MitosisUnit 4: Cellular Processes

Background

1. Most plant and animal cells reproduce asexually- no DNA swap between other cells

a. This means the cells produced are exact copies or clones of the original cell.

b. The number of cells changes, but the DNA does not.

2. Binary Fission: cellular division of unicellular organisms that produces identical offspring

a. This is how Prokaryotes reproduce

3. Why do cells reproduce?

a. Increase size of organism

b. Repair injuries

c. Replace worn out cells

4. Pros and Cons of Asexual Reproduction

A. Proi. Can produce

offspring more quickly

ii. Can produce offspring more easily

iii. Do not need a partner cell to reproduce

B. Coni. All cells are alikeii. Species can’t

change and adaptiii. Do not need a

partner cell to reproduce

iv. One disease can wipe out a whole population

Eukaryotic Life Cyclea. Eukaryotic life cycle called the “cell cycle”

b. Consists of 6 “phases”i. Interphaseii. Prophaseiii. Metaphaseiv. Anaphasev. Telophasevi. Cytokinesis

c. The cell is usually in Interphase (about 90% of cells are in this phase at any given time!)

i. Nerve cells can stay in this phase for decades

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Visualize the Cell Cycle:

Interphase

Mitotic Phase (M Phase)

C Phase

G1

G2S (or G0)

Prophas

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6.Interphasea. This is when the cell is under “normal”

conditions

b. No cell division occurs at this time

c. Cell obtains nutrients and duplicates its chromatids.

i. Chromatids are connected by a centromere ii. Have a long and short arm

d. Comprised of a few “sub phases”:i. G1

ii. S Phase

iii. G2

iv. G0

ChromosomeStuff

7. G1a. G1: Means “growth 1”

b. Cell creates organelles and begins metabolism

c. Occurs after a new “daughter cell” has been created (cytokinesis) and before S Phase

d. Major period of cell growth

e. New organelles are synthesizedi. Lots of protein synthesis occurs

Provide structural support and enzymes catalyze reactions to make new organelles

8. S Phasea. S phase: means synthesis phase

b. Between G1 and G2

c. DNA synthesis (replication) occurs during this phase

d. Chromosomes in the cell are copied

e. Each chromosome has one coiled DNA double helix, called a chromatid

f. At the end of this phase, each chromosome has two identical DNA double helix molecules

i. Makes 2 sister chromatids

ii. Centrosome is also duplicated

9. G2a. G2: means growth 2

b. Shortest part of interphase, occurs after S phase and usually lasts around 4-5 hours.

c. Even though chromosomes copied, hard to find distinct chromosomes

i. Chromosomes are still in the form of loosely packed chromatin fibers.

d. Cell grows in preparation for cell division (Mitosis)

10. G0a. Sometimes the cell exits the cell cycle into a state called “G0”

i. Usually happens from G1

b. Cells are alive and metabolically active

c. But cells do NOT:i. Divide

ii. Copy DNA

iii. Prepare for cell division

d. Examples of cells in G0 phase:i. Heart muscle cells

ii. Eye cells

iii. Brain cells

e. If these cells are damaged, they can not be replaced.

11. What IS Mitosis?a. Mitosis occurs when a cell needs to reproduce itself

i. Most often happens in Eukaryotic cells

b. Makes 2 cells that are genetically identical to their “parent” cell and to each other (like twins)

i. We call this “2n” cells

ii. Mitosis makes somatic (body) cells

c. Mitosis is usually followed by cytokinesis (cell splits into 2 daughter cells)

i. Together, these make up “M Phase”

Important Structures

Asters

Centrioles

Polar Fibers

Kinetechore Fibers

Equator

Kinetechore

12.Prophasea. DNA Compresses into

Chromosomes

b. Centrioles appear in centrosome region & move to poles

i. Centrosome organizes spindle

c. Nuclear membrane & nucleolus disappear

d. Spindle fibers form & attach to chromosomes

13.MetaphseA. Chomosomes line up in

the middle of the cell

B. Think Meta- Middle

14. Anaphasea. Centromeres

split chromatids and move them apart

15.Telphasea. Reverse Prophase

b. Two nuclei form

c. Nuclear membrane and nucleolus returns

d. Centrioles and spindle fibers disappear

e. DNA spreads out as chromatin

16. Cytokinesis Cytoplasm splits into 2 cells