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Unformatted text preview: Continuity and variety Lectures by Mark Manteuffel, St. Louis Community Colege Chapter 6: Chromosomes and Cell Division Learning Objectives ! Understand and be able to describe the different types of cell division ! Understand and be able to explain how through mitosis worn out old cells are replaced with fresh new duplicates ! Understand and be able to explain how sperm and eggs are generated through meiosis ! Describe the sex differences in the chromosomes ! Discuss the consequences of deviations from the normal chromosome number Once you are fully grown, do you have just one set of cells that live as long as you do? No!!! Constant replacement of old worn-out cells 6.1 Immortal cells can spell trouble: cell division in sickness and health. Normal cells have telomeres to keep track of the Number of cell divisions Uncontrolled cell growth = cancer Telomeres ! The telomere is like a protective cap at the end of the DNA. ! Every time a cell divides, the telomere gets a bit shorter. Occasionally, however, people are born with telomeres that are much shorter than normal = progeria Cells and tissue begin to appear aged very soon after birth “Cancer cells are those which have forgotten how to die.” —Harold Pinter Cancer is just a term that describes runaway cell division Therefore, discovering a cure for cancer will necessarily involve a deep understanding of cell division. Take-home message 6.1 ! Cells have a protective section of DNA called the telomere . ! Telomeres get shorter every time the cell divides. ! When the telomere becomes too short, the cell dies. ! Cells that rebuild the telomere with each division can become cancerous 6.2 Some chromosomes are circular, others are linear. Histones ensure orderly, tight, and efficient packing of DNA Take-home message 6.2 ! In prokaryotes, genetic information is carried in a single, circular chromosome. ! This strand of DNA is attached at one site to the cell membrane. ! Eukaryotes have much more DNA. ! In eukaryotes, genetic information is organized into linear chromosomes. ! Eukaryotic chromosomes float freely in the nucleus. 6.3 Prokaryotes divide by binary fission = fast, 20 min Asexual reproduction Genetically identical Take-home message 6.3 ! Bacteria divide by binary fission. ! The circular chromosome duplicates itself and the cell splits into two identical new cells. 6.4 A time for everything: the cell cycle. Cells that divide infrequently spend most time in Gap I Mitosis = shortest phase of cell cycle Errors in cell cycle control = cancer Take-home message 6.4 ! Eukaryotic somatic cells go through a cycle of phases. ! Cell division occurs in the mitotic phase. ! The rest of the cell cycle is called interphase....
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This note was uploaded on 09/14/2009 for the course MCDB 20 taught by Professor Cooper during the Summer '08 term at UCSB.
- Summer '08