Notes: Cell Division & the
Cell Cycle (Ch. 12)
• One of the major characteristics of a
living thing is the ability to GROW.
• What does growth mean in terms of
the cell? Bigger cells or more cells?
Why more cells?
• cell size is limited by its surface
area to volume ratio (SA:V)
– if a cell gets too large, it wouldn’t be
possible for it to get oxygen/nutrients
in and wastes out by diffusion
Cell Division
• In simple terms: 1 cell divides into 2
new cells
3 main stages of the Cell Cycle
1. Interphase
•
longest stage (90%); preparation for
cell division
2. Mitosis (10%)
•
nucleus divides into 2 nuclei, each with
the same # and kind of chromosomes
(DNA) as the parent cell
3. Cytokinesis
•
cytoplasm divides forming 2 distinct
cells
Cell Cycle
G1 = growth (producing
proteins & organelles)
S = DNA Synthesis
(duplicated) & more
growth
G2 = growth &
completes preparation
for division
• MITOSIS = the division of the
nucleus
• Why is it important that the
nucleus divides?
– it stores the DNA (information of life)
– all new cells need this information
• Chromosomes = tightly
coiled chromatin
(DNA); consist of 2
identical chromatids
(sister chromatids);
which are connected in
the center by a
CENTROMERE
**a human cell entering mitosis contains
46 chromosomes (=DIPLOID number)
chromosome
centromere
chromatin
DNA
How Does Chromatin Coil so Tightly?
• Chromatin wraps around 8 histone proteins
• A second type of histone (H1) holds the
nucleosome “beads” together to increase
compaction further
Mitosis is one, continuous event, but it can
be described as happening in 5 phases:
1.
2.
3.
4.
5.
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
**Remember, the cell
is coming out of
Interphase…
PROPHASE
• chromatin condenses
& chromosomes
become visible
• Centrosomes/
centrioles separate
and start to move to
the opposite sides of
the nucleus;
PROMETAPHASE
• nuclear envelope
breaks down and the
nucleolus disappears
• spindle fibers (from
centrioles) connect to
chromosomes at their
centromeres
(kinetochore);
METAPHASE
• **chromosomes line up in
the center of the cell
(metaphase plate);
**fibers connect from
the poles (end) of the
spindle to the
centromere/kinetochore
of each chromosome
ANAPHASE
• centromeres split,
causing the sister
chromatids to
separate, becoming
individual chromosomes
• chromosomes are
pulled apart to opposite
ends of the cell
TELOPHASE
•
chromosomes uncoil into
chromatin;
•
new nuclear envelope
forms around the
chromatin
•
spindle breaks apart
•
nucleolus reappears in
each new nucleus
Finally…
CYTOKINESIS
• in animal cells: cell
membrane pinches
in & divides
(cleavage furrow)
• in plant cells: a cell
plate (new cell wall)
forms
Then the cell returns to
Interphase… and the
process continues
Which of the following processes take SL
place during interphase?
A.
B.
C.
D.
Cell division
Cell division & Active Transport
Active Transport & Protein Synthesis
Active Transport, Protein Synthesis, Replication of DNA
How are all cells formed?
A.
B.
C.
D.
By cell division
By mitosis
By fragmentation
By cytokinesis
Chromatids are
A.
B.
C.
D.
Made of microtubules
Bacterial chromosomes
Strands of duplicate genetic material
Supercoils of protein
What is the correct order for Mitosis?
A. Interphase, Prophase, Prometaphase, Metaphase, Anaphase,
Telophase
B. Prophase, Prometaphase, Metaphase, Anaphase, Telophase
C. Telophase, Anaphase, Metaphase, Prometaphase, Prophase
D. Interphase, Prophase, Prometaphase, Metaphase, Anaphase,
Telophase, Cytokinesis
This cell is in which phase of Mitosis?
A.
B.
C.
D.
Prophase
Prometaphase
Anaphase
telophase