Download Cellular Structure and Function

Section 1
Cellular Structure and Function
Cell Discovery and Theory
The Cell Theory
• 1600 – Anton Van Leeuwenhoek improved the
simple light microscope
• 1665 – Robert Hooke examined cork and noticed
small cubicles he called “cells”
• Over time it was noticed that cells are filled with a
jellylike fluid and most have a round, central structure
• 1838 – Matthias Schleiden concluded all plants
are composed of cells and cells are the basis of a
plant’s functions
Section 1
Cellular Structure and Function
Cell Discovery and Theory
The Cell Theory
• 1839 – Theodor Schwann concluded all animals
are composed of cells
• 1858 – Rudolf Virchow stated all cells come from
other living cells
Section 1
Cellular Structure and Function
Cell Discovery and Theory
The Cell Theory
• These 3 men and a few other discoveries
contributed to the development of the cell
theory:
1. All organisms are composed of one or more cells
or cell fragments
2. The cell is the basic unit of structure & function
in all organisms
3. All cells are produced from other cells
Section 1
Cellular Structure and Function
Cell Discovery and Theory
The Cell Theory
• Recall – a theory is a hypothesis that has
stood the test of time
• The 3rd statement of the cell theory supports
the Theory of Evolution – all organisms are
descendants of an original organism, a
single cell. Organisms evolved and adapted,
but cells remain the basic unit of life.
Section 1
Cellular Structure and Function
Cell Discovery and Theory
Prokaryotic Cell
 Simple structure
 Contains a plasma
membrane
 Does not contain
membrane-bound
organelles
Steven P. Lynch
Section 1
Cellular Structure and Function
Cell Discovery and Theory
Eukaryotic Cell
 More complex
structure
 Contains a plasma
membrane
 Contains membranebound organelles
The McGraw-Hill Companies, Inc./Al Telser, photographer
Section 1
Cellular Structure and Function
The Plasma Membrane
Plasma Membrane
 Thin, flexible outer boundary between
the cell and its environment
 Allows nutrients the cell needs into the cell
(glucose, amino acids)
 Allows waste to leave the cell (CO2)
Section 2
Cellular Structure and Function
The Plasma Membrane
Selective Permeability
 The plasma membrane controls the movement
of substances into and out of the cell.
 Only certain particles can pass through
Plasma Membrane
 Controls the amount of a
substance entering and
leaving the cell
Section 2
Cellular Structure and Function
The Plasma Membrane
Selective Permeability
• Example: a tea bag –
permeable to water but not
tea leaves
• If particles could pass freely,
the cell could not maintain
organization. It would be
like a parking lot without
lines!!
Section 2
Cellular Structure and Function
The Plasma Membrane
Selective Permeability
• Depending on the type of cell, different types
of particles will be allowed through.
• Certain particles can cross more freely than
others:
– Small vs. Large molecules
– Lipid Soluble vs. Insoluble
– Uncharged vs. Charged Ions
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of the Plasma Membrane
 The plasma membrane is composed of the
phospholipid bilayer.
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of the Plasma Membrane
• The plasma
membrane is
composed of two
layers of
phospholipids backto-back.
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of the Plasma Membrane
 A phospholipid
molecule is composed
of a glycerol backbone,
two fatty acid chains,
and a phosphate group.
Phosphate
Group
Two Fatty
Acid Chains
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of the Plasma Membrane
• The phosphate group is polar and soluble in
water.
– This is why polar heads point towards the outside
environment and inside of the cell where water is
plentiful.
– The fatty acid tails point toward the middle of the
membrane away from water.
• Polar Heads = hydrophilic (attracted to water)
• Fatty Acid Tails = hydrophobic (afraid of water)
– Drawing***
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of the Plasma Membrane
 The phospholipid
bilayer allows other
molecules to “float”
in the membrane.
Other Components
 Proteins
 Cholesterol
 Carbohydrates
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of the Plasma Membrane
• The plasma membrane contains proteins
throughout the bilayer – some embedded and
some lie on top. Proteins have polar and
nonpolar areas that determine where in the
bilayer they lie.
Section 2
Cellular Structure and Function
The Plasma Membrane
Fluid Mosaic Model
• Components in the
bilayer are constantly
moving. The
embedded proteins
create a pattern.
Thus, the current
model of membrane
structure is called the
fluid mosaic model.
