Chapter 12 The Cell Cycle

1
Chapter 12 The Cell Cycle
2
Rudolf Virchow-1855

• Omnis cellula e cellula
• Every cell from a cell.
• In this chapter we will learn how cells reproduce
  to form genetically equivalent daughter cells.

3
Roles of Cell Division

• Reproduction
• Growth
• Repair
• In all cases, cell division must distribute
  identical genetic material to two daughter cells.

4
Cell Division
5
Introductory Vocab

• Genome all of a cells genetic information
• Somatic cell body cell
• Gamete reproductive cell (sperm or egg cell)
• Chromosome single DNA molecule
• Chromatin DNA-protein complex

6
DNA Coiling

• Why does DNA coil anyway?
• DNA Coiling Animation http//www.biostudio.com/de
  mo_freeman_dna_coiling.htm

7
Introductory Vocab

• Sister Chromatids replicated strands of a
  chromosome (identical)
• Centromere narrowing waist of sister
  chromatids
• Mitosis nuclear division resulting in 2
  identical nuclei
• Cytokinesis cytoplasm division

8
The Cell Cycle

• Interphase (90 of cycle)
• G1 phase growth
• S phase synthesis of DNA
• G2 phase preparation for cell division
• Mitotic phase
• Mitosis
• Cytokinesis

9
Mitosis

• Goal To split the sister chromatids and give one
  to each new nucleus.
• 5 Steps
• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase

10
Prophase

• Chromosomes visible
• Nucleoli disappear
• Sister chromatids
• Centrosomes start to separate
• Mitotic spindle forms

11
Prometaphase

• Nuclear membrane fragments
• Kinetochore develops
• Spindle interaction with chromosomes

12
Metaphase

• Centrosomes at opposite poles
• Centromeres are aligned at metaphase plate
• Kinetochores of all sister chromatids attached to
  microtubules (spindle)

13
Anaphase

• Paired centromeres separate sister chromatids
  liberated
• Chromosomes move to opposite poles
• Nonkinetochore microtubules lengthen the cell
• By end Each pole will have a complete set of
  chromosomes

14
Kinetochores

• Appear to ratchet the chromosome down the
  spindle fiber microtubule with a motor protein.
• Microtubules dissolve behind the kinetochore.

15
Telophase

• Cell elongates further
• Nuclear envelopes re-form
• Chromosomes become less coiled
• Cytokinesis usually begins

16
Cytokinesis
17
Nerve cell mitosis Movie
18
Binary Fission
19
Regulation of Cell Division

• Must be controlled.
• How? By what?
• See fig 12.12
• Rate of cell division depends on the cell type.
• Ex - skin frequently
• liver - as needed
• brain - rarely or never

20
External Cues Controlling Division

• Growth Factors
• Ex. Platelet Derived Growth Factor (PDGF)
• Density-Dependent Inhibition
• Anchorage Dependence

21
Checkpoints
Hey buddy, I dont care whatcha say! I am not
letting you through unless your DNA is correct!

• Critical control points in the cell cycle.
• Several are known.
• Cells must receive a go-ahead signal before
  proceeding to the next phase.

22
G1 Checkpoint

• Also called the restriction point in mammalian
  cells.
• Allows progression to S
• If not passed
• Places cells in a non-dividing phase called the
  Go phase.
• Most of your body cells are in this quiescent
  state.
• Some cells can reenter G1 with proper stimulus

23
G2 checkpoint

• Controls entry into M phase
• When enough cyclin is made to bind Cdk form
  MPF, cell can progress
• Control of cell cycle video

24
Mitotic Checkpoint

• Occurs in metaphase
• When all necessary microtubules have bound a
  kinetochore, Anaphase promoting complex (APC) is
  activated
• will activate proteolytic enzymes split
  centromeres

25
Cancer

• Transformation
• Tumors Benign or Malignant
• Metastasis

26
(No Transcript)
27
Comment

• Regulation of cell division is a balance between
  Mitosis Apoptosis
• Cancer can result if either process doesnt work.

28
G1 Checkpoint Tumor Supressor Proteins

• Key Tumor supressor proteins Rb p53
• Video

29
Rb and cdks
P
P
P
Rb
Cyclin
cdk
P
P
E2F
P
Rb
E2F
S-phase Gene
Transcription
S-phase Gene
No Transcription No S-phase genes No
continuation through the cell cycle
S-phase genes transcribed! Lets go start S-phase!
30
Cdk inhibitors p21 p16
P53 prompts transcription of p21 Both p21 p16
inhibit the cyclin/cdk complex from forming
p53
p16
p21
P
P
P
Rb
P
Cyclin
cdk
P
E2F
P
Rb
E2F
S-phase Gene