Cells
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Cells
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Cells are small.
There are 100 trillion cells in the body.
They range in size from 7.5 µm = micrometers
(micrometer is 1 millionth of a meter) to 250
µm, which is visible to the naked eye.
There are thousands of types of cells, each is
specialized for a task: skin, liver, kidney, etc.
Each cell has specialized structures for their
function.
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Cells
Every cell has three things in common:
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Metabolic functions (using nutrients such as sugars
and oxygen, and creating waste products)
Responds to its environment
Capable of maintaining homeostasis within itself
and within the body.
HOMEOSTASIS is maintaining a constant and
appropriate internal environment, such as
temperature, pH, and glucose levels.
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Introduction to Cells
 All
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cells have several main components
Plasma membrane
Cytoplasm and cytosol
Nucleus
Organelles (are surrounded by a
membrane)
Ribosomes (are not surrounded by a
membrane)
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Structure of a Generalized Cell
Figure 2.1
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Cytoplasm and Cytosol
CYTOPLASM: the watery liquid inside and outside the
organelles, but outside the nucleus.
 NEUCLEOPLASM: the liquid inside the nucleus.
 CYTOSOL: another liquid that is thicker than water, and is
NOT inside the organelles. It is only found outside of the
organelles and nucleus.
 Cytosol contains the following:
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Mostly water
Things dissolved in water (amino acids, sugars like glucose,
nucleic acids, and ATP, which is a molecule used for energy).
Cytoskeleton: made up of long protein fibers, extend
throughout cytosol.
Function of cytoskeleton:
1) Maintains cell shape
2) Movement (such as muscle cell contraction,
organelles within the cell, or the cell itself moving around).
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Cell Membrane
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The cell membrane is semi-permeable to
allow only certain things into and out of
the cell.
Functions of the Plasma Membrane:
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Movement of materials into and out of
cell, and acts as a barrier to the external
environment
Acts as a site for receiving signals from the
rest of the body
Helps hold the cell in place
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Plasma (cell) Membrane
 The
plasma (cell) membrane is made up of two
layers of molecules = PHOSPHOLIPIDS.
 It’s therefore called a phospholipid bilayer
 Phospholipids are amphipathic molecules.
 That means they have one end that has an
affinity for something and another end that does
not have an affinity to that substance. In this
case, the affinity is to water.
 A substance that likes water is called
HYDROPHILIC (likes water).
 A region of a molecule that is hydrophilic is
called a POLAR region.
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Plasma (cell) Membrane
A
substance that dislikes water is called
HYDROPHOBIC (afraid of water).
 A region of a molecule that is hydrophobic is
called a NON-POLAR region.
 Therefore, the phospholipids, being
amphipathic, will have a polar region and a
non-polar region.
 The polar region is the PHOSPHATE HEADS
 The non-polar region is the FATTY ACID TAILS .
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Phosphate
heads
Fatty Acid
tails
The cell membrane is like a film of oil on water. Is oil flexible? (yes) Is oil strong? (no)
But it prevents materials from going across into the water.
PLASMA MEMBRANE
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Plasma (cell) Membrane
 The
plasma membrane has proteins in it that are
made in the RIBOSOMES and transported to the
cell membrane in this case (other proteins are
carried elsewhere).
 Ribosomes carry out the three functions of the
plasma membrane.
 Around each organelle is a membrane identical
to the plasma membrane except for the
proteins.
 Each cell has hundreds of membranes.
 Ribosomes are not organelles because they do
not have a plasma membrane.
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Phospho-lipid Bilayer
The Cell Membrane
Figure 2.2a
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Endoplasmic Reticulum
 The
ER is a network of channels.
 Two types:
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Rough ER: contains ribosomes
 Function
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of ribosomes is to make proteins.
Smooth ER: no ribosomes
 Function
the cell.
is to detoxify chemicals that enter
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ROUGH ENDOPLASMIC RETICULUM
(endoplasmic = within cytoplasm;
reticulum = network; rough = surface of
membrane covered with ribosomes. This is
an organelle, but the ribosomes are not.
 Function of RER is the synthesis (making) of
proteins:
a. Membrane proteins
b. Proteins for export (such as digestive
system enzymes)
c. Proteins for use within the cell
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SMOOTH ENDOPLASMIC RETICULUM (no ribosomes)
Function of SER
a. SER is continuous with the rough ER, but lacks
ribosomes and has several functions
1) Detoxifies harmful substances (alcohol, drugs,
medicines)
NOTE: in CSI, when they suspect poisoning, they
first look at the SER in the liver.
2) Stores calcium
3) Involved in lipid production (lipid bodies)
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The Endoplasmic Reticulum
and Ribosomes
Figure 2.5
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Golgi Complex
 When
the proteins have finished their journey in
the RER, their edges are exposed, and are
vulnerable to oxidative damage. Therefore,
they first go to the Golgi complex, which puts
chemical bonds on the ends of the proteins.
