The Cell Cycle
Section 5.1
Objectives
• SWBAT describe the stages of the cell cycle.
• SWBAT compare rates of division in different
types of cells.
• SWBAT identify factors that limit cell size.
Starter
• Why do you always have to cut your hair, your
fingernails, and the lawn?
• The answer is, of course, that new cells are
being made – and will be made all the way up
to the time of your death.
• So, in this section and the following section,
we will learn how new cells are created.
Crash Course
• Crash Course (SciShow) video on Mitosis
– https://www.youtube.com/watch?v=L0kenzoeOM
Vocabulary – Section 5.1
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Cell cycle
Mitosis (called M Phase)
Cytokinesis (also part of M Phase)
Interphase
Gap 1 (G1)
Gap 2 (G2)
Synthesis (S Phase)
Metaphase of Mitosis
Onion Root Tip Seen Through Electron
Microscope
Varying
phases of
mitosis.
Note, not all
cells are
dividing at
the same
time.
Cell cycle
of a
species of
asparagus
Cell Cycle Diagram
Out of control cell
growth is
abnormal and is
known as cancer.
This is a cycle of
growth, DNA
synthesis
(replication), and
cell division.
Controlled cell
growth is essential
to allow you (or any
organism) to grow
and heal.
Cell Cycle
Cell cycle definition: the regular pattern of growth,
DNA duplication, and cell division that occurs in
eukaryotic cells.
It consists of four stages:
three of the stages (Gap
1, Synthesis, and Gap 2)
are collectively known as
Interphase.
Cell Cycle – Stage 1
• Gap 1 (G1) – cells spend most of their time in
this stage.
• During G1, a cell carries out its normal
functions.
– For example: if it is a skeletal muscle cell, it
contracts to move joints; if it is an intestinal cell,
it absorbs nutrients; etc.
• In this stage, the cell needs enough nutrition,
maturity (size), and undamaged DNA before
it can move into the next stages.
Cell Cycle – Stage 2
• DNA Synthesis (S) – when your cell copies its
nuclear DNA
– Remember, in eukaryotes DNA is kept in the
nucleus
– By the end of S stage, the cell nucleus contains 2
complete sets of DNA.
• It is hard to see the DNA in this phase because it is long
and stringy. It hasn’t formed condensed, easily seen,
chromosomes yet.
Cell Cycle – Stage 3
• Gap 2 (G2) – cells continue to carry out
normal functions and growth continues.
– Like in G1, there are critical factors like adequate
nutrition, cell size, and undamaged DNA.
– Duplicated DNA is present.
Cell Cycle – Stage 4
• Mitosis – the division of the cell nucleus and
its contents.
• Cytokinesis – divides the cell’s cytoplasm
(remember, the new cells need cytoplasm
and organelles to function).
• The result of mitosis and cytokinesis is two
genetically identical daughter cells (they are
clones of the parent cell).
Mitosis
• During mitosis:
– the nuclear membrane dissolves;
– the duplicated DNA condenses into easily seen chromosomes (more in
next section);
– and then separates to form two new nuclei.
Your cells and the cells of all other
eukaryotes are controlled by the
same proteins.
This has been demonstrated – for
instance, yeast regulator proteins can
work in human cells and vice versa.
Why is this?
Cells divide at different rates –
depending on type of cell.
Some cells,
like
neurons,
appear not
to divide
ever. They
are
referred to
as G0
because
they never
divide.
Cells that
receive a lot
of wear and
tear divide
frequently,
others hardly
at all (like
internal
organs)
The size of cells
• Cells have upper and lower size limits.
– Too small and cannot contain all the organelles
and molecules they need.
– Too big and the cell would surpass the minimum
surface area, cell membrane, to volume ratio it
needs to be able to move all of the oxygen,
nutrients, wastes, etc. into and out of the cell as
quickly as is necessary.
• Volume increases much faster than surface area.
Cell size is limited
Volume increases faster than surface area
Cell size is limited
• Surface area must allow for adequate exchange of
materials.
– Cell growth is coordinated with
division.
– Cells that must be large have
unique shapes.