1. Chapter 12 Cellular Biology
Cell Cycle & Mitosis
Chapter 12
Cellular Biology

2. What you need to know!
Mitotic Cell division results in genetically identical daughter cells
The mitotic phase alternates with interphase in the cell cycle

3. Cell Division Life depends on the ability of cells to reproduce/copy
Cell Division = 1 cell divides into 2
Unicellular organisms cell division = reproduction
Prokaryotes, Protists
Bacteria = binary fission

4. Cell Division
Multicellular organisms cell division = growth and development, repair and replace.
Protists, fungi, plants and animals
2 types of multicellular organism cells:
Somatic Cells: Body cells of an organism that do all the daily function of the organism
Germ Cells: reproductive cells (eggs and sperm)

5. Cell Cycle
G0: the cell spends its life working and growing (i.e. breaking down sugars, making ATP, enzymes)
Sometimes a cell will prepare to divide
1 mother cell  2 daughter cells
Interphase
G1 (Gap1): Growth, development, organelle production, etc. Cell must enter reproduction (S phase) or not (G0)
S (Synthesis): DNA replication
G2 (Gap2): continued growth and preparation for division (centrosomes/centrioles duplicate)

6. Cell Cycle Mitosis (M): nuclear division
Cytokinesis: division of cytoplasm and cell membrane/cell wall

7. DNA
Chromatin: spread out DNA-protein complex. In Eukaryotes the proteins are histones. Human cells have 3 billion base pairs.
Chromosomes: condensed strands of DNA distinct in number and length for each organism. One chromosome is made up of 30 to 150 million base pairs.

8. DNA Humans have 46 chromosomes (23 pairs).
Each chromosome contains a few thousand genes that code for cellular proteins

9. DNA
Diploid indicates that our somatic (body) cells have 23 pairs of chromosomes (2n)
Haploid indicates that our gametes (sex cells) have 23 chromosomes (1n or n)

10. Mitosis: Division of the Nucleus
Problem: distribution of one exact copy of each of their chromosomes to each new cell.
Each chromosome contains thousands of genes, each necessary to the proper functioning of the organism.
Humans have ~120,000 genes spread over 46 chromosomes in each somatic cell.

11. Mitosis
During Mitosis all access to the DNA stops as chromatin coils up and condenses into visible chromosomes
Each replicated chromosome is composed of 2 identical parts (sister chromatids) held together by a centromere.

12. Mitosis
Sister chromatids are pulled apart during mitosis, and partitioned into 2 daughter cells
Result of mitosis & cytokenesis: 2 daughter cells genetically identical to the parent cell.

13. Stages of Mitosis
Prophase: Chromosomes condense, centrosomes are pushed apart by growing spindle, nuclear envelope disintegrates

14. Stages of Mitosis
Prometaphase: the 2 centromeres of each chromosome attach to one kinetochore spindle fiber; centrosomes move to opposite poles
Kinetochore spindle fiber
Non Kinetochore spindle fiber

15. Stages of Mitosis
Metaphase: Chromosomes line up at the metaphase plate (equator); centrosomes are at opposite poles

16. Stages of Mitosis
Anaphase: Chromosomes separate due to shortening of kinetochore spindle fibers; cell elongates due to lengthening of non-kinetochore spindle fibers
Non Kinetochore spindle fiber
Kinetochore spindle fiber

17. Stages of Mitosis
Telophase: Chromosomes immediately uncoil and resume transcription activities; spindle proteins disassemble; nuclear envelope reassembles

18. Mitosis Animation

19. Cytoskeleton Creates Chromosome Migration
Spindle fibers are microtubules made of tubulin proteins that are always present in the cytoplasm
Enzymes assemble and disassemble spindle fibers

20. Centromere region contains
Centromere protein clamp, holding the 2 sister chromatids together; deactivated during anaphase
Kinetochore motor protein; 1 on each sister chromatid

21. Kinetochore microtubule
Several microtubules attach to each kinetochore motor protein
Motor protein starts moving (walks along the spindle fibers); kinetochore microtubules shorten, pulling chromsomes (at the metaphase plate) apart
ATP hydrolysis powers the motion

22. Non Kinetochore Microtubules
Microtubules lengthen, pushing the two poles apart (cell expands)
Non Kinetochore spindle fiber
Kinetochore spindle fiber

23. Cytokinesis Animal: Cleavage furrow
Made by microfilaments (actin fibers)
A drawstring around the middle of the cell
Cell pinches off into 2 daughter cells

24. Mitosis & Cytokinesis in Plant Cells
Plants have centrosomes w/out centrioles
No cleavage furrow
plant cells cannot separate due to cell wall
Cell plate grows through divided cell

25. Duration of the Cell Cycle
Prokaryotic Cells – 20 minutes
No DNA/Histone complex + fast DNA replication (500 NT/sec)
No spindle fibers, no mitosis
2 DNA rings are attached to 2 spots of the plasma membrane which grows apart
1 plasmid

26. Review

27. Duration of the Cell Cycle
Eukaryotic Cells – hrs
Longest phase of the cell cycle is interphase
Longest phase of mitosis is prophase

28. Frequency of Cell Cycles
Depends on cell type:
Cell type
Life span/frequency
Esophagus, epidermis
2-3 days
Small intestine
1-2 days
Large intestine
6 days
Red blood cells
3 months
White blood cells
Up to 10 years
Nerve cells
Lifetime (G0)