Section 2
Cellular Structure and Function
The Plasma Membrane
Function of Membrane Proteins
• Membrane proteins regulate which particles
can pass across the membrane. Some act
as enzymes, others act as markers so
chemicals can recognize the cell.
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of Plasma Membrane
• Cholesterol is a rigid structure that binds to
phospholipids to restrict movement. It keeps
them from sticking together, maintains strength of
the membrane, and allows for flexibility.
Cholesterol
Molecule
Section 2
Cellular Structure and Function
The Plasma Membrane
Structure of Plasma Membrane
• Cytoskeleton is made of long, thin structures
made by proteins which give shape and
support to the cell (like a skeleton does for
us.)
• The cytoskeleton is made of microfilaments
and microtubules.
Section 2
Cellular Structure and Function
The Plasma Membrane
Cytoskeleton
Section 2
Cellular Structure and Function
Membrane Function
Passive Transport
• Recall that the function of the plasma
membrane is to transport materials in and
out of the cell.
• Passive Transport – movement of particles
across the membrane that requires no
energy by the cell.
Section 2
Cellular Structure and Function
Membrane Function
Passive Transport
Plasma
membrane
Concentration
gradient
Section 2
Cellular Structure and Function
Membrane Function
Passive Transport
• There are 3 types of passive transport:
– Diffusion
– Osmosis
– Facilitated Diffusion
Section 2
Cellular Structure and Function
Membrane Function
Passive Transport
• Diffusion – movement of particles from high
concentration to low concentration.
– Until particles are evenly distributed throughout
– Particles continue to move, but net movement is
zero
• At this point it is called dynamic equilibrium
– Particles that will diffuse across the membrane
include H2O, lipids and particles that dissolve in
lipids like O2 and CO2, or are small enough to
squeeze through.
Section 2
Cellular Structure and Function
Membrane Function
Passive Transport
• Diffusion
Section 2
Cellular Structure and Function
Membrane Function
Passive Transport
• Osmosis – the diffusion of water into and out
of the cell.
• Regulating the water flow through the
plasma membrane is an important factor in
maintaining homeostasis within a cell.
• Osmotic Balance = dynamic equilibrium:net
movement of water into and out of the cell is
equal
Section 2
Cellular Structure and Function
Membrane Function
What Controls Osmosis?
• Unequal
distribution of
particles, called
a concentration
gradient, is one
factor that
controls
osmosis.
Before
Osmosis
Selectively permeable
membrane
After
Osmosis
Water molecule
Sugar molecule
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Cellular Structure and Function
Membrane Function
Osmosis in Cells - Isotonic
• In blood: cells in blood
plasma have equal
concentrations so there is
no net movement.
• This is an isotonic solution:
the concentration of
dissolved substances inside
the cell = the concentration
outside the cell.
Section 2
Cellular Structure and Function
Membrane Function
Osmosis in Cells - Isotonic
• Cells in an isotonic
solution maintain
their shape and
normal pressure.
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Cellular Structure and Function
Membrane Function
Osmosis in Cells
• The environment around cells are not pure water
so if the cell was removed and placed in water,
the concentration of dissolved particles is greater
inside the cell, and concentration of pure water is
greater outside, so water would flow into the cell
causing it to burst (cytolysis).
– This is why an IV is NOT pure water, but a
saline solution with dissolved salts and sugars
Section 2
Cellular Structure and Function
Membrane Function
Osmosis in Freshwater Plants
• Turgor Pressure – pressure created within
plant cells to support flowers.
– Without turgor, plants will wilt or collapse
• Plant cells have dissolved particles inside
them so water naturally flows inward.
Section 2
Cellular Structure and Function
Membrane Function
Osmosis in Cells - Hypotonic
• The cell wall is adapted in certain plants
(Elodea) to prevent bursting. As the cell
swells, the cell wall pushes back inward to
prevent more water from entering.
• Hypotonic Solution – concentration of
dissolved particles in the water outside the
cell is lower than inside the cell.
– Concentration of water outside the cell is greater
than inside.
Section 2
Cellular Structure and Function
Membrane Function
Osmosis in Cells - Hypotonic
• Hypotonic
solutions result in
water flowing into
the cell causing it
to swell.
Section 2
Cellular Structure and Function
Membrane Function
Osmosis in Cells - Hypertonic
• However, in a salt water solution, water
would flow out of the cell causing it to shrink
and die.
– Shrink = Plasmolysis
• This is a hypertonic solution – concentration
of dissolved substances is greater outside
the cell than inside.
