Cell Cycles and Mitosis

1
Cell Cycles and Mitosis
2
The Cell Cycle
3
So are my cells dividing.right now?

• At this exact moment, what phase of the cell
  cycle would most of your body cells be in?
• Interphase

• Some cells constantly divide to form new cells
• EXAMPLE skin cells, stomach cells, stem cells,
  and cells in a developing embryo).
• Other cells dont divide at all after the
  organism matures
• EXAMPLE nerve and muscle cells.

4
Summary of Events in the Process of Mitosis and
Cell Division
Begin with DNA Replication
Condense DNA Split chromatids End
with
46 (or 23 pairs) of double arm chromosomes
46 pieces of replicated chromatin
92 single arm chromosomes
46 pieces of chromatin per cell
46 pieces of chromatin in humans
5
PHASES OF THE CELL CYCLE
6
Interphase

• Period of cell growth and DNA replication.
• What types of processes might be taking place in
  a cell during interphase?
• Production of organelles, photosynthesis,
  Most of the cells metabolism occurs here.
• Is the cell shown below an animal or plant cell?
• Animal
• How can you tell?
• Does not have a cell wall

7
Interphase

• A. G1 phasePeriod of Cell Growth
• Synthesis of proteins and cell organelles occurs
  in preparation for division.
• B. S phaseDNA Replication!
• C. G2 phaseContinued growth and preparations
  for cell division. Centrioles in animal cell
  divide.

8
MITOSIS Prophase

• 1. Replicated DNA condenses into double-arm
  chromosomes.
• 2. Nuclear membrane breaks down and nucleoli
  disappear.
• 3. Spindle fibers form at ends of the cell.
• 4. Centrioles in animal cells move to opposite
  ends of the cell.

9
MITOSIS Metaphase

• 1. Double-arm chromosomes line up on the middle
  or equator of the cell.
• 2. Spindle fibers attach to chromatids at the
  centromere.

Equator
Pole
Pole
10
MITOSIS Anaphase

• 1. Spindle fibers contract, causing centromeres
  to split and identical chromatids to separate.
• 2. Single-arm chromosomes move to opposite ends
  or poles of the cell.

11
MITOSIS Telophase

• 1. Chromosomes unravel into chromatin.
• 2. Nuclear membrane reforms and nucleolus
  reforms.
• 3. Spindle fibers break down.
• 4. Furrow in animal cell forms (or cell plate in
  plant cells) as the cytoplasm begins to divide.

12
CYTOKINESIS

• A. Cytoplasm divides
• B. Furrow or cell plate is completed.
• C. Two, identical daughter cells are formed.

13
Differences Between Animal and Plant Mitosis and
Cytokinesis

• Centrioles
• organelles that aid in cell division that are
  only found in animal cells
• Cytokinesis
• 1) Furrow-in animal cells indentations in the
  cell membranes
• 2) Cell plate in plant cells- formation of the
  cell membrane from vesicles budding off the golgi
  apparatus-a new cell wall then grows from the
  formation of cellulose.

14
Frequency and length of time for the cell cycle
depends on

• Kingdom of cell-
• Plants 10-30 hours Animals _18-24 hours
• Type of cell-
• Skin, stomach, embryonic cells frequently
  divide
• Mature nerve, blood and muscle cells do not
  divide.
• Size of cell (SA/V ratio)
• Nutrients available
• Density of cells.
• Age of Cells-
• the ends of chromosomes (called telomeres)
  shorten each time a cell divides. After a
  certain number of divisions (about 50) the cell
  stops dividing. 

15
Cancer

• Uncontrolled mitotic division in cells. This can
  be caused by bad genes or environmental
  mutagens like UV radiation, cigaraette smoke,
  etc.)