Cell Reproduction Chapter 8
Feb 25, 2016
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 division3. 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