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Ch 6. Chromosomes and Cell Reproduction Where it all began… You started as a cell smaller than a period at the end of a sentence… And now look at you… How did you get from there to here? Getting from there to here… Going from egg to baby…. the original fertilized egg has to divide… and divide… and divide… and divide… Enduring Understanding Biological systems utilize free energy & molecular building blocks to grow, reproduce, & maintain dynamic homeostasis. Essential Questions How do organisms grow bigger after they are born? How do cells know when to divide? What is cancer? 6.1: Chromosomes About 2 trillion cells are produced by an adult human body every day! - about 25 million new cells per second! Type of cell division differs depending on: - the organism - why the cell is dividing WHY Cells Divide: 1. growth & repair 2. creation of gametes (sex cells) 3. method of reproduction in unicellular organisms Regardless of the type of cell division that occurs, all of the information stored in the molecule DNA must be present in each of the resulting cells. When a cell divides, DNA is first copied & then distributed. Each cell ends up with a complete set (copy) of the DNA. Prokaryotic Cell Division Binary Fission - type of reproduction that occurs in bacteria - single celled organism splits & becomes two identical organisms 3 stages STAGE 1 - Chromosome, which is attached to the inside of membrane, makes a COPY of itself STAGE 2 - Cell grows till about TWICE Normal Size. CELL WALL forms between the two Chromosomes. STAGE 3 - Cell SPLITS into 2 NEW CELLS. 2 identical haploid cells Binary fission - 2:22 Chromosomes and DNA Chromosomes are DNA wrapped around proteins to form an X-shaped structure. 1. Chromosomes are found in the nucleus 2. Chromosomes are made of DNA 3. Sections of chromosomes are called genes DNA - deoxyribonucleic acid (it is the genetic code that contains all the information needed to build and maintain an organism) Journey into DNA Chromosome Numbers Each organism has a distinct number of chromosomes Humans, 46 chromosomes = 2 copies of 23 chromosomes 2 copies of 23 TYPES of chromosomes Other organisms have different numbers EX: Dog 78 chromosomes Diploid numbers of some commonly studied organisms (as well as a few extreme examples) Homo sapiens (human) 46 Mus musculus (house mouse) 40 Drosophila melanogaster (fruit fly) 8 Caenorhabditis elegans (microscopic roundworm) 12 Saccharomyces cerevisiae (budding yeast) 32 Arabidopsis thaliana (plant in the mustard family) 10 Xenopus laevis (South African clawed frog) 36 Canis familiaris (domestic dog) 78 Gallus gallus (chicken) 78 Zea mays (corn or maize) 20 Muntiacus reevesi (the Chinese muntjac, a deer) 23 Muntiacus muntjac (its Indian cousin) 6 Myrmecia pilosula (an ant) 2 Parascaris equorum var. univalens (parasitic roundworm) 2 Cambarus clarkii (a crayfish) 200 Equisetum arvense (field horsetail, a plant) 216 Chromosome Numbers Somatic Cells - body cells, such as muscle, skin, blood ...etc. Contain a complete set of chromosomes & are called DIPLOID. DIPLOID = 2 SETS OF 23 CHROMOSOMES 2 copies of 23 TYPES of chromosomes 23 pairs of homologues 2n Diploid –23 pairs (or 2 sets of 23) Sex Cells - also known as gametes. Contain half the number of chromosomes as body cells and are called HAPLOID HAPLOID – 1 SET OF 23 CHROMOSOMES 1 set of 23 TYPES of chromosomes n Haploid – 1 set only Sets of chromosomes Homologous Pairs (or homologues). Similar in size, shape, and genetic content Each homolog comes from one parent Imagine as a matching set, but they are not exactly alike, like a pair of shoes. Sets of chromosomes Diploid cells 23 homologous pairs = total of 46 2 sets of chromosomes 2n Haploid cells 23 chromosomes (that are not paired) = total of 23 One set of chromosomes n Homologous Chromosomes BOTH CHROMOSOMES IN A HOMOLOGOUS PAIR CONTAIN INFORMATION THAT CODE THE SAME TRAIT (GENES). Example Eye Color. Why have homologues? The chromosomes of many organisms come in pairs – WHY? Mutations are common. Cells with two copies of each gene are more likely to survive a mutation in one of them, b/c the remaining gene can still produce a normally functioning protein. Not all cells have pairs of homologues – sex cells do not. Creation of a Zygote 2 sex cells, or gametes come together, the resulting fertilized egg is called a ZYGOTE Zygotes are diploid and have the total 46 chromosomes (in humans) Sex Chromosomes Autosomes not directly involved in determining the sex (gender) of an individual. in humans 22 pairs All other genetic info Sex chromosomes determines the sex on the individual. one pair Sex Chromosomes In humans and many other organisms, referred to as X & Y Male Y Female X Male can donate X or Y Female can donate X or X Y X XX and XY karyotype Sex chromosomes Structure & number vary EX: Grasshoppers – no Y chromosome Female is XX Male is XO O indicates the absence of a chromosome EX: Birds, moths, & butterflies – male has two X and female has only one X Change in chromosome number Each of an individual’s 46 chromosomes has thousands of genes. ALL important for normal development. Trisomy – human with more than two copies of a chromosome Will not develop correctly Down syndrome – have 3 copies of chromosome 21 Karyotype –a photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size. Standard Human Karyotype Down syndrome Trisomy – human with more than two copies of a chromosome Nondisjunction MUTATIONS– Change in chromosome structure 1. Deletion mutation –a piece of a chromosome breaks off completely 2. Duplication mutation- 2 copies of a certain set of genes 3. Inversion – chromosome reattaches but in reverse orientation 4. Translocation –piece reattaches but in different spot What type of mutation is it??? Genes are permanently lost as they become unattached to the centromere Deletion •Information from one of two homologous chromosomes breaks and binds to the other. - Usually this sort of mutation is LETHAL! Translocation - Mutants genes are displayed twice - Can be advantageous as no genetic information is lost or altered and new genes are gained Duplication -Connections break & sequence reversed - New sequence may not be viable to produce an organism, depending on which genes are reversed. - Advantageous characteristics also possible Inversion Mini quiz Prokaryotes reproduce asexually by A. Disjunction B. Binary fission C. Cytokinesis D. Mitosis Put the following steps in order 4 New cell wall forms around the new membrane. _____ 2 New cell membrane is added to a point on the _____ membrane between the two DNA copies. 5 _____ The bacterium is pinched into two independent cells. 3 _____ The growing cell membrane pushes inward, and the cell is constricted in two. 1 _____ DNA is copied. Chromosomes that are similar in size, shape, and genetic content are called _______________. homologous A cell, such as a somatic cell, that contains two sets of chromosomes is said to be diploid ________________. n Biologists use the symbol ______to represent one set of chromosomes. A fertilized egg cell, the first cell of a new zygote individual, is called a(n) __________. What is the difference between an autosome and a sex chromosome? Autosome = do not determine sex = all others Sex chromosome = determine sex What is a karyotype? Photograph of the chromosomes in a dividing cell that shows the chromosomes arranged by size. T or F 1. At cell division, each chromosome consists of two chromatids attached at a centromere. T 2. The normal diploid number for humans is 23. F 3. A person with the sex chromosomes XX would be a female. T 6.2: The Cell Cycle The Cell Cycle Cell division in eukaryotes is more complex than cell division in bacteria b/c it involves dividing cytoplasm & chromosomes inside the nucleus. The life of a eukaryote cell is typically shown as a cell cycle. THE PHASES OF LIFE OF A CELL ARE CALLED THE CELL CYCLE 3 PHASES: A. INTERPHASE – first growth phase S phase – synthesis phase G2 phase – second growth phase G1 B. MITOSIS C. CYTOKINESIS. CELL CYCLE -Repeating events that make up the life of a cell. Know function of each phase Note G0 G0 – said to be quiescent •May re-enter the cell cycle later, may not divide, may die Mitosis (division of the nucleus) & cytokinesis (splitting of the cell) produce new cells that are identical to the original cells & allow organisms to: grow replace damaged cells reproduce asexually (in SOME organisms) Control of the cell cycle If a cell spends 90% of its time in interphase, how does it “KNOW” when to divide? Cells have checkpoints (red light/ green light) Checkpoints are controlled by many PROTEINS Controls at 3 main checkpoints G1 – Cell growth checkpoint 1. Makes the decision of whether the cell will divide If healthy & large, proteins will stimulate cell to begin the S phase and copy DNA G2 – DNA synthesis checkpoint 2. DNA replication is checked at this point by DNA repair enzymes If this checkpoint is passed, proteins help to trigger mitosis Mitosis checkpoint 3. Triggers the exit from mitosis Signals the beginning of G1 growth phase See picture in your textbook! Cells alive animation Cell control lost = CANCER Cancer is uncontrolled growth of cells. Can occur when a gene that codes for proteins that regulate cell growth & division mutates. Cancer cells do not respond normally to the body’s control mechanisms. Some mutations cause cancer by speeding up the cell cycle, & others by inactivating the control proteins. CANCER Group of more than 100 diseases that develop over time & involve the uncontrolled division of the body’s cells. Cancer cells are genetically unstable prone to rearrangements, duplications, & deletions of their chromosomes that cause their progeny to display unusual traits. Stand up to cancer – PSA - odds Stand Up to Cancer Intro – 5 min The stages of tumor development. Malignant tumor develops across time, as a result of mutations - the number of mutations involved in other types of tumors can vary. We do not know the exact number of mutations required for a normal cell to become a fully malignant cell, but the number is probably less than ten. http://science.education.nih.gov/supplements/nih1/cancer/guide/understanding1.htm The Biology of Cancer - 11 min How cancer grows - animation How cancer spreads video Development of Cancer Cancer develops only after a cell experiences ~6 key mutations (“hits”) – exact number of mutations not known – some say over 10 mutations to same cell unlimited growth ignore checkpoints turn ON chromosome maintenance genes promotes blood vessel growth turn OFF suicide genes immortality = unlimited divisions