Transcript Cell Growth and Division (Honors)

Cell Growth and Division
Why do cells divide?
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DNA “Overload”
– Not enough information for a big cell
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Exchanging Materials
– Must be able to obtain nutrients and
eliminate wastes easily
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Ratio of Surface Area to Volume
– Volume increases faster than the surface
area
Surface Area vs. Volume
Chromosomes
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DNA and proteins
Each chromosome
consists of two
identical sister
chromatids
Centromeres – area
where the chromatids
are attached
The Cell Cycle
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Series of events that cells go through as they
grow and divide
4 phases
– M phase (mitosis and cytokinesis) – the division of
the nucleus and the cell
– G1 phase (the first “gap”) – cells increase in size and
synthesize new proteins and organelles
– S phase (synthesis of DNA) – the chromosomes are
replicated
– G2 phase (the second “gap”) – many of the
organelles and molecules needed for mitosis are
produced
The Cell Cycle
The Cell Cycle
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Interphase – G1 + S + G2
M phase
– Prophase
– Metaphase
– Anaphase
– Telophase
– Cytokinesis
Mitosis
Interphase
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Cell spends most of
its time in interphase
Cell grows
Carrying out basic
cell functions
Making organelles
Copying
chromosomes
Prophase
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Nucleoli disappear
Chromatin condenses
(becomes shorter &
thicker)
Chromosomes become
visible
Centrioles separate &
move to opposite poles
Spindle fibers form
between the centrioles
Nuclear membrane
disappears
Metaphase
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Chromosomes
attach to the
spindle fibers at the
centromere
Chromosomes align
at the equator
Anaphase
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Centromeres split
apart
Chromatids
separate & move
apart
Sister chromatids
are pulled to
opposite poles
Telophase
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Cell membrane
pinches together at
the equator
Nucleoli reappear
Nuclear membrane
encloses each set
of chromosomes
Chromosomes
loosen up
Cytokinesis
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Division of the
cytoplasm
Begins during
telophase
Cell membrane
continues pinching until
it separates forming 2
daughter cells
Plant cells have a cell
plate that forms
Videos…
Life Spans of Human Cells
Controls on Cell Division
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Cell-to-cell contact – when cells come
in contact with other cells, they stop
dividing
Cell Cycle Regulators
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Cyclin – a protein which regulates the
cell cycle
– Cyclins bind to enzymes called cyclindependent kinases
– Different cyclin/CDK combinations control
different activities throughout the cycle
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Quality control checkpoints occur
throughout the cycle
– If something goes wrong the cycle stops
Cell Cycle Regulation
Cell Cycle Regulators
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Internal regulators – proteins that
respond to events inside the cell
– Part of the checkpoint process
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External regulators – proteins that
respond to events outside the cell
(e.g. growth factors)
– Direct cells to speed up or slow down the
cell cycle
Uncontrolled Cell Growth
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Cancer – uncontrolled cell growth
– Cells no longer respond to the control
mechanisms
– Occurs due to mutations in the DNA
– Cancer cells crowd out normal cells,
resulting in loss of tissue function
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Tumor – cluster of cancer cells
Carcinogens – cancer causing
substances
Cancer
Apoptosis
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Programmed cell death
Occurs when:
– Webbing between human fingers and
toes disappears before birth
– Leaves fall from trees
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Also occurs in cells with DNA damage
to prevent cancerous growths
Stem Cells
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Unspecialized cells that can become
specialized under certain conditions
Embryonic stem cells – unspecialized cells
from an embryo
– Can develop into a wide variety of specialized
cells
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Adult stem cells – found in certain types of
tissues
– Might be able to develop into different types of
cells