Transcript Cell Growth and Reproduction

Cell Growth and
Reproduction
• Cells cannot survive if there is not
enough DNA
• Cells divide before they become
too big to function properly
Cell Reproduction
• Cell division is a process in which new
cells are produced from one cell
• Diagram:
– 2 daughter cells are identical to the
original parent cell
Discovery of Chromosomes
• before cells divide, several short, stringy structures
suddenly appear inside the nucleus
– vanish right after the cell divides
– called chromosomes
• contain DNA
• carriers of genetic material
• copied and passed through generations of cells
• Has 2 halves called sister
chromatids
–Held together by a
centromere
• Chromosomes usually exist as chromatin
– long strands of DNA wrapped around
histone proteins
– Coils up into visible chromosomes during
mitosis (cell division)
Cell Cycle
• Sequence of the
growth and
division of a cell
• 2 general periods
Mitosis
G2
G1
S
Growth (called Interphase)
• Majority of cell’s life spent
in this phase
• Cell grows in size
• Carries on metabolism
• Chromosomes are
duplicated
Interphase
• Busiest phase
• Divided into 3 parts
– G1 Phase: rapid growth and metabolic activity
• Cell grows
• High production of proteins
– S Phase: DNA synthesis and replication
• Cell copies its chromosomes
– G2 Phase: Cell prepares for division
• Organelles are made
• Centrioles replicate
Division (called Mitosis)
• Nuclear division
• 2 daughter cells
are formed from
1 parent cell
Prophase
• 1st phase (longest)
• chromosomes become visible
– centrioles separate to opposite sides of
the nucleus (in animal cells only)
• nucleus begins to disappear
– nuclear envelope and nucleolus begin to
disintegrate
• spindle forms  role in separating sister
chromatids
Metaphase
• Chromosomes become attached to
the spindle fibers by a centromere
• Chromosomes begin to line up in
the middle of the cell
• Very short phase (lasts a few
minutes)
Anaphase
• Centromeres split apart
• Separation of sister chromatids
from each other
• Shortening of spindle fibers
• Individual chromosomes result in 2
groups
Telophase
• Final phase of mitosis
• Chromosomes unwind (become a
tangle of material)
• Spindle breaks down
• Nucleolus reappears
• New nuclear envelope forms around
the chromosomes
• Membrane forms between 2 nuclei
Cytokinesis
• Cell’s cytoplasm divides
• Usually occurs at the same time as telophase
• Animal cells: plasma membrane pinches in
along the middle of the cell
• Plant cells:
– Have rigid cell wall
– Cell plate goes across the center of the cell
– Cell membrane forms around each cell
– New cell wall forms on each side of cell
plate
Animal Cell
Plant Cell
Control of Cell Cycle
• Cells can lose control of the cell cycle
– Can result from failure o produce certain
enzymes, overproduction of enzymes, or
producing enzymes at the wrong time
– leads to uncontrolled cell division (called
cancer)
• Genes: segment of DNA that controls production
of proteins like enzymes
Cancer
• Result of uncontrolled cell division
• Forms masses of tissue called tumors
– Deprives normal cells of their nutrients
• Metastasis: cancer spreads throughout body
infecting circulatory system
• 2nd leading cause of death
• Can affect any tissue in the body
Causes of Cancer
• Environmental
– Cigarette smoke
– Air and water pollution
– Exposure to UV
radiation
– Damages genes that
controls cell cycle
• Genetic
– Viral diseases and
infections can damage
genes
Cancer Prevention
• Diets low in fat and
high in fiber
• Vitamins and
minerals