Transcript The Cell Cycle and Mitosis

Be able to:

Explain the problems that growth causes for
cells.

Describe how cell division solves the
problems of cell growth.

Name and describe the main events of the
cell cycle.
Let’s do some math!

Calculate the
surface area of S.A. = 4 (pi) r 2
each sphere.

Calculate the
volume of each
sphere.

Then, calculate the
surface area to
volume ratio. Round #’s
up or down to make it easier.
Radius 2cm
S.A. = ________
Radius 2cm
V = __________
S.A. = ___50cm2__
Ratio SA:V = ________
V = __33cm3____
Ratio SA:V = 50:33_or 1.51:1
Radius
1cm
Radius 1cm
Radius 2cm
Radius 3cm
2___
= _____
S.A.S.A.
= __13cm
S.A. = ___50cm2__
S.A.
S.A.
= __113cm
= _____ 2_
3____
= ______
V =V__4cm
V = __33cm3____
V =V___113cm
= ______3___
RatioSA:V
SA:V==_13:4
___
Ratio
or 3.25:1__
Ratio SA:V =
50:33_or 1.51:1
Ratio
Ratio
SA:V
SA:V
= ___
=
_113:113 or 1:1__
S.A. = 4 (pi) r 2
1. As the spheres get larger what happens to the SA:V ratio?
1st problem:
Cell size and material exchange

The larger a cell
grows the more
trouble it has…

moving enough
nutrients in

Moving all the
waste materials
out
2nd problem: DNA overload
A larger cell makes greater demands on
its genetic library.
Checkpoint!

What are two problems that cell growth
causes for cells?


The larger a cell becomes, the more demands
the cell places on its _____ and the more trouble
the cell has moving enough _________and
_________ across the cell membrane.
What is viable solution for cells solve these
problems?

Cell Division – A larger cell splits into two smaller
daughter cells.
The Cell Cycle - series of events that cells
go through as they grow and divide

The cell cycle is
divided into two
halves
 Interphase period of the cell
cycle between
cell divisions
 M phase –
period of time
when mitosis
and cell division
occurs
Parts of Interphase



G1 Phase
 Growing
 Synthesize new proteins and
organelles
 Doing their jobs
 Longest phase of cell cycle
S Phase
 Chromosomes(DNA) are
replicated
 Key proteins associated with
replication are made
(centromeres)
G2 Phase
 Shortest of the 3 phases of
interphase
 Organelles and molecules for
cell division are produced
(centrioles)
 Check-up phase before mitosis
Chromatin and Chromosomes
Chromatin - A complex of DNA and proteins
in the cell nucleus that condenses to form
chromosomes during cell division.
 Chromosomes – Condensed Chromatin
 They are the same stuff, just in different
forms

Chromatin condenses in chomosomes
before mitosis begins

Chromatin

Chromosomes
Chromosomes

Different organisms have different #’s of
chromosomes
cells – 46
 Fruit Fly cells – 8
 Carrot cells – 18
 King Crab cells - 208
 Humans
Note: Chromosomes are not visible in most cells except
during cell division.
Chromosomes Replication



During the cell cycle (before
cell division can take place)
chromosomes are replicated to
form an identical copy of
itself.
Two identical copies of a
chromosome are called “sister”
chromatids – (one of two
identical “sister” parts of a
duplicated chromosome)
Centromere - area where
each pair of the chromatids
of a chromosome are
attached
M Phase, Cell Division and Mitosis
Mitosis
(PMAT)


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
Prophase
1. Chromosomes become
visible
2. Centrioles take up positions
on opposite sides of the
nucleus
Metaphase
1. Chromosomes line up
across center of cell
(Metaphase-Middle)
Anaphase
1. The chromosomes move
until they form two groups
near the poles of the spindle
(guides that help separate the
chromosomes)
Telophase
1. A nuclear envelope reforms around each cluster of
chromosomes
2. The nucleolus becomes
visible in each daughter
nucleus
Cytokinesis
Cytoplasmic division and other changes exclusive of nuclear
division that are a part of mitosis or meiosis
In animal cells the
cell membrane is
drawn inward until
the cytoplasm is
pinched into two
nearly equal parts
In plant cells a cell
plate forms midway
between the divided
nucleus
In plant cells, a cell plate forms. The cell plate is
synthesized by the fusion of multiple membranebounded vesicles. Their fusion supplies new plasma
membrane for each of the two daughter cells. Synthesis
of a new cell wall between the daughter cells then
occurs at the cell plate.
Controls on Cell Division
Answer

The cells would form more layers but would
probably begin to die off when space and
nutrients ran short and wastes accumulated.
How do cells know when to divide
and when not to?

Internal regulators – proteins that respond to
events inside the cell.
Some proteins make sure cells do not enter
mitosis until all of the chromosomes have been
replicated.
 What stage of the cell cycle do you think these
proteins work?
 G2 phase


Cyclins – (internal regulator) one of a family
of closely related proteins that regulate the
cell cycle in eukaryotic cells
Cyclins
External Regulators




External regulators - Proteins that respond to
events outside the cell are called external
regulators.
External regulators direct cells to speed up or slow
down the cell cycle.
Growth factors are among the most important
external regulators, which tell cells to speed up
division. When is this important?
(Answer: During embryonic development and
wound healing)
Molecules found on the surfaces of neighboring
cells often have an opposite effect, causing cells to
slow down or stop their cell cycles.
Uncontrolled Cell Growth

Cancer cell

Various forms of cancer have many causes
 Smoking
 Radiation
 Viral
infections
The common thread in all cancers is that
control over the cell cycle has broken down.
 Many cancer cells have a defect in the p53
gene which makes a protein that stops the
cell cycle if the chromosomes have not been
replicated properly

Checkpoint!
1. The break down of a cell’s entire life is the
_______ ________.
 2. The phase of the cell cycle when the cell
is growing, replicating DNA and getting ready
for mitosis is _____________.
 3-6. What are the four phases of Mitosis?
 7. The process of a cell actually splitting in
two is called _______________.
