1. Gene Control Turning off and on

2. Gene Control Molecular mechanisms that govern when and how fast genes will be transcribed and translated. Not all genes are working all the time in all cells

3. Controls are triggered by… Programmed schedules of development (think of a fetus developing in the womb) In response to chemical conditions Receiving a signal, such as a hormone

4. Examples of controls Programmed schedule: the changes that take place in puberty Chemical conditions: Methylation of DNA often inactivates a gene; demethylation might turn it on later Acetylation; acetyl group attaches to a histone, loosens the wrap and makes it easier to transcribe Receiving a signal: a hormone triggers a response from a cell

5. What does the controlling? Mostly regulatory proteins Negative control: slows or stops gene activity (methylation) Positive control: turns on or enhances gene activity (acetylation)

6. Gene Control Is different in prokaryotes versus eukaryotes Less complicated in prokaryotes Often controlled by operons: one promoter and a set of 2 operators. Operator is a binding site for an oppressor.

7. Prokaryote Example Lac operon: controls the production of enzymes that digest lactose. Only turned on when lactose and present and glucose is absent. Glucose is the preferred sugar, only make provisions for lactose if it’s the only energy source available

8. Eukaryote examples All cells contain all genes. Many are basic cell function genes that operate regularly. Cells also differentiate by activating only certain genes For example, a neuron does not do the same thing as a cell in the pancreas

9. When do the controls happen? Page 242-243 Can occur during transcription, in mRNA processing, in translation, and following translation

10. Types of Controls in Eukaryotes Homeotic genes: interact with others to control development X chromosome inactivation makes sure only one X is working in both sexes This is dosage compensation (females are mosaics)

11. More Examples Signaling: hormones in animals Protein hormones attach to a receptor outside the cell membrane and stimulate a chain of events known as the 2 nd messenger system

12. More Examples Steroid hormones pass through the cell membrane to find its receptor inside An activator protein winds up next to the promoter for the targeted gene. A hormone always triggers a response

13. Loss of control Can mean cancer Mutations in the checkpoint genes of the cell cycle and/or repressor genes or enhancer genes lead to too much mitosis