Chapter 10 – Cell Growth and
Division
10.1 Cell Growth, Division, and Reproduction
As cells grow,
a few problems arise.
These problems limit a cell’s ability to
grow and
grow and
grow.
The 2 Major Problems:
1. As the cell grows larger, the demands on the
DNA become too large.
2. A larger cell is not as able to remove wastes
and take in nutrients through its cell
membrane.
So how does a cell solve this problem?
By Dividing!
Types of Reproduction
Reproduction is the formation of new individuals.
For a single-celled (unicellular) organism, cell division
is considered a form of reproduction called…
Asexual Reproduction – production of genetically
identical offspring from a single parent.
Examples:
Binary Fission
Types of Reproduction
And then there is…
Sexual Reproduction – where offspring is produced
by two parents, inheriting some genetic info
from each parent.
This mixture of genetic info creates offspring that are
different looking from the parents and their siblings.
10.2 – The Process of Cell Division
Eukaryotic Chromosomes
Recall that Eukaryotes keep their DNA enclosed in a Nucleus.
DNA molecules are linear (think long strands of
thread) and for 99% of a cell’s life they are so thin,
they’re basically invisible.
Key Terms to get straight:
Chromatin – uncoiled DNA molecules. (99%)
Chromosomes – coiled DNA molecules. (1%)
When cells prepare for Cell Division, they coil up their DNA
for the process. At that point they become visible.
Eukaryotic Chromosomes
Sister chromatids – two identical chromosomes.
Produced during S phase’s
DNA replication process.
Centromere – constricted region where the two
chromatids are joined.
Weird Side note: the entire structure is referred to as a
chromosome. The process of Mitosis separates the
sister chromatids. At that point, each separate sister
will now be referred to as a chromosome.
The Cell Cycle
A cell’s life exists in a cycle, with no definite
beginning or end.
It’s basically just…
Growth  Preparation  Division  Repeat
***It could be said that the cell’s life***
is lived between divisions.
For humans, the cycle is the same for any type of cell,
it’s the timing that varies.
For skin cells, a cycle could last one week.
Nerve cell cycles could last a lifetime.
The Cell Cycle
There are 4 distinct phases of the cell cycle.
Even though this is a cycle,
let’s consider this point as
the start
G1 Phase: Cell Growth
In G1 phase - cells grow
in size and make new
proteins/organelles.
S Phase: DNA Replication
In S (or synthesis)
phase - new DNA is
synthesized when the
chromosomes are
replicated (copied).
G2 Phase: Preparing for Cell
Division
In the G2 phase, many
of the organelles and
molecules required for
cell division are
produced.
M Phase: Cell Division
In eukaryotes, cell
division occurs in two
stages: mitosis and
cytokinesis.
Mitosis is the
division/splitting of the
cell nucleus.
Cytokinesis is the
division of the
cytoplasm.
Important Cell Structures
Involved in Mitosis
– Centrioles – tiny structures located in the
cytoplasm of animal cells that help organize
the spindle
– Spindle – a fanlike microtubule structure that
helps separate the chromatids
4 Phases of Mitosis
P - prophase
M - metaphase
A - anaphase
T - telophase
Prophase
1) The chromatin
coils and becomes
chromosomes.
Prophase
1) The chromatin
coils and becomes
chromosomes.
2) The centrioles
move to opposite
sides of nucleus and
organize the spindles.
Prophase
1) The chromatin coils
and becomes
chromosomes.
2) The centrioles move
to opposite sides of
nucleus and organize the
spindles.
3) The spindle forms and
attaches to the
centromeres.
Prophase
1) The chromatin coils and
becomes chromosomes.
2) The centrioles move to
opposite sides of nucleus
and organize the spindles.
3) The spindle forms and
attaches to the
centromeres.
4) The nuclear membrane
breaks down.
Metaphase
The chromosomes line
up across the middle of
the cell.
Anaphase
The chromatids are
pulled apart and
separate to become
individual
chromosomes.
Telophase
The chromosomes
unravel back into
chromatin.
Telophase
1) The chromosomes
unravel back into
chromatin.
2) A nuclear membrane
re-forms around each
cluster of chromosomes.
Cell Timeline, from division to division.
Cytokinesis
Cytokinesis is the division of the cytoplasm - it
splits the cell into two daughter cells.
The process of cytokinesis is different in animal
and plant cells.
Cytokinesis in Animal Cells
– The cell membrane is squeezed in until the
cytoplasm is pinched into two equal parts.
– Each part contains its own nucleus and
organelles.
Cytokinesis in Plant Cells
– In plants, a cell plate forms between the two
nuclei that develops into cell membranes.
– A cell wall then forms in between the two
new membranes.
The Stages of Cell Division