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Chapter 3: Cells
• Evolution of multicellular organisms allowed cell
specialization and cell replacement
• Eukaryotes have a much more complex cell
structure than prokaryotes
• The structure of biological membranes makes
them fluid and dynamic.
• Membranes control the composition of cells by
active and passive transport
• There is an unbroken chain of life from the first
cells on Earth to all cells in organisms alive today.
I. Cytology: study of all aspects of a cell
A. Cell: smallest functional units of an
organism
1. Organisms range in size from a
single cell to trillions of cells, must
study cells to understand organisms
2. As our understanding of the cell
has increased, so has our ability to
understand all form of life on Earth
II. Cell theory, cell specialization, and cell
replacement
A. Cell Theory: many scientist over
several hundred years have contributed to
the three main principles of the theory
• All organisms are composed of one or more
cells
• Cells are the smallest units of life
• All cells come from pre-existing cells Cells
1. Robert Hooke: 1665 was the first to
describe a cell by using a self-built
microscope
a) Observed dead cork cells
b) Gave the name cell since it
reminded him of a monk’s cell (room)
2. Antonie van Leeuwenhoek: 1668 observed
first living cells and called “animalcules”little animals them (he made better lenses)
3. Matthias Schleiden: 1883 “plants are made
of independent, separate beings” called cells
4. No one today has be able to find any living thing
that is not made of at least one cell (Second
principle)
5. Louis Pasterur: 1880’s performed experiments to
support the third principle: Sterilizing chicken broth
by boiling he showed that living organisms would
not “spontaneously” reappear. Only after exposure
to pre-existing cells was life able to re-establish in
the sterilized broth
6. Functions of life: all organisms exist in either a
unicellular or multicellular form and carry out all
the functions of life
a) Metabolism: all chemical reactions
b) Growth
c) Reproduction
d) Response to stimuli: adapt to environment
e) Homeostasis: maintain stable internal
environment
f) Nutrition: energy to maintain life
g) Excretion: release toxins from system
B. Cells and sizes
1. Cells are made up of different subunits
and they are all microscopic
2. Microscope with high magnification and
resolution (clarity of object) to observe cells
and their subunits
a) Light microscope: light passing
through living or dead specimen to form
an image
b) Electron microscope: electrons
passing through dead specimen to form
image with magnification over100,000x
Scanning electron microscope
• Used to scan the surface
• Magnification of
200,000x
Transmission electron microscope
•Used to see inside the cell
•Thin specimen prepared
Magnification of up to
100,000x
3. Relative sizes of cells and subunits
(largest to smallest)
a) Cells
b) Organelles (subunits within the
cell “little organs”)
c) Bacteria
d) Viruses
e) Membranes
f) Molecules
4. Calculating the actual size of a specimen seen
with a microscope
a) Need the diameter of the microscopes field
of vision (ruler) and size can then be
determined
b) Drawings or photographs of specimens
are often enlarged and a formula can be used
Magnification = size of image/size of specimen
c) Scale bars are often used so actual size can
be determined
• Humungous Fungus
C. Limiting cell size
1. Cells stay small due to the surface area to
volume ratio principle
2. In cells, the rate of heat and waste
production depend on the volume of the cell
3. The size of the cell affects the rate of the
reactions
4. The surface of the cell, the membrane,
controls what materials move in and out of the
cell
5. Cell with more surface area per unit volume is
able to move more materials in an out of the cell
6. Large cell, compared with a small cell, has
relatively less surface area to bring in materials
that are needed and to get rid of wastes
7. Cells are limited in the size they can reach and
still be able to carry out the functions of life
8. Large cells have modifications
a) long and thin
b) infoldings or outfoldings to increase
their surface area
Surface area to volume ratios:
• Volume increases by a factor calculated by
cubing the radius
• Surface area increase
by a factor calculated by
