Mitosis and the Cell Cycle

Chromosomes• Made of tightly coiled DNA and proteins• Chromatid= 2 identical halves of a chromosome.

– Called “sister chromatids”

• Centromere= point where chromatids join• Chromatin= uncoiled chromosome

– during Interphase DNA= thin strands of chromatin.

– DNA is easier to use/transcribe when uncoiled

– DNA is easier to move around when tightly packed into chromosomes for cell division.

Shown after replication in S phase

In G1, chromosomes are haploid (1 half)

Cell Cycle• The dividing and non-dividing (growth) stages

in the life of the cell.• Phases:

– Interphase (growth & DNA replication)– Mitosis (4 stages of nuclear division)– Cytokinesis

(separation of the

cytoplasm)

• http://www.cellsalive.com/cell_cycle.htm

INTERPHASE90% of cell’s life:

• G1: “Growth 1” (or Gap 1)

– Growth, cell metabolism and function

• S: “Synthesis”– DNA replication

• G2: “Growth 2” (or Gap 2)

– Extra growth and

preparation for

division (M phase)

*cell also has other organelles

CELL DIVISION• Cells need to divide when:

– A cell gets too big to support itself– New cells are needed for repair or replacement– An organism’s body grows

• Mitosis is asexual- no new genes mixed in

• Bacteria & other single celled organisms do binary fission for reproduction– Another form of asexual reproduction– No genetic variation, unless mutation occurs.

Phases of MITOSIS• Prophase

• Metaphase

• Anaphase

• Telophase

• PMAT!

PROPHASE• Longest part of mitosis• The chromatin coils into chromosomes

– So they’re packed, easier to move around.

• The CENTRIOLES move to the poles– Only in ANIMAL cells (no centrioles in plants)

• The spindle forms, attaches to chromosomes• The nuclear membrane & nucleolus break down.

– Allows chromosomes to escape

centrioles=Organelles that are always in animal cells, mostly used in mitosis

METAPHASE

• “Meta”= middle• Chromosomes line up at the middle, pulled

like a tug-o-war from the spindles at each pole of the dividing cell

ANAPHASE

• Centromeres split• Chromosomes split (from diploid to haploid)

• The sister chromatids get torn apart and begin to move toward opposite poles.– Each sister chromatid now becomes a

chromosome (With only 1 copy of DNA= haploid)

TELOPHASE

• The chromosomes uncoil ( = chromatin)• Nuclear membrane reforms around each new

set of chromosomes.• The spindle breaks down• Centrioles leave poles. “cleavage furrow” starts to

form in animal cells

CYTOKINESIS• The cytoplasm splits into 2 separate,

genetically identical “DAUGHTER CELLS.”• Cell division is complete.• Animal cells = “cleavage”

– Cell membrane pinches to form 2 separate cells

• Plant cells form a new Cell Wall (= “cell plate”)AnimalPlant

CELL CYCLE: BIG PICTURE

Cytokinesis

UNCONTROLLED CELL DIVISION

(a.k.a. “Cells Gone Wild”)• CANCER = when cells don’t stop dividing

– They are unable to receive normal chemical signals from the body that would stop division.

– Sometimes inherited (runs in the family)– Sometimes environmental (damaged DNA)

• TUMORS are masses of unnecessary cells.– Can be benign (harmless, doesn’t spread)– Can be malignant (invasive, spreads, “metastasizes”)

A

B

C

D

EWhat phases are these onion cells in?