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Cell Structure and Function
(Ch. 7)
Movement through the Membrane Overview:
http://programs.northlandcollege.edu/biology/biology1111/animations/passive1.swf
Osmosis: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html
Diffusion: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html
Facilitated Diffusion: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html
Active Transport: Sodium/ Potassium Pump: http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html
Cell Signaling: Bacteria Talks TED Talk: http://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate
LIFE IS CELLULAR
The cell – basic unit of life, all living things
are made of a cell (unicellular) or more
than one cell (multicellular).
• The invention of the microscope in the
1600’s made possible for cells to be
discovered.
– Robert Hooke – examined cork saw many
boxes.
– Anton van Leeuwenhoek - discovered that
pond water contained many tiny living
organisms.
Cell Theory
1. All living things are composed of one or
more cells.
2. In organisms, cells are the basic units of
structure and function.
3. New cells are only produced from other
existing cells.
Cells Are Small
• A meter is not useful for measuring
cells.
• Scientists uses a unit called a
micrometer (micron) to measure cells.
– 1 micrometer=1/1000 of a millimeter.
• There are 1000 microns in a mm.
All cells have a cell membrane,
genetic material, and cytoplasm
• The cell membrane (aka plasma
membrane) is a flexible, thin barrier
that:
– Separates the cell from its surroundings.
– Regulates what moves in and out of the
cell.
• Genetic material provides instructions
that control the cell’s activities.
• The cytoplasm is the material inside
the cell that supports the organelles.
Prokaryotic Cell
• What is a prokaryote?
– Single celled organisms that lack a nucleus and
other internal membrane-bound organelles.
• Genetic material (DNA or RNA) is found free floating in
a cell, not in a compartment or nucleus.
– All bacteria (ex. E. Coli, Streptococcus) are
prokaryotic.
– Prokaryotes are unicellular.
Eukaryotic Cell
• What is a eukaryote? (YOU are a
eukaryote!)
– Have membrane bound organelles
(specialized organ-like structures).
– Genetic material is found in a nucleus.
– The Kingdoms Animal, Plant, Fungi, and
Protista are Eukaryotes.
– Eukaryotes can be unicellular or
multicellular.
Nucleus
• What is the nucleus?
– Often found in the center of the cell.
– Largest and most easily seen organelle.
– Surface is bound by a double lipid
membrane called the nuclear envelope.
• Is a double membrane system.
• Contains nuclear pores - allow for protein and
other molecules to pass through.
– Genetic material, or DNA, is found here
(in the form of chromsomes) in eukaryotic
organisms only!
Nucleolus
• The nucleolus is…
– Structure found inside the
nucleus.
– Responsible for making
ribosomes which will function
in protein synthesis.
• Remember that proteins regulate
cellular processes and make you
you!
Cellular boundaries
• What is the cell wall?
– Found in many organisms like plants,
fungi, algae, and nearly all prokaryotes.
– Not found in animal cells.
– Function is to support, provide
strength, and protect the cell.
– Composed of the polysaccharide
cellulose.
– Are porous and allow water, oxygen,
CO2, and other substances to pass
through.
Cellular boundaries
• All cells contain a cell membrane
– Composed of a phospholipid bilayer
– Regulates what enters and leaves the cell
– Protects and supports the cell
Organelles that build proteins
• What is a ribosome?
– Protein manufacturer.
• Makes proteins to be used within
the cell or be exported out of the
cell to be used in other places.
– Are composed of RNA and
protein.
– Produced by the nucleolus
within the nucleus.
Organelles that build proteins
• The endoplasmic reticulum
is…
– Found in eukaryotic cells.
– Structure is an extensive system
of internal membranes.
– Location where lipid
components of the cell
membrane are assembled,
proteins are exported.
Organelles that build proteins
• Rough ER
– Ribosomes found on the surface.
– Functions to make proteins and transport proteins
that will be released/secreted from the cell.
– Also functions to make proteins destined for
lysosomes or other locations in the cell.
• Smooth ER
– Does NOT have ribosomes.
– Contains enzymes for making lipids, detoxification
of drugs.
