Human Skin (Epidermis) Cell Replacement Cell Division Hydra Top layers = dead cells ●Multicellular organisms: Are constantly shed –Growth –Cell replacement and repair –Asexual reproduction Middle Layers = Living Cells Replace dead cells ●Unicellular organisms: –Reproduction (asexual) Bottom Layers = Dividing Cells Replace living cells Kinetochore Chromosomes Chromosomes proteins chromosome = ●All chromosomes have a partner, condensed DNA w/protein ●These pairs of chromosomes are called homologous during cell division chromosomes and contain genes for the same traits ●During cell division, a single chromosome consists of 2 identical sister chromatids Chromosomes Chromosomes Chromatin = uncondensed DNA with associated proteins ●Humans have 46 Histones = proteins that help maintain shape of chromosomes / 23 pairs chromosome and aid in packing ●Most chromosomes are called autosomes ●Karyotype = photo- micrograph of chromosomes Chromosomes Cell Division ●Chromosomes which determine sex are called sex Eukaryotes – 2 types: Mitosis = division of the nucleus, chromosomes results in 2 identical diploid “daughter” cells ●In humans these are called X and Y Meiosis = division to produce gametes = sex cells, results in 4 haploid gametes ●Diploid vs. haploid: in humans: normal cells = diploid - have 46 chromosomes (23 pairs) sex cells = haploid - have 23 chromosomes Cell Division Cytokinesis ●Prokaryotes ●Cytokinesis = the division of the cytoplasm ●all are unicellular so division = reproduction ●Happens at the same time as mitosis (and meiosis) ●called Binary Fission ●Except in cells with multiple nuclei ●Animals – cells pinch inward The Cell Cycle Cytokinesis •4 stages for cells ●In Plants – new cell wall forms that divide: •G1 ●Called a cell plate •S •G2 •M •1 for cells that don't: •G0 The Cell Cycle The Cell Cycle ●G1 phase – Gap 1 ●G2 phase – Gap 2 –cell growth –continued cell growth –organelles duplicate ●M phase – Mitosis and Cytokinesis ●S phase – Synthesis –cell division –DNA is replicated The Cell Cycle The Cell Cycle ●Controlled by checkpoints ●M checkpoint – checks to see if spindle is assembled, checks to see if chromosomes are ●G1 checkpoint – checks to see if DNA is aligned properly damaged ●If the cell fails a checkpoint, either the problem ●G2 checkpoint – checks to see if DNA was (ex. damaged DNA) is fixed (DNA is repaired) replicated properly or the cell undergoes apoptosis Mitosis Interphase ●I+PMAT+C (not condensed) ●Before Mitosis → Interphase ●Prophase → Metaphase → Anaphase → Telophase ●During/after Mitosis → Cytokinesis ●Mnemonic device: Internet President Milford Ate Tacos Constantly –Or, Interesting People Make A Terrific Conversation Prophase Chromosome Prophase detailed consisting of Pair of ●During prophase: two sister –the nuclear envelope breaks down and chromatin Centrioles chromatids condense (Condensed) –Spindle fibers attach to chromosomes at centromeres Centromere Aster Prophase Prophase detailed Metaphase Nonkinetochore Kinetochore microtubules ●Two types of spindle fibers microtubules –Kinetochore microtubules = attach to kinetochore proteins at centromere of chromosomes / move chromosomes –Nonkinetochore microtubules = attach to other Mitotic nonkinetochore microtubules from other side of the cell / lengthen cell to prepare for cytokinesis Chromosomes line up in the center Anaphase Telophase & Cytokinesis Sister Cell pinches inward in chromatids the center, separate 2 nuclei begin and move to reforming opposite ends of the cell Telophase & Cytokinesis detailed Telophase & Cytokinesis detailed ●During telophase & cytokinesis: - In plants, cell plate forms which will become new cell wall - 2 new daughter cells are formed –Nuclear envelope reforms & chromosomes uncoil into chromatin –Mitotic spindle breaks up –Cleavage furrow forms (pinching inward of plasma membrane) Mitosis in actual cells Factors Affecting Cell Division ●Growth factors (hormones) stimulate growth/division ●Anchorage – cells need to be attached to a surface ●Cell density – if cells touch each other they stop growing ●Checkpoints in the cell cycle The Cell Cycle and Checkpoints Density of Cells - Growth factors control whether cells can pass checkpoints and divide G1 checkpoint M checkpoint G2 checkpoint Tumors Tumors ●Form when mutations in DNA cause ●may be benign = non-cancerous, remain in place checkpoint system to malfunction –cysts, warts and moles are all benign tumors ●Cells grow without growth factors and despite ●tumors can also be malignant = uncontrolled dividing a high density cells that invade and destroy healthy tissues ●When cells grow out of control they form a –called cancerous tumors or just cancer tumor = abnormal growth of cells caused by uncontrolled cell division Types of Cancer Causes of Cancer ●Carcinoma = in the skin or cells that line organs ●Mutations in DNA that mess up how the cell regulates division ●Sarcoma = grow in bone and muscle tissue –can be spontaneous mutations – ●Lymphoma = solid tumors in tissues that form blood cells mostly caused by Carcinogens = any substance that increases the risk of cancer –can cause Leukemia = uncontrolled production of white blood cells Causes of Cancer Meiosis ●many carcinogens are mutagens = cause ●Meiosis = cell division which reduces the number of mutations to occur in cells chromosomes –examples: tobacco, asbestos, X-Rays, UV ●Divides twice: Meiosis I and Meiosis II radiation ●Produces 4 daughter cells ●cancer risk and incidence increases with exposure to carcinogens and age Meiosis Meiosis ●4 daughter cells: Are haploid ●Essential for sexual ●Have unpaired chromosomes reproduction – gametes ●Are not identical to each other combine in the process of ●Most are gametes = sex cells (sperm and egg) fertilization to form a diploid zygote Diploid parent cell ●The reduction in chromosomes allows the zygote and thus the offspring to be diploid Haploid daughter cells Sexual Reproduction The Phases of Meiosis 23 Before Meiosis → still have Interphase chromosomes ●Meiosis I ●Meiosis II in humans –Prophase I –Prophase II 46 chromosomes –Metaphase I –Metaphase II in humans –Anaphase I –Anaphase II –Telophase I & –Telophase II & ●Zygote is the first cell in the new organism Cytokinesis I Cytokinesis II ●Offspring = new organism (aka child) Interphase (Before Meiosis) Chromosomes review Kinetochore ●During cell division, a single proteins chromosome consists of 2 identical sister chromatids ●All chromosomes have a partner, ●These pairs of chromosomes are called homologous chromosomes ●Ordinary cell processes (G1 and G2) and contain genes for the same ● DNA is replicated (S) traits ●Pretty much the same as interphase before mitosis Prophase I of Meiosis I Metaphase I of Meiosis I Spindle fibers Nonkinetochore centrioles microtubules Kinetochore microtubules ●Tetrads line up in the middle of the cell ●Synapsis occurs = homologous chromosomes ●Chromosomes are lined up 2 by 2 pair up to form a tetrad ●Homologous chromosomes next to each other ●Crossing over occurs at chiasma Anaphase I of Meiosis I Telophase I & Cytokinesis I of Meiosis I Cleavage furrow ●Cytokinesis divides the cytoplasm to form 2 cells ●Homologous chromosomes separate and ●Most cells undergoing meiosis I proceed directly into move to opposite ends of the cell meiosis II ●Nuclei don't really fully reform Homologous chromosomes Crossing Over Crossing over = the exchange of genes Chiasma between homologous chromosomes These genes are for the same trait but may Crossing over occurs during be a different version Ex. - gene for the trait prophase I of meiosis I hair color may be for New recombined chromosomes brown or black hair The 4 chromosomes that end up in the 4 daughter cells after meiosis Prophase II of Meiosis II Metaphase II of Meiosis II ●Essentially the same as prophase in mitosis, except: ●Chromosomes line up in the center of the cells ●2 cells ●cells don't have a full set of chromosomes ●Essentially the same as metaphase in mitosis Anaphase II of Meiosis II Telophase II and Cytokinesis II of Meiosis II ●Chromosomes separate and the sister chromatids move to opposite ends of the cell ●4 unique haploid daughter cells produced ●Essentially the same as anaphase in mitosis Independent Assortment Importance of Genetic Variation ●Homologous chromosomes line up randomly during ●Allows for variations in traits amongst individuals in a metaphase I of meiosis I and separate randomly population during anaphase I of meiosis I ●Helps ensure survivability of a population and species ●Results in increased genetic variation ●ex. A factor (disease, predator, etc.) that effects an individual with a particular trait will only effect those that have the trait ●Necessary for evolution Sources of Genetic Variation ●Independent assortment ●Crossing over ●Meiosis producing non identical cells w/ unpaired chromosomes ●Sexual reproduction.