Control of Gene Expression

2. Control of Gene Expression ROLE OF GENE EXPRESSION: • Activation of a gene that results in a protein • Cells DO NOT need to produce proteins for every code. GENOME: • Complete genetic material of an individual • Cells can regulate what genes get expressed.

3. Gene expression in Prokaryotes Lac Operon: • Control system that regulates the production of enzymes to break down lactose. 3 Regulatory Elements Control the Expression • Structural Genes: Genes that code for proteins • Promoter: Recognizes RNA Polymerase and promotes transcription • Operator: Binding site for inhibitory protein that blocks transcription.

4. Lac operon Collection of 3 types of genes working together • Genes for lactose utilization were expressed only when lactose is present 2 Forms of Control: • REPRESSION • ACTIVATION

5. Repression: • Repressor attaches to the operator when lactose is absent • Blocks RNA Polymerase from binding to structural genes Activation: • Lactose binds to the repressor and removes it • RNA Polymerase transcribes the gene • Lactose acts as an INDUCER • A molecule that initiates gene expression

6. Lac Operon

7. Gene expression in eukaryotes • Much larger and more complex than in prokaryotes • DNA is located on several chromosomes • Control is at the individual chromosome level • Related to coiling and uncoiling of DNA EUCHROMATIN: • Relaxed state of DNA when transcription is possible

8. Two types of genes in eukaryotes • Introns: Non-coding for proteins • Exons: Genes that when expressed code for PROTEIN

9. Rna splicing

10. Control after transcription • Transcription produces Pre-mRNA Contains introns and exons • mRNA is formed when INTRONS are removed and EXONS are spliced together.

11. Enhancer Control Non-coding control sequences that facilitate transcription Transcription Factors: Bind to Enhancers and RNA Polymerase and regulate transcription Activation Enhancers: Have been studied in the expression of the gene controlling the production of estrogen.

12. Gene expression and development Cell Differentiation: • Development of cells with specific functions. Morphogenesis: • Development of form

13. Homeotic Genes: • Regulatory genes that determine where anatomical structures will develop during MORPHOGENESIS

14. Homeotic Genes: • Master genes of development • Determine the overall body organization HOMEOBOX: • Specific DNA sequence that regulates patterns of development Mutations of these genes may have devastating impacts

15. Cancer • Tumor: Abnormal proliferation of cells that result from uncontrolled, abnormal cell division. • Benign: Cells remain within a mass. Generally pose no threat to life. Exception: If the mass grows large enough that is compresses against vital organs. Examples: Fibroid Cysts, warts Most benign tumors can be surgically removed.

16. Malignant Tumors KNOWN AS CANCER • Uncontrolled dividing cells invade and destroy healthy tissues elsewhere in the body METASTASIS: • The spreading of cancer cells beyond their original site • Cancer cells break away from the malignant tumor and spread to other body parts where they begin to form new tumors.

17. Metastasis

18. Benign vs. Malignant Tumors

19. Metastasis

20. Kinds of Cancer: • Tumors are classified by the types of tissues they affect • Link to national cancer institute CARCINOMAS: • Grow in the skin and the cells that line the organs of the body. • Examples: Lung cancer and breast cancer breast cancer

21. Types of Cancer: Sarcoma: • Cancer that grows in the bone and muscle tissues Lymphomas: • Solid tumors that grow in the tissues that form blood cells • May cause LEUKEMIA – • The uncontrolled production of white blood cells It usually takes several years for cancer to develop, but it may be accelerated in vital organs like the pancreas or liver

23. Cancer and the Cell Cycle In normal cells, the frequency of cell division is controlled by several factors: 1. Adequate nutrition 2. Must be attached to another cell, membrane or fibers 3. NOT ALL CELLS ARE DESTINED TO DIVIDE (Neurons) 4. Normal cells stop dividing when it becomes too crowded 5. Normal cells will only divide 20-50 times before they die: • Apoptosis – programmed cell death

24. What do cancer cells need to survive?

25. How cancer cells differ from normal cells: 1. Loss of DENSITY DEPENDENT INHIBITION: • Cells continue to grow even when they are densely packed together 2. Continue to grow when they become unattached to other cells 3. Block apoptosis: don’t allow natural cell suicide 4. Angiogenesis: • Cancer cells can stimulate the formation of new blood vessels to supply the growing tumor

26. Causes of Cancer • Normal cells use genes that code for GROWTH FACTORS that control the process of cell division. • Mutations of the genes that code for the growth factors lead to cancer 1. May occur due to a SPONTANEOUS MUTATION 2. Most likely they occur due to an exposure to CARCINOGENS.

27. Carcinogens: • Any substance that increases the risk of cancer with exposure. EXAMPLES: • Tobacco (90% of all lung cancers), • Asbestos • Ionizing Radiation (X-rays or UV light) MUTAGEN: (most carcinogens are also mutagens) • Agents that cause mutations to occur

28. What determines Who develops Cancer? Depends on many factors: 1. Family history (some families have higher than normal rates of cancer) 2. The number of exposures to the carcinogen 3. The amount of carcinogen in each exposure 4. Usually more than one mutation is needed to cause cancer. 5. Risk of cancer increases with age due to more exposures throughout a lifetime.

29. Oncogenes Gene that causes cancer or other uncontrolled cell proliferation • Begin as normal PROTO-ONCOGENES – Controls a cells growth and differentiation. • Code for proteins that regulate the rate of the cell lifecycle • An error causes the rate of cell division to increase

30. Tumor-Suppressor Genes • Code for proteins that prevent uncontrolled cell division. • When they mutate they do not get expressed properly and lead to a predisposition to cancer

31. Viruses and Cancer • May cause cancer to develop in plants or animals • Many viral genes are actually oncogenes • May cause mutations in the Proto-oncogenes and tumor suppressing genes • Viruses have been found to cause various types of Leukemia.