11/9/2011 AICE Biology Ch 6 Jones; Ch 10 Raven
Content • Replication and division of nuclei and cells • Understanding of chromosome behavior in mitosis Learning Outcomes Candidates should be able to: (a) explain the importance of mitosis in the production of genetically identical cells, growth, repair and asexual reproduction; (b) [PA] describe, with the aid of diagrams, the behavior of ( )[ ] chromosomes during the mitotic cell cycle and the associated behavior of the nuclear envelope, cell membrane, centrioles and spindle (names of the main stages are expected); (c) explain how uncontrolled cell division can result in cancer and identify factors that can increase the chances of cancerous growth; (d) explain the meanings of the terms haploid and diploid and the need for a reduction division (meiosis) prior to fertilization in sexual reproduction; (e) use the knowledge gained in this section in new situations or to solve related problems. ? Multicellular organisms begin as a single cell ? Mitosis ? Cell division ? Also used in repair ? Asexual reproduction p Cell Size ? Bacteria ? E. Coli doubles every 30 minutes ? Heart & nervous system cells rarely divide, if at all ? Skin cells and digestive tract cells divide throughout life ? Some every 6 hours ? Grow to a certain size and stop ? Controls are turned on and off ? During injury, cells are stimulated and rapidly divide and grow – produces new cells, . i. e. ealing ? After healing, cell growth slows and returns to normal ? Uncontrolled cell growth results in cancer Surface Area (length x width x 6) Volume (length x width x height) Ratio of Surface Area to Volume ? Surface area and volume do not increase at the same rate ? Larger cells have difficulty exchanging oxygen and waste in and out of the cell ? Before cell becomes too large it undergoes cellular division and forms 2 daughter cells 1 11/9/2011 Cell Cycle includes G1 phase Two G phases and S phase make up Interphase Interphase M phase (Mitosis) M phase S phase is divided into is divided into G1 phase S phase G2 phase Prophase Metaphase
Anaphase Telophase G2 phase The cell has several systems for interrupting the cell cycle if something goes wrong… ? Check point at end of S phase ? Monitor for presence of Okazaki fragments on lagging strand during replication ? Cell is not permitted to proceed in the cell cycle until fragments ? DNA Overload ? must be enough DNA material in the nucleus ? Larger the cell = information crisis ? Materials must be able to pass through the are gone cytoplasm quickly ? Speed is determined by size of cell ? Rate at which food and oxygen are used is ? DNA Damage checkpoints ? Sense DNA damage before cell enters S phase (G1 checkpoint) ? During S phase ?
After DNA replication at G2 checkpoint ? Spindle Checkpoints ? Detect any failure of spindle fibers ? Detect improper alignment of spindle itself and block cytokinesis ? Trigger apoptosis if damage is irreparable determined by volume ? Volume increases faster than surface area as cell’s size increases ? Cell’s DNA no longer able to serve the increasing needs of the growing cell ? Cells constantly divide ? Dead cells replaced by new cells ? Cancer ? mistake in cell cycle ? cancerous cells form tumors (masses of tissue) ? tumors deprive normal cells of nutrients 2 11/9/2011 ? Mutagen ? A factor that brings about a mutation ? Genetic ? Mutations ? Oncogene Carcinogen ? Any agent that causes cancer ? Some factors which can increase mutation rates, thus promoting cancer ? Ionizing Radiation: Xrays, gamma rays particles from ? Environmental ? cigarette smoke ? air and water pollution ? UV radiation from the sun ? viral infections ? Carcinogen ? Any substance that can induce or promote cancer ? Most carcinogens are mutagens (change in genes) radioactive decay? breakdown of DNA strands ? Chemicals: tobacco smoke, certain dyes ? Virus Infection: Lymphoma, Papilloma viruses ? Hereditary predisposition – genetic link ? Benign Tumors (tumours) ? Do not spread from their site