HONORS
How does this happen??
It all begins with a fertilized egg
• Once the sperm fertilizes
the egg, that fertilized egg
(zygote) goes through cell
division repeatedly.
• Cell division through
mitosis gives rise to many
identical cells.
• Differentiation: a process
that creates special
structures and functions.
– Specialized cells become
tissues → organs → organ
systems.
Cell
Differentiation
• Organism: one individual member of a
species
• Organ System: set of organs working
together for a common function (Ex.
digestive system)
• Organ: set of tissues working together for
a common function (Ex. stomach)
• Tissue: group of cells working together for
a common function (Ex. muscle tissue)
• Cell: most basic unit of life that has all the
characteristics of life. (Ex. muscle cell)
It all begins with a fertilized egg
Cell Differentiation
• Implanted blastocyst becomes a gastrula = embryo
with 3 differentiated germ layers
• Organogenesis = the process of body organ and
organ system formation that follows gastrulation
Cell Differentiation
• Stem cells = undifferentiated cells that can become
differentiated into one or more types of specialized
cells.
– Two Types:
• Embryonic
stem cells:
cells that have
never
differentiated
• Adult stem cells: cells found
in adult bone marrow that are
partially differentiated and can
become bone, blood,
cartilage, fat, and connective
tissue
What are stem cells
Clapper board with solid fill
Cell Cycle
• Cell Cycle= a repeated pattern of growth, DNA
duplication and cell division that occurs in eukaryotic
cells.
• 2 purposes = GROWTH
and REPAIR
• The Cell Cycle consists
of 3 main phases:
– Interphase = cell growth
– Mitosis = cell division
– Cytokinesis = cytoplasm
separation which begins
at the end of mitosis
Check out this simulation
Cell Cycle
Interphase
• Interphase = the growth phase of the cell
cycle.
• 3 parts:
– G1 phase = Gap 1 phase = cell grows and G0 phase
makes proteins
– S phase = Synthesis phase = DNA replication
occurs, doubling the number of chromosomes
– G2 phase = Gap 2 phase = more cell growth and
protein synthesis
G0 phase = Gap 0 phase = Cell is doing its job
**At the end of interphase the cell has 2 full sets of
chromosomes!**
DNA vocabulary
• Chromosome: one long continuous thread of DNA that
consists of thousands of genes and regulatory information.
– Gene = a section of DNA that contains the instructions for making a
protein
– Each human body cell has all of your DNA organized into 46
chromosomes.
• In normal body cells, chromosomes always occur in pairs of homologous
chromosomes
Your DNA,
Half of your
chromosomes (23 organized in 46
in each cell) came chromosomes
from your and thousands
biological mother of genes,
and half from your provides the
biological father. instructions for
This is why they making proteins,
often occur in
which run your
pairs.
body.
DNA vocabulary
• Chromatid – one sister chromatids
half of a duplicated
chromosome.
– Sister Chromatids –
two identical
chromatids
• Centromere – region
of the condensed
chromosomes that
looks pinched.
• Telomere – ends of
the DNA molecule.
Cell Cycle
A closer look at S phase
Unduplicated
homologous chromosomes Duplicated homologous chromosomes
DNA Replication
During S phase
of Interphase
**Because of S phase, at the
end of interphase the cell has Sister chromatids Sister chromatids
2 full sets of chromosomes!**
Cell Cycle
MITOSIS
• Mitosis = the division phase of the cell cycle.
- 1 cell becomes 2 identical daughter cells
Cell Cycle
MITOSIS
Prophase Metaphase Anaphase Telophase Cytokinesis
begins
Clapper board with solid fill Clapper board with solid fill
Video showing Mitosis in real cells Link to Simulation
Cell Cycle
Prophase
• Chromosomes
condense & are
visible as sister
chromatids (in X’s).
• Nuclear membrane
disappears.
• Spindle fibers form
out of centrioles.
Cell Cycle
Metaphase
• Spindle fibers connect
to the centromere of
each sister chromatid.
• Chromosomes line up
in middle of the cell.
Cell Cycle
Anaphase
• Sister chromatids
separate, pulling
away from each other
and becoming
individual
chromosomes.
• Chromatids move to
opposite ends of the
cell.
Cell Cycle
Telophase
• Chromosomes
decondense and start to
look like chromatin again
(threadlike instead of rodlike)
• Nuclear membrane re-
forms around
chromosomes at each
pole.
• Spindle fibers break down.
• Cytokinesis begins.
Cell Cycle
Cytokinesis
• The division of the
cytoplasm into 2
individual cells.
• In plant cells – cell
plate forms midway
between divided nuclei
and gradually develops
into a membrane.
• In animal cells - forms
a cleavage furrow that
pinches the cell into 2 End result = 2 identical
equal parts. body cells
How often do cells divide?
• Every cell divides at a different rate based on its
need.
• Examples:
– Internal lining of intestines = 5 days
– Skin cells = every 2 weeks
– Red blood cells = 4 months
– Liver cells = 1 year
Why do body cells divide?
• **Growth and repair**
– Cells can’t just get bigger to grow either – they have to
stay small to maintain a high surface area to volume ratio.
• This is most efficient energy-wise and allows substances to move
in and out of the cell more easily.
How do cells know when to divide and when not to?
What happens if this regulation fails?
Regulation of the Cell Cycle
• Cell cycle is controlled by a chemical control
system that starts & stops events in the cell
cycle.
– Proteins play a key role!
• Regulation is:
– External – signals that come
from outside of the cell; Ex.
Hormone, nutrients, etc.
– Internal – signals that come
from the cell’s own nucleus; Ex.
DNA inside of the cell
Checkpoints
• Checkpoint – critical point where “stop” &
“go” signals can regulate the cycle.
M
Check out this simulation
G2
G1
Key:
G1 = Gap 1 of
interphase
S Note: Cell
division is mostly
S = S phase of in the “off”
position in
interphase
G0 animal cells if
G2 = Gap 2 of
(Resting there is no
interphase
State) stimulus present.
M = Mitosis
Apoptosis
• Apoptosis = programmed cell death
– Internal/external signals activate genes that
produce self-destructive enzymes.
– Nucleus shrinks and breaks apart.
– Ex: Web fingers & toes during development
Cancer
• Cancer = uncontrolled cell division
– Happens when the regulation
of the cell cycle breaks down.
– Cancer cells divide much
more often than healthy cells
do.
– Leads to the formation of tumors.
• Tumors = clumps of cells that divide uncontrollably
Tumors
• Benign – abnormal cells
typically remain clustered
together
– It may be harmless & easily
removed
• Malignant – cancer cells
that break away from the
tumor and move to other
parts of the body → more
tumors
– Metastasize = spreading of
disease from one organ to
others
Causes
• Many things can cause cancer, such as:
– Biological factors
• Ex. Age, inherited genetic mutations, skin type, etc.
– Lifestyle choices
• Ex. Diet, physical activity, exposure to UV radiation, etc.
– Viruses and other infections
• Ex. HPV can cause cervical cancer
– Exposure to carcinogens = cancer causing agents;
chemicals that cause cancer by mutating DNA
• Ex. Tobacco smoke, asbestos, etc.
