Chapter 8:
Cell Growth and
Reproduction
• Cells cannot survive if there is not enough DNA
• Cells divide before they become too big to
function properly
– Volume increases more rapidly than surface
area
– Uses more food and oxygen
– Problems with cell transport
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
• Copies DNA before it divides (goes to each
daughter 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 and proteins
• 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 in size
• 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)
• M-phase
• Nuclear division
and cytokinesis
• 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
Bell Ringer:
1. The four phases of mitosis are ______.
2. Label each event with the correct phase of mitosis:
______ The chromosomes line up across the middle of the
cell
______ Chromosomes become visible
______ Two new nuclear envelopes form
______ The individual chromosomes move apart
• Not all cells go through cell cycle at
same rate
–Ex: muscle and nerve cells (do not
divide at all); skin, digestive, and
bone marrow cells (grow and divide
rapidly)
Cell Cycle Regulators
• Cyclin: regulates cell cycle timing (protein)
– 2 types of regulatory proteins
• Internal regulators
–Respond to events inside the cell
–Ex: cyclins
• External regulators
–Respond to events outside the cell
–Speeds up or slows down cell cycle
Controls on Cell Division
• Cells grow when room for growth is
available
–Will not grow when in contact with
other cells
Control of Cell Cycle
• Cells can lose control of the cell cycle
– Can result from failure to 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
– Can damage surrounding tissues
• 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
– Gene p53
• Normally stops cell cycle until chromosome
replication
• Defect: causes chromosome damage to build
up
Cancer Prevention
• Diets low in fat and
high in fiber
• Vitamins and
minerals
Bell Ringer:
1. Proteins known as _____ regulate the
timing of the cell cycle in eukaryotic cells.
2. ______ is a disorder in which some of the
body’s own cell lose the ability to
control growth.
3. What is the name for tumors that form and
can cause damage to surrounding tissue?
a. cyclins
b. mitosis
c. cytokinesis
d. cancer