The Cell, Cell Theory, &
Inside The Cell
Chapter 7
Robert Hooke
• 1663
• Used a small hand held “microscope” to
view small chambers within cork
• Called these chambers “Cells”
Anton Van Leeuwenhoek
• 1675
• Dutch lens maker
• Took a close look at the pond water
through a better microscope that he made
by himself
• Saw things moving
• He called it "animalcules"
• These were single celled organisms
The Cell Theory
• This story all starts with a dinner
conversation between 2 friends
• Theodore Schwann, an animal scientist
who believed that all animals were made
of cells
• Mathias Schleiden, a plant scientist who
believed all plants were made of cells
• Bringing this up during dinner, the two
scientists began to devise the cell theory
The Original Theory
• These two scientists devised one of the
best “Life” theories
• The original cell theory stated these 3
ideas:
– 1. The cell is the unit of structure, physiology,
and organization in living things
– 2. The cell retains a dual existence as a
distinct entity and a building block in the
construction of organisms
– 3. Cells form by free-cell formation, similar to
the formation of crystals
1. The cell is the unit of structure,
physiology, and organization in
living things
• This basically means that:
–All living things are made of cells
• Our current belief is, “If it doesn’t have
cells, it isn’t classified as what we currently
consider alive in the scientific community
2. The cell retains a dual existence
as a distinct entity and a building
block in the construction of
organisms
• This basically means that:
–Cells are the basic units of
structure and function in living
things
• Cells are THE MOST basic building blocks
of life
– If you get any smaller than a cell, you are no
longer dealing with something that is ALIVE
3. Cells form by free-cell formation,
similar to the formation of crystals
• This basically means that:
– Cells (and life) form very similar to the way
salt crystal form on your skin after you swim in
the ocean
– They Spontaneously Generate themselves
– Is this true???
Spontaneous Generation
• Years ago, it was generally believed that
life just “formed” in lower life forms
• A mouse formed from leaving cheese in a
barn
• Mold formed from leaving food out in the
sun
• They just appeared
• This was the current scientific belief at that
time
Theory
• Again, this is an excellent example of how
a theory can be WRONG!
• Schwann and Schleider were very
intelligent men, who came up with a great
theory
• BUT, the third rule was VERY WRONG
Rudolf Virchow
• Rudolf Virchow corrected this third rule
with his research on cellular reproduction
• He concluded that a cell only arises
from pre-existing cells
• Cells ONLY come from other cells
• Generally, they only come form the same
type of cell as well
The Last 2 Rules
• (NOT IN YOUR BOOK)
• Various other scientists worked together
and decided on the last 2 rules that are not
in your book (No single scientist is credited
for these last two rules)
• 4. Cells contain hereditary information
which is passed from cell to cell during
cell division
• 5. All cells are basically the same in
chemical composition
Current CELL THEORY
• 1. All living things are made up of cells
• 2. The cell is the structural & functional
unit of all living things
• 3. All cells come from pre-existing cells by
division
• 4. Cells contain hereditary information
which is passed from cell to cell during cell
division
• 5. All cells are basically the same in
chemical composition
Scientist Method
• After his death on August 30, 1723, a member of
the Royal Society wrote... "Antony van
Leeuwenhoek considered that what is true in
natural philosophy can be most fruitfully
investigated by the experimental method,
supported by the evidence of the senses; for
which reason, by diligence and tireless labour he
made with his own hand certain most excellent
lenses, with the aid of which he discovered
many secrets of Nature, now famous throughout
the whole philosophical World". No truer
definition of the scientific method may be
found.
Advances in Technology
• Through the advances in technology made
by Anton van Leeuwenhoek science was
able to move through new doors
• Of course, since he advanced the science,
he had first dibs on the discoveries
More Cells?
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Are the cells in our bodies the only type?
-Animal Cells
-Plant Cells
-Protist Cells
-Fungal Cells
Bacterial Cells
To Nucleus or not to Nucleus?
• When we get into the various structures
found inside the cell, we will learn about
an organelle called a nucleus
• It is the largest and most important
organelle in many cells
• It controls the other parts of the cell &
controls reproduction
• Its presence or absence is one of the
MOST important distinguishers between
the different types of cells
To Nucleus
• If a nucleus is present, the cell is called
Eukaryotic
• Every cell in our bodies have a nucleus
• That is why we are called Eukaryotic
Organisms
• Most of the organisms that are considered
“Highly Evolved” are Eukaryotes
Not to Nucleus
• If there is no nucleus present, it is a
Prokaryotic Cell
• These are much simpler cells
• They are much more likely to be free-living
as a single cell, then a eukaryotic cell
– If a cell is Free-living, it can survive as just a
single celled organism
– Sometimes a single, prokaryotic cell can be parasitic also
Review
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What did Anton van Leeuwenhoek do?
