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Cell Reproduction Chapter 8 • Henrietta Lacks – cervical cancer – HeLa Cells Cell Division • Mitosis – How body cells divide – Makes exact copy – clone - of parent cell – Identical daughter cells • Meiosis – Makes sex cells – eggs and sperm – Contain only one chromosome of a pair – Half the normal number of chromosomes Prokaryotic cell division • No nucleus or organelles, and only one circular chromosome • Process is called binary fission – Not mitosis since there is no nucleus to divide http://www.anselm.edu/homepage/jpitocch/genbio/binfission.JPG Eukaryotic cell division • More complicated • More DNA • Chromosomes come in pairs: – homologous chromosomes Cell cycle • All the processes from one division to the next: 1. Interphase – “resting stage” 2. Mitosis – nuclear division 3. Cytokinesis – division of the cytoplasm Interphase • Cell is busy doing its job – just not dividing – Nerve cells spend most of life in interphase – Cancer cells spend little time in interphase • Three parts: – G1 or Gap 1 or growth phase – S phase : Synthesis of DNA ; cell is committed to division – G2 or Gap 2 Mitosis • Refers specifically to division of the nucleus • Four phases: – Prophase – Metaphase – Anaphase – Telophase PMAT Prophase • Chromosomes wind up or condenses – 2 meters / cell – Linked by centromere – Sister chromatids • Nucleoli disappear; mitotic spindle forms from the centrioles Prometaphase or late prophase • Transition phase – to cell it is all part of one process • Nuclear membrane disappears • Chromatids attach to fibers of mitotic spindle by means of specialized structure called a kinetochore Metaphase • Chromosomes line up in the center of the cell at the metaphase plate – a disc • Remain this way for about an hour Anaphase • Centromere splits • Microtubles of mitotic spindle pull members of each pair of duplicate chromosomes to opposite sides of the cell. Telophase • Mitotic spindle disappears • Nuclear membranes form • Chromosomes unwind Cytokinesis • Division of the cytoplasm • Accompanies mitosis • Begins in anaphase and finishes after telophase • Animal cells form a contractile ring using actin – one of the proteins found in muscles. • Indentation is called the cleavage furrow • Pinches the cells apart Plant cells • Mitosis occurs in plants as in animal cells, but cytokinesis is different because of the plant cell wall. • A disc of new membrane called the cell plate forms between the two cells during telophase and expands until it reaches the edges of the cell membrane. • The new cells then make cellulose fibers to form new cell walls. Control of cell division • Cell senescence – cells reproduce only a certain number of times and then stop. – May be due to telomeres –repeating series of bases at the end of chromosomes that decrease with each division – Telomerase • Apoptosis – programmed cell death – ”suicide genes” http://www-ermm.cbcu.cam.ac.uk/fig001nkg.gif Contact inhibition • Cells divide until they establish contact with other cells on all sides. Other factors • • • • • • Cell size hormones Growth factors Cyclins Genes: Oncogenes – want these turned off – Oncology – the study of cancer • Tumor suppressor genes – want these turned on Tumors - neoplasms • Cells have lost control over cell division • Benign tumors grow only in one area • Cancers invade local tissues (look like a crab) and can metastasize or spread to other areas of the body through the vascular or lymphatic systems