Ch 10- Cell Growth
• What problems does growth cause for the cell?
– Larger a cell becomes, the more demands that cell
places on its DNA
– The cell has more trouble moving enough nutrients
and wasted across the cell membrane
• Where is the information that tells cells what to
do stored at?
– DNA
• Understanding the relationship between a cell’s
volume and surface are is key to understanding
why cells must divide as they grow
Division of the Cell
• If cell got to large, it would be more difficult to
get sufficient amounts of oxygen and nutrients in
and waste products out
• Cell division- process by which a cell divides into
two new daughter cells
– Copies DNA, each daughter cell gets one complete set
of genetic information- solves the problem of
information storage
– Solves the problem of increasing size by reducing cell
volume- each daughter cell has an increased ratio of
surface area to volume
Sec 2- Cell Division
• Prokaryotes- process of cell division is simply
separating the contents of the cell into two parts
• Eukaryotes- process is more complex and occurs
in 2 stages
• Mitosis- division of cell nucleus
– Asexual, cells produced are identical to parent cell
– Source of new cells as multicellular organism grows
and develops
– Begins shortly after egg is fertilized
• Cytokinesis- division of cytoplasm
Chromosomes
• What are they?
– Carries the genetic information passed from one
generation to the next, made of DNA and proteins
• How many chromosomes do human cells have?
– 46
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Fruit flies have 8 chromosomes
Not visible except during cell division
Before cell division, chromosomes are replicated
Each chromosomes consist of 2 identical “sister”
chromatids- when cell divides one chromatid goes to
each of two new cells
• Centromeres- area where chromatids are attached,
usually located near middle
Cell Cycle
• During the cell cycle, a cell grows, prepares for
division, and divides to form two daughter cells,
each of which then begins the cycle again
• Interphase- the in between time between cell
division
• Cell cycle- series of events that cells go through as
they grow and divide
• Cell cycle consists of 4 phases
– Mitosis and cytokinesis take place during M phase
– Chromosome replication takes place during S phase
– G phases are periods of intense growth and activity
Events of the Cell Cycle
• Interphase- phase is quite long, made up of G₁, S,
and G₂ phases
• G₁ phase- where cells do most of their growing
– Cells increase in size and synthesize new proteins and
organelles
• S phase- chromosomes are replicated and
synthesis of DNA molecules takes place
• G₂ phase- many of organelles and molecules
required for cell division are produced
• Cell is ready for the M phase and begin process of
cell division
Mitosis
• Divided into 4 phases- prophase, metaphase,
anaphase, and telophase
• May last anywhere from few minutes to several daysdepends on type of cell
• Prophase- chromatin condenses into chromosomes,
centrioles separate and a spindle begins to form,
nuclear envelope breaks down
– Centrioles- two tiny structures located in cytoplasm near
nuclear envelope, separate and take position on opposite
sides of nucleus
– Spindle- fan-like microtubule structure that helps separate
the chromosomes
• Metaphase- chromosomes line up across the
center of cell, each chromosome is connected
to a spindle fiber at its centromere
• Anaphase- sister chromatids separate into
individual chromosomes and are moved apart
• Telophase- chromosomes gather at opposite
ends of cell and lose their distinct shapes, two
new nuclear envelopes will form
• Mitosis is complete
Cytokinesis
• Result of mitosis= two nuclei each with
duplicate set of chromosomes formed within
cytoplasm of a single cell
• Cytokinesis- division of cytoplasm, usually
occurs at same time of telophase
– Cytoplasm pinches in half, each daughter cell has
an identical set of duplicate chromosomes
• Mitosis and Cytokinesis
Sec 3- Regulating the Cell Cycle
• Cyclin- proteins that regulate the timing of the cell cycle in
eukaryotic cells
• Discovered by Tim Hunt and Mark Kirschner
• Many more proteins have been discovered since- 2 types of
proteins- regulatory proteins in and outside of cell
• Internal Regulators- allow cell cycle to proceed only when
certain processes have happened inside cell
– Make sure cell does not enter mitosis until all chromosomes
have been replicated
• External Regulators- direct cells to speed up or slow down
cell cycle
– Growth factors among most important external regulators
Uncontrolled Cell Growth
• Why is cell growth regulated so carefully?
• Cancer- disorder in which some of body’s own
cells lose the ability to control growth
– Do not respond to the signals that regulate the
growth of most cells
– Divide uncontrollably and form masses of cells called
tumors
– May break free from tumor and spread to rest of
body
• What causes the loss of growth control that
characterize cancer?
– Smoking tobacco, radiation exposure, viral infection