Cell Cycles and Mitosis

The Cell Cycle

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 don’t divide at all after the organism matures

EXAMPLE: nerve and muscle cells.

SUMMARY OF EVENTS IN THE PROCESS OF MITOSIS AND CELL DIVISION

Begin with: DNA Replication: Condense DNA: Split chromatids: End with:

46 pieces of chromatin in humans

46 pieces of replicated chromatin

46 (or 23 pairs) of double arm chromosomes

92 single arm chromosomes

46 pieces of chromatin per cell

PHASES OF THE CELL CYCLE

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

InterphaseA. G1 phase—Period of Cell

GrowthSynthesis of proteins and cell organelles occurs in preparation for division.

B. S phase—DNA Replication!

C. G2 phase—Continued growth and preparations for cell division. Centrioles in animal cell divide.

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.

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

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.

MITOSIS: Telophase1. 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.

CYTOKINESIS

A. Cytoplasm dividesB. Furrow or cell plate is

completed.C. Two, identical

“daughter” cells are formed.

Differences Between Animal and Plant Mitosis and Cytokinesis

• Centriolesorganelles that aid in cell division that are only found in animal cells

• Cytokinesis1) Furrow-in animal cells indentations in

the cell membranes2) 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.

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 divideMature 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.

Cancer

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