1. Cell Division
Chapter 8

2. Cell Division Doubling organelles and proteins DNA replication
Nuclear division
Cytoplasmic division

3. Cell Increase and Decrease
Maintain homeostasis
Cell numbers kept in check by this mechanism
Through cell division of somatic cells and cell death
Cell division – interphase, mitosis and cytokinesis
Cell death – apoptosis

4. Cell Increase and Decrease
Somatic cells
Asexual reproduction
increase in number of somatic cells
Increase in number unicellular organisms
Germ cells
Sexual reproduction
requires the production of eggs and sperm

5. Chromosomes

6. Mitosis verse Meiosis?? Mitosis Meiosis
Division of somatic cell nuclei
Meiosis
Division of gamete nuclei

7. Cell Cycle – Somatic cells
Set of stages that involves cell growth and nuclear division
Consists of:
Interphase G1 S G2
Meiotic stage
Mitosis and Cytokinesis

8. Interphase When the cell carries on its usual functions Main stages:
Gap before DNA synthesis begins S
Time when DNA duplicated*************** G2
Gap between time DNA duplication ends and mitosis begins

9. Interphase in Meiosis? Meiosis is a "one-way" process
Cannot be said to engage in a cell cycle as mitosis does
Preparatory steps that lead up to meiosis are identical in pattern and name to the interphase of the mitotic cell cycle

10. Cytokinesis in Animal Cells
Cytoplasmic cleavage
Accompanies mitosis
Separate process
Cleavage furrow forms between daughter nuclei
Contractile ring contracts deepening the furrow
Continues until separation is complete

11. Human DNA in somatic cells
22-23 pairs of homologous chromosomes
Difference?
Autosomes (1-22)
Sex chromosomes (23)
Somatic cells have 46 chromosomes
Diploid 2n

12. Human DNA in gametes Due to reductional division
Halves the diploid number (2n) to a haploid number (n)
23 total chromosomes

13. DNA Replication Duplicated chromosome Sister chromatids
Composed of 2 sister chromatids
held together by a centromere
Sister chromatids
Genetically identical
When separate, each daughter nucleus gets a chromosome
DNA copied
DNA divided

14. Division of the Nucleus
Nucleus must be divided
Parent cell’s DNA into 2 nuclei
2 ways nucleus can divide:
Mitosis
Meiosis

15. Maintaining the Chromosome Number
Mitosis
Maintaining the Chromosome Number

16. Mitosis
Mitosis
4 main stages:
Prophase
Metaphase
Anaphase
Telophase

17. The Cell Cycle 1. Prophase – Mitosis begins! Threadlike form
Spindle fibers appear
DNA start to condense
Aster formed
Nuclear envelope starts to break apart
Centrioles move to opposite sides of the cell

18. The Cell Cycle 2. Metaphase
Duplicated chromosomes aligned midway between the poles
Associated with spindle fibers

19. The Cell Cycle 3. Anaphase
Sister chromatids separate from each other and move to opposite poles
Become daughter chromosomes

20. The Cell Cycle 4. Telophase Return to threadlike form as in prophase
New nuclear envelope separates each chromosome cluster
2 new nuclei!!!!!

21. Reducing the Chromosome Number
Meiosis
Reducing the Chromosome Number

22. Meiosis Mechanism for dividing the nucleus of germ cells
Oogonia and spermatogonia 2n
Meiosis must take place prior to formation of gametes
Sperm and eggs n
First stage in sexual reproduction

23. Meiosis Overview
Occurs in the life cycle of sexually reproducing organisms
Reduces the chromosome number
2 divisions, 4 daughter cells
Cells are diploid at beginning of meiosis
TWO consecutive divisions
Result is 4 haploid nuclei
Divided into:
Meiosis I
Meiosis II

25. Comparisons between males and females
Spermatogenesis
Begins at puberty and continues throughout life
Oogenesis
Begins in the fetus
Primary oocytes are arrested in prophase I
At puberty, one primary oocyte continues the process of meiosis during each menstrual cycle

26. Reducing the Chromosome Number
Genetic Recombination
Promotes genetic variability
Occurs in Two Ways
Crossing Over
Independent Assortment of paired chromosomes

27. How Plant Cells Divide Occurs in meristematic tissues
Same phases as animal cells
Plant cells do not have centrioles or asters 27

28. Plant Cells

29. Cytokinesis in Plant Cells
Flattened, small disk appears between daughter cells
Golgi apparatus produces vesicles which move to disk
Release molecules which build new cell walls
Vesicle membranes complete plasma membranes 29

30. Cell Division in Prokaryotes
Binary Fission
Prokaryotes have a single chromosome
Chromosomal replication occurs before division
Cell elongates to twice its length
Cell membrane grows inward until division is complete 30

31. Comparisons Mitosis Meiosis DNA replication occurs only once
Requires only one division
Produces two daughter cells
Diploid daughter cells 2n
Genetically identical cells produced
Occurs all the time
Meiosis
DNA replication occurs only once
Requires two divisions
Produces four daughter cells
Haploid daughter cells n
Genetically variable cells produced
Occurs only at certain times

32. Comparisons

33. Overview of the Life Cycle of Humans

34. Mitosis and Meiosis Gone Awry
Cancer
Chromosomal Abnormalities

35. Cancer disease of the cell cycle Cancer cells
do not respond normally to the cell cycle control system
can form tumors
if malignant, can spread to other parts of the body

36. Important Terms Tumor Benign Malignant Metastasis Cancer Carcinoma
Sarcoma
Lymphoma

39. Cancer Treatment Cancer treatment can involve Radiation therapy
which damages DNA and disrupts cell division
Chemotherapy
which uses drugs that disrupt cell division

40. Chromosomal Abnormalities
Nondisjunction
members of a chromosome pair fail to separate during anaphase
produces gametes with an incorrect number of chromosomes
If normal sperm fertilizes an egg with an extra chromosome
result is a zygote with a total of 2n + 1 chromosomes

41. Chromosomal Abnormalities
Down Syndrome:
Trisomy 21
condition in which an individual has an extra chromosome 21
Affects about one out of every 700 children

42. Chromosomal Abnormalities
Nondisjunction can also affect the sex chromosomes
Klinefelter's Syndrome
XXY males
Turner Syndrome
XO female