1. Chapters 15 – 17 Regulation of Gene Expression Development, Stem Cells, and Cancer Viruses

2. Purpose of Gene Regulation Unicellular (bacteria, protists) ▫Prevents waste of cell’s resources creating unnecessary proteins Multicellular ▫Allows for cell differentiation  All cells have identical genome, yet express different portions of it  Different cells perform different functions Works with feedback inhibition

3. Operons Found in unicellular organisms “On-Off switch” for genes w/related functions Components ▫Operator  Region of DNA where repressor protein binds ▫Controlled genes ▫Regulatory gene (and its product – repressor protein)  Always expressed in cell

4. lac Operon Classic example of operon function Involves genes associated with lactose digestion

5. Eukaryotic Gene Regulation Regulation occurs at multiple points ▫In the nucleus:  Chromatin modification  Protein synthesis  RNA processing ▫In the cytoplasm:  RNA transcription  Protein processing

6. In the Nucleus … Chromatin modification ▫Histone acetylation  Acetyl group (–COCH 3 ) added to histone proteins  DNA packaged more loosely, promoting transcription ▫DNA methylation  Methyl group (–CH 3 ) added to bases – usually cytosine  Prevents protein interaction with that region of chromatin ▫Alternative RNA splicing

7. In the Cytoplasm…

8. Embryonic Development Zygote to adult involves cell division, cell differentiation and morphogenesis ▫Cell division increases number of cells ▫Cell differentiation results in different types of cells ▫Morphogenesis produces new structures (shaping)

9. Stem Cells Stem cells are unspecialized cells that can reproduce indefinitely (no Hayflick limit) and can differentiate into specialized cells of one or more types ▫Totipotent – exist only early on after fertilization; can become ANY cell type ▫Pluripotent– descendants of totipotent; can become any cell derived from the three germ layers ▫Multipotent– can result in any cell type belonging to a family of cells

10. Abnormal Regulation of Genes Faulty gene expression regulation can lead to cancer Research has lead to the discovery of cancer causing genes: oncogenes ▫Oncogenes can arise from a change to a normally- functioning gene or from certain types of viruses  Proto-oncogenes are NORMAL genes that are involved with NORMAL cell growth and division  Ex. Tumor-supressor genes code for proteins that curb uncontrolled cell growth ▫Over HALF of all human tumors are the result of damage to the p53 gene  Viruses play a role in about 15% of human cancers

11. Viral Structure Viruses are obligate, intracellular parasites ▫Must infiltrate a cell and utilize it’s resources and machinery to complete viral “life cycle” ▫Infectious agent made of little more than a protein coat and nucleic acid  Capsid – protein coat surrounding genetic material ▫Bacteriophages (or phages) are viruses that infect bacteria ▫Most viruses are limited to a specific host or set of hosts they can infect – host range

12. Typical Viral Life Cycle

13. Phage Replication After infecting a bacterium, phage genetic material may become incorporated into the bacterial chromosome ▫The lysogenic cycle often doesn’t harm the bacterium ▫Integrated viral DNA known as a prophage  Viral DNA is replicated and passed to daughter cells ▫Changes to environmental conditions may trigger switch to lytic cycle Lytic cycle involves replication of viral particles and assembly of new phages ▫Typically results in rupture (and death) of cell

14. Animal Viruses A greater diversity of viruses exist that infect animals ▫Type of genetic material ▫Outer covering Retroviruses utilize RNA as genetic material ▫Carry reverse transcriptase to produce DNA from RNA ▫Viral genome incorporated into host’s DNA – provirus  Permanent resident of host cell  Unlike phages, cell typically isn’t ruptured during viral production

15. Vaccines Vaccines are derivatives of pathogens that stimulate the immune system ▫Current vaccines CANNOT cause the illness they vaccinate against  Efficacy often decreases with time ▫Anti-virals can treat viral infections after they’re contracted … not a cure  Antibiotics have NO EFFECT on viral infections  Antibiotics combat bacterial infections