 Thus, in the Golgi complex, the proteins are
modified and prepared for transport out of the
cell.
 The Golgi complex is like a Fed-Ex center that
packages and ships the proteins that were
made in the ribosomes.
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Golgi Apparatus
Figure 2.8
RER to Golgi Complex
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Vesicles
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Vesicles (vacuoles) are bubble-like containers
for various substances. Some are created by
the end of the Golgi complex: a piece of
membrane pinches off, leaving a protein in
the vesicle, which carries the protein to the
cell membrane, where it merges with the cell
membrane, pops, and releases its contents
outside of the cell.
Other vesicles are storage containers for food
or enzymes.
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Vesicles
VESICLES: a sphere of membrane with something in
it. This is an organelle. Many types:
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LYSOSOMES: are sacs of powerful digestive enzymes to
dissolve an old organelle, bacteria, or foreign debris. They
are also used to commit cell suicide (APOPTOSIS is the term
for programmed cell death).
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When bacteria enter a cell, the lysosome will fuse with the
bacteria and release its enzymes on them to destroy them.
TRANSPORT VESICLES: when material needs to move from
RER to Golgi complex, or from Golgi complex to cell
membrane, etc.
STORAGE VESICLES: one vesicle may store carbohydrates,
one may store lipids, one may store enzymes.
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Disorder of Lysosomes
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Tay–Sachs disease
A genetic disorder that causes deterioration
of mental and physical abilities that
commences around six months of age and
usually results in death by the age of four.
Caused by insufficient activity of an enzyme
needed by lysosomes to break down
phospholipids.
The lipids accumulate in the brain.
Mitochondria
 Mitochondria
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are considered the smallest living
units in the body because they can make their
own energy (ATP). Cells have hundreds of
mitochondria.
 Function of mitochondria is to make most of the
cell’s ATP, which is cellular energy (ATP is an
energy source).
 Some ATP is made in the cytosol, but most is
made in the mitochondria.
 NOTE: Mitochondria must have OXYGEN to
convert nutrients to ATP for energy.
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Mitochondria
 Mitochondria
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generate most of the
cell’s energy (ATP);
most complex
organelle.
 Contains curves
known as cristae that
can be seen under a
microscope.
Figure 2.9
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Fun Facts
Mitochondrial DNA (mtDNA)
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Nuclear and mitochondrial DNA are thought
to be of separate evolutionary origin, with the
mtDNA being derived from the DNA of the
bacteria that were engulfed by the early
ancestors of today's eukaryotic cells.
mtDNA is inherited from the mother
(maternally inherited).
This enables researchers to trace maternal
lineage far back in time.
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Mitochondrial DNA
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Biologists can determine and then compare
mtDNA sequences among different species
and use the comparisons to build an
evolutionary tree for the species examined.
Studies have used mtDNA to trace the
ancestry of domestic dogs to wolves.
However, they have recently found that the
Sabre-tooth tiger is not the ancestor of the
domestic cat.
Nucleus
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 NUCLEUS:
Usually the largest structure in a cell. It
does not contain cytoplasm; it is called
nucleoplasm.
 The nuclear membrane contains pores, called
nuclear pores. These allow certain materials into
and out of the nucleus.
 Functions of the nucleus:
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Stores DNA (chromosomes are made up of DNA)
Makes RNA (RNA is the code for making a protein. It
is copied from DNA).
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The Nucleus
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Nucleolus
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Within a nucleus there are areas that are
darker. These are regions of condensed RNA.
Remember, the function of the RNA is to carry
copies of the genes for proteins to the
ribosomes.
The nucleolus is NOT an organelle, but the
nucleus is. Don’t get “nucleolus” mixed up with
the word “nucleus” on the test. The nucleolus
does not contain the DNA; the nucleus does.
The nucleolus is within the nucleus, but it does
NOT contain DNA.
The nucleolus contains RNA, which is important
for protein synthesis.
Do not get nucleus and nucleolus mixed up!
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Centrioles
 Centrioles
are filaments within the cell that
function during mitosis.
 When the cell goes from metaphase to
anaphase of mitosis, the chromatids
separate and follow the spindles of the
centrioles towards the opposite ends of
the cell.
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Centrioles
Centrioles
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Flagellum
 Some
cells have a flagellum, which is a
whip-like tail used to help them move
(locomotion).
 An example is a sperm cell.
Microvilli
 Some
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cells have microvilli on their cell
membrane, which increase the surface
area of cells by approximately 600 fold,
thus facilitating absorption and secretion.
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Cilia
 Some
cells have cilia, which are small, hair-like
structures that can wave back and forth,
causing substances to move along across the
top of the cell.
