The Cell Cycle and MitosisThe Cell Cycle and Mitosis

What is Mitosis?What is Mitosis?

Mitosis is the process by which eukaryotic cells divide.

Prokaryotes divide through a simpler process called binary fission.

What is the purpose of What is the purpose of Mitosis?Mitosis?

When single celled organisms go through mitosis, they are reproducing: there are now two new organisms (asexual reproduction).

Multicellular organisms go through mitosis to produce new cells to grow or to replace dying or damaged cells (growth and repair).

Human DevelopmentHuman Development

Sperm Motility

Cleavage and Implantation

Development of a fetus

Key termsKey termsChromosome- structure made of

highly coiled or condensed DNA.Chromatin – the uncoiled form of

DNA.Sister chromatids – two identical

sections (copies) of DNA joined together at the centromere.

Pictures on next slide

Often confused termsOften confused terms 1. Single strand of

chromatin (DNA’s normal structure in the nucleus)

2. Two sister chromatids joined at centromere (After replication)

3. Replicated or double stranded chromosome after condensation. Each half is still considered a sister chromatid (During the cell cycle)

Gap1 Synthesis Prophase

1 2 3

What is the cell cycle?What is the cell cycle?All cells pass through a series of

events called the cell cycle.Some cells cycle continually, other

cell types only a limited number of times before they die.

Cell CycleCell CycleOnly one hour out of 22 is spent in active division (Mitosis)Depending upon the type of cell undergoing the cycle.

Relationship of StagesRelationship of StagesInterphase

consists of:Gap 1 (G1)Synthesis (S)Gap 2 (G2)Total time : 21

Hours

Mitosis consists of:ProphaseMetaphaseAnaphaseTelophaseTotal time : 1 Hour

InterphaseInterphase Typical Cell spends

95% of its time in interphase

Centrioles replicate during Gap 1

DNA copies itself during Synthesis

Growth occurs during all three phases.

WhatWhat’’s the DNA s the DNA doing?doing?

Chromatin in Gap 1Replicates in

SynthesisCondenses into

chromosome during early mitosis (prophase).

ProphaseProphaseChromatin starts to coil into

chromosomesNucleus, Nucleolus and Nuclear

membrane (N guys) start to dissolve

Centrioles moving to opposite ends of cell

By end, chromosomes fully formed, N guys gone, and centrioles at opposite ends of cell.

MetaphaseMetaphaseAll chromosomes line up

on equator of cellSpindle fibers attach to

each chromosome

AnaphaseAnaphase Spindle fibers contract

and pull sister chromatids apart

Full set of DNA eventually pulled to opposite ends of cell.

TelophaseTelophaseChromosomes begin to uncoilNuclear membrane begins to reformIn plants, cell plate forms to divide

cytoplasmIn animals, cleavage furrow forms

to divide cytoplasm