<p> Cell Reproduction C-10-1</p><p>Living things get larger because there are more cells produced - not because the cells get bigger!</p><p>Reasons: ~ larger cells have more demand put on their DNA ~ larger cells have more trouble moving materials across the cell membrane</p><p>DNA overload - if a cell gets too big, there may not be enough info on the DNA to meet the cells needs! ie: library in a small town - everyone can check out a book with no problem - if the town gets bigger, but the library stays the same, not enough books for everyone - people have to wait!</p><p>Exchanging materials - the rate at which food and waste is brought across the membrane depends on the surface area of the cell - the rate at which the food and waste is produced depends on the volume of the cell ex: if a town gets bigger, but the roads stay the same, it's harder for people to get around town - same applies to cell materials in a large cell!</p><p>So before a cell gets too big... it divides!</p><p>Chromosomes! Ch. 14</p><p>Chromosome - rod shaped structure that forms when a single DNA molecule and its associated proteins coil tightly before cell division *Made up of genes which make up DNA - segment of DNA that carries info from the parent to the offspring</p><p>*Usually the DNA strand is uncoiled when in use. *When the cell prepares to divide, the DNA coils up and compacts for easier division</p><p>DNA looks like this:</p><p>Chromatid - one of a pair of strands of DNA that make up a chromosome *DNA replicates itself before cell division so each new cell will have the same genes The chromatids are joined in the center by a centromere made of protein. </p><p>They look like this:</p><p>We have 23 chromosomes! *body cells have 2 of each type of chromosome (diploid) *the 2 copies of each type are homologous chromosomes *one copy from Dad, one from Mom Ex:</p><p>*sex cells (gametes) only have 1 of each (haploid)</p><p>When a sperm fertilizes and egg, a zygote is formed! The new cell is now diploid!</p><p>Chromosomes affect development: *Most babies with less than 46 die before they become a fetus. * A person can live with more…like 47: ~ Down Syndrome = has extra chrom. #21 ~ trisomy – extra chromosome in a 2n cell ~ can determine this with a karyotype – look at a map of the chromosomes… Features of Down Syndrome:  short stature  round face  upper eyelids that cover the inner corner of the eyes  some degree of mental retardation</p><p>Can happen to any race!</p><p>Usually seen born to mothers older than 35 years but can happen to anyone. ` Due to the eggs’ DNA deteriorating over time and chrom. not separating properly</p><p>Chrom. # 21 does not separate at time of cell replication = nondisjunction ie: one cell gets both chrom’s and the other gets none.</p><p>Can test through amniocentesis or chorionic villi sampling:  are very invasive tests  can sometimes cause premature labor  use needles to obtain amniotic fluid or a sample of the villi from the placenta and make a karyotype to look for genetic abnormalities</p><p>Alterations in chromosome structure: Mutations – changes in an organism’s genetic material</p><p>Types of mutations: 1.) Deletion – piece of chrom. breaks off and is lost when the cell divides</p><p>2.) Duplication – piece could attach to its homologous chrom. and then the new cell will have 2 copies</p><p>3.) Inversion – piece reattaches itself to the original chrom. in the reverse order</p><p>4.) Translocation – piece may attach itself to a nonhomologous chrom.</p><p>Chromosomes determine your sex Autosomes – the 22 pairs that are NOT sex chromosomes</p><p>Sex chromosomes are the only pair the determine whether you’re female or male! 2 forms = X and Y The presence or absnce of the Y chromosome is what determines the sex…this is because the hormone that makes a male is located on the Y </p><p> Without it, the organism is female!</p><p>With us… Females = XX Males = XY</p><p>Since females only have an X to donate to their offspring, sex is always determined by the males.</p><p>Some oddities may arise like these: XXY = Klinefelter’s syndrome = male will be strerile  affects genital development  may have slight breasts  little body hair  long limbs</p><p>XYY = male is fertile (no syndrome name) XXX = Triplo-X syndrome = female is fertile</p><p>Mitosis and cell division! C-10-2</p><p>The simplest form of cell division is done by bacteria – binary fission *This is an asexual process that produces identical offspring</p><p>Bacteria: have no nucleus and no membrane bound organelles - DNA is circular and attached to the inner plasma memebrane - cell division has 2 steps: o copy DNA o divide the cell</p><p>It looks like this:</p><p>In eukaryoteic cells, the process is more complicated.  undergo the Cell Cycle – sequence of growth and division</p><p>In 5 Phases: G1 – S – G2 – M – C</p><p>1.) G1 phase – growth phase, takes place between divisions 2.) S phase – DNA is copied , at end you have a chromosome with 2 chromatids 3.) G2 phase – growth, mitochondria and other organelles replicate, microtubules reassemble ( form spindle apparatus) 4.) M phase – Mitosis occurs! a. nucleus divides into 2 nuclei: each with same # chrom. 5.) C phase – cytokinesis = cytoplasm divides </p><p>* The first 3 phases are collectively called Interphase ~ this is what the cell spends most of its life in</p><p>* When interphase ends, Mitosis now begins (M phase) Here’s what takes place now…</p><p>Prophase: * chrom. begin to condense * enzymes break down nuclear envelope * cylindrical centrioles start to separate and move to opposite ends of the cell – called “polar bodies” * protein fibers from centriole form spindle fibers – made of microtubules **NOTE! Plants do NOT have centrioles!**</p><p>Metaphase: * chrom. keep condensing * chrom. line up in the center of the cell – “equator” * more microtubules extend out of the centromere at the kinetochore – hold the chroms in place * one chromatid is attached to one centriole, one to the other</p><p>Anaphase: * centromere divides and the 2 chromatids separate * the new chroms move to opposite sides as the spindle fibers shorten</p><p>Telophase: * chroms uncoil at either end of cell *new nuclear envelope forms * spindle fibers break down and disappear</p><p>Cytokinesis begins – cell is cleaved in half * cell membrane grows to close both * done by a belt of protein threads</p><p>In plants… golgi bodies form a cell plate at the center of the cell to build a new cell wall - once the wall is complete, the cell separates!</p><p>Regulating the Cell Cycle C-10-3</p><p>Some cells divide often while others stop dividing once they are grown. Controls on Cell Division: - place cells in a nutrient broth in a petri dish - cells will grow until they cover the bottom - when they touch, they stop growing - if remove cells from center, cells will grow until the gap is closed! - shows that cell division can be turned on and off</p><p>* same happens in the body when a cut or injury happens! ~ cells divide to until they close the gap - then slows down and returns to normal</p><p>Checkpoints: Cell inspects itself prior to cell division to make sure everything is good to go!</p><p>Several checkpoints... 1.) G1 checkpoint - checks surroundings before copying DNA if good - go to S phase if bad - rests and waits</p><p>2.) G2 checkpoint - checks for mistakes in DNA copying and makes sure cell is big enough to divide</p><p>3.) Mitosis checkpoint - checks at metaphase to see if chrom. are lined up correctly and attached to spindle fibers ~ ensures DNA is evenly split between daughter cells</p><p>Cancer ~ uncontrolled division of cells ~ can cause tumors which invade and damage healthy tissues</p><p>* Caused by loss of control of DNA ~ if division isn't regulated, damaged DNA could be copied and therefore cause more defective cells to be produced - causes tumors * Tumors - 2 kinds ~ benign - does not spread ~ malignant - can spread - called metastasis - invades and destroys healthy nearby tissues</p><p>* Treatment ~ drugs kill cancerous cells - chemotherapy ~ radiation therapy - high energy rays focus on the cells and kill them</p><p>* Prevention ~ avoid cancer causing agents! - UV rays - cigarettes / smoke</p>