Molecular Genetics and Mitosis

2. Molecular Genetics and Mitosis Genetic Processes – Unit 3: Asexual Reproduction – Lesson 1

3. Genetics is the science of heredityand variationin living organisms. • In this strand we will examine how that variation occurs and the mechanisms of inheritance that allow organisms to exhibit different traits.

4. Big Ideas in this unit: • The continuity of life depends on reproduction. • Variationin traits is the foundation for evolutionarychange. • Terminology in this lesson: • DNA, sugar-phosphate backbone, double helix, adenine, guanine, cytosine, thymine, histones, nucleosomes, chromatin, chromosomes, sister chromatids, centromere, cell cycle, mitosis, apoptosis, diploid, somatic cell, spindle fibres, interphase, prophase, metaphase, anaphase, telophase, cytokinesis, mutations, oncogenes.

5. I. The Structure of DNA (Deoxyribonucleic Acid) • DNA is geneticmaterial found in the nucleusof eukaryoticcells. • Chromosomes, shown as an ‘X” in the picture below, are made up of long strands of DNA that have been replicated, wrapped around histoneproteins, and coiled. • The two replicated strands are called sister chromatids, and are attached at the centromere. • Unraveling chromosomes reveals that DNA is a double helix.

6. The sides of the helical ‘ladder’ are comprised of alternating sugars and phosphates. • The ‘rungs’ of the ladder are comprised of four nitrogenous bases: Adenine, Thymine, Guanine & Cytosine. Bases in DNA always bond the same way, called ‘Chargaff’s Rule’: Adenine-Thymine A-T Guanine-Cytosine G-C

7. Metaphase Chromosome: • replicated • fully condensed • Supercoiling: • the coil itself coils… • and coils again… • Nucleosomes: • 8 histones wrapped in DNA = nucleosome • Coiling: • nucleosomes condense and coil • DNA Base Pairs: • Adenine-Thymine • Guanine-Cytosine

8. Chromatin comprising ~3% of one human chromosome (there are 46 remember!)

9. Metaphase Chromosome: • replicated • fully condensed • Supercoiling: • the coil itself coils… • and coils again… • Nucleosomes: • 8 histones wrapped in DNA = nucleosome • Coiling: • nucleosomes condense and coil • DNA Base Pairs: • Adenine-Thymine • Guanine-Cytosine

10. Nucleosomes: • 8 histones wrapped in DNA = nucleosome

11. Metaphase Chromosome: • replicated • fully condensed • Supercoiling: • the coil itself coils… • and coils again… • Nucleosomes: • 8 histones wrapped in DNA = nucleosome • Coiling: • nucleosomes condense and coil • DNA Base Pairs: • Adenine-Thymine • Guanine-Cytosine

12. Supercoiling: • the coil itself coils… • and coils again… • Coiling: • nucleosomes condense and coil

13. Metaphase Chromosome: • replicated • fully condensed • Supercoiling: • the coil itself coils… • and coils again… • Nucleosomes: • 8 histones wrapped in DNA = nucleosome • Coiling: • nucleosomes condense and coil • DNA Base Pairs: • Adenine-Thymine • Guanine-Cytosine

14. Metaphase Chromosome: • replicated • fully condensed

15. Metaphase Chromosome: • replicated • fully condensed

16. II. The Cell Cycle • Why do cells undergo mitosis? • To solve the inefficiencyproblem (to increase surface area-to-volume ratio) • To replace worn out/damaged cells of a multicellular organism • For growth through an increase in numbers • For asexualreproductionof individuals in unicellular organisms

17. Centrioles and chromosomes replicate Cell increases in size following mitosis Cell double checks DNA for replication errors G0 Cell cycle arrest

18. III. Review of Mitosis

19. III. Review of Mitosis

20. The Stages of Mitosis

23. IV. Errors in Mitosis • Mitosis is a traumatic process! The cell goes through dramatic changes in ultrastructure, its organelles disintegrate and reform in a matter of hours, and chromosomes are jostled constantly by probing microtubules. • Occasionally, chromosomes may become damaged. Mutations can be inherited, they can be caused by certain viruses, or they can be caused by radiation or toxic compounds.

24. If a mutation occurs during the process of mitosis, only the offspring of the mutated somatic cell will have the alteration present. • Errors in the prior replication of the genome or the process of separating the cell into two halves can have serious consequences for the organism and its offspring. Cancer is essentially a disease related to mitosis, involving uncontrollable cell division.

26. V. Cancer • Carcinogenesis (meaning literally, “the creation of cancer”) is the process of derangement of the rate of cell division. • Typically, several mutations are required before a cell becomes a cancer cell. • The process involves both oncogenes and tumor suppressor genes. • Oncogenespromotecancer when "switched on" by a mutation, whereas tumor suppressor genes preventcancer unless "switched off" by a mutation.

28. The first signs of a cell developing into a tumor cell are: • Immortality. The usual number of cell divisions for a mammalian cell is 50-60, then it ceases to divide (cell senescence). Tumor cells keep dividing forever. • Altered morphology (shape, size, colour). • Loss of contact inhibition (the natural process of arresting cell growth when two or more cells come into contact with each other). • Low or no need for growth factors (naturally occurring substances capable of stimulating cellular growth, proliferation and differentiation; usually proteins or hormones).

29. The End! Read p. 17, p. 68, & p. 152-159 in your text. Add/integrate any new information into your notes.