squaring the radius
Demo
D. Cell reproduction and differentiation
1. Many cells can reproduce
a) growth in multicellular organisms
b) replace damage or dead cells
2. Differentiation: process to produce all
the required cell types of an organism
a) multicellular organism starts as a
single cell and rapidly reproduce
b) resulting cells begin to
differentiate
c) Differentiation is the result of the
expression of certain specific genes
but not others
3. Each cell contains all of the DNA or genetic
information, but each cell will become a specific
type of cell depending on which DNA segments
(genes) become active
4. Some cells lose the ability to reproduce once
they become specialized (nerve and muscle
cells)
5. Some cells can reproduce rapidly throughout
their life (epithelial cells like skin cells): new
cells become the same type of cells as the
parent cell
6. Emergent properties: properties that depend
on the interactions between all the different parts
of a biological unit like a cell
E. Stem Cells: cells that retain their ability to divide and
differentiate into various cell types
1. Meristematic tissue: occurs near root and stem
tips of plants and produces new cells capable of
becoming various types of tissue within that root or
stem
2. When stem cells divide to form a specific type
of tissue, they also produce some daughter cells
that stay as stem cells
a) allows for the continual production of a
particular type of tissue
b) scientists saw the possibilities of using
these cells to treat human disease, but stem
cells cannot be distinguished by their
appearance
3. Embryonic or pluripotent stem cells:
retain the ability to form any type of cell in
an organism
4. Tissue specific stem cells: located in
certain tissues types and can only produce
new cells of that type
F. Stem cell research and treatments
1. Research to grow large numbers of
embryonic stem cells in culture so they can
be used to replace cells lost as a result of
injury or disease (Parkinson’s and
Alzheimer’s)
a) implanted stem cells could replace
lost or defective brain cells
b) research being done on mice, some
time before human treatment
2. Tissue specific stem cells have been used on
human patients
a) blood stems cells used to replace
damaged bone marrow of some
leukemia patients
3. Stargardt’s disease: inherited disease that has a
defect in the processing of vitamin A which is
important in the retina of the eye (leads to
blindness)
a) Embryonic stem cells treatments have
begun to protect and regenerate the
photoreceptors in the retina that are damaged
by the disease
4. Ethical Issues of pluripotent/embryonic stem
cells
a) Cells are obtained from embryos usually
from labs carrying out in vitro fertilization
b) Harvesting the cells involves the death
of the embryo
c) One side: taking of a human life
d) Another side: research could result in a
significant reduction in human suffering
Stem Cells
III. The Ultrastructure of Cells
A. Characteristics of prokaryotic cells
Structures of Prokaryotic
Function
1.Cell wall
Protects and maintain shape of cell
Composed of peptidoglycan
2. Plasma membrane
Controls movement of materials in and out
Role in binary fission
3.Flagella
Hair-like structure for cell movement
4.Pili
Hair-like growth for attachment
Joining bacterial cells together for
reproduction
5. Ribosomes
Site for protein synthesis
6.Nucleoid
Contains single. Long circular thread of
DNA
Size
Less than 10 μm
Membrane-bound organelles
Yes or No
Location of DNA
Free in cytoplasm/nucleoid
Structure of DNA
Ring without protein
Types of organisms
Bacteria
Type of ribosome
70s ribosome
Cytoplasm: location of cellular processes in prokaryotes
Prokaryotic Cells
• Small
• Simple
• Unicellular
• Bacteria
• No nucleus or
membrane bound
organelles
• DNA is free, not
attached to
proteins
Prokaryotic Cells divide by binary fission
Process
• DNA is copied
• Chromosomes attach
to plasma membrane
• Cell elongates and
partitioning the cell
using microtubule
fibers called FtsZ
• Cell divides into two
genetically identical
daughter cells
Prokaryotes and eukaryotes
B. Characteristics of eukaryotic cells
Size
More than 10μm
Membrane-bound
organelles
Location of DNA
Yes or No
Structure of DNA
Chromosomes with
proteins
Animals, plants, protists,
fungi
80S
Types of organisms
Types of ribosomes
Nucleus
Organelle
Endoplasmic Reticulum