What is spontaneous generation?
What is the cell theory?
What are the 5 steps of the cell theory?
What were the three rules of the cell theory
devised by Schwann and Schleiden?
• What is the name for a cell with no nucleus?
• What is the name for a cell with a nucleus?
• What did Rudolf Virchow do?
Inside the Cell
Thanks to the selective permeability of the
phospholipid bilayer and the activity of
membrane transport proteins, the plasma
membrane creates an environment that is
different from conditions outside the cell.
Plasma Membrane
• What does it mean to be selectively
permeable?
• What is a membrane transport protein?
• The job of the plasma membrane is to
separate the cell from the world
• If it does its job correctly, the outside world
will have very little affect on the cell
• What is the plasma membrane made out
of?
Diffusion
• In a solution, particles are ALWAYS
moving
• Under normal pressure, particles try to
spread out evenly across a solution
• As a result, particles tend to move from
high concentration to lower concentration
– This decreases collision
• This is the process of Diffusion
• Once the concentration is the same
throughout, it is called Equilibrium
Facilitated Diffusion
• Water and small molecules can diffuse
across the lipid bilayer in the plasma
membrane, but what about large
molecules like glucose???
– These large molecules require doors in the
plasma membrane called protein channels
– By limiting the amount of these large protein
channels, the cell can control how much
glucose enters the cell
Active Transport Diffusion
• Both diffusion and facilitated diffusion do not
require energy to move particles into and out of
cells
• However, some particles do require energy to
allow them to cross the cell membrane
• These particles use transport protein pumps that
use cell energy (ATP) to allow items to enter the
cell or leave the cell
• Often times this against a concentration gradient
– From low concentration to high concentration
Cytoplasm
• The contents inside the cell that are not the
nucleus are collectively termed Cytoplasm
• Often times it is considered just the jelly like
material surrounding the organelles, but aside
from the nucleus it contains the organelles
• The fluid portion of the cytoplasm is called the
cytosol
• It contains HIGH levels of solutes (dissolved
substances) and is therefore hypertonic relative
to most environments
• This causes water to enter the cell via osmosis
Osmolarity & Tonicity
• Osmosis is the movement of water from
an area of high water concentration (low
solute concentration) to an area of lower
water concentration (higher solute
concentration)
• Tonicity is relative to view point
• ALWAYS consider if you are considering
the cell or solution when deciding tonicity
Osmolarity & Tonicity
• 3 different tonicities:
– HYPERTONIC solution: There is more dissolved
substances and less water OUTSIDE the cell than
inside the cell, therefore water EXITS the cell via
osmosis pressure through the lipid bilayer
– HYPOTONIC solution: There is more dissolved
substances and less water INSIDE the cell than
outside the cell, therefore water ENTERS the cell via
osmosis pressure through the lipid bilayer
– ISOTONIC solution: There is THE SAME AMOUNT
of dissolved substances and water outside the cell as
inside the cell, therefore water move equally
throughout the cell and the pressure does not change
Osmolarity & Tonicity
• The reason osmosis works the way it does
is that water moves through the semipermeable membrane through very small
gaps in between the lipid bilayer
• Once in the area of high solute
concentration, the water molecules bond,
bind, or are attracted to the various solute
• Now, they are to large to fit back through
the semi-permeable membrane
Tonicity to a Cell
• The solution a cell is in and its relative
tonicity to a cell is essential to the survival
of a cell
• This regulation is one of the most
important aspects of the plasma and cell
membrane
The Organelles
• NOT ALL CELLS ARE THE SAME
• But they do have a very similar chemical
makeup and mechanism
• Cells make up nearly every part of
everything that is alive or ever has been
alive, therefore to understand cells is to
understand life
The NUCLEUS
• Structurally, the nucleus is composed of three
main parts:
– The nucleolus: which contains and forms the large
and small ribosomes, RNA, DNA, and proteins
– The nuclear envelope: allows the nucleus to control
the rest of the cell, such as by sending out ATP. The
envelope will let molecules like ATP through but will
keep other things in or out, so the nucleus is isolated
from the cytoplasm.
