• Cell Division and Mitosis

• -Chapter 9-

• Honors Biology Program• Mountain Pointe High School

Development Of A Human Hand

future arm and hand of embryo, five weeks old

Overview: Key Roles of Cell Division

• Reproduction distinguishes living from non-living• Multicellular organisms develop from a zygote.• Cell division aids in repair & renewing of cells

Overview: Key Roles of Cell Division

• Cell division results in genetically identical daughter cells.• Exact copy in each daughter cell.• A cells genetic information, package in DNA, is called its genome.• In prokaryotes DNA a long single strand• Eukaryotes several DNA molecules.

Overview: Key Roles of Cell Division

• In meiosis gametes are produced (egg & sperm cells).• Meiosis yields 4 non-identical daughter cells with ½ the number of chromosomes.

The Cell CycleEukaryotic cells

divide in a series of steps known as the Cell Cycle.

Three main parts:

(a) Interphase

(b) Mitosis

(c) Cytokinesis

End result: two genetically identical “daughter cells”.

InterphaseInterphase

• It’s important to understand that

during Interphase, no division is taking

place!• Interphase is divided into three

stages:• G1

• S• G2

InterphaseInterphase• G1 phase, the cell grows

and protein production is high.

• S phase, DNA is replicated. Chromosomes aren’t visible, since the DNA is in the form of chromatin.

• The number of cytoplasmic components is doubled.

nucleus

cytoplasm

cytoplasm

DNA ReplicationDNA Replication

one chromosome (unduplicated)

one chromosome (duplicated)

one chromatid

sister chromatid

CENTROMERE

• “S” stage of Interphase, DNA must copy itself so that each new daughter cell will have its own copy of the genetic code.

• The two sister chromatids are held together by a centromere.

Chromosome Structure

Kinetochore

One nucleosome

DNA

Attached to both sides of a centromere are connecting points

known as kinetochores.

These function as attachment points for the spindle

microtubules.

This diagram shows how DNA wraps around protein spools known as histones. A histone & its DNA

together are known as a nucleosome.

MitosisMitosis

• The process of the nucleus dividing is known as “mitosis”.

• Mitosis has four stages: Prophase, Metaphase, Anaphase and Telophase.

EARLY PROPHASE

LATE PROPHASE LATE PROPHASE

ProphaseProphaseThe first stage of mitosis is

prophase.

Chromatin condenses and coils into visible chromosomes.

Nucleolus & nuclear envelope disintegrate.

Spindle apparatus starts to form between centrioles.

Centrioles (found only in animal cells) begin moving to

opposite ends of the cell.

• MetaphaseMetaphase

The shortest stage of mitosis is metaphase.

During this phase, the sister chromatids are

arranged at the equator of the cell.

The spindle microtubules attach to

the kinetochores of each chromatid.

• During anaphase, the two sister

chromatids are separated from each other by the spindle

microtubules and moved to opposite

poles.• Once separated, they

are referred to as chromosomes, not

chromatids.

AnaphaseAnaphase

• The final stage of mitosis is telophase.

• Chromosomes uncoil into chromatin.

• Nucleoli & nuclear envelopes reappear.

• Spindle microtubules disintegrate.

TelophaseTelophase

• The division of the cytoplasm is known as cytokinesis.

• Cytokinesis is the final step in the Cell Cycle.

CytokinesisCytokinesisIn animal cells, a cleavage furrow forms, microfilaments contract and cut the cell in two.

• In plant cells, the cell wall prevents the cell from being pinched in two.

• Instead, a “cell plate” forms between the two nuclei.• Cellulose deposits begin to form at the cell plate, forming a crosswall

that divides the parent cell into two daughter cells.

CytokinesisCytokinesis