Ribosomes
Lysosomes
Golgi apparatus
Mitochondria
Function
Nucleus
Nucleolus
Centrosomes
Vacuoles
Cytoplasm
Chloroplasts (plants and algae)
Cell Wall
Cytoplasm
Endoplasmic Reticulum
• Structure: a system of membranous tubules and sacs
• Function: intercellular highway (a path along which
molecules move from one part of the cell to another)
• Two types:
– Rough Endoplasmic Reticulum
– Smooth Endoplasmic Reticulum
ER
Rough Endoplasmic Reticulum
• Rough Endoplasmic Reticulum
(rER):
• Protein development and
transport
• Proteins may become parts of
membrane, enzymes, or
messengers between cells
• Covered with ribosomes
Smooth Endoplasmic Reticulum
Smooth Endoplasmic Reticulum
(sER): involved in
• Production of lipids
• Breakdown of toxic substances
• Production of hormones
• Helping liver release glucose
• Not covered with ribosomes
Ribosomes
• Structure: consist of two
subunits made of protein and
RNA
• Function: location of protein
synthesis
• No membrane
• Free floating or on ER
• Eukaryotes: 80S (size)
Lysosomes
• Structure: spherical organelles that
contain more than 40 hydrolytic
enzymes within single membranes
• Function: breaks down food
particles, invading objects, or worn
out cell parts (proteins, nucleic
acids, lipids, and carbohydrates)
• Acidic environment to hydrolyze
large molecules
Golgi Apparatus
• Structure: stacked flat sacs (cisternae)
• Function: receives proteins from the
rER and distributes them to other
organelles or out of the cell
(receiving, processing, packaging, and
shipping of materials made in the cell)
• Cis side: receives products from ER
and moves into cisternae
• Trans side: discharging side
• Vesicles: carry modified material to
where they are need either inside or
outside of cell Golgi
Mitochondria
• Structure: folded membrane
within an outer membrane
– The folds of the inner
membrane are called cristae
• Function: -converts energy
stored in food into usable
energy for work
– cellular respiration
Nucleus
• Structure: the nucleus is a
sphere that contains another
sphere called a nucleolus
• Function: -storage center of
cell’s DNA
-manages cell functions
Nucleus
Centrioles
• Structure: composed of
nine sets of triplet
microtubules arranged
in a ring
– Exist in pairs
• Function: centrioles
play a major role in
cell division (mitosis)
Vacuoles
• Structure: a sac of fluid
surrounded by a membrane
– Very large in plants
• Function: used for temporary
storage of wastes, nutrients,
and water
Chloroplasts
• Structure: stacked sacs
(thylakoids) that contain
chlorophyll surrounded
by a double membrane
• Function: photosynthesis
(conversion of light
energy to chemical
energy stored in the
bonds of glucose)
Chloroplast
Cell Wall
• Structure: rigid wall made up
of cellulose, proteins, and
carbohydrates
• Function: boundary around the
plant cell outside of the cell
membrane that provides
structure and support
Cell Wall
Cytoplasm
• Structure: gelatin-like fluid that lies inside the cell membrane
• Function: -contains salts, minerals and organic molecules
-surrounds the organelles
Plant
Animal
Outer cell wall and then plasma
membrane
Plasma membrane
Chloroplast
No chloroplast
Large vacuole
Small or no vacuoles
Carbohydrates stored as starch
Carbohydrates stored as glycogen
No centrioles within a centrosome
area
Contains centrioles within a
centrosome area
Fixed, angular shape do to rigid cell
wall
Flexible and more round shape
because of no cell wall
D. Outermost parts of different cells
Cell
Bacteria
Outermost part (cell
wall/membrane)
Cell wall of peptidoglycan
Fungi
Cell wall of chitin
Yeasts
Cell wall of glucan and mannan
Algae
Cell wall of cellulose
Plants
Cell wall of cellulose
Animals
No cell wall, plasma membrane
Cytoskeleton
• Structure: a network of thin,
fibrous elements made up of
microtubules (hollow tubes)
and microfilaments (threads
made out of actin)
• Function: -acts as a support
system for organelles
-maintains cell shape
IV. Membrane structure
A. History
1. 1915: scientists were aware that
the membrane structure contained
proteins and lipids
2. Davson-Danielli model in 1935:
suggested a lipid bilayer model suggesting
that the bilayer was covered on both sides
by a thin layer of globular protein
3. Singer and Nicolson in 1972: proposed
that proteins were inserted into the
phospholipid layer and didn’t form a
protein layer