turn OFF tumor suppressor genes (p53) escape apoptosis turn ON growth promoter genes turn ON blood vessel growth genes overcome anchor & density dependence turn OFF touch-sensor gene It’s like an out of control car! What causes these “hits”? Mutations in cells can be triggered by UV radiation chemical exposure radiation exposure heat cigarette smoke pollution Others? age Genetics Tumors - Mass of abnormal cells Benign tumor = does NOT spread abnormal cells remain at original site as a lump p53 has halted cell divisions most do not cause serious problems & can be removed by surgery Malignant tumors = SPREAD cells leave original site lose attachment to nearby cells carried by blood & lymph system to other tissues start more tumors = metastasis impair functions of organs throughout body Traditional treatments for cancers Treatments target rapidly dividing cells high-energy RADIATION kills rapidly dividing cells Common chemotherapy side effect is hair loss b/c drugs attack rapidly growing cells in your body — including those in your hair roots. CHEMOTHERAPY – chemical therapy (IV, injection, or pill) stop DNA replication stop mitosis & cytokinesis stop blood vessel growth New “miracle drugs” Drugs targeting proteins (enzymes) found only in cancer cells Gleevec treatment for adult leukemia (CML) & stomach cancer (GIST) 1st successful drug targeting only cancer cells without Gleevec Novartes with Gleevec Host of therapies Fighting Cancer Read Exploring Further: Cancer p. 127 Discussion Where in the cell cycle would scientists target anticancer drugs? What type of environmental factors have been associated with the onset of cancer? Checkpoints, DNA replication, or cytokinesis • Diet, UV radiation, hormones, environmental pollution • Mini quiz Define cell cycle. A repeating sequence of cell growth & division in the life of an organism. Define mitosis. The division of the NUCLEUS into two nuclei. In which phase of the cell cycle is DNA copied A. B. C. D. G1 S G2 Mitosis A typical eukaryotic cell spends 90% of tis time in _______. A. B. C. D. Mitosis Interphase Anaphase Cytokinesis In the cell cycle of typical cancer cells, mutations have caused A. B. C. D. Slower growth A failure in mitosis Uncontrolled growth A halt in cell division If you were stricken with a severe form of cancer, do you know enough to make educated choices about your treatment? • No one is immune to cancer. • Treatment options are available, but it’s important to understand the implications of each option. Some forms of cancer are linked to diet, smoking, & other avoidable conditions. What responsibility does the government have to prevent such cancers? • Some people knowingly accept a higher risk of cancer by the choices they make. • $ spent researching & treating avoidable cancers is not available to help in other areas of society. • Government’s role is complex. Personal freedom is in direct conflict with social & familiar responsibilities. 6.3: Mitosis and Cytokinesis Every second about 2 million new red blood cells are produced in your body by cell divisions occurring in the bone marrow. Human red blood cells CELL DIVISION INVOLVES 2 STEPS: CALLED MITOTIC CELL DIVISION. 1. MITOSIS - NUCLEUS DIVIDES INTO TWO NUCLEI W/ IDENTICAL GENETIC MATERIAL. 2. CYTOKINESIS - CYTOPLASM DIVIDES INTO TWO NEW CELLS CALLED DAUGHTER CELLS. During mitosis, the chromatids on each chromosome are physically moved to the opposite side of the dividing cell with the help of the spindle. Spindles- made up of centrioles & microtubule fibers that move chromosomes during cell division. At each pole is a centrosome –an organelle that organizes the assembly of the spindle. (Centrioles in centrosome). P.128 picture Read p. 129 on chromatid movement Know graphics on p. 130-131 all steps & phases!!! Mitosis video Know BOOK diagram of STAGES OF MITOSIS cell division - animation Cytokinesis in Animal Cells As mitosis ends, cytokinesis begins. Cytoplasm is divided in half, & cell membrane grows to enclose each cell. In animal cells, the cell is pinched in half by a belt of protein threads. Cytokinesis in Plant Cells In plant cells & other cells that have rigid cell walls, cytoplasm is divided in a different way. Vesicles, formed by Golgi apparatus, fuse at the middle & form a CELL PLATE. A new cell wall will form at either side of this cell plate. Cytokinesis in Plant Cells Remember…. For both animal & plant cells offspring are: Equal in size Has an identical copy of the original cells’ chromosomes Talk about Meiosis In next chapter! Mini quiz Chromatids are A. B. C. D. Dense patches within the nucleus Prokaryotic chromosomes Two exact copies of DNA that make up each chromosome Structures that move chromosomes during mitosis As a result of mitosis each resulting cell A. Receives an exact copy of all the chrom present in the original cell B. Receives most of all the chrom present in the original cell C. Donates a chrom to the original cell D. Receives exactly half the chrom from the original cell How does cell division differ between plant & animal cells A. B. C. D. Plant cells do not have centrioles Animal cells form a cell plate Plant cells are always haploid Animal cells do not have centrioles Name that phase Metaphase Name that phase Prophase Name that phase Telephase Name that phase Anaphase Name that phase Interphase