cell reproduction
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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 - PowerPoint PPT PresentationTRANSCRIPT
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Cell Reproduction
Chapter 8
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• Henrietta Lacks – cervical cancer– HeLa Cells
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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
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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
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http://www.anselm.edu/homepage/jpitocch/genbio/binfission.JPG
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Eukaryotic cell division
• More complicated• More DNA• Chromosomes come in pairs:
– homologous chromosomes
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Cell cycle
• All the processes from one division to the next:
1. Interphase – “resting stage”2. Mitosis – nuclear division3. Cytokinesis – division of the cytoplasm
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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
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Mitosis• Refers specifically to division of the nucleus• Four phases:
– Prophase– Metaphase– Anaphase– Telophase
PMAT
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Prophase• Chromosomes wind up or condenses
– 2 meters / cell– Linked by centromere– Sister chromatids
• Nucleoli disappear; mitotic spindle forms from the centrioles
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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
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Metaphase• Chromosomes line up in the center of the
cell at the metaphase plate – a disc• Remain this way for about an hour
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Anaphase• Centromere splits• Microtubles of mitotic spindle pull
members of each pair of duplicate chromosomes to opposite sides of the cell.
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Telophase• Mitotic spindle disappears• Nuclear membranes form• Chromosomes unwind
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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
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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.
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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”
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Contact inhibition• Cells divide until they establish contact
with other cells on all sides.
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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
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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
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