Cell Division

Chapter 8

http://www.youtube.com/watch?v=Q6ucKWIIFmg

Cell Division

Doubling organelles and proteins DNA replicationNuclear divisionCytoplasmic division

Cell Increase and Decrease

Maintain homeostasisCell numbers kept in check by this

mechanismThrough cell division of somatic cells and cell

death Cell division – interphase, mitosis and cytokinesisCell death – apoptosis

Cell Increase and Decrease

Somatic cells Asexual reproduction

increase in number of somatic cells

Increase in number unicellular organisms

Germ cells Sexual reproduction

requires the production of eggs and sperm

Chromosomes

Mitosis verse Meiosis??

MitosisDivision of somatic

cell nuclei

MeiosisDivision of gamete

nuclei

Cell Cycle – Somatic cells

Set of stages that involves cell growth and nuclear division

Consists of: Interphase

G1

SG2

Meiotic stageMitosis and

Cytokinesis

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

Interphase

When the cell carries on its usual functions

Main stages:G1

Gap before DNA synthesis begins

STime when DNA

duplicated***************G2

Gap between time DNA duplication ends and mitosis begins

Interphase in Meiosis?

Meiosis is a "one-way" processCannot be said to

engage in a cell cycle as mitosis does

Preparatory steps that lead up to meiosis are identical in pattern and name to the interphase of the mitotic cell cycle

Cytokinesis in Animal Cells

Cytoplasmic cleavageAccompanies mitosis

Separate processCleavage furrow forms

between daughter nuclei

Contractile ring contracts deepening the furrow

Continues until separation is complete

Human DNA in somatic cells

22-23 pairs of homologous chromosomesDifference?Autosomes (1-22)Sex chromosomes (23)

Somatic cells have 46 chromosomes Diploid2n

Human DNA in gametes

Due to reductional division

Halves the diploid number (2n) to a haploid number (n)

23 total chromosomes

DNA Replication

Duplicated chromosome Composed of 2 sister

chromatids held together by a

centromere

Sister chromatids Genetically identical When separate, each

daughter nucleus gets a chromosome

DNA copied

DNA divided

Division of the Nucleus

Nucleus must be divided Parent cell’s DNA into 2

nuclei

2 ways nucleus can divide:MitosisMeiosis

Mitosis

Maintaining the Chromosome Number

Mitosis

Mitosis4 main stages:

ProphaseMetaphaseAnaphaseTelophase

The Cell Cycle

1. Prophase – Mitosis begins!Threadlike form Spindle fibers appearDNA start to condenseAster formedNuclear envelope starts

to break apartCentrioles move to

opposite sides of the cell

The Cell Cycle

2. MetaphaseDuplicated chromosomes

aligned midway between the poles

Associated with spindle fibers

The Cell Cycle

3. AnaphaseSister chromatids

separate from each other and move to opposite polesBecome daughter

chromosomes

The Cell Cycle

4. Telophase Return to threadlike form

as in prophaseNew nuclear envelope

separates each chromosome cluster

2 new nuclei!!!!!

http://www.cellsalive.com/mitosis.htm

Meiosis

Reducing the Chromosome Number

Meiosis

Mechanism for dividing the nucleus of germ cells

Oogonia and spermatogonia2n

Meiosis must take place prior to formation of gametes

Sperm and eggsn

First stage in sexual reproduction

Meiosis Overview

Occurs in the life cycle of sexually reproducing organisms

Reduces the chromosome number2 divisions, 4 daughter cellsCells are diploid at beginning of meiosisTWO consecutive divisions

Result is 4 haploid nucleiDivided into:

Meiosis IMeiosis II

Comparisons between males and females

SpermatogenesisBegins at puberty and

continues throughout life

Oogenesis Begins in the fetus

Primary oocytes are arrested in prophase I

At puberty, one primary oocyte continues the process of meiosis during each menstrual cycle

Reducing the Chromosome Number

Genetic Recombination Promotes genetic

variabilityOccurs in Two Ways

Crossing Over Independent Assortment of

paired chromosomes

How Plant Cells Divide

Occurs in meristematic tissuesSame phases as animal cellsPlant cells do not have centrioles or asters

Plant Cells

Cytokinesis in Plant Cells

Flattened, small disk appears between daughter cells

Golgi apparatus produces vesicles which move to disk

Release molecules which build new cell walls Vesicle membranes complete plasma

membranes

Cell Division in Prokaryotes

Binary Fission Prokaryotes have a single

chromosome Chromosomal replication

occurs before division Cell elongates to twice its

length Cell membrane grows

inward until division is complete

Comparisons

MitosisDNA replication occurs

only onceRequires only one

divisionProduces two daughter

cellsDiploid daughter cells

2nGenetically identical

cells produced Occurs all the time

MeiosisDNA replication occurs

only onceRequires two divisionsProduces four daughter

cellsHaploid daughter cells

nGenetically variable

cells producedOccurs only at certain

times

Comparisons

Overview of the Life Cycle of Humans

Mitosis and Meiosis Gone Awry

Cancer

Chromosomal Abnormalities

Cancer

disease of the cell cycleCancer cells

do not respond normally to the cell cycle control system

can form tumorsif malignant, can spread to other parts of the body

Important Terms

TumorBenignMalignantMetastasisCancerCarcinomaSarcomaLymphoma

Cancer Treatment

Cancer treatment can involveRadiation therapy

which damages DNA and disrupts cell division

Chemotherapywhich uses drugs that disrupt cell division

Chromosomal Abnormalities

Nondisjunction members of a

chromosome pair fail to separate during anaphase

produces gametes with an incorrect number of chromosomes

If normal sperm fertilizes an egg with an extra chromosome result is a zygote with a

total of 2n + 1 chromosomes

Chromosomal Abnormalities

Down Syndrome:Trisomy 21condition in which an

individual has an extra chromosome 21

Affects about one out of every 700 children

Chromosomal Abnormalities

Nondisjunction can also affect the sex chromosomesKlinefelter's Syndrome

XXY malesTurner Syndrome

XO female