CHAPTER 12 - THE CELL CYCLE (pgs. 228-245) CHAPTER SEVEN TARGETS I. Describe the importance of mitosis in single-celled and multi-cellular organisms. II. Explain the organization of DNA molecules and their relationship to cell parts in the process of chromosomal separation during mitosis. (Use the following terms in your explanation: genome, chromosome, chromatin, centromere, centrosome, aster, kinetochore, mitotic spindle, sister chromatid, metaphase plate). III. Differentiate between sexual and asexual cell division. (Use the following terms in your explanation: meiosis, somatic cell, cells of gonad, gamete, sister chromatid, mitosis, cytokinesis). IV. State several, specific cellular activities occurring during each stage of the cell cycle: G1, S, G2, and M. V. Identify the stages of mitosis in photographs or diagrams. Explain what is occurring in each stage (interphase, prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis). VI. Compare and contrast animal cell cytokinesis with plant cell cytokinesis. VII. Compare and contrast binary fission with mitosis. VIII. Define checkpoint in the cell cycle. Describe the role of checkpoints and the mechanism of their operation. IX. Define MPF and explain how it relates to the cell cycle. Describe the relative concentrations of MPF, Cdk, kinases, and cyclin and how they interact. X. Explain how the loss of normal cell cycle controls results in cancer. OVERVIEW: THE KEY ROLES OF CELL DIVISION Cell Division - the reproduction of cells Cell Cycle - the life of a cell from the time it is first formed from a dividing parent cell until its own division into two cells 12.1 AP BIOLOGY OUTLINES - CHAPTER 12 - THE CELL CYCLE CELL DIVISION RESULTS IN GENETICAL IDENTICAL DAUGHTER CELLS Most cell division involves distribution of identical genetic material - DNA - to two daughter cells CELLULAR ORGANIZATION OF THE GENETIC MATERIAL Genome - A cell s endowment of DNA - genetic information Chromosome - A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells. Each chromosome consists of one very long DNA molecule and associated proteins. A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded Somatic Cells - Any cell in a multicellular organism except a sperm or egg (46 chromosomes, 2 pairs) Gametes - Reproductive cells - sperm and eggs - have half as many chromosomes as somatic cells (23) Chromatin - a complex of DNA and associated protein molecules Associated proteins maintain structure of the chromosome and help control activity of the genes Sister Chromatids - Either of two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms. While joined, two sister chromatids make up one chromosome; chromatids are eventually separated during mitosis or meiosis II. Centromere - The specialized region of the chromosome where 2 sister chromatids are most closely attached 1
DISTRIBUTION OF CHROMOSOMES DURING EUKARYOTIC CELL DIVISION Mitosis - division of the nuecleus Cytokinesis - the division of the cytoplasm Meiosis - A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. results in cells with half the number of chromosome sets as the original cell. 6.2 EUKARYOTIC CELLS HAVE INTERNAL MEMBRANES THAT COMPARTMENTALIZE THEIR FUNCTIONS Mitotic (M) Phase - includes both mitosis and cytokinesis (shortest part of cell cycle) [<1 hour] Interphase - phase in which cell grows and copies its chromosomes in preparation for cell division G1 Phase - first gap [5-6 hours] (most variable with different types of cells) S Phase - synthesis (chromosomes only duplicated here) [10-12 hours] G2 Phase - second gap [4-6 hours] 2
Five Major Phases of Mitosis 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase THE MITOTIC SPINDLE: A CLOSER LOOK Mitotic Spindle - An assemblage of microtubules and associated proteins that is involved in the movements of chromosomes during mitosis. Centrosome - Structure present in the cytoplasm of animal cells, important during cell division; functions as a microtubuleorganizing center. A centrosome has two centrioles.(not necessary for cell division) Aster - A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis. Kinetochore - Structure of proteins associated with specific sections of chromosomal DNA at the centromere Metaphase Plate - An imaginary plane midway between the two poles of a cell in metaphase on which the centromeres of all the duplicated chromosomes are located. 3
CYTOKINESIS: A CLOSER LOOK Cleavage - The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. Cleavage Furrow - shallow groove in the cell surface near old metaphase plate (first sign of cleavage) Cell Plate - A double membrane across the midline of a dividing plant cell, between which the new cell wall forms during cytokinesis. BINARY FISSION Binary Fission - A method of asexual reproduction by division in half. In prokaryotes, binary fission does not involve mitosis In single-celled eukaryotes that undergo binary fission, mitosis is part of the process. Origin of Replication - Site where the replication of a DNA molecule begins in a prokaryote, consisting of a specific sequence of nucleotides (under current research). THE EVOLUTION OF MITOSIS Since prokaryotes preceded eukaryotes by more than a billion years, it is likely that mitosis evolved from prokaryotic cell division. Certian protists exhibit types of cell division that seem intermediate between bacterial binary fission and the process of mitosis carried out by most eukaryotic cells. 4
12.3 THE EUKARYOTIC CELL CYCLE IS REGULATED BY A MOLECULAR CONTROL SYSTEM Cell cycle differences result from regulation differences at the molecular level Contributes to understanding of how Cancer manages escape normal controls THE CELL CONTROL SYSTEM The cell cycle control system - cyclically operating set of molecules in the cell that both triggers & coordinates key events in the cycle Checkpoint - control point where stop and go ahead signals can regulate the cycle G0 Phase - non-dividing state reached if it does not receive a go-ahead signal at the G1 checkpoint. 5
The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases Cyclins and Cyclin-Dependent Kinases cause rhythmic fluctuations in the abundance and activity of cell cycle control molecules pace the sequential events of the cell cycle. Cyclin - protein that gets its name from its cyclically fluctuating concentration in the cell Cyclin-Dependent Kinases (Cdks) - A protein kinase that is active only when attached to a particular cyclin. MPF - Maturation-promoting factor (M-phase-promoting factor); a protein complex required for a cell to progress from late interphase to mitosis. The active form consists of cyclin and a protein kinase. 6