Download Cell Size, Cell Cycle, and Uncontrolled Cell Division

Cell Growth and Division
Cell Size, Cell Cycle, and Uncontrolled Cell Division
37.2 Trillion
Cells in the Human Body
Limits to Cell Size
As the cell grows, two problems arise…
Demands on DNA
● DNA controls the
processes of the cell.
● As the cell grows, no
extra DNA is made but
more demand is put on
the DNA.
Nutrient Exchange
●
●
Food, O2, and H2O enter and
wastes exit across the
membrane
Must understand surface area
and volume
○ Exchange rate depends on
surface area of membrane
○ Rate of waste production
depends on the cell’s
volume
As the cell grows, two problems arise…
Demands on DNA
Example: Small town library
has enough books for
people to borrow. However,
if a lot of people move into
town, some people may
have to wait for popular
books (more demand).
Nutrient Exchange
Example: It is easier to
transport materials in a
swimming pool than the
ocean
Volume increases at
a faster rate than
Surface area
This is a problem for the cell!
Example: Traffic increases as size
of city increases, but the roads stay
the same size.
Calculations:
Surface Area = length x width x # of sides
Volume = length x width x height
1 cm
SA= 6 cm2
Volume= 1 cm3
SA/Volume ratio= 6:1
2 cm
SA= 24 cm2
Volume= 8 cm3
SA/Volume ratio= 3:1
SA/Volume Ratio
The lower the SA/Volume ratio, the harder it is to get material into/out of
the cell.
So what does the cell do instead?
It divides!!
This is called Cell Division
● A cell divides into 2 daughter
cells
● Cell copies all of its DNA
● Each cell will get a copy of the
DNA
Solves DNA problem as well as
reducing the cell's volume so that
materials can be exchanged
across the membrane.
So whose cells are bigger…
an adult or a baby?
It divides!!
This is called Cell Division
●
●
●
A cell divides into 2 daughter
cells
Cell copies all of its DNA
Each cell will get a copy of
the DNA
Solves DNA problem as
well as reducing the cell's
volume so that materials
can be exchanges across
the membrane.
We wrote this down last time, just reviewing!
Why do cells need to
divide? Do they divide at
the same rate?
2 main reasons
Growth
Repair
THE CELL CYCLE
● 3 main stages of the cell
cycle:
○ Interphase
○ Mitosis
○ Cytokinesis
Interphase: growth and
DNA replication
Mitosis: division of the cell
nucleus
Cytokinesis: division of the
cytoplasm
Before we go over each of the phases, let’s talk about
DNA...
- During interphase, it is in
chromatin form (Depictions
often look like Ramen)
- During mitosis, it condenses
into X shape called
chromosomes
- Humans have 46 chromosomes
(23 pairs) in their body
(somatic) cells
Chromosomes
Sister
The Cell Cycle Broken down
Mitotic phase has 4 phases:
Interphase is divided into 3
sections:
1. G1(Gap 1)
2. S (synthesis)
3. G2 (Gap 2)
Prophase
Metaphase
Anaphase
Telophase
____________________________
Cytokinesis: when 1 cell becomes 2
- Completed by the end of
Telophase
Interphase
DNA in chromatin
form
Nucleolus visible
1. G1(Gap 1):
everyday life of
cell
2. S (synthesis): DNA
replicates
3. G2 (Gap 2): All
organelles
replicate
Prophase
DNA condenses into X
shape (chromosomes)
Nuclear membrane
breaks down
Centrioles migrate to
opposite sides of
nucleus
The spindle forms and
chromosomes attach
at centromere
Metaphase
The spindle fibers
pull the
chromosomes by
their centromeres
until they line up
down the middle
*M=metaphase=middle
Anaphase
Centromeres of the
sister chromatids
split
The individual
chromatids separate
Spindle fibers move
them to opposite
sides
A for Anaphase -- Chromatids looks like A’s.
Telophase
Spindle fiber
breaks down
Two new nuclear
membrane returns
“Pinch” forms in
the middle
Cytokinesis
Cytoplasm pinches
in half
One cell becomes
two cells
Each cell has
identical set of
chromosomes
Mitosis Summary and Animation
When does the nuclear
membrane breakdown?
Reform?
Prophase; Telophase
T/F: Chromatids are pulled
to opposite sides in
Metaphase.
False; Anaphase
A . Interphase
B. Telophase
C. Prophase
D. Metaphase
E. Anaphase
So how quickly are
cells replacing
themselves?
Video
What is telling the
cell it is time to
divide?
Cyclins - proteins
that regulate the
timing of the cell
cycle
What about uncontrolled
cell division?
Cancer
A disorder in which some of the body’s own cells lose the
ability to control growth.
These cells do not respond to the regulators of normal cells
Tumors can grow and cause damage to normal tissues.
Truth or Myth?