cell division chapter 8
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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
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