The cell cycle: The cell cycle: interphase, mitosis, interphase, mitosis, cytokinesiscytokinesis

InterphaseInterphase

Is divided into 3 parts:Is divided into 3 parts:1.1. Rapid growth Rapid growth

2.2. DNA synthesis and replicationDNA synthesis and replication

3.3. Centrioles replicate: cell prepares Centrioles replicate: cell prepares for divisionfor division

Interphase Part 1: Interphase Part 1: rapid growthrapid growth The cell growsThe cell grows Protein production is highProtein production is high

Interphase Part 2: DNA Interphase Part 2: DNA synthesis and synthesis and

replicationreplication The cell copies its chromosomesThe cell copies its chromosomes DNA synthesis does not occur all DNA synthesis does not occur all

through interphase but is through interphase but is confined to this specific timeconfined to this specific time

Interphase part 3: Interphase part 3: Centrioles replicate: cell Centrioles replicate: cell prepares for divisionprepares for division Centrioles replicateCentrioles replicate Mitochondria and other organelles Mitochondria and other organelles

are manufactured and cell parts are manufactured and cell parts needed for cell division are needed for cell division are assembledassembled

As interphase As interphase ends…ends…

Mitosis begins!Mitosis begins!

MITOSISMITOSIS Mitosis is the period of nuclear cell Mitosis is the period of nuclear cell

division in which two daughter cells are division in which two daughter cells are formed, each containing a complete formed, each containing a complete set of chromosomesset of chromosomes

Cells undergo mitosis (divides) as they Cells undergo mitosis (divides) as they approach the maximum cell size at approach the maximum cell size at which the nucleus can provide which the nucleus can provide blueprints for proteins and the plasma blueprints for proteins and the plasma membrane can efficiently transport membrane can efficiently transport nutrients and wastes into and out of nutrients and wastes into and out of the cell.the cell.

Stages of MitosisStages of Mitosis

It has 4 stages:It has 4 stages:– ProphaseProphase– MetaphaseMetaphase– AnaphaseAnaphase– telophasetelophase

Prophase: the first Prophase: the first stagestage This is the first and longest phase This is the first and longest phase

of mitosis.of mitosis. The long stringy chromatin coils The long stringy chromatin coils

up into visible chromosomes.up into visible chromosomes. Each duplicated chromosome is Each duplicated chromosome is

made up of 2 halves. The two made up of 2 halves. The two halves of the doubled structure halves of the doubled structure are called are called SISTER CHROMATIDS.SISTER CHROMATIDS.

The DNA of The DNA of sister sister chromatids are chromatids are exact copies of exact copies of each other and each other and are formed are formed when DNA is when DNA is copied during copied during interphase.interphase.

Prophase continued:Prophase continued:

Sister chromatids Sister chromatids are held together are held together by a structure by a structure called a called a centromere.centromere.

The centromere The centromere palys a role in palys a role in chromosome chromosome movement during movement during mitosismitosis

Prophase continued:Prophase continued:

As prophase continues, the As prophase continues, the nucleus begins to disappear as nucleus begins to disappear as the nuclear envelope the nuclear envelope disintegrates.disintegrates.

The centrioles begin to migrate to The centrioles begin to migrate to opposite ends of the cellopposite ends of the cell

Centrioles are made up of Centrioles are made up of microtubules and are located just microtubules and are located just outside of the nucleus.outside of the nucleus.

Prophase continuedProphase continued

As the pairs of centrioles move to As the pairs of centrioles move to opposite ends of the cell the spindle opposite ends of the cell the spindle begins to form between them.begins to form between them.

The spindle is a football-shaped The spindle is a football-shaped cagelike structure made of thin cagelike structure made of thin fibers of microtubules.fibers of microtubules.

Spindle fibers play a vital role in the Spindle fibers play a vital role in the separation of sister chromatids.separation of sister chromatids.

Metaphase: the second Metaphase: the second stage of mitosisstage of mitosis The doubled chromosomes The doubled chromosomes

become attached to the spindle become attached to the spindle fibers by their centromeres.fibers by their centromeres.

The chromosomes are pulled by The chromosomes are pulled by the spindle fibers and begin to the spindle fibers and begin to line up on the midline, or equator, line up on the midline, or equator, of the spindle.of the spindle.

Metaphase continuedMetaphase continued

Each sister chromatid is attached to its Each sister chromatid is attached to its own spindle fiber.own spindle fiber.

One sister chromatid’s spindle fiber One sister chromatid’s spindle fiber extends to one pole, and the other extends to one pole, and the other extends to the opposite pole. extends to the opposite pole.

This arrangement is important This arrangement is important because it ensures that each new cell because it ensures that each new cell receives an identical and complete set receives an identical and complete set of chromosomesof chromosomes

Anaphase: the third Anaphase: the third stage of mitosisstage of mitosis Sister chromatids begin to Sister chromatids begin to

separate.separate. The centromers split apart and The centromers split apart and

chromatid pairs separate from chromatid pairs separate from each other.each other.

The chromatids are pulled apart The chromatids are pulled apart by the shortening of the by the shortening of the microtubules in the spindle fibers.microtubules in the spindle fibers.

Telophase: the fourth Telophase: the fourth & final phase of & final phase of mitosismitosis Telophase begins as the chromatids Telophase begins as the chromatids

reach the opposite poles of the cell.reach the opposite poles of the cell. The chromosomes unwind so they can The chromosomes unwind so they can

begin to direct the metabolic activities begin to direct the metabolic activities of the new cells.of the new cells.

The spindle begins to break down.The spindle begins to break down. The nuclear envelope begins to The nuclear envelope begins to

reappearreappear A new double membrane begins to A new double membrane begins to

form between the two new nuclei.form between the two new nuclei.

The end of Mitosis… The end of Mitosis… The beginning of The beginning of cytokinesis.cytokinesis. Cytokinesis – the division of the Cytokinesis – the division of the

cells cytoplasmcells cytoplasm Cytokinesis is different in animals Cytokinesis is different in animals

and plantsand plants Cytokinesis in animals:Cytokinesis in animals:

– The plasma membrane pinches in The plasma membrane pinches in along the equator and the two cells along the equator and the two cells are seperated.are seperated.

Cytokinesis in Plants:Cytokinesis in Plants:– Plant cells have a rigid cell wall so the Plant cells have a rigid cell wall so the

plasma membrane does not pinch in.plasma membrane does not pinch in.– A structure called the cell plate is laid A structure called the cell plate is laid

down across the cell’s equator.down across the cell’s equator.– A cell membrane forms around each A cell membrane forms around each

cell and new cell walls form on each cell and new cell walls form on each side of the cell plate until separation side of the cell plate until separation is complete.is complete.

Plant cell undergoing Plant cell undergoing cytokinesis.cytokinesis.