Mitosis and Meiosis 8.2, 8.3, & 10.2

Levels of Biological organization Cells  Tissues Tissues  Organs Organs  Organ Systems Organ Systems  Organisms

From zygote to Trillions of Cells Zygote=Cell that forms when sperm and egg join Sperm gives you DNA from dad, egg gives you DNA from mom Shortly after sperm fertilizes egg, the zygote splits into a 2nd cell These 2 cells split into 4, then 8, then 16, etc. Each of these cells contains IDENTICAL DNA (Recall DNA replication)

Why must cells divide Diffusion limits cell size Cells get materials from surroundings through their membrane. This is also how they expel wastes If the cell gets too large, it would take a long time for these processes to occur DNA also limits cell size DNA  RNA  Proteins There is a limit on how fast this can happen. If the cell is too large, it takes too long to make all of the structures from the proteins.

Surface area-to-volume

Cell Cycle

I-PMAT The cell cycle can be divided into 2 (or 3) stages Interphase, Mitosis, and Cytokinesis Interphase and Mitosis are further divided by certain events that happen Interphase=G1, S, G2 Mitosis=Prophase, Metaphase, Anaphase, Telophase NEITHER INTERPHASE NOR CYTOKINESIS ARE PARTS OF MITOSIS

Interphase (G1, S, G2) Think “Intermission” Most of the cell’s life is spent in Interphase Period of growth and development G1 (Growth Phase 1) Cell grows in size and synthesizes mRNA and proteins S Phase (Synthesis phase) DNA replicates G2 (Growth Phase 2) Cell grows again, organelles are duplicated, and proteins are synthesized to prepare for cell division

Mitosis Period of division 4 parts (PMAT) Prophase (“Prologue”) Metaphase (“Middle”) Anaphase (“Apart”) Telophase (“Two”) Happens only in somatic (body) cells

Prophase (“Prologue”) First and longest stage of mitosis Prophase begins as strands of chromatin coil around proteins called histones and become a chromosome (tightly wound strand of DNA and proteins) Each copy of DNA (from Interphase) coils and forms 2 identical strands Called sister chromatids These sister chromatids join together at the center (called a centromere) Each chromosome has a “partner” (remember, you get one from your mom and one from your dad) These are called homologous chromosomes The nucleus disappears Centrioles move to opposite ends of the cell A structure called a spindle forms Made up of rod-like structures called microtubules

DNA to Chromosomes

Chromosome Structure

Metaphase (“Middle”) Spindle fibers attach to centromeres of chromosomes Spindles extend from centriole on one side and attach to sister chromatid on that same side Fibers help chromosomes line up in the middle Very important because it ensures that ½ of the chromosomes end up in each cell

Anaphase (“Apart”) Spindle fibers shorten and pull sister chromatids apart at the centromere Each identical sister chromatid moves to one of the sides of the cell

Telophase (“Two”) Chromatids reach opposite ends Chromatids begin to unwind into chromatin Nuclei form around chromatin Spindle breaks down Cells begin to split This ends Mitosis

Cytokinesis Division of cytoplasm Cell divides and 2 new daughter cells are formed Process differs in plants and animals In plant cells, a structure called a cell plate forms and separates the 2 daughter cells In animals cells, the cells “pinch in” until the cells are separated

Control of the Cell cycle Cancer=uncontrolled cell division Proteins (called cyclins) created during protein synthesis help to regulate the cell cycle When these proteins are damaged by mutations of DNA, the cell’s normal cycle is disrupted and cells divide out of control Forms a tumor Cancer cells take nutrients from healthy cells, and can occasionally move around in the body. When cancer cells move around, it is called metastasis. This forms new tumors throughout the body

Meiosis Occurs only in sex cells (males-sperm and female-egg cells) The goal is to cut the original number of chromosomes in half Offspring need to inherit from both parents If the number was not cut in half, the offspring would have 2x the chromosomes as the parents Terms A diploid cell is a cell that contains 2 of each chromosome (di=2) These are typical body cells A haploid cell is a cell that contains 1 of each chromosome (hap~half) These have ½ the number of chromosomes as typical cells

Phases of Meiosis Very similar to mitosis IPMATPMAT Starts with Interphase Only occurs once before meiosis begins Basically does mitosis twice Meiosis I Prophase I, Metaphase I, Anaphase I, Telophase I Meiosis II Prophase II, Metaphase II, Anaphase II, Telophase II Each ends with cytokinesis

Meiosis-Interphase Exactly the same as in Mitosis Occurs only before Meiosis I, NOT Meiosis II

Meiosis-Prophase I Very similar to Prophase in Mitosis One huge difference Homologous chromosomes line up and form a structure called a tetrad They tangle up and can actually break portions off and exchange DNA Process is called crossing over Increases genetic diversity by potentially allowing you to pass on traits from both grandparents to offspring

Meiosis-Metaphase I Again, similar to Metaphase in Meiosis, but with a key difference Spindle fibers attach to tetrads, and line them up in the middle This means that there are 2 chromosomes next to one another in the center, instead of one as was the case in Mitosis Mitosis Meiosis

Meiosis-Anaphase I Probably the most different from Mitosis Whereas in Mitosis, sister chromatids separate at the centromere and move towards opposite ends of the cell, in Meiosis, tetrads are pulled apart and chromosomes (the pair of sister chromatids) move to each side of the cell This ensures that there will be a full chromosome in the daughter cells

Meiosis-Telophase I Occurs exactly as it did in Mitosis, except this time there is an entire chromosome (pair of sister chromatids) in each of the 2 new cells Another division is necessary to split the genetic material in half Cytokinesis occurs, same as Mitosis 2 diploid cells are formed

Meiosis II NO INTERPHASE This process occurs EXACTLY THE SAME AS MITOSIS Only it is occurring in 2 cells at once

Results of Mitosis and Meiosis In Mitosis, 1 cell splits into 2 daughter cells The daughter cells are identical In Meiosis I, a single cell splits into 2 daughter cells Each of these cells contains the same amount of chromosomes as the parent cell Still diploid, and not identical In Meiosis II, the 2 daughter cells from Meiosis I undergo another cell division, and split into 2 more daughter cells Each of these cells contains ½ of the original genetic material Now haploid, and each unique