Section 2
Cellular Structure and Function
Membrane Function
Osmosis in Cells - Hypertonic
• Plant cells
lose pressure
as the plasma
membrane
shrinks away
from the cell
wall.
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion
• Facilitated Diffusion - diffusion with the use
of transport proteins to aid the passage of
particles across the membrane.
– From high concentration to low concentration (passive
transport)
– Needed for particles like ions, sugars, and amino acids.
• Proteins that function as a regulator of
particles in and out of the cell are called
“transport proteins.”
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion
• Each transport protein is highly selective and
aids the passage of only certain particles.
– Selective due to shape and charge
– Therefore, must have several types of transport
proteins to accommodate different particles.
1. Channel Proteins
2. Carrier Proteins
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion – Transport Proteins
• Channel Proteins – AKA “pores”
– Extend throughout the bilayer and form water
filled tunnels that allow certain ions to pass
through.
– Different ions pass through different pores
• Depends on the size and charge of ion and diameter
of the pore
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion
• Channel Protein
Channel
proteins
Plasma
membrane
Concentration
gradient
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion – Transport Proteins
• Carrier Proteins
– Proteins that transport specific substances across
the cell membrane by first binding to an active
site.
– Molecules transported via carrier proteins are
sugars, amino acids, glucose, salts, etc.
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion – Transport Proteins
• Carrier Proteins – How they work
– Particle can directly fit into the protein to activate a
change in shape so particle is released on other side
of membrane – then the protein’s original shape is
restored
• Figure 4.14
– A particle combines with a protein to change shape
and allow a gate to open so another particle can pass
through.
• Gate opens when hormone attaches, then ion passes
through
• Figure 4.15
Section 2
Cellular Structure and Function
Membrane Function
Facilitated Diffusion
• Carrier Protein
Carrier proteins
Plasma
membrane
Concentration
gradient
Step 1
Step 2
Section 2
Cellular Structure and Function
Membrane Function
Active Transport
• Active Transport is the movement of particles
from low concentration to high concentration
which requires energy by the cell.
• Transport proteins known as “pumps” are used to
move particles across the membrane against (or
up) the concentration gradient.
• Each pump binds to a particle whose shape fits
it. Chemical energy changes the shape of the
pump sending the particle across the membrane.
Then, the protein’s original shape is restored.
Section 2
Cellular Structure and Function
Membrane Function
Active Transport
• Active Transport
Carrier
proteins
Plasma
membrane
Step 1
Cellular
energy
Concentration
gradient
Step 2
Section 2
Cellular Structure and Function
Membrane Function
Transport of Large Particles
• Endocytosis – process by which the plasma
membrane engulfs and then takes in
substances from a cell’s environment.
– Common in unicellular organisms (ex: amoeba).
– There are 3 types of Endocytosis:
• Phagocytosis
• Pinocytosis
• Receptor-Aided Endocytosis
Section 2
Cellular Structure and Function
Membrane Function
Transport of Large Particles
• Endocytosis
Nucleus
Wastes
Digestion
Exocytosis
Endocytosis
Section 2
Cellular Structure and Function
Membrane Function
Transport of Large Particles
• Phagocytosis – form of endocytosis in which
solid chunks of material are taken in.
– Food is detected, the membrane forms a small
sac called a vesicle around it, which breaks off
and goes inside the cell to be digested.
• Pinocytosis – form of endocytosis in which
liquids are taken in.
Section 2
Cellular Structure and Function
Membrane Function
Transport of Large Particles
• Receptor-Aided Endocytosis – Particles first
bond to receptor proteins in the plasma
membrane, a vesicle forms around it,
particles are released inside the cell, a
vesicle takes the receptors back to the cell
membrane.
– Commonly used to bring cholesterol into the cell.
Section 2
Cellular Structure and Function
Membrane Function
Transport of Large Particles
• Exocytosis – reverse process of endocytosis
in which cell products or wastes are
enclosed in vesicles and released to
surrounding environment.
– Substances enclosed in a vesicle inside the cell
that moves toward and binds to the plasma
membrane. Vesicle breaks open and particles
are released.
Section 2
Cellular Structure and Function
Membrane Function
The Cell Wall
• Cell Wall is a structure that lies outside the
plasma membrane and provides support and
protection in plant cells.
– Often made of cellulose
– Does not regulate permeability of particles
– Functions = support and protection
– Organisms that have a cell wall – plants, fungi,
bacteria, algae