1. Chapter 9.1 Overview of Cell Division Mechanisms AP Biology Fall 2010

2. Objectives • Determine the function of mitosis, meiosis, and prokaryotic fission • Analyze the structural components of chromosomes

3. Mitosis, Meiosis, and Prokaryotes • Before cells reproduce, there must be a division of the nucleus and its DNA

4. Mitosis, Meiosis, and Prokaryotes • Mitosis and meiosis are eukaryotic nuclear division mechanism that lead to the distribution of DNA to new nuclei in forthcoming daughter cells

5. Mitosis • Mitosis is used by multicelled organisms for growth by repeated divisions of somatic cells • Responsible for: • Increases in body size during growth • Replacement of worn out or dead cells • Tissue repair

6. Mitosis • Used by multicelled organisms • Plants, animals, fungi and single celled protists produce asexually by mitosis

7. Meiosis • Meiosis occurs only in reproductive cells that divide to form gametes or spores • Sexual reproduction • Gemetes kown as sperm and eggs develop from germ cells • Spores form in life cycle of protists, plants, and fungi

8. Meiosis

9. Prokaryotes • Prokaryotic cells reproduce asexually by an entirely different mechanism called prokaryotic fission

10. Prokaryotes

11. Chromosome Structure • Each chromosome is a molecule of DNA complexed with proteins • Eukaryotic species have a characteristic number of chromosomes • Before cell enters nuclear division, duplicates every chromosome • Forms two sister chomatids held together by centromere

12. Chromosome Structure

13. Chromosome Structure • During early stages of mitosis and meiosis: • Duplicated chromosomes coil back on itself into highly condensed form

14. Chromosome Structure • Proteins called histones tightly bind to DNA and cause spooling into structural units called nucleosomes • Prevent tangling during nuclear division • DNA winds twice around histones

15. Chromosome Structure • Nucleosome: consists of part of DNA molecule looped twice around a core of histone proteins

16. Chromosome Structure • Centromere: constricted region • Location is different for each type of chromosome, unique characteristic • Kinetochore: during nuclear division, located at centromere • Is docking station for microtubules that help move chromatids

17. Chromosome Structure

18. Review • What is the point of structural organization of chromosomes? • What is the function of mitosis?

19. Answers • Tight packaging keeps chromosomes from getting tangled, also between cell divisions nucleosome packaging can be loosened in specific regions (enzymes gain access to heredity information that cell requires). • The function of mitosis is to increase in body size during growth, replacement of dead or worn-out cells, and repair of damaged tissues.