Download Regulating the Cell Cycle

Regulating the Cell Cycle
Controls on Cell Division
• Most cells divide until they come in contact
with other cells
• Injury in body stimulates cells to divide
– As healing processes nears completion the rate of
cell division slows
Cyclins – family of proteins that regulate
the timing of the cell
• The cell cycle is controlled by regulatory proteins
both inside and outside the cell
– Internal regulators (inside): allow cell cycle to proceed
only when certain events have occurred in the cell
itself
• Keeps cell from dividing if DNA has not been replicated
– External regulators (outside): direct cells to speed up
or slow down the cell cycle
• Growth factors – stimulate growth & division of cells
– Embryonic development or wound healing
• Some cause cells to slow down or stop their cell cycles
– Prevents cells from over growing environment
– Keeps body tissues from disrupting on another
Apoptosis
• # of cells is closely regulated
– Not just by regulating cell cycle, but also by
controlling when a cell dies
– If cells are not needed then they will activate an
intracellular death program (programmed cell
death or apoptosis)
• Key role in developing structures
Cancer
• Occurs when cell growth/division is not carefully
regulated
• Cancer cells do not respond to the signals that
regulate the growth of most cells
– Cells divide uncontrollably and form a tumor
– Several have a defect in p53 gene
– Several do not respond to external or internal
regulators
• Treatment
– Radiation, chemotherapy, surgery
Cell Differentiation
From One Cell to Many
• All living things pass through a developmental
stage called an embryo
– As organisms develop the cells become more
differentiated and specialized for specific
functions
• Determines the cell’s ultimate identity
• Controlled chemically
Stem Cells and Development
• Totipotent – cells that have the ability to
everything, to develop into any type of cell
– Only first few divisions
• Blastocyte – a hollow ball of cells with a
cluster of cells on the inside
– Outer cells become tissues that attach embryo to
mother
– Inner cells become the embryo itself
• Pluripotent – can develop into most cells, but cannot
form the tissues surrounding embryo
• Pluripotent cells can develop into most, but
not all, of the body’s cells
– They cannot form the tissues surrounding an
embryo
STEM CELLS
• The unspecialized cells from which differentiated
cells develop are known as stem cells
• Embryonic stem cells – pluripotent
• Adult stem cells – multipotent
– They can develop into many types of differentiated
cells
– More limited than pluripotent
– Bone maroow can develop into different types of
blood cells˜
Stem Cell Research
• Potential Benefits
– Repair or replace badly damaged cells and tissues
• Ethical issues
– Human embryonic stem cells are harvested
causing destruction of an embryo