of origin but can compress nd displace surrounding tissues ? Warts, ovarian cysts, some brain tumors ? Malignant ? Cancerous ? Dangerous and spread throughout the body ? Invade other tissues and destroy them ? Healthy ? Cancer – yellow spots ? Staging is important to determine if the patient is potentially in a curable early stage or otherwise: ? Stage 0 ? Cancer in Situ ? Stage I ? Cancer is less than 2 cm. ? Stage II ? Cancer is between 2 to 5 cm with or without involvement of the glands in the armpit i l f h l d i h i ? Stage III ? Cancer is larger than 5 cm or there is extensive involvement of the glands in the armpit ? Stage IV ? Cancer has spread outside the breast and nvolves other organs in the body Cause of 1 out of 17 deaths in Britain in 1990 1 in 13 deaths in men; 1 in 27 deaths in women ? Stage I & II are considered early and curable. ? Stage IV disease is not curable. 3 11/9/2011 ? Chromosome ? two identical halves connected together by a centromere ? Ch Chromatid tid ? half of one chromosome ? Contains one complete set of information ? Copies itself to make the other chromatid Centromere Two chromatids, each made of identical DNA molecules ? The karyotype of a normal human female contains 23 pairs of homologous chromosomes: ? 22 pairs of autosomes ? 1 pair of X chromosomes ? The karyotype of a normal uman male contains: ? the same 22 pairs of autosomes ? Uncoiled DNA called chromatin? between cell divisions ? Happens during cell division ? DNA wraps tightly around proteins called histones ? one X chromosome ? one Y chromosome 4 11/9/2011 Sex chromosomes Spindle forming Centrioles Nuclear envelope Chromatin Centromere Chromosomes (paired chromatids) Centriole Interphase Cytokinesis Telophase Nuclear envelope reforming Prophase p Spindle Centriole Individual chromosomes Metaphase Anaphase ? Daughter cells genetically identical to parent nucleus ? Replacement / repair of tissues ? Skin ? Lining of gut A sample of cytoplasm is removed from a cell in mitosis.
The sample is injected into a second cell in G2 of interphase. ? Basis of asexual reproduction As a result, the second cell enters mitosis. Cyclins regulate the timing of the cell cycle in eukaryotic cells 5 11/9/2011 Golgi apparatus produces vesicles ? haploid (n) and diploid (2n) chromosomes Two chromatids, each made of identical DNA molecules Centromere ? reduction division (meiosis) prior to fertilization in sexual reproduction Chapter 17: Meiosis, genetics and gene control goes into more detail Genetic variation Crossing over in Prophase I 6 11/9/2011 Maternal set of chromosomes Possibility 1 Paternal set of chromosomes Possibility 2
Two equally probable arrangements of chromosomes at metaphase I Metaphase II Prophase II Metaphase II Anaphase II Telophase II Meiosis II results in four haploid (N) daughter cells. Meiosis I results in two The chromosomes line up in a The sister chromatids haploid (N) daughter cells, similar way to the metaphase separate and move toward each with half the number of stage of mitosis. opposite ends of the cell. chromosomes as the original. Daughter cells Combination 1 Combination 2 Combination 3 Combination 4 Prophase I of meiosis Nonsister chromatids MITOSIS Parent cell (before chromosome replication) MEIOSIS Chiasma (site of crossing over) MEIOSIS I Prophase
Prophase I Chromosome replication Chromosome replication 2n = 6 Tetrad Duplicated chromosome (two sister chromatids) Chiasma, site of crossing over Metaphase I Tetrad formed by synapsis of homologous chromosomes Metaphase Chromosomes positioned at the metaphase plate Tetrads positioned at the metaphase plate Metaphase I Metaphase II Anaphase Telophase Sister chromatids separate during anaphase Homologues separate during anaphase I; sister chromatids remain together Anaphase I Telophase I Haploid n=3 Daughter cells of meiosis I MEIOSIS II Daughter cells 2n Daughter cells of mitosis 2n n n n n Daughter cells of meiosis II Recombinant chromosomes Sister chromatids separate during anaphase II