated chromosome can be observed in the
  interphase nucleus as Barr body
• Genes on the inactivated chromosome are not
  expressed

13
Cancer and the Cells That Forget to Die

• Characteristics of Cancer
• Uncontrolled cell division
• Skin warts
• Benign or malignant tumors
• Metastasis
• 15-20 of all deaths in developed countries
• Oncogenes

14
Characteristics of Cancer Cells

• Changes in plasma membrane in cytoplasm
• Abnormal growth and division
• Weakened capacity for adhesion
• Lethality

15
In Conclusion

• Cells control gene expression and are dependent
  on type of cell, chemical conditions and
  environmental signals
• Regulatory proteins, enzymes and hormones
  interact with DNA and RNA and with the gene
  products
• Negative and positive control systems operate to
  block or enhance transcription

16
In Conclusion

• Most bacteria do not require many genes to grow
  and reproduce
• Promoters, operators, and enhancers work in
  operating systems
• Eukaryotes require more complex gene controls
  which respond to short-term shifts in the
  environment

17
In Conclusion

• Different types of cells activate and suppress
  genes in different ways
• Cell differentiation is an outcome of selective
  gene expression
• Cancer results when controls are lost over a
  cells cycle and death machinery