Download Membrane Structure and Function

Slide 1 ___________________________________ Chapter 7
___________________________________ Membrane Structure and
Function
___________________________________ PowerPoint® Lecture Presentations for
Biology
___________________________________ Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 2 ___________________________________ Overview: The Membrane Barrier
• The plasma membrane is the boundary that separates the
living cell from its surroundings
___________________________________ • All eukaryotic membranes exhibit selective permeability,
allowing some substances to cross them more easily than
others
___________________________________ Membrane
Channel
Protein
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 3 ___________________________________ Concept 7.1: Cellular membranes are fluid mosaics
of lipids and proteins
• Phospholipids are the most abundant lipid in membranes
___________________________________ • Phospholipids are amphipathic molecules, containing
hydrophobic and hydrophilic regions
___________________________________ The fluid mosaic model
states that a membrane
is a fluid structure with a
“mosaic” of various proteins
embedded in it
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 4 Fig. 7-5
___________________________________ The Fluidity
of Membranes
Lateral movement
(~107 times per second)
Flip-flop
(~ once per month)
(a) Movement of phospholipids
Fluid
Unsaturated hydrocarbon
tails with kinks
Viscous
Saturated hydrocarbon tails
(b) Membrane fluidity
Most of the
lipids, and
some proteins,
drift laterally
___________________________________ ___________________________________ Rarely does a
molecule flip-flop
transversely
across the
membrane
___________________________________ Cholesterol
(c) Cholesterol within the animal cell membrane
___________________________________ ___________________________________ ___________________________________ Slide 5 Fig. 7-6
___________________________________ Demonstration of Protein Drift in a Membrane
___________________________________ RESULTS
Membrane proteins
Mouse cell
___________________________________ Mixed proteins
after 1 hour
Human cell
Hybrid cell
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 6 Fig. 7-5b
___________________________________ •Membranes rich in unsaturated fatty acids are more
fluid that those rich in saturated fatty acids
•Membranes must be fluid to work properly; they are
usually about as fluid as salad oil
Fluid
___________________________________ Viscous
___________________________________ Unsaturated hydrocarbon
tails with kinks
___________________________________ Saturated hydrocarbon tails
___________________________________ ___________________________________ ___________________________________ Slide 7 Fig. 7-5c
___________________________________ •The steroid cholesterol has different effects on membrane fluidity
at different temperatures
•At warm temperatures (such as 37°C), cholesterol restrains
movement of phospholipids
___________________________________ •At cool temperatures, it maintains fluidity by preventing tight
packing
___________________________________ ___________________________________ Cholesterol
___________________________________ ___________________________________ ___________________________________ Slide 8 ___________________________________ Fig. 7-7
Fibers of
extracellular
matrix (ECM)
___________________________________ Carbohydrate
Glycoprotein
Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Transmembrane
protein
___________________________________ Cholesterol
Proteins provide most
membrane-specific
functions
Peripheral
proteins
___________________________________ Integral
protein
CYTOPLASMIC SIDE
OF MEMBRANE
___________________________________ ___________________________________ ___________________________________ Slide 9 Fig. 7-8
___________________________________ N-terminus
EXTRACELLULAR
SIDE
What
types
of
side
chains
are on
outside
of
these
helices?
___________________________________ ___________________________________ C-terminus
α Helix
___________________________________ CYTOPLASMIC
SIDE
___________________________________ ___________________________________ ___________________________________ Slide 10 Fig. 7-9ac
___________________________________ Signaling molecule
___________________________________ Receptor
Enzymes
___________________________________ ATP
Signal transduction
(b) Enzymatic activity
(a) Transport
(c) Signal transduction
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 11 Fig. 7-9df
___________________________________ ___________________________________ Glycoprotein
(d) Cell-cell recognition
(e) Intercellular joining
Carbohydrates often