Cell Cycle Mitosis vs. Meiosis

AP Biology Review Another Resource: Biology Web Page http://faculty.clintoncc.suny.edu/faculty/michael.gregory/default.htm

Cell cycle and its regulation How does the cell cycle assure genetic continuity? How does mitosis allow for the even distribution of genetic information to new cells? What are the mechanisms of cytokinesis? How is the cell cycle regulated? How can aberrations in the cell cycle lead to tumor formation?

The Cell Cycle - Mitosis

In 1855 Rudolf Virchow stated “where a cell exists, there must have been a preexisting cell, just as animal arises from animal and plant arises from plant.” “Omnis cellula e cellula” means every cell from a cell.

How does an organism such as Amoeba produce offspring compared to a human? Amoeba - one cell divides to create an entire organism. Human - cells divide to repair, maintain, or become part of a multicellular organism ; gametes (half the chromosomes) are made for reproduction

What might be a disadvantage to the progeny of an Amoeba compared to the offspring of humans? Offspring of humans have more variation because gametes are continuously mixing chromosomes from different organisms while in Amoebas the organisms itself is copied and divided to make more which leads to less variation which is bad if the environment changes and the population is not suited for the change.

Vocab genome – all genetic information in a cell (organism) chromosomes - packages of DNA molecules (46 in humans) somatic cells - all body cells except reproductive cells gametes - reproductive cells with half the # of chromosomes chromatin - DNA-protein complex 6) sister chromatids - identical copies of chromosomes 7) centromere - the “waist” where sisters are connected 8) Mitosis - division of the nucleus (P,PM,M,A,T) which produces genetically equivalent cells 9) cytokinesis - division of the cytoplasm 10) Meiosis - division that produces gametes

Mitotic Cell Cycle

Interphase G1 - cell growth; organelles double S-phase - DNA replication G2 - prepare for mitosis

Mitosis Prophase - chromatin condenses, mitotic spindles form, nucleoli disappears Prometaphase - nuclear enveloope disappear, spindle fibers reach chromosomes, kinetechores form Metaphase - chromosomes align on metaphase plate, centromosmes on oppositte sides Anaphase - spindle fibers pull chromsomes by centromeres to oppositte sides Telophase - new nuclei form at each plate, cell starts to pinch

Mitosis

Mitosis

Cytokinesis Division of the cytoplasm

More Vocab mitotic spindle - fibers made of microtubules; pull chromosomes to middle of cell centrosome - non-membranous organelle; assembly of spindle microtubules starts kinetochore - structure of protein and chromosomal DNA at the centromere; “walks” the chromosome down the microtubule metaphase plate - the plane midway between the two poles where the chromomomes line-up during metaphase

What is the function of kinetochore and non-kinetochore microtubules? kinetechore - “walk” the chromosomes to one pole non-kinetechore - elongating the whole cell during anaphase

Animal vs. Plant Animal Plant cleavage; cleavage furrow appears, deepens until cell is spit in two Plant cell plate; vesicles from Golgi apparatus move to middle of cell

Binary Fission – “division in half” What brings about the separation of the two daughter cells? Still a mystery …

Evolution of Mitosis

Regulation of the Cell Cycle The cell cycle is driven by specific chemical signals in the cytoplasm.

1970’s – Experimentation: Two cells in different phases of the cell cycle are fused together. If one is in S while another in G1, the G1 immediately enters S. Likewise, if one is undergoing Mitosis the second nucleus also enters Mitosis.

More Vocab Cell Cycle Control System: A cyclically operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle. Checkpoint: Point where stop and go-ahead signals regulate the cycle. 2 main regulatory molecules: Protein kinases Cyclins Cdks: proteins that drive the cell cycle and rise and fall depending on the concentration of cyclin. MPF: “maturation or M-phase promoting factor” cyclin-Cdk complex Triggers cells passage past the G2 checkpoint and into M-phase

Figure 12.14 – Campbell 6th Edition http://www.cellsalive.com/cell_cycle.htm

Role of Cdk, cyclin, and MPF: Binds to cyclin to form MPF Cyclin: Binds to Cdk to form MPF MPF: Cdk + cyclin Promotes mitosis by phosphorylating proteins Breakdown of its own cyclin Which is conserved? Why? Cdk: It’s an enzyme so it’s reusable!

Kinetechore Involvement: Kinetechores not yet attached to microtubules trigger a signal that delays the onset of anaphase by keeping the Anaphase Promoting Complex (APC) in an inactive state. After all kinetochores are attached the “wait” signal ceases and APC becomes active. Cyclin is broken down and proteins holding sister chromatids together are inactivated.

More Vocab: Growth Factor: PDGF: Density dependent inhibition: Protein released by certain body cells that stimulate other cells to divide. PDGF: Stimulates the division of fibroblast cells; helps heal wounds. Density dependent inhibition: Crowded cells stop dividing. Anchorage dependence: Cells must be attached to substratum in order to divide.

Cancer Failure to exhibit density dependent inhibition Failure to exhibit anchorage dependent inhibition Cell cycle control system is abnormal Manufactures its own growth factors or abnormal signal pathway

Last of the Vocab: Transformation: Tumor: Benign Tumor: Process that converts normal cells to cancer cells Tumor: Mass of abnormal cells within otherwise normal tissue Benign Tumor: Remain at original site Can be removed Malignant Tumor: Abnormal cells move to different regions, impair function of one or more organs; CANCER Metastasis: Spread of cancer cells to locations distant from the original site

Breast Cancer

Heredity and Evolution Hereditary events control the passage of structural and functional information from one generation to the next Meiosis is a driving force for evolutionary change as it provides a variety of possible gametes to be passed to the next generation

Heredity Meiosis and gametogenesis What features of meiosis are important in sexual reproduction? Why is meiosis important in heredity? How is meiosis related to gametogenesis? What are the similarities and differences between gametogenesis in animals and gametogenesis in plants?