– The chromatin: (meaning "colored substance")
contains DNA and proteins formed into packets of
code called chromosomes
• Heterochromatin: One section of the chromatin that is highly
compacted, supercoils
• Euchromatin: Area of chromatin that is composed of long,
unwound, filamentous strands
The NUCLEUS
• The largest organelle inside the cell
• Causes a cell to be Eukaryotic or
Prokaryotic (Presence or absence of a
nucleus)
• Only found one per Eukaryotic cell
• Often considered the brain or central
organelle of the cell
• Major purpose is cell control and
reproduction
Eukaryotic vs. Prokaryotic
• As just mentioned, if a cell has a nucleus it
is considered Eukaryotic, and higher
evolved
– IE: Humans, Animals, Plants
• If it lacks a nucleus it is considered
Prokaryotic and is less involved
– IE: Protists, Bacteria
Ribosomes
• Assemble Proteins
– It translates Messenger RNA (mRNA) into a
polypeptide chain (e.g., a protein). It can be
thought of as a factory that builds a protein
from a set of genetic instructions
• Comprised of two subunits:
– Each subunit contains a large RNA molecule
and several different protiens
– Small subunit
– Large subunit
• In Eukaryotes, the large subunit also contains two
small RNA molecules
– In Prokaryotes it has only one small
Rough Endoplasmic Reticulum
• Though many ribosomes are found
floating freely in the cytosol, there are
some associated with membranes
• Hundreds of thousands of ribosomes are
attached to a network of membrane bound
sacs & tubules called the R.E.R.
• It is attached to the outer membrane of the
nuclear envelope
• From there, the layers of sacs extend into
the cytoplasm
Rough Endoplasmic Reticulum
• reticulum is a network of tubules, vesicles
and sacs that are interconnected.
• They may serve specialized functions in
the cell including protein synthesis,
sequestration of calcium, production of
steroids, storage Endoplasmic and
production of glycogen, and insertion of
membrane proteins
• Most of the proteins made in the R.E.R.
are destined for the cell membrane or
beyond
Smooth Endoplasmic Reticulum
• Location of lipid processing
– Area of the cell where fats are made
• Many of these lipids will be shipped to the
cell membrane to repair the lipid bilayer or
stored as fats in the body
• Very similar in structure to the RER but
lacks ribosomes
• The smooth ER also plays a role in
detoxification of drugs and alcohol in the
cell
Golgi Apparatus
• In most cases, the products from the R.E.R.
pass through the Golgi Apparatus before they
reach their final destination
• The Golgi Apparatus is the equivalent of a mail
depot for the cell
• It is here that the items that are leaving the cell
are sent for packaging and shipping.
• If it leaves the cell, it goes through the Golgi
• Remember, the cells make what the body uses,
but each cell type is fairly unique to its job
Lysosomes
• These are the cell’s clean up crew and first line
of defense
• Lysosomes are golgi vesicles that are filled with
enzymes that have a low pH (acidic)
• Lysosomes use these enzymes to break down
lipids, carbohydrates, and proteins inside of the
cell
• They clean up the “junk” that would otherwise
build up inside of the cell
• They also are essential for destroying foreign
material inside of the cell
Vacuoles
• Vacuoles are simply membrane bound storage
containers within a cell
• They can store water, salts, proteins, and
carbohydrates
• In plants there is a Large Central Vacuole
inside of the cell that is filled with water
– This LCV is what gives non-woody plants
Turgor pressure which is what allows them
to stand up.
– If a plant wilts, its LCV is low on water causing
a low turgor pressure
Mitochondria
• The powerhouse of the cell
– This is the area where chemical compounds
found in food are converted into useable ATP
– in a process called the Kreb’s cycle (Chptr 9)
• They are essential to the cells energy
process
• They are enclosed in two membranes
– The inner membrane is folded up inside of the
organelle
• Mitochondria have circular “prokaryotelike” DNA
Mitochondria
• Mitochondria also reproduce on their own
within your cells
– They reproduce faster when there is a higher
demand for ATP and shrink away and
disappear if that demand is low
• Mitochondria are also all derived from the
cytoplasm of the ovum (egg).
– You get your mitochondria from your mom
• Would you expect muscle cells to have a
lot of mitochondria????
Chloroplasts
• Chloroplasts are the organelle that
captures the suns energy and converts it
into chemical energy
• This is how plants make glucose
• They, like mitochondria, have two
membranes, prokaryotic DNA, and
reproduce individually within a cell
• The inner membrane contains chlorophyll
which give leaves their green color
Fall
• As the suns energy grows weaker (further
away) during the months of fall, the
chloroplasts become less necessary
• As the chloroplasts begin to shrink away,
other pigments that where hidden in a
plant become visible
• These pigments were always there, but
they were covered by the numerous
chlorophylls
• This is why leaves change color in the fall
Endosymbiotic Theory
• Endosymbiosis is when an organism
engulfs a smaller organism (to eat it), but
rather than eating it, the prey organism
becomes part of the predator.
• This happens when the prey organism
offers something to the predator
• It is believed this happened early in
Eukaryotic evolution with the mitochondria
and chloroplast
– Prokaryotic DNA, Double membraned,
reproduces on its own inside the cell