Cell Division & Its Regulation: (Mitosis & Meiosis) (Outline)• Why do cells divide?• New Terms: gamete, zygote, somatic cells, germ cells, haploid, and diploid. • Types of eukaryotic cell division- Mitosis & Meiosis• Cell division of somatic cells and germ line cells.• Comparison of Mitosis & Meiosis in terms of # of cell divisions, # of daughter
cells, DNA content in comparison to mother cell, haploid/diploid state of daughter cells, genetic sameness or variability of daughter and mother cells.
• Cell cycle and its phases; Interphase and the Mitotic phase and events and outcomes of subphases of Interphase: G1, S, G2
• State of chromatin in non-dividing and dividing cells: looses chromatin and condensed chromosome.
• The Mitotic phases: (a) Mitosis: Prophase, Metaphase, Anaphase, Telophase, and (b) Cytokinesis.
• Cytokinesis in animal and plant cells.• Cell Cycle control checkpoints: G1, G2, & M. Cancer cells. • Meiosis and events and outcomes of its two divisions. • Sources of variability in sexually reproducing organisms
Sperm cell (haploid)
NucleicontainingDNA
Egg cell (haploid)
Fertilized eggwith DNA fromboth parents
Embryo cells with copies of same inherited
DNA Offspring with traitsinherited fromboth parents
Zygote (diploid)
Eukaryotic multi-cellular organisms• From gametes -sperm or egg (haploid)• Fertilization of sperm and egg produces zygote
(diploid) • Somatic cells- Body cells of multi-cellular
organism (diploid)
Cell Division & Its Regulation
Key Roles of Cell Division• .• .
Purpose: distribution of genetic material to daughter cells
Types of cell division
Two types in eukaryotic cells:Mitosis produces genetic sameness
(asexual reproduction)Meiosis produces genetic variability
(sexual reproduction)
Eukaryotic Cell division1. Asexual reproduction
(Identical cells)- Unicellular/ Amoeba
- Some multi-cellular eukaryotes plants and some animals like hydra, by budding cells
Eukaryotic Cell division ( cont’d)
2. Sexual reproduction (gametes, non-identical cells- for genetic variety of offspring)
Most multi-cellular organisms have both asexual and sexual reproduction
Cell Reproduction in HumansSomatic cells (sameness)Germ line cells of the gonads (variability)
Mitosis produces 2 genetically identical cellsMeiosis produces 4 genetically non-identical cells each with ½ the number of chromosomes Mitosis and
development
Multicellulardiploid adults
(2n = 46)
Diploidzygote
(2n = 46) 2n
Meiosis Fertilization
Egg cell
Sperm cell
n
Haploid gametes (n = 23)
n
Cell Division• One mother cell divides into two identical
cells following an ordered sequence of events (Cell Cycle)
• Summary of event of dividing cells• Replicate the genetic material• Manufacture additional cellular content• Divide the nucleus• Separate the cytoplasm
Overall Comparison of Mitosis and Meiosis
Interphase with gaps for growthMitosis- division of the nucleusCytokinesis- division of the cytoplasmwww.cellsalive.com
Cell Cycle Phases
Phases of cell Cycle
InterphaseChromosomes duplicate and cell parts are made
MitosisDuplicated chromosomes are evenly distributed
into two daughter nuclei
State of DNA inside a living cell
In a non dividing and in a dividing cell• Packaging of long strands of DNA in small
nucleus (loose chromatin: non-dividing).
• Condensed chromosomes in a dividing cell.
• Chromosomes are visible only when the cell is in the process of dividing during the mitotic phase
Chromatin
Figure 2.3
Replication of Chromosomes
Chromosomes are replicated during S phase prior to mitosis
The result is two sister chromatids held together at the centromere
The mitotic spindle is an apparatus of microtubules that controls chromosome movement during mitosis. It arises from the centrosome.
Figure 2.3
MitosisUsed for growth and repair
Consists of a single division that produces two identical daughter cells
A continuous process divided into 4 sub-phases
- Prophase- Metaphase- Anaphase- Telophase
http://highered.mheducation.com/sites/0072437316/student_view0/chapter11/animations.html#
- Centrosome- a pair of centrioles, microtubule organizing center (MOC).
- Spindle fibers- mirotubules (tubulin)- Nuclear membrane- Nucleolus- Loose chromatin- Condensed chromosome –two sister
chromatids held by centromerewww.cellsalive.com /mitosis http://www.biology.arizona.edu/cell_bio/tutori
als/cell_cycle/cells3.html
Mitosis in a fish blastula
Mitosis in an onion root
Cytokinesis in animal and plant cells
Cleavagefurrow
SEM
140
×
Daughter cells
Cleavage furrow Contracting ring ofmicrofilaments
TEM
7,
500 ×
Cell plateforming
Wall ofparent cell
Daughternucleus
Cell wall New cell wall
Vesicles containingcell wall material
Cell plate Daughter cells
CytokinesisAnimal cells Plant Cells
Cleavage furrowCell plateMicrofilament (actin) and myosin contracting ringGolgi-derived vesicles
Frequency of cell division varies with the type of cell
• Very oftenSkin cellsBone marrowLining of stomach and intestines
• SometimesLiver cells
• Do not divide in mature animal Nerve cells
The Cell Cycle Control SystemThe sequential events of the cell cycle
are directed by a distinct cell cycle control system of regulatory proteins
G2 checkpoint
Control system
M checkpoint
G1 checkpoint
G1
S
G2M
Three major checkpoints are found in the G1, G2, and M phases
www.cellsalive.com
Density-dependent inhibition of cell division
Anchorage dependence of cells
Mortality of cells-limited numbers of cell divisions
Behavior of normal and cancer cells in cell
culture
Tumor
Glandulartissue
A tumor grows from asingle cancer cell.
Cancer cells invadeneighboring tissue.
Cancer cells spread throughlymph and blood vessels toother parts of the body.
Lymphvessels
Bloodvessel
Figure 8.10
Cancer cells- grow out of cell cycle control
- form masses called tumors- malignant tumors spread and invade other tissues
MEIOSIS AND CROSSING OVERGenetic Variability
Chromosomes are matched in homologous pairs
– The somatic (body) cells of each species contain a specific number of chromosomes
– For example human cells have 46 chromosomes making up 23 pairs of homologous chromosomes
Chromosomes are matched in homologous pairs which carry genes for the same characteristics at the same place, or locus
Chromosomes
Centromere
Sister chromatids
Figure 8.12
Meiosis
• Two consecutive cell divisions, meiosis Iand meiosis II
• Results in four daughter cells• Each final daughter cell has only half as
many chromosomes as the parent cell
Meiosis animation• Stages of Meiosis
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#
• http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.html
• www.cellsalive.com / Meiosis
The results of crossing over during meiosis
Sources of variation in sexually reproducing organisms
1. Independent assortment of chromosomes during meiosis
2. Crossing over during meiosis3. Random fertilization
The results of independent assortment of homologous chromosome pairs at the metaphase plate in meiosis I
Chromosome Abnormalities involving chromosome numbers are caused by non-disjunction of
- Homologous chromosomes during Meiosis I- Sister chromatids during Meiosis II