Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download Chapter 8 - Advanced Biology
Document related concepts
Transcript
Chapter 8 Cellular Reproduction Problems with Cell Division Too much division ◦ Cancer Too little division ◦ Irreversible brain damage (i.e. Alzheimer's) Cell death ◦ Heart attacks Understanding mitosis could potentially help fix all of these problems The Basics We all start out as one cell End up as trillions of cells after only 9 months Even as adults, mitosis replaces old, worn out cells and damaged cells Single-celled organisms reproduce through mitosis All cells come from cells ◦ 1 parent cell2 identical daughter cells Chromosomes Essential: making a copy of the cell’s genetic material before it divides BUT…each cell has ≈ 5 cm of DNA How do you move 5 cm of stuff across a tiny space in an organized way? Condense the DNA into chromosomes Chromosomes are >10,000x more compact than loose chromatin Chromosomes (cont.) By the time we can see individual chromosomes with a microscope, the DNA has already been copied 2 halves = sister chromatids ◦ Exact copies Held together in middle by the centromere The Cell Cycle Orderly sequence of events from the beginning of one cell to the time when it divides into 2 new cells Mostly spent in interphase ◦ Normal cell functions ◦ Timeframe varies widely A couple of hours your whole life ◦ G1 S G2 A cell not planning on dividing is in G0 Mitotic Stage When the cell actually divides Nucleus divides ◦ Equal sets of chromosomes sent to each new cell The rest of the cell (cytoplasm divides) ◦ cytokinesis Mitosis and Cytokinesis At the end, you get two identical cells ◦ So, if the parent cell has 8 chromosomes, the daughter cells each have the same 8 chromosomes Every animal has an even # of chromosomes b/c they got 1 set from each parent ◦ 2 parents = some multiple of 2 for the chromosomes for each species The Spindle Many illustrations in science books only show 2 or 4 chromosomes In reality, many organisms have 30-60 chromosomes Much harder to keep track of ◦ Even when the chromosomes are condensed The structure that keeps everything straight is the spindle ◦ Network of microtubules Spindle Details Organized by the centrosome (contain centrioles in animal cells) One on each side Organize spindle fibers ◦ Some overlap in the center (equator) ◦ Others attach to the duplicated chromosomes Array of microtubules = aster Phases of Mitosis Divided into phases for convenience in studying BUT it’s a continuous, fluid process Prophase, Metaphase, Anaphase, Telophase In rapidly dividing, adult mammal cells ◦ Whole cycle lasts about 24 hours ◦ Actual mitosis, about 2 hours Animals vs. Plants Cytokinesis is a little different in each group Animal Cells ◦ Cleavage furrow = indentation ◦ Contractile ring = actin fillaments in a circle around cell in center, like a drawstring Plant Cells ◦ Cell wall prevents furrowing and pinching ◦ New cell membrane and wall grows between ◦ Cell plate comes from concentrated vesicles from the Golgi Cell Cycle Control Like a washing machine Each stage only occurs when conditions are right and the previous step has been completed Checkpoints There are lots of checkpoints 3 Main ◦ G1 Decision between deciding to divide and going into/staying in G0 Integrity of DNA checked, proper growth signals ◦ G2 DNA damage & make sure DNA is copied ◦M MetaphaseAnaphase Make sure all chromosomes are properly attached to spindle Signals Molecule that stimulates or inhibits an event Internal ◦ Kinases activate cyclins ◦ Cyclins—only present at certain stages in the cycle—make things happen ◦ Telomeres and senescence—aging cells— inhibit External ◦ Growth factors, hormones—stimulate ◦ Contact inhibition—due to crowding Apoptosis A fun word to say! Try it! Programmed cell death Events ◦ ◦ ◦ ◦ ◦ Cell gets rounder Nucleus fragments Cell membrane blisters Cell fragments “Eaten” by white blood cells Apoptosis (cont.) Cell routinely harbors the enzymes that cause all of this Normally held in check by inhibitors Can start from internal or external signals Part of normal delvelopment ◦ Separate fingers and toes ◦ Tadpole loses its tail Also prevents tumors from developing from abnormal cells Cell Cycle and Cancer Failure to regulate the cell cycle Classified according to location ◦ Carcinomas—lining tissues ◦ Sarcomas—muscle or connective ◦ Leukemias—blood Cancer Development Gradual process Lack differentiation Abnormal nuclei No apoptosis Form tumors Undergo metastisis & promote angiogenesis
