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Cell Reproduction/Mitosis
Chapter 12
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What you need to know!
• Mitotic Cell division results in genetically identical daughter cells
• The mitotic phase alternates with interphase in the cell cycle
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Overview
I. Cell Division Overview
II. The Cell Cycle
III. Mitosis – nuclear division/cytokinesis
IV. Stages of Mitosis
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Cell Division
• Life depends on the ability of cells to reproduce/copy
• Cell Division = 1 cell divides into 2
• Unicellular organisms cell division = reproduction– Prokaryotes, Protists– Bacteria = binary fission
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Cell Division
• Multicellular organisms cell division = growth and development, repair and replace.
– Protists, fungi, plants and animals
• 2 types of multicellular organism cells:
1. Somatic Cells: Body cells of an organism that do all the daily function of the organism
2. Germ Cells: reproductive cells (eggs and sperm)
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Cell Cycle
• G0: the cell spends its life working and growing (i.e. breaking down sugars, making ATP, enzymes)
• Sometimes a cell will prepare to divide– 1 mother cell 2 daughter cells
• Interphase– G1 (Gap1): Growth, development, organelle
production, etc. Cell must enter reproduction (S phase) or not (G0)
– S (Synthesis): DNA replication
– G2 (Gap2): continued growth and preparation for
division (centrosomes/centrioles duplicate)
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Cell Cycle
• Mitosis (M): nuclear division
• Cytokinesis: division of cytoplasm and cell membrane/cell wall
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DNA
• Chromatin: spread out DNA-protein complex. In Eukaryotes the proteins are histones. Human cells have 3 billion base pairs.
• Chromosomes: condensed strands of DNA distinct in number and length for each organism. One chromosome is made up of 30 to 150 million base pairs.
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DNA
• Humans have 46 chromosomes (23 pairs).
• Each chromosome contains a few thousand genes that code for cellular proteins
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DNA
• Diploid indicates that our somatic (body) cells have 23 pairs of chromosomes (2n)
• Haploid indicates that our gametes (sex cells) have 23 chromosomes (1n or n)
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Mitosis: Division of the Nucleus
• Problem: distribution of one exact copy of each of their chromosomes to each new cell.
• Each chromosome contains thousands of genes, each necessary to the proper functioning of the organism.
• Humans have ~120,000 genes spread over 46 chromosomes in each somatic cell.
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Mitosis
• During Mitosis all access to the DNA stops as chromatin coils up and condenses into visible chromosomes
• Each replicated chromosome is composed of 2 identical parts (sister chromatids) held together by a centromere.
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Mitosis
• Sister chromatids are pulled apart during mitosis, and partitioned into 2 daughter cells
• Result of mitosis & cytokenesis: 2 daughter cells genetically identical to the parent cell.
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IV. Stages of Mitosis
• Prophase: Chromosomes condense, centrosomes are pushed apart by growing spindle, nuclear envelope disintegrates
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Stages of Mitosis
• Prometaphase: the 2 centromeres of each chromosome attach to one kinetochore spindle fiber; centrosomes move to opposite poles
Kinetochore spindle fiber
Non Kinetochore spindle fiber
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Stages of Mitosis
• Metaphase: Chromosomes line up at the metaphase plate (equator); centrosomes are at opposite poles
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Stages of Mitosis
• Anaphase: Chromosomes separate due to shortening of kinetochore spindle fibers; cell elongates due to lengthening of non-kinetochore spindle fibers
Kinetochore spindle fiber
Non Kinetochore spindle fiber
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Stages of Mitosis
• Telophase: Chromosomes immediately uncoil and resume transcription activities; spindle proteins disassemble; nuclear envelope reassembles
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Mitosis Animation
• http://vcell.ndsu.nodak.edu/animations/mitosis/movie-flash.htm
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Cytoskeleton Creates Chromosome Migration• Spindle fibers are microtubules
made of tubulin proteins that are always present in the cytoplasm
• Enzymes assemble and disassemble spindle fibers
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Centromere region contains
1. Centromere protein clamp, holding the 2 sister chromatids together; deactivated during anaphase
2. Kinetochore motor protein; 1 on each sister chromatid
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Kinetochore microtubule
• Several microtubules attach to each kinetochore motor protein
• Motor protein starts moving (walks along the spindle fibers); kinetochore microtubules shorten, pulling chromsomes (at the metaphase plate) apart– ATP hydrolysis powers the motion
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Non Kinetochore Microtubules
• Microtubules lengthen, pushing the two poles apart (cell expands)
Kinetochore spindle fiber
Non Kinetochore spindle fiber
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Cytokinesis
Animal:
•Cleavage furrow– Made by microfilaments (actin fibers)– A drawstring around the middle of the
cell
•Cell pinches off into 2 daughter cells
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Mitosis & Cytokinesis in Plant Cells• Plants have centrosomes w/out
centrioles
• No cleavage furrow– plant cells cannot separate due to cell
wall
• Cell plate grows through divided cell
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Duration of the Cell Cycle
• Prokaryotic Cells – 20 minutes
• No DNA/Histone complex + fast DNA replication (500 NT/sec)
• No spindle fibers, no mitosis
• 2 DNA rings are attached to 2 spots of the plasma membrane which grows apart
• 1 plasmid
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Duration of the Cell Cycle
• Eukaryotic Cells – 12-48 hrs
• Longest phase of the cell cycle is interphase
• Longest phase of mitosis is prophase
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Frequency of Cell Cycles
• Depends on cell type:Cell type Life span/frequency
Esophagus, epidermis 2-3 days
Small intestine 1-2 days
Large intestine 6 days
Red blood cells 3 months
White blood cells Up to 10 years
Nerve cells Lifetime (G0)