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The Cell Cycle & Mitosis
Chapter 5
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5.1 – The Cell Cycle
• Key Concept:– Cells have distinct phases of growth,
reproduction, and normal functions.
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The cell cycle has 4 main stages.
• The cell cycle is a regular pattern of
growth, DNA replication, and cell
division.
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The main stages of the cell cycle are Gap 1, Synthesis, Gap 2, & Mitosis.
• Gap 1 (G1): cell growth and normal functions, copy organelles
• Synthesis (S): copies DNA
• Gap 2 (G2): additional growth
• Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)–Mitosis occurs only if the cell is large
enough and the DNA undamaged.
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Cells divide at different rates.• The rate of cell division varies with the need for
that type of cell.
• Some cells are unlikely to divide (in Gap 0/G0 of the cell cycle)– Example: neurons
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Cell size is limited.• Volume increases faster than surface
area.– Cells need to stay small to allow
diffusion and osmosis to work efficiently.
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• Surface area must allow for adequate
exchange of materials.
– Cell growth is coordinated with division.
– Cells that must be large have unique
shapes.
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5.2 – Mitosis & Cytokinesis
• Key Concept:– Cells divide during mitosis and
cytokinesis.
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Chromosomes condense at the start of mitosis.
• DNA wraps around proteins (histones) that condense it.
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• DNA plus proteins is called
chromatin.
• One half of a duplicated
chromosome is a
chromatid.
• Sister chromatids are held
together at the centromere.
• Telomeres protect DNA and
do not include genes.
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Mitosis and cytokinesis produce two genetically identical daughter cells.
• Interphase prepares the cell to divide.
• During interphase, the DNA is duplicated.
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Mitosis divides the cell’s nucleus in four phases.
• Prophase– Chromosomes condense, spindle fibers
form, and the nuclear membrane disappears
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Mitosis divides the cell’s nucleus in four phases.
• Metaphase– Chromosomes line up in the middle of
the cell
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Mitosis divides the cell’s nucleus in four phases.
• Anaphase– Sister chromatids are pulled apart to
opposite sides of the cell
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Mitosis divides the cell’s nucleus in four phases.
• Telophase– Two nuclei form at opposite ends of the
cell, the nuclear membranes reform, and the chromosomes uncoil back into chromatin
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Cytokinesis differs in animal and plant cells.
• Cytoplasm separates– Animal cells: membrane
pinches the two new cells apart
– Plant cells: a cell plate (new cell wall) separates the two new cells
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5.3 – Regulation of the Cell Cycle
• Key Concept:– Cell cycle regulation is necessary for
healthy growth.
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Internal and external factors regulate cell division.
External Factors• Include physical and
chemical signals– Cell to cell contact:
when one cell touches another, they stop growing
– Growth factors: chemical signals released by cells that tell other cells to grow
• Trigger internal factors, which affect the cell cycle
Internal Factors• Kinases and cyclins
– Kinases: enzymes in cells, some of which help control the cell cycle – those that do are activated by cyclins
– Cyclins: proteins that are made and destroyed during the cell cycle; activate kinases
• Both help to advance a cell to different parts of the cell cycle
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Apoptosis is programmed cell death.
• Some cells need to grow and divide but other cells need to die.
• Apoptosis is the process of programmed cell death.– Normal feature in healthy organisms– Caused by a cell’s production of self-
destructive enzymes– Occurs during fetal development
(responsible for separation of fingers and toes)
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Cell division is uncontrolled in cancer.
• Cancer cells form disorganized clumps called tumors.– Benign tumors remain clustered and can
be removed.–Malignant tumors metastasize, or break
away, and can form more tumors.
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• Cancer cells do not carry out normal cell functions.
• Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation.
• Carcinogens are substances known to cause cancer (they damage those genes)– Chemicals, tobacco smoke, X-rays, UV rays
• Standard cancer treatments typically kill both cancerous and normal, healthy cells.
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5.4 – Asexual Reproduction
• Key Concept:
–Many organisms reproduce by cell
division.
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Binary fission is similar to mitosis.
• Asexual reproduction is the creation of offspring from a single parent.– Binary fission produces
two daughter cells genetically identical to the parent cells.
– Binary fission occurs in prokaryotes.
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Environment determines which form of reproduction is most advantageous
• Asexual reproduction is an advantage in consistently favorable conditions.
• Sexual reproduction is an advantage in changing conditions.
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Some eukaryotes reproduce by mitosis.
• Budding forms a new organism from a small projection growing on the surface of the parent.
• Fragmentation is the splitting of the parent into pieces that each grow into a new organism.
• Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.
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5.5 – Multicellular Life
• Key Concept:– Cells work together to carry out complex
functions.
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Multicellular organisms depend on interactions among different cell
types.• Tissues are groups of cells that perform a similar function.
• Organs are groups of tissues that perform a specific or related function.
• Organ systems are groups of organs that carry out similar functions.
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Specialized cells perform specific functions.
• Cells develop into their mature forms through the process of cell differentiation.
• Cells differ because different combinations of genes are expressed.
• A cell’s location in an embryo helps determine how it will differentiate.