1. Control over Genes
Chapter 15

2. Squamous Cell Carcinoma
Skin Cancer
Basal Cell Carcinoma
Squamous Cell Carcinoma
Malignant Melanoma

3. Changes in DNA Trigger Cancer
Ultraviolet radiation can cause breaks
In-text figure Page 238

4. Gene Control • Type of cell • Internal chemical conditions
Which genes are expressed in a cell depends upon:
• Type of cell
• Internal chemical conditions
• External signals
• Built-in control systems

5. Mechanisms of Gene Control
Controls related to transcription
Transcript-processing controls
Controls over translation
Post-translation controls

6. Regulatory Proteins
Can exert control over gene expression through interactions with:
DNA
RNA
New polypeptide chains
Final proteins

7. Control Mechanisms Negative control
Regulatory proteins slow down or curtail gene activity
Positive control
Regulatory proteins promote or enhance gene activities

8. Chemical Modifications
Methylation of DNA can inactivate genes
Acetylation of histones allows DNA unpacking and transcription
Figure 15.2 Page 240

9. Gene Control in Prokaryotes
No nucleus separates DNA from ribosomes in cytoplasm
When nutrient supply is high, transcription is fast
Translation occurs even before mRNA transcripts are finished

10. The Lactose Operon operator regulatory gene gene 1 gene 2 gene 3
transcription,
translation
promoter
lactose operon
repressor protein
Figure 15.3a Page 241

11. Low Lactose Repressor binds to operator Binding blocks promoter
Transcription is blocked
Figure 15.3b Page 241

12. High Lactose allolactose lactose mRNA RNA polymerase operator promoter
gene 1
Figure 15.3c Page 241

13. Lac-Operon Analogy
Like an elephant that likes to sit on a railroad track blocking the train.
The only thing that the elephant likes better than to sit on his spot on the track is peanuts.
If peanuts are available, the elephant leaves the track and eats the peanuts.
While he is gone the train can proceed down the track until the elephant goes back to sit on the track after eating all the peanuts.

14. Controls in Eukaryotic Cells
Control of transcription
Transcript processing controls
Controls over translation
Controls following translation

15. Most Genes Are Turned Off
Cells of a multicelled organism rarely use more than 5-10 percent of their genes at any given time
The remaining genes are selectively expressed

16. Homeotic Genes Occur in all eukaryotes
Master genes that control development of body parts
Encode homeodomains (regulatory proteins)
Homeobox sequence can bind to promoters and enhancers

17. X Chromosome Inactivation
One X inactivated in each cell of female
Creates a “mosaic” for X chromosomes
Governed by XIST gene
Figure 15.6 Page 245

18. Hormones Signaling molecules
Stimulate or inhibit activity in target cells
Mechanism of action varies
May bind to cell surface
May enter cell and bind to regulatory proteins
May bind with enhancers in DNA

19. Vertebrate Hormones Some have widespread effects
Somatotropin (growth hormone)
Others signal only certain cells at certain times
Prolactin stimulates milk production

20. Phytochrome Signaling molecule in plants
Activated by red wavelengths, inactivated by far-red wavelengths
Changes in phytochrome activity influence transcription of certain genes

21. Controlling the Cell Cycle
Cycle has built-in checkpoints
Proteins monitor chromosome structure, whether conditions favor division, etc.
Proteins are products of checkpoint genes
Kinases
Growth factors

22. Oncogenes Have potential to induce cancer
Mutated forms of normal genes
Can form following insertions of viral DNA into DNA or after carcinogens change the DNA

23. Cancer Characteristics
Plasma membrane and cytoplasm altered
Cells grow and divide abnormally
Weakened capacity for adhesion
Lethal unless eradicated

24. Apoptosis Programmed cell death
Signals unleash molecular weapons of self-destruction
Cancer cells do not commit suicide on cue