a) Proteins formed a mosaic floating
in a layer of phospholipids
b) Differences from Davson-Danielli model
i) Not all membranes are identical or
symmetrical
ii) Membranes with different functions also
have a different composition and different
structure (seen with electron microscope)
iii) Protein layer is unlikely because it is
largely non-polar and would not
interface with water as shown be cell studies
c) Evidence for the changes was gathered by using
the electron microscope and study of cells in
various solutions
d) Ability to culture cells in the lab allowed many
of these studies
e) Further studies since 1972 have made slight
changes to the Singer-Nicolson model
f) Current model is called the fluid mosaic model
Fluid mosaic
B. Phospholipids: composed of a glycerol, two
fatty acids, and highly polar organic alcohol
1. Hydrophilic head (water loving): side with
the polar alcohol group and is water soluble
2. Hydrophobic tails
(water fearing): side with
nonpolar fatty acids and
is not soluble in water
3. Phospholipids align to form a bilayer when water
is present
a) large number of phospholipid molecules
b) the fatty acids tails are not attract to each
other very strongly so the membrane tends to
be fluid or flexible
i) allows animals cells to have a
variable shape
ii) Water forming hydrogen bonds helps
to maintain the overall structure of the
membrane
C. Cholesterol
1. Cholesterol molecules throughout the
membrane help to maintain its fluidity
2. Fluidity can change with temperature
changes, so cholesterol allows membranes
to function at a wider range of temperatures
3. Plant cells do not have
cholesterol
D. Proteins
1. Create diversity in membrane function
2. Proteins are embedded in the fluid
matrix of the phospholipid bilayer and this
creates the mosaic effect
3. Integral proteins: amphipathic (hydrophilic and
hydrophobic regions) go all the way through the
lipid bilayer
a) Hydrophobic region in the middle of the
bilayer with the tails
b) Hydrophilic region is exposed to the
water solutions on the outside and inside of
the cell
c) Used to transport polar substances and ions
across the membrane
4. Peripheral proteins: bound to the surface of
the membrane and often attached to an
integral protein
a) glycoprotein: forms when a
carbohydrate attach to the peripheral
protein- used in the recognition of cells and
involved in the immune response
Proteins
E. Membrane protein functions
1. Hormone-binding sites: specific shapes
exposed to exterior that fit the shape of the
hormone and the attachment changes the shape of
the protein which results in the message being
sent to the inside of the cell
2. Enzymatic action: catalyze many reactions
and can be on the interior or exterior of the cell:
often grouped together to form metabolic
pathway
3. Cell adhesion: proteins that can hook
together in various ways to provide
permanent or temporary connections called
gap junctions or tight junctions
4. Cell to cell communication: have
carbohydrate molecules attached and provides
an identification label to represent the
different types of species
5. Channels for passive transport: provides
passageways for substances
6. Pumps for active transport: proteins shuttle
a substance from one side of the membrane to
another by changing shape and requires ATP
Drawing a membrane
V. Membrane transport
A. Passive transport: does not require energy
(ATP) to transport materials
1. Diffusion: particles move from area of higher
concentration to an area of lower concentration
a) living systems: diffusion often
requires a membrane
Diffusion in a liquid
Concentration gradient
2. Facilitated Diffusion: diffusion using a
carrier protein to move substances across a
member from higher concentration to lower
concentration
3. Osmosis: movement of water across a
partially permeable membrane from higher
concentration to lower concentration
Osmosis
Due to difference
between solute
concentrations
on either side of the
membrane
Osmosis
Section 7-3
Higher Concentration
of Water
Water molecules
Cell
membrane
Lower Concentration
of Water
Sugar molecules
Go to
Section:
a) Hypotonic: concentration of solute molecules
outside the cell is lower than the concentration
inside the cell
(less water in the cell) (fresh water)
i) water diffuses into the cell until
equilibrium is reached
ii) causes cell to swell