 For
example, the cells of the lungs are lined with
cilia, which move mucous up from the lungs so it
can be coughed up and swallowed.
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Cell Cycle
 CELL
CYCLE: the life cycle of a cell. Some
cells never divide (neurons).
 When getting ready to divide, cells
undergo MITOSIS to make one cell into
two.
 Some cells divide rapidly (every few
days), some rarely (every 1-2 months),
some never.
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Stem Cells
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STEM CELLS: A population of cells are always
available to replace the cells that died.
Muscle stem cells give rise to new muscle cells.
Bone marrow stem cells give rise to new blood
cells.
Embryonic stem cells give rise to any type of
cells, including neurons (adults don’t have
neural stem cells) and pancreatic cells
(diabetics don’t have pancreatic stem cells).
Stem cells are named by type + suffix: BLAST
Erythrocyte = RBC. Erythroblast = stem cell that
gives rise to an erythrocyte.
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Mitosis Overview
Human Cell Division
 All
cells in our body divide by duplicating
their chromosomes and then splitting into
two cells, a process called mitosis
 Mitosis produces two daughter cells with
the same number and kind of
chromosomes as the parent cell.
 If a parent cell has 46 chromosomes prior
to mitosis, how many chromosomes will the
daughter cells have?
 Answer = 46.
 This condition is called diploid (2n).
Sex Cells (Gametes; egg and sperm cells)
 After
mitosis, sex cells undergo another cell
division without duplicating the chromosomes.
This is called meiosis: each daughter cell has
only half of the chromosomes.
 In males, it produces the cells that become
sperm
 In females, it produces the cells that become
eggs.
 The sperm and the egg are the sex cells, or
gametes.
 GAMETES contain half the number of
chromosomes compared to the rest of the
body cells (23 chromosomes).
 This condition is called haploid (n).
Mitosis Stages
 Interphase:
Chromosomes duplicate
stage)
 Prophase: Chromosomes shorten and
thicken.
 Metaphase: Chromosomes line up in the
middle of the cell
 Anaphase: Chromosomes pull apart
 Telophase: Cytoplasm divides in two,
forming two daughter cells
Video Clip of Mitosis
MEIOSIS
 Meiosis
only occurs in the testes and
ovaries when they are ready to make an
egg cell or a sperm cell.
 First, mitosis occurs as normal.
 But right after that, the two daughter cells
divide again (meiosis), but this time there
is no reproduction of the chromosomes.
Crossing Over
 During
meiosis, when the second cell
division is at the metaphase stage, the
chromosomes touch each other and
exchange a few genes.
 The exchange of genetic material
between chromatids is called crossingover.
 That is what allows for genetic
variation.
Crossing Over
MEIOSIS
 Meiosis
results in four daughter cells,
each having half the number of
chromosomes as the parent cell.
 The daughter cells are not genetically
identical, and neither is identical to the
parent cell.
 For example, in MEIOSIS, if the parent cell
has 46 chromosomes, the GAMETE will
have 23.
 It will be haploid (n).
Gametes to Zygote
 When
a sperm and egg (gametes)
combine and contribute their
chromosomes, the fertilized egg (called a
zygote) will now have 46 chromosomes
again.
 It will be diploid (2n).
Nondisjunction
 Chromosomes
can become abnormal if
the sister chromosomes do not separate
properly during meiosis. This is called
nondisjunction.
Video Clip of Blastula
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 The
rate of cell division is close to the rate
of cell death.
 200 billion erythrocytes die every day, so
200 billion erythrocytes have to be made
every day.
 Too few = anemia; too many is also a
problem.
 Body needs to do two things:
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Control the rate of cell division
Control the rate of cell death (apoptosis)
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Tumors
TUMOR (an abnormal growth from excess cells).
Two types of tumors:
 BENIGN (“harmless”, although can cause
harm by pressing on vital structure)
 MALIGNANT (cancerous). These are
dangerous because the cells in the tumor
METASTASIZE (leave original site, go elsewhere
and grow).
 Cancer is hundreds of diseases, each with a
different cause, symptoms, treatment, and
prognosis. Any cell type can become
malignant, producing different types of
cancer.
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Cancer
FOUR TYPES OF CANCER
 CARCINOMA: epithelial tissue
 SARCOMA: Connective tissue (bones,
muscles, organs)
 LYMPHOMA: Lymph nodes
 LEUKEMIA: Blood or blood-forming tissues
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Cancer
 How
do you distinguish between
cancers?
 If there’s a tumor in the lung, BIOPSY (take
a sample of cells, examine under a
microscope to see what kind of cells they
are).
 If pancreas cells are in lung tumor,
indicates pancreatic cancer.
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Inner Life of a Cell
 http://multimedia.mcb.harvard.edu/anim
_innerlife.html
 Click
on Super Speed