The Cell Cycle &
Mitosis
Chapter 5
5.1 – The Cell Cycle
• Key Concept:
• Cells have distinct phases of growth, reproduction, and normal
functions.
When a living thing grows,
what happens to its cells?
• Does an animal get larger because
each cell increases in size or because
it produces more of them?
• What are some things that all cells in
your body must have?
The cell cycle has 4 main stages.
• The cell cycle is a regular pattern of growth, DNA replication, and
cell division.
The main stages of the cell cycle are:
Gap 1, Synthesis, Gap 2, & Mitosis.
• Gap 1 (G1): cell growth and normal functions, copy organelles (most
cells spend most of their time here)
• Only proceed to S if the cell has enough nutrition, adequate size,
undamaged DNA
• Synthesis (S): copies DNA
• Gap 2 (G2): additional growth
• Mitosis (M): includes division of the cell nucleus (mitosis) and
division of the cell cytoplasm (cytokinesis)
• Mitosis occurs only if the cell is large enough and the DNA
undamaged.
Cells divide at different rates.
• The rate of cell division varies with the need for that
type of cell.
• Some cells are unlikely to divide
• Example: neurons – stay in G0
Cell size is limited.
• Cell volume increases faster than surface area.
• Cells need to stay small to allow diffusion and osmosis to work
efficiently.
• Surface area must allow for adequate exchange of materials.
• Cells that must be large have unique shapes (i.e. neurons)
5.2 – Mitosis & Cytokinesis
• Key Concept:
• Cells divide during mitosis and cytokinesis into two new daughter cells.
Chromosomes condense at the
start of mitosis.
• Chromosomes: carry genetic information (DNA) that is passed from
one generation of cells to the next.
• DNA wraps around proteins (histones) that condense it.
• Chromatin: DNA plus proteins (histones) is
called chromatin.
• Chromatid: Each duplicated chromosome
is composed of two chromatids
• Centromere: Sister chromatids are held
together at the centromere.
• Telomeres: protect DNA and do not
include genes (like the caps on shoelaces)
Mitosis and cytokinesis produce two
genetically identical daughter cells.
• Interphase prepares the cell
to divide.
• DNA is duplicated.
• Includes G1, S, G2
Mitosis divides the cell’s nucleus in
four phases - PMAT
• Prophase – first & longest
• Chromosomes condense, spindle fibers
form, and the nuclear membrane
disappears.
Mitosis divides the cell’s nucleus in
four phases.
• Metaphase
• Chromosomes line up across the
middle of the cell.
Mitosis divides the cell’s nucleus in
four phases.
• Anaphase
• Sister chromatids are pulled apart
to opposite sides of the cell.
Mitosis divides the cell’s nucleus in
four phases.
• Telophase
• Two nuclei form at opposite ends of the cell,
the nuclear membranes reform, and the
chromosomes uncoil back into chromatin
Cytokinesis differs in animal and
plant cells.
• Cytokinesis is when the cytoplasm
separates
• Animal cells: membrane pinches the
two new cells apart
• Plant cells: a cell plate (new cell wall)
separates the two new cells
Mitosis in a Plant Cell
• http://www.youtube.com/watch?v=VlN7K1-9QB0
• http://www.youtube.com/watch?v=Wy3N5NCZBHQ
5.3 – Regulation of the Cell Cycle
• Key Concept:
• Cell cycle regulation is necessary for healthy growth.
Internal and external factors
regulate cell division.
External Factors: come from outside
cell
• Include physical and
chemical signals
• Cell to cell contact, Growth
factors
• Trigger internal factors, which
affect the cell cycle
Internal Factors: come from inside
cell
• Help to advance a cell to
different parts of the cell cycle
What happens when the cell
cycle isn’t regulated properly?
Cell division is uncontrolled in cancer.
• Cancer cells form disorganized clumps called tumors.
• Benign tumors remain clustered and can be removed.
• Malignant tumors metastasize, or break away, and can form more
tumors.
Apoptosis is programmed cell death.
• Apoptosis is the process of programmed cell death.
• Normal feature in healthy organisms
• Caused by a cell’s production of self-destructive enzymes
• Example of apoptosis in healthy organisms: Occurs during fetal
development
(responsible for
separation of
fingers and toes)
• Cancer cells do not carry out normal cell functions (this is part of
why they’re so bad!)
• Cancer cells come from normal cells with damage to genes involved
in cell-cycle regulation.
• Carcinogens are substances known to cause cancer (they damage
those genes)
• Chemicals, tobacco smoke, X-rays, UV rays, HPV
• Cancer can also be caused by genetics (i.e. BRCA1)
• Standard cancer treatments typically kill both cancerous and
normal, healthy cells.
5.4 – Asexual Reproduction
• Key Concept:
• Many organisms reproduce by cell division.
Binary fission is similar to mitosis.
• Asexual reproduction is the creation of
offspring from a single parent – leads to
genetically identical offspring.
• Binary fission produces two daughter cells
genetically identical to the parent cells.
• Binary fission occurs in prokaryotes.
Environment determines which form of
reproduction is most advantageous
• Asexual reproduction is an advantage in consistently favorable
conditions.
• Sexual reproduction is an advantage in changing conditions.
Some eukaryotes reproduce by mitosis.
• Budding forms a new organism from a small
projection growing on the surface of the
parent.
• Fragmentation is the splitting of the parent
into pieces that each grow into a new
organism.
• Vegetative reproduction forms a new plant
from the modification of a stem or
underground structure on the parent plant.
5.5 – Multicellular Life
• Key Concept:
• Cells work together to carry out complex functions.
Multicellular organisms depend on
interactions among different cell types.
• Tissues are groups of cells that perform a similar
function.
• Organs are groups of tissues that perform a specific
or related function.
• Organ systems are groups of organs that carry out
similar functions.
Specialized cells perform specific
functions.
• Cells develop into their mature forms through the process of cell
differentiation.
• Cells differ because different combinations of genes are expressed.
• A cell’s location in an embryo helps determine how it will
differentiate.