b) Hypertonic: concentration of solute
molecules outside the cell is higher than the
concentration inside the cell
(less water outside) (salt water)
i) water diffuses out of the cell until
equilibrium is reached
ii) causes cell to shrink
c) Isotonic: concentrations of solutes outside
and inside the cell are equal
i) water diffuse into and out of the cell at
equal rates
Hypotonic
4. How easily a substance can move across a
membrane depends on two factors: size and
charge
a) Small and non-polar: move across easily
i) oxygen, carbon dioxide, and nitrogen
ii) water and glycerol are small enough
b) Large and polar: more difficult to move across
i) charged ions (Cl-, K+, and Na+) difficult
ii) large molecules (glucose and sucrose) difficult
B. Active transport: requires energy (ATP) and
membrane protein to move substance from
lower concentration to higher concentration
(against concentration gradient)
1. Sodium-potassium pump: mechanism
for actively moving sodium and potassium
ions (animal cells have a higher
concentration of K+ ions than their exterior
environment)
Carrier protein
Sodium potassium pump
Active Transport
Section 7-3
Molecule to
be carried
Low
Concentration
Cell
Membrane
High
Concentration
Molecule
being carried
Low
Concentration
Cell
Membrane
High
Concentration
Energy
Go to
Section:
Energy
Steps of sodium-potassium pump
1. Protein binds to 3 intracellular Na+
2. Binding causes ATP energy to be used and
forms ADP (phosphorylation)
3. Protein changes shape and expels Na+ to
exterior
4. 2 K+ bind to protein and phosphate is released
5. Loss of phosphate restores the protein’s original
shape and releases the K+ ions
2. Endocytosis: allows macromolecules to
enter the cell when the portion of the plasma
membrane is pinched off to enclose
macromolecules
a) changes shape of membrane and forms a
vesicle
b) Vesicle enters cytoplasm
c) End of the membrane reattach
because of the hydrophobic and
hydrophilic properties
Endocytosis
3. Exocytosis: allows larger molecules to leave
the cell and is the reverse of endocytosis
a) fluidity of membrane is essential to
allow fusion and secretion of vesicle
contents
Exocytosis
Endo and Exo clip
Steps for protein exocytosis
a) proteins produced by the ribosomes of
rough ER
b) protein exits the ER and enters cis side
of Golgi (vesicle forms)
c) protein modified in Golgi and exists on
the trans side
d) Vesicle with modified protein moves to
and fuses with the plasma membrane
VI. Origin of cells
A. Cell theory: has three parts and there are
some problems and exceptions to the theory
1. All organisms are composed of one or
more cells
2. Cells are the smallest units of life
3. All cells come from other pre-existing
cells
B. Theory: well-substantiated explanation of a
natural phenomenon that incorporates tested
hypotheses and laws: represents understandings
that have developed from extensive observation,
experimentation, and logical inferences
1. Cell theory is a good example
2. Modified over the years and will
continue to be modified as cellular research
progresses
C. Missing component: How the first cell arose
1. No evidence today that new cells arise
form non-living materials, but the first cell
had to form
a) 19th century: Louis Pasteur
experiment using nutrient broth to show
that cells didn’t spontaneously appear
b) Francesco Redi: 200 years before
Pasteur did experiment with meat in jars
c) Many experiment to show doubt on
spontaneous generation of cells
D. Exceptions to cell theory
1. Multinucleated cells of striated muscle
cells, fungal hyphae, and giant algae
2. Very large cells with continuous cytoplasm
that are not compartmentalized into separate
smaller cells
3. Viruses
4. Explaining the “first” cells
*Continued research is needed to see how these
exceptions “fit” in with the current cell theory
E. Common origin for all cells on Earth: how a cell
could progress from a simple prokaryote to
complex eukaryote
1. Endosymbiotic theory by Lynn Margulis in
1981
a) 2 billion years ago, bacterial cell
resided inside an eukaryotic cell
b) Two cells formed a symbiotic
relationship
c) Bacterial cell went through changes
to become a mitochondria
d) Evidence to support the theory based
on characteristics of mitochondria (own
DNA, size of bacteria, own ribosomes)
2. Chloroplast also provides evidence for theory
of endosymbiosis since it also has its own
DNA