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. What is a karyotype and when is it used? Lab Meiosis and events and outcomes of its two divisions. Sources of variability in sexually reproducing organisms
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) Nuclei containing DNA Sperm cell (haploid) Zygote (diploid) Egg cell (haploid) Fertilized egg with DNA from both parents Embryo cells with copies of same inherited DNA Offspring with traits inherited from both parents
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 division 1. 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 Humans Somatic cells (sameness) Germ cells of the gonads (variability) Meiosis Haploid gametes (n = 23) n Egg cell n Sperm cell Fertilization Mitosis produces 2 genetically identical cells Meiosis produces 4 genetically non-identical cells each with ½ the number of chromosomes Multicellular diploid adults (2n = 46) Mitosis and development Diploid zygote (2n = 46) 2n
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
Cell Cycle Phases Interphase with gaps for growth Mitosis- division of the nucleus Cytokinesis- division of the cytoplasm www.cellsalive.com
Phases of cell Cycle Interphase Chromosomes duplicate and cell parts are made Mitosis Duplicated chromosomes are evenly distributed into two daughter nuclei
Overall Comparison of Mitosis and Meiosis
State of DNA inside a living cell In a non-dividing cell- DNA (2-3 m) is coiled as Chromatin (DNA + proteins/histones) In a dividing cell- chromatin condenses to form chromosomes (Chromatin + scaffold proteins)
State of DNA inside a living cell http://www.biostudio.com/demo_freeman_dna_coil ing.htm 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
Replication of Chromosomes Chromosomes are replicated during S phase prior to mitosis The result is two sister chromatids held together at the centromere Figure 2.3
The Mitotic Spindle An apparatus of microtubules that controls chromosome movement during mitosis Arises from the centrosome
Mitosis Used for growth, repair, and replacement Consists of a single division that produces two identical daughter cells A continuous process divided into 4 subphases - Prophase - Metaphase - Anaphase - Telophase Figure 2.3
- 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 centromere www.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 Cell plate forming Wall of parent cell Daughter nucleus Cleavage furrow SEM 140 TEM 7,500 Cleavage furrow Contracting ring of microfilament s Cell wall New cell wall Daughter cells Vesicles containing Cell plate cell wall material Daughter cells
Cytokinesis Animal cells Plant Cells Cleavage furrow Cell plate Microfilament (actin) and myosin contracting ring Golgi-derived vesicles
Frequency of cell division varies with the type of cell Very often Skin cells Bone marrow Lining of stomach and intestines Sometimes Liver cells Do not divide in mature animal Nerve cells
The Cell Cycle Control System The sequential events of the cell cycle are directed by a distinct cell cycle control system of regulatory proteins G 1 checkpoint Three major checkpoints are found in the G1, G2, and M phases G 1 M Control system G 2 S www.cellsalive.com M checkpoint G 2 checkpoint
The Cell Cycle Control Progression through cell cycle is controlled by regulatory proteins
Behavior of normal and cancer cells in cell culture Density-dependent inhibition of cell division Mortality of cellslimited numbers of cell divisions Anchorage dependence of cells
Cancer cells - grow out of cell cycle control - form masses called tumors - malignant tumors spread and invade other tissues Lymph vessels Tumor Blood vessel A tumor grows from a single cancer cell. Glandular tissue Cancer cells invade neighboring tissue. Cancer cells spread through lymph and blood vessels to other parts of the body. Figure 8.10
MEIOSIS AND CROSSING OVER Genetic 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
Genetic Variability Offspring acquire genes from parents by inheriting chromosomes
Meiosis Two consecutive cell divisions, meiosis I and meiosis II Results in four daughter cells Each final daughter cell has only half as many chromosomes as the parent cell
Meiosis animation http://www.sumanasinc.com/webcontent/a nisamples/majorsbiology/meiosis.html www.cellsalive.com / Meiosis Stages of Meiosis http://highered.mcgrawhill.com/sites/0072437316/student_view0/ chapter12/animations.html#
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 meiosis 3. 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