Meiosis and Sexual Life Cycles

Definitions Heredity: transmission of traits from generation to the next Variation: slight differences in appearance Genetics: scientific study of heredity and hereditary variation

Genes Genes: coded information in the form of hereditary units (lots of genes on each chromosome) Where else can you find DNA beside the nucleus of the cell? Mitochondria Chloroplast

Asexual Reproduction Asexual reproduction single individual is sole parent and passes copies of all its genes to its offspring Clone the offspring of asexual individuals

Sexual reproduction Two parents give rise to offspring with unique combinations of genes; results in more variation

Animals Life Cycle Plants and some algae Fungi and some algae sequence of stages from an organisms conception to production of its own offspring Animals

More Vocab somatic cell: body cells; any cell other than sperm or ovum karyotype: micrograph of the 46 human chromosomes in which they are lined up in pairs starting with the longest homologous chromosomes: same length, centromere position, staining pattern; carry genes governing the same inherited characters sex chromosomes: X and Y chromosomes autosomes: all non-sex chromosomes (1 through 22)

Amniocentesis

Karyotype

Meiosis and Sexual Reproduction Sexual Reproduction – chromosomes of two parents combine to form offspring 23 23 + (N) + Gametes Fertilization (2N) 46 Zygote

About Chromosomes (2N) = diploid – any cell with 2 complete sets of chromosomes (N) = haploid – a cell with 1 complete set of chromosomes Zygote (2N) – egg cell after fertilzation = egg + sperm Each chromosome in egg has a matching chromosome from sperm Homologous Pairs – matching chromosomes

Homologous pairs chromosomes occur in pairs one set from each parent Diploid or 2N Cells that contain both sets of chromosomes. Haploid =1N Sex cells have only half the chromosome number

Just before Meiosis begins, during interphase identical sister chromatids are attached at the centromere, and centrioles have been duplicated. Centrioles

Meiosis: Prophase I During Prophase I: chromosomes condense nucleus breaks down spindle fibers form Homologous chromosomes form tetrads (fours)

Meiosis: Prophase I the chromosomes condense centrioles move to opposite poles of the parent cell and begin building the spindle microtubules. the nuclear envelope breaks down

Meiosis: Prophase I Homologous chromosomes pair up, forming tetrads.

Meiosis: Prophase I Homologous chromosomes pair up, forming tetrads...

Meiosis: Prophase I …. and crossing over may occur. Crossing over- pieces of DNA are exchanged with the matching homologous chromosome

Meiosis: Prophase I centrioles begin building the spindle fibers.

Meiosis: Prophase I Spindle fibers grab each chromosome at the centromere. Move the chromosomes towards the poles.

Meiosis: Metaphase I During Metaphase I: Homologous chromosomes line up in the middle. Equator = metaphase plate

Meiosis: Metaphase I Each pair is assorted independently; this means that the maternal homolog in each pair randomly faces up or down. And this pair could have assorted like this. So this pair could have assorted like this.

Meiosis: Anaphase I During Anaphase I: Homologous pairs of separate. Sister chromatids remain attached at the centromere.

Meiosis: Anaphase I

Meiosis: Anaphase I

Meiosis: Telophase I During Telophase: spindle fibers break down new nuclear membrane forms

Meiosis: Telophase I the spindle fibers break down

Meiosis: Telophase I new nuclear membrane forms around each group of chromosomes

Cytokinesis: Splitting of the cytoplasm

Now these two haploid cells will begin Meiosis II; in this division, sister chromatids will separate.

Meiosis: Prophase II Meiosis II is very much like Mitosis. During Prophase II: nuclear membrane breaks spindle fibers reform

Meiosis: Prophase II the nuclear membrane breaks down

Meiosis: Prophase II centrioles move to opposite poles of the parent cell and begin building new spindle fibers

Meiosis: Prophase II

Meiosis: Prophase II centrioles begin building the spindle fibers

Meiosis: Prophase II The spindle fibers attach to the chromosomes at the centromere

Meiosis: Metaphase II The spindle fibers move the chromosomes to the center (metaphase plate) of the cell.

Meiosis: Anaphase II Sister chromatids separate.

Meiosis: Anaphase II

Meiosis: Telophase II During Telophase II: the spindle fiber break down nuclear membrane reforms around each group of chromosomes

Meiosis: Telophase II the spindle fibers break down

Meiosis: Telophase II new nuclear membrane form around each group of chromosomes

Cytokinesis: Result: Four non-identical haploid cells are formed.

Mitosis vs. Meiosis

A comparison of mitosis and meiosis Mitosis and Mieosis Chromosomes replicate only once Mitosis Cell divides once Produces 2 identical daughter cells Meiosis Synapsis occurs and tetrads form Cell divides twice Daughter cells with half the number of chromosomes Daughter cells are not all alike Produces 4 cells (gametes)

Independent Assortment

Crossing Over

Genes on the same chromosome do not sort independently but can be recombined during a cross-over. Allows us to map genes. Further distance = more likely cross-over.