Chapter 8 Reproduction a key characteristic of life Cell division o Reproduction at the cellular level o Duplication of chromosomes o New chromosomes sorted as daughter cells o Used for Asexual reproduction of single celled organisms Growth of multicellular organisms from conception to adult Repairing replacing cells Producing sperm and eggs meiosis Two methods of reproduction o Asexual reproduction produces offspring that are identical to the original cell or organism All Example Yeast cell Sea star genes inherited from one parent o Sexual reproduction produces offspring that are similar to the parents but show trait variations Inheritance of a unique set of genes from 2 parents Prokaryotes bacteria archaea o Chromosome is a single DNA molecule associated with proteins much smaller than those of eukaryotes o Reproduce by binary fission dividing in half 3 stages 1 Duplicate the chromosome and separate the copies 2 Continued elongation of the cell and movement of the copies 3 Division into two daughter cells Eukaryotic Cell Cycle Mitosis o Eukaryotic cells More complex larger than prokaryotes Have more genes Store most genes on multiple chromosomes within the nucleus Chromosomes composed of chromatin One long DNA molecule and proteins that help maintain structure control activity of its genes Become highly compact to prepare for division visible with microscope Before dividing cell divides its chromosomes resulting in Two copies called sister chromatids joined together by a narrowed waist called the centromere After dividing the sister chromatids separate from each other into chromosomes and sort into separate daughter cells o Cell cycle an order sequence of events From the time a cell is first formed from a dividing parent cell until its own division 2 stages 1 Interphase duplication of cell contents G1 growth increase in cytoplasm S duplication of chromosomes G2 growth preparation for division 2 Mitotic phase division Mitosis division of the nucleus Cytokinesis division of cytoplasm Mitosis includes prophase prometaphase metaphase anaphase and telophase often overlapped by cytokinesis Mitotic spindle Required to divide the chromosomes Composed of microtubules Produced by centrosomes structures in the cytoplasm that organize microtubule arrangement and contain a pair of centrioles in animal cells Cell Cycle Interphase o Cytoplasmic contents double o Two centrosomes form o Chromosomes duplicate in the nucleus during the S phase o Nucleoli sites of ribosome assembly are visible Prophase o In cytoplasm microtubules begin to emerge from centrosomes forming the spindle o In nucleus chromosomes coil and become compact nucleoli disappear Prometaphase Metaphase spindle Anaphase o Spindle microtubules reach chromosomes attach at kinetochores on the centromeres of sister chromatids and move chromosomes to the center of the cell through associated protein motors o Other microtubules meet those from the opposite poles o Nuclear envelope disappears o Mitotic spindle is fully formed o Chromosomes align at the cell equator o Kinetochores of sister chromatids are facing the opposite poles of the o Sister chromatids separate from the centromeres o Daughter chromosomes are moved to opposite poles of the cell as motor proteins move the chromosomes along the spindle microtubules and kinetochore microtubules shorten o Cell elongates due to lengthening of nonkinetochore microtubules Telophase o Cell continues to elongate o Nuclear envelope forms around chromosomes at each pole establishing a daughter nuclei o Chromatin uncoils and nucleoli reappear o Spindle disappears Cytokinesis o Cytoplasm is divided into separate cells o Process is different in animal and plant cells o In animal cells cleavage furrow forms from a contracting ring of microfilaments interacting with myosin deepens to separate the contents into 2 cells o In plant cells cell plate forms in the middle from vesicles containing cell wall material grows outward to reach edges dividing contents into 2 cells o Each cell now possesses a plasma membrane and cell wall The cells within an organism s body divide and develop at different rates Cell division is controlled by o The presence of essential nutrients o Growth factors proteins that stimulate division o Density dependent inhibition crowded cells stop dividing o Anchorage dependence need for cells to be in contact with solid surface to divide The cell cycle control system is a cycling set of molecules in the cell that triggers and coordinates key events in the cell cycle Checkpoints in the cell cycle can stop an event or signal an event to proceed 3 major checkpoints 1 G1 checkpoint allows entry into S phase and causes cell to leave the cycle entering a nondividing G phase 2 G2 checkpoint 3 M checkpoint Cancer cells o Escape control of the cell cycle o Divide rapidly often in the absence of growth factors o Spread to other tissues through the circulatory system o Grow without being inhibited by other cells o Named by organ or tissue in which they originate Carcinomas external or internal body coverings Sarcomas supportive and connective tissue Leukemias and lymphomas blood forming tissues Tumor an abnormally growing mass of body cells o Benign tumors remain at the original site o Malignant tumors spread to other locations metastasis Cancer treatments high energy radiation o Chemotherapy is used for metastatic tumors o Growth o Replacement of damaged and lost cells o Asexual reproduction In humans somatic cells have o 23 pairs of homologous chromosomes o One member of each pair from each parent o Localized tumors can be removed surgically and or treated with concentrated beams of When cell cycle operates normally mitosis produces genetically identical cells for The human sex chromosomes X and Y differ in size and genetic composition The other 22 pairs of chromosomes are autosomes with the same size and genetic composition Homologous chromosomes are matched in o Length o Centromere position o Gene locations A locus is the position of a gene Different versions of a gene may be found at the same locus on maternal and paternal An organism s life cycle is the sequence of stages leading from the adults of one generation to chromosomes the adults of the next Humans and many animals and plants are diploid with body cell that have 2 sets of chromosomes 1 from each parent Meiosis is a process that converts diploid nuclei to haploid nuclei o Diploid cells have two homologous sets of chromosomes o