Organelles that build proteins
• What is the Gogi apparatus:
– Receives vesicles (transport vacuoles)
from the RER that contains proteins.
– Structure in eukaryotic cells that is a
stack of flattened membranes.
– Modifies molecules that it receives,
packages, and distributes molecules into
vesicles.
• Marks the molecules inside the vesicle to
determine what their final destination will be.
• Destination is often storage in a vacuole or
release to the outside of the cell.
Organelles that store, cleanup, and support
• What is a lysosome?
– Organelle filled with digestive
enzymes.
– Digests and recycles the used
components of a cell for reuse.
– Destroy bacterial cells.
– Found in animal cells and
specialized plant cells.
Organelles that store, clean-up,
and support
• What is the role of the vacuole?
– Store waste products, large amounts of
water and nutrients.
– Help plant cells hold their shape.
– Plant cells have large vacuoles; animal
cells have very small vacuoles.
– Vesicles are transport vacuoles found in
eukaryotic cells.
• Move materials between organelles
and to and from the cell surface.
Organelles that store, clean-up,
and support
• What is the cytoskeleton?
– Mesh-like network that helps the cell keep its shape.
– Supports the organelles of the cell.
– Microtubules – hollow protein tubes that form the “tracks”
for the organelles to move on.
• Centrioles - special microtubules found in animal cells involved in
cell division.
• Cilia - short thread-like structures important for movement of
unicellular organisms.
• Flagella - whip-like microtubules that help unicellular organisms
move.
– Microfilaments – support the cell and function in helping
cytoplasm move through the cell.
Organelles that capture &
release energy (plastids)
• What are chloroplasts?
– Capture sunlight to make sugars –
photosynthesis.
• Ultimately are the energy source for all
living things.
– Are surrounded by two membranes.
– Contain the green pigment
chlorophyll.
– Are not found in animal cells.
– Contains its own DNA.
Organelles that capture &
release energy (plastids)
• What are mitochondria?
– Convert the chemical energy stored in
food into useable compounds.
• ATP is the energy molecule created by the
cell.
– Made of a double membrane (inner is
folded).
– Also contains its own DNA (from
Mom).
– Present in nearly all eukaryotic cells.
Movement Through the
Membrane
• All cells exist in a liquid environment.
• The cell membrane functions as a
barrier but must let certain materials in
and out of the cell.
Structure of the Plasma/Cell
Membrane
• Plasma Membranes consist of 2 types of
molecules – phospholipids and proteins.
• A phospholipid has 2 regions – head and
tail.
– Polar head region with a phosphorus group.
• Remember, water is polar.
– Non-polar 2 tail region composed of long
carbon chains (fatty acids).
Structure of a phospholipid
Diagram of a Phospholipid
• Polar head
attracts water
molecules
(hydrophilic),
nonpolar tails
repel water
molecules
(hyrdrophobic).
Phospholipid bilayer
• Due to the hydrophobic
and hydrophilic nature
of the phospholipid, a
double layer is formed
where the heads protect
the tails from the water.
– This is called the
phospholipid bilayer.
– The bilayer is fluid, not a
hard shell.
Structure of phospholipid bilayer
• The phospholipid bilayer is called semipermeable or selectively permeable – it
allows some materials through and blocks
others.
• Polar (head) portion is the true boundary
between a cell and its surroundings.
Proteins are Embedded Within
the Bilayer
• Proteins act as passageways for nonpolar
(hydrophobic) molecules to pass through.
• Without proteins embedded in the bilayer,
essential molecules needed for communication,
energy, etc., would not reach the interior of the
cell.
• Carbohydrates are attached to the proteins.
– Allow for cell recognition and communication.
Proteins are Embedded Within
the Bilayer (continued)
• The model of the lipid bilayer with embedded
proteins is called the Fluid Mosaic Model.
TWO Types of Transport
Through a Cell Membrane
1. Passive Transport – the movement
of molecules through a cell membrane
without the expenditure of energy.
1. Active Transport – the movement of
molecules through a cell membrane
using energy.
3 Types of Passive Transport
1. Diffusion - Movement of molecules from
areas of high concentration to low
concentration.
2. Osmosis - Diffusion of water molecules
from higher concentration of water to lower
concentration of water.
3. Facilitated Diffusion - Diffusion through
pores or channel proteins.
Diffusion
• Molecules tend to move from areas where there is
more of them (high concentration) to where there
is less (low concentration).
– This is called moving WITH the concentration gradient.
• Diffusion continues until equilibrium is reached,
or where molecules are equally distributed.
– Once equilibrium is reached, particles will move at the
same rate across the membrane in both directions.
• If a membrane separates two regions of liquid the
solutes within the liquid will move from high to low.
– Some solutes will be able to move through when others
will not.
Diffusion (continued)
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
Facilitated Diffusion
• Molecules like small lipids and alcohol can
diffuse directly through a membrane
(diffusion).
• Facilitated diffusion occurs because the cell
membrane is semi-permeable and some
molecules cannot diffuse through on their
own, they will need assistance (need
facilitated).
Facilitated Diffusion
• Membranes have protein channels that are
designed to fit specific solutes. When a
difference in concentration occurs, solute
molecules will diffuse through these protein
channels.
– Hundreds of proteins exist to help particles cross
membranes.
• Solute must have a specific size, shape, or
polarity in order to fit through the protein
channel.
– Is fast and specific!
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
Osmosis: an example of
facilitated diffusion
• Water passes through cell membranes
rapidly.
• Osmosis is a specialized form of facilitated
diffusion that moves water molecules through
membranes via aquaporins.
– Aquaporins are special water channel proteins in
membranes.
OSMOSIS
Types of Solutions
– A hypertonic solution is one in which the
solute concentration is HIGHER in the solution
than in the cell.
• Water will move out of the cell.
– A hypotonic solution is one in which the solute
concentration is LOWER in the solution than in
the cell.
• Water will move in to the cell.
– An isotonic solution is one in which there are
EQUAL solute concentrations in the solution and
in the cell.
• Water will move in and out of the cell at equal rates.
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
Osmosis: an example of
facilitated diffusion
• Osmotic pressure – the pressure that occurs when
more water molecules accumulate inside a cell.
– Caused by water moving into or out of a cell.
Active processes expend energy
• Active transport is the use of energy to
move molecules from LOW concentration to
HIGH concentration (against or opposite the
concentration gradient).
• Some molecules exist in low amounts on one
side of a membrane and need to be moved to
areas of high amounts.
• Cell membranes have mechanisms to move
these molecules against their concentration
gradients.
http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html
Types of Active Transport
•
Molecules can be carried through the membrane by
membrane-associated protein pumps.
– Na, K, Ca ions are transported in this manner.
•
Cells have an ability to engulf large particles by
forming a vesicle around a particle in a process
called endocytosis.
– If the particles have been partially broken down into a liquid
of tiny dissolved molecules, it is called pinocytosis (cell
drinking).
– If the particles are cell fragments or organic matter, it is
called phagocytosis (cell eating).
Types of Active Transport
•
Exocytosis is the process by which wastes
or secretions (hormones) are brought to the
cell membrane, packaged into vesicles and
sent out of the cell.
– It is the reverse of endocytosis.
Unicellular vs. Multicellular
•
Unicellular organisms – single celled.
•
•
•
Include both prokaryotes and eukaryotes.
Maintain homeostasis by growing, responding to
the environment, transforming energy, and
reproducing.
Multicellular organisms – many cells
working together to create an organism.
•
Cells are specialized – different cell types play
different roles.
•
•
Ex. Move, respond, communicate, substance
production.
Cells communicate with one another to maintain
homeostasis for the organism.
Levels of organization
•
Multicellular organisms have increasing
levels of organization:
•
•
•
•
•
•
•
Organelles
Cells
Tissue
Organs
Organ systems
Multi-cellular organisms
The organization allows them to divide labor
in order to maintain homeostasis.
Cellular communication
•
Cells in large organisms must communicate
with one another in order to work together to
maintain homeostasis!
•
•
Occurs via chemical signals that influence the behavior of
the cells receiving the signals.
Receptors are often found on the outside of cells where
they bind chemical signaling molecules and influence
cellular activity.