Cell division results in genetically identical daughter cells Cells duplicate their genetic material o Before they divide ensuring that each daughter cell receives an exact copy of the genetic Biology Lecture Notes Exam 3 Chapter 12 The Cell Cycle The Cell Cycle The continuity of life o Is based upon the reproduction of cells or cell division Unicellular Organisms o Reproduce by cell division Multicellular organisms depend on cell division for 1 Development from a fertilized cell 2 Growth 3 Repair The cell division process o Is an integral part of the cell cycle But not the only part material DNA Cellular Organization of the Genetic Material A cell s endowment of DNA its genetic information o Is called its genome The DNA molecules in a cell o Are packaged into chromosomes Chromosomes Eukaryotic Chromosomes In animals o Somatic cells have two sets of chromosomes Soma body o Gametes have one set of chromosomes Gametes are sex cells Distribution of Chromosomes During Cell Division In preparation for cell division o DNA is replicated and the chromosomes condense Each duplicated chromosome o Has two sister chromatids which separate during cell division Eukaryotic cell division consists of 1 Mitosis the division of the nucleus 2 Cytokinesis the division of the cytoplasm In meiosis o Sex cells are produced after a reduction in chromosome number The mitotic phase alternates with interphase in the cell cycle A labeled probe can reveal patterns of gene expression in different kinds of cells Phases of the Cell Cycle The cell cycle consists of Interphase 1 The mitotic phase 2 Interphase can be divided into subphases 1 G1 phase o Consist of chromatin a complex of DNA and protein that condenses during cell division 2 S Phase 3 G2 Phase The mitotic phase o Is made up of mitosis and cytokinesis Mitosis consists of five distinct phases PPMAT o Prophase o Prometaphase o Metaphase o Anaphase o Telophase The Mitotic Spindle A Closer Look The mitotic spindle The spindle arises from the centrosomes o And includes spindle microtubules and asters Some spindle microtubules plate In anaphase sister chromatids separate o Is an apparatus of microtubules that controls chromosome movement during mitosis o Attach to the kinetochores of chromosomes and move the chromosomes to the metaphase o And move along the kinetochore microtubules toward opposite ends of the cell Nonkinetechore microtubules from opposite poles o Overlap and push against each other elongating the cell o Genetically identical daughter nuclei form at opposite ends of the cell In telophase Cytokinesis A Closer Look In animal cells o Cytokinesis occurs by a process known as cleavage forming a cleavage furrow In plant cells during cytokinesis o A cell plate forms What about Prokaryotes Binary Fission Prokaryotes bacteria o Do NOT go through mitosis o Reproduce by a type of cell division called binary fission In binary fission o The bacterial chromosome replicates o The two daughter chromosomes actively move apart The Evolution of Mitosis Since prokaryotes preceded eukaryotes by billions of years o It is likely that mitosis evolved from bacterial cell division Certain protists diatoms and yeasts carried out by most eukaryotic cells How is it Controlled The cell cycle is regulated by a molecular control system The frequency of cell division o Varies with the type of cell These cell cycle differences o Results from regulation at the molecular level Evidence for Cytoplasmic Signals o Exhibit types of cell division that seem intermediate between binary fission and mitosis Molecules present in the cytoplasm o Regulate progress through the cell cycle The Cell Cycle Control System The sequential events of the cell cycle o Are directed by a distinct cell cycle control system which is similar to a clock The clock has specific checkpoints o Where the cell cycle stops until a go ahead signal is received The Cell Cycle Clock Cyclins and Cyclin Dependent Kinases Two types of regulatory proteins are involved in cell cycle control Cyclins and cyclin dependent kinases Cdks The activity of cyclins and Cdks o Fluctuates during the cell cycle Stop and Go Signs Internal and External Signals at the Checkpoints Both internal and external signals o Control the cell cycle checkpoints Growth Factors Stimulate other Cells to Divide In density dependent inhibition o Crowded cells stop dividing Most animal cells also exhibit anchorage dependence o In which they must be attached to a substratum to divide Cancer cells o Exhibit neither density dependent inhibition nor anchorage dependence Loss of Cell Cycle Controls in Cancer Cells Cancer cells o Do not respond normally to the body s control mechanisms o Form tumors Malignant tumors invade surrounding tissues and can metastasize o Exporting cancer cells to other parts of the body where they may form secondary tumors Chapter 13 Meiosis and Sex Hereditary Similarity and Variation Living Organisms o Are distinguished by their ability to reproduce their own kind o Is the transmission of traits from one generation to the next o Shows that offspring differ somewhat in appearance from parents and siblings Heredity Variation Genetics o Is the scientific study of heredity and hereditary variation Plant and animal breeding Offspring acquire genes from parents by inheriting chromosomes Inheritance of Genes Genes o Are the units of heredity o Are segments of DNA Each gene in an organism s DNA We inherit Like an address o Has a specific locus on a certain chromosome o One set of chromosomes from our mother and one set from our father Comparison of Asexual and Sexual Reproduction In asexual reproduction In sexual reproduction o One parent produces genetically identical offspring by mitosis o Two parents give rise to offspring that have unique combinations of genes inherited from the two parents Sets of Chromosomes in Human Cells In humans o Each somatic soma body cell has 46 chromosomes made up of two sets o One set of chromosomes comes from each parent 23 23 A karyotype o Is an ordered visual representation of the chromosomes in a cell Homologous chromosomes o Are the two chromosomes composing a pair o Have the same characteristics genes o May also be called autosomes Sex Chromosomes o Are distinct from each other in their characteristics o Are represented as X and Y in humans o Determine the sex o the individual XX being female XY being male Ploidy is a measure of the number of sets of chromosomes A diploid cell o Has two sets of each
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