Course Information

Mitosis

Department of AGB

Veterinary College

Bangalore

Mitotic Cell Division

Functions:

• Growth, maintenance, repair of body

tissues

• Forms the basis of

Asexual Reproduction

What is mitosis?

• Mitosis is nuclear division plus cytokinesis,

and produces two identical daughter cells

during prophase, prometaphase,

metaphase, anaphase, and telophase.

• Interphase is often included in discussions

of mitosis, but interphase is technically not

part of mitosis, but rather encompasses

stages G1, S, and G2 of the cell cycle.

Mitosis

• Somatic cells divide by mitosis – Involves 1 cell cycle / division

• Parental and 2 daughter

cells are genetically identical

• Parental cells are diploid

(46 chromosomes)

• 2 daughter cells are diploid

(46 chromosomes)

Interphase

The cell is engaged in metabolic activity and

prepare for mitosis (the next four phases

that lead up to and include nuclear

division).

Chromosomes are not clearly discerned in

the nucleus, although a dark spot called

the nucleolus may be visible.

Mitosis

4 phases:

1st – Prophase

2nd – Metaphase

3rd – Anaphase

4th – Telophase

and Cytokinesis

Prophase

i) chromosomes condense

• 3 major events

ii) spindle fibers form

iii) chromosomes are captured by

spindle

Chromosomes Condense

• Each chromosome consists

of 2 sister chromatids

attached to each other at the

centromere

Mitotic Spindle Forms

• Spindle fibers are specialized

microtubules

• Spindle fibers radiate out from

centrioles, forming the “aster”

• Centrioles occur in pairs, and are

duplicated during interphase

• One pair of centrioles migrates to

one pole of cell, the other pair

migrates to opposite pole of cell

chromatin

nucleolus

nucleus

centrioles

condensing

chromosomes

Spindle Captures Chromosomes

• When spindle fibers are fully formed

nuclear envelope disintegrates and

nucleolus disappears

• Spindle fibers attach to chromosomes

at the kinetochore, a structure located

at the centromere

• Function of spindle fibers is to

organize division of sister chromatids

into daughter cells

chromatin

nucleolus

nucleus

centrioles

condensing

chromosomes

Prometaphase

• The nuclear membrane dissolves, marking

the beginning of prometaphase. Proteins

attach to the centromeres creating the

kinetochores. Microtubules attach at the

kinetochores and the chromosomes begin

moving.

Metaphase

• Chromosomes align along

equator of the cell, with one

kinetochore facing each pole

centrioles

spindle fibers

chromosomes

•Spindle fibers align the chromosomes along the

middle of the cell nucleus.

•This line is referred to as the metaphase plate.

•This organization helps to ensure that in the next

phase, when the chromosomes are separated, each

new nucleus will receive one copy of each

chromosome.

Metaphase

Anaphase

• Sister chromatids separate

• Spindle fibers attached to

kinetochores shorten and pull

chromatids poleward

• Free spindle fibers lengthen and push

poles of cell apart

free spindle fibers

V-shaped chromatid

Anaphase

Anaphase

• The paired chromosomes separate at the kinetochores and move to opposite sides of the cell.

• Motion results from a combination of kinetochore movement along the spindle microtubules and through the physical interaction of polar microtubules.

Telophase

• Spindle fibers disintegrate

• Nuclear envelopes form around both

groups of chromosomes

• Chromosomes revert to their extended

state

• Nucleoli reappear

Telophase

Chromatids arrive at opposite poles of cell, and

new membranes form around the daughter

nuclei.

The chromosomes disperse and are no longer

visible under the light microscope.

The spindle fibers disperse, and cytokinesis or the

partitioning of the cell may also begin during this

stage.

• Cytokinesis occurs, enclosing each

daughter nucleus into a separate cell

chromosomes

decondensing

nuclear envelope

reforming

nucleolus reappears

pinching of cell

membrane at equator

cytokinesis

Cytokinesis

In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells, each with one nucleus.

In plant cells, the rigid wall requires that a cell plate be synthesized between the two daughter cells.

Cytokinesis

• Animal cells:

– microfilaments attached to plasma

membrane form a ring around

equator of cell

– ring contracts, like a drawstring,

dividing the cytoplasm