Focus Questions:
◦ Why do cells need to grow and divide?
◦ How do cells divide?
◦ What happens when cells divide
incorrectly?
Reasons we need our cells to grow!
Growth of organisms
Repair of tissues
There are limits to a cell’s growth
• A larger cell may experience
“DNA overload”
• As cells get larger they become
less efficient at exchanging
nutrients and materials such as
oxygen, water, and food with its
environment
DNA Overload

If a cell is large, there are more demands
on its single copy of DNA

Think of a book in a library: the more
people there are, the greater the likelihood
that they will have to wait to read it
Exchanging Nutrients
As a cell gets larger, what gets bigger?
◦ Its volume!
Its surface area also gets larger, but not large
enough!
◦ Only so many materials are able to pass
through the cell membrane at once
The surface area of many small cells is greater
than one cell (or ever a few large cells)
Remember, cells must use diffusion and osmosis
to obtain important nutrients, like oxygen and
glucose
Cell Division - process by which a cell splits
into two identical daughter cells
Occurs in two main phases:
Interphase – cell copies its DNA and prepares for division
Mitosis – chromosomes separate into two new cells
Chromosomes
DNA containing cell’s genetic code
During interphase, chromosomes are copied
- this produces two identical “sister chromatids”
The Cell Cycle
The Cell Cycle
Interphase (longest phase)
G1 - first growth (gap) phase, new organelles produced
Synthesis - DNA makes a copy
G2 - second growth (gap) phase, preparing for mitosis
G0 - no growth phase, a cell may enter this phase
Mitosis - nucleus divides, ensuring each new cell has the
exact number of chromosomes as parent
Life Cycle of the Cell
•Mitosis = nuclear division
•Mitosis is followed by cytokinesis (cell division)
•The steps of mitosis ensure that each new cell
has the exact same number of chromosomes
as the original
First, a little background info

Centrioles – produce
spindle fibers during cell
division

Spindle fiber – a tiny
protein that helps
chromatids separate during
mitosis
Anatomy of a chromosome

Chromosome is
composed of a pair of
chromatids (sister
chromatids)

Centromere is the
center, where the two
chromatids connect
•Interphase • Prophase • Metaphase • Anaphase •
Telophase
IPMAT
Interphase

Most of the time in the cell cycle is
spent in interphase (95%)

Technically, it is not mitosis
(Includes G1, S, G2)

Most cellular activity occurs in
interphase

Reproduction of DNA and
organelles
Prophase

Chromatin (stringy DNA) condenses into
chromosomes (more compact DNA, which is more
visible)
Prophase

Centrioles migrate
to opposite poles of
the cell.

Spindle fibers form

Nuclear envelope (covering around nucleus)
disappears.
Draw Prophase
Metaphase

Nuclear envelope is gone

Microtubules connect to
chromosomes

Chromosomes aligned along
middle of nucleus (on the
equator)
Draw Metaphase
Anaphase

Chromosomes pulled apart by spindle
Draw Anaphase
Telophase

Chromatids arrive on opposite sides
of cell

Nuclear envelope begins to reform
around each set of chromatids

Chromosomes unwind

Spindle fibers disperse
Draw Telophase
Cytokinesis

Cell membrane pinches off

New cell wall forms in plants
Interphase

Two new genetically identical cells

Cell Cycle continues
Mitosis: Can you name the stages?
1
2
3
4
5
Mitosis: Can you name the stages?
Prophase
2
3
4
5
Mitosis: Can you name the stages?
Prophase
Metaphase
3
4
5
Mitosis: Can you name the stages?
Prophase
Metaphase
Anaphase
4
5
Mitosis: Can you name the stages?
Prophase
Metaphase
Anaphase
Telophase
5
Mitosis: Can you name the stages?
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Phases of cell cycle - IPMATC
Important
People
Must
Analyze
Tasks
Correctly
CELL CYCLE IMAGES
1. chromosomes visible (chromatids)
2. centrioles migrate to the poles
3. nuclear membrane disappears
4. nucleolus disappears
5. spindle forms
1. chromosomes line up on the equator, spindle
attaches
1. chromatids separate and move to opposite poles
1. chromosomes disappear • chromatin
2. nuclear membrane reforms
3. nucleoli reappears
4. spindle disappears
5. centrioles duplicate
- division of the cytoplasm to form 2 new daughter
cells
- organelles are divided
- daughter cells are genetically identical
Cells return to interphase
 Phases of cell cycle - IPMATC
Important
Impatient
People
People
Must
May
Analyze
Attack
Tasks
Teachers
Correctly
Constantly
1.Name the phases
starting at the top.
1.Name the phase
2.Identify X
3.Identify Y
5. Name the
phase
6. Name the
phase