Download Cell Cycle and Cell Division notes

Cell Cycle and Cell Division
Objectives
1.
2.
3.
4.
5.
6.
7.
8.
9.
What problems does growth cause for cells? What factors
control cell growth?
Why do cells divide? What factors control cell division?
What are the phases of the cell cycle? What is each for?
Describe the processes that occur in each stage of cell division
(mitosis).
Compare and contrast plant and animal cell division.
How does cell division in prokaryotes differ from eukaryotes?
Why do chromosomes form?
How many chromosomes are in each cell before and after cell
division?
What is cancer?
Objective #1
What problems does
growth cause for
cells?
Cell Size Limits (Part A)

Cells grow until they reach their maximum size
limit. Then they must divide or die.
 Unfortunately, everything the cell needs to
take in or get rid of must leave through the cell
membrane, which is proportional to the cell’s
surface area.
Cell Size Limits (Part B)
As a cell grows, surface area does not grow as fast
as volume.
 At some point, the cell’s needs are too great to be
met by diffusion through its cell membrane. That
is the cell’s maximum size limit.

Cell Size
(Length of a
Side)
Cell Volume
(Needs)
Cell Surface Area
(Ability to Meet Needs)
1
1
6
2
8
24
3
27
54
4
64
96
5
125
150
6
216
216
7
343
296
Cell Size Limits (Part C)

Cellular communications also limit the
maximum size of a cell.
 In a cell’s normal activities, signaling proteins,
raw materials, and enzymes must diffuse
through the cell’s cytoplasm to get to areas
where they are needed.
 If the cell gets too big, then these materials
move too slowly to be used in the reactions
needed to keep the cell alive.
Summary #1
When a cell grows, a much
greater demand is placed on
the limited amount of DNA. The
instructions for making proteins
can’t be used fast enough. This
is called DNA overload.
Summary #2
Volume increases much faster
than surface area.
Surface area to volume ratio
decreases, which means
eventually there is not enough
cell membrane to do the job.
Summary #3
The space inside the
membrane is too great; thus
the cell cannot efficiently
move materials within the
cell.
Objective #2
Why do cells divide?
Cell Division
The process a
cell undergoes
in order to
replace aging
or dying cells.
Cell division helps to…
Reduce the volume to increase
the import/export of materials
2. Reduce the volume to more
easily move materials within the
cell
3. Minimize DNA “overload”
1.
Objective #3
What are the phases
of the cell cycle?
The Cell Cycle
Stages or
phases:

Interphase
 Mitosis
 Cytokinesis
Interphase (G1 phase)
“Growth 1”
= making
proteins and
organelles
(“inter” = between)
Interphase (S phase)
“Synthesis”
= replication
(sister chromatids
form)
Interphase (G2 phase)
“Growth 2”
= making more
organelles and
fulfilling cell’s
function
(until maximum SA:V)
Length of Cell Cycle
Varies depending on type of cell.
 If cell cycle took 12 hours:
G1:5 hrs
S: 4.5 hrs
G2: 2 hrs
M: 0.5 hrs
*Which stage does the cell spend most of
it’s time?

Objective #4
Describe the processes
that occur in each
stage of cell division
(or mitosis).
Mitosis begins…Prophase





“pro” = before
chromosomes form
nucleus breaks up
centrioles appear
spindle fibers form
Which of these is in prophase?
A
D
B
C
E
Mitosis: Metaphase



“meta” = after
or next in line
Spindles attach
to chromatids
Centromeres
align at middle
Which of these is metaphase?
A
D
B
C
E
Mitosis: Anaphase



“ana” = leading
up to…
chromatids
separate
chromatids pull to
opposite ends of
the cell
Which of these is in anaphase?
A
D
B
C
E
Mitosis: Telophase




“telo” = end
2 new nuclei form
Coiled
chromosomes
change back to
relaxed chromatin
Mitosis ends
Which of these is in telophase?
A
D
B
C
E
Cytokinesis

Cytoplasm and cell
contents divide as
cell membrane
moves inward to
create 2 daughter
cells – each with its
own nucleus &
identical DNA
Other pictures of mitosis
Other pictures of mitosis
Other pictures of mitosis
Other pictures of mitosis
Other pictures of mitosis
Other pictures of mitosis
Objective #5
Compare & contrast
cell division in plant
and animal cells.
Animal cell mitosis
Plant cell mitosis
Cytokinesis differs…
CELL PLATE
TOTD
A scientist is observing an animal cell with a
microscope. She notices that the chromosomes
are becoming visible. Which phase of the cell
cycle is the cell MOST likely entering into?
a) Prophase
b) Interphase
c) Metaphase
d)
Anaphase
Objective #6
Compare cell division in
prokaryotes (bacteria)
and eukaryotes.
Prokaryotic Cell Division
Replication: copy the DNA*
2. Cell splits in half, called binary
fission
3. This is a form of asexual
reproduction
*Each cell has identical DNA copy
1.
Eukaryotic Cell Division
Replication
2. Mitosis: chromosomes are
assembled, sorted, and divided
up through a series of phases
3. Cytokinesis: cytoplasm divides
1.
* Each cell has an identical DNA
copy
Objective #7
Why do chromosomes
form?
Chromosome Structure…

DNA is usually in the form of
chromatin. (very loose
strands)

Chromatin is made of DNA
that is coiled around proteins
called Histones and organized
into groups called
Nucleosomes

Chromatin continues to
condense as the cell prepares
for replication
Chromosome structure…

Before the cell divides, the
super-condensed chromatin is
duplicated as sister
chromatids.

Sister chromatids are like
matched socks and are held
together by a Centromere

This forms homologous
chromosomes
To handle the amount of DNA
Cells organize the DNA into
chromosomes – condensed
colored bodies that can be
sorted during cell division.
Objective #7
How many
chromosomes are in
each cell before and
after cell division?
Mitosis = diploid to diploid
Diploid means: The somatic (body) cell
contains two copies of each chromosome.
In humans we have 46 chromosomes. There
are 23 chromosomes you get from Mom and
23 chromosomes you get from Dad.
46
S phase
92
46
When a somatic cell divides each new
daughter cell must have the same amount of
DNA. That’s the purpose of Replication and
Mitosis.
46
Mitosis
46
What factors control
cell division?
Control of the Cell Cycle

Cells require growth factors to
divide (cyclins or hormones)
 Cells need room to grow - if it’s
cramped, no division
 Cells normally stop dividing if
they lose their anchorage
Objective #9
What is cancer?
Apoptosis
Programmed cell death
 Apoptotic cells shrink in size, break into
smaller pieces that other body cells
recognize and eat

For tissue development
 To remove damaged cells
 To destroy viral infected cells
 To balance mitosis rate

What is Cancer?

Disease of defective apoptosis
 Cyclins and CDK (cyclin dependent kinases)
control transition from G1 to S and G2 to M. If
these don’t work properly it leads to…
tumor growth
“Mitosis gone mad”
Cancer causes

Mutated genes (called
oncogenes) can over-stimulate
cell division
 Mutated tumor supressor genes
fail to prevent tumor growth
*Mutagenic factors (mutation producing) include
radiation, some foods, drugs & chemicals, viruses &
microbial agents, smoke, dust like asbestos,
inhalants, gasoline, lead…
Healthful Decisions to reduce Cancer Risk






Avoid carcinogens! (smoking)
Eat whole foods (fresh fruit and grains)
Exercise regularly to boost immune system
Don’t drink alcohol in excess
Don’t get sunburned or overexpose your skin
to UV (watch out tanning bed victims)
Undergo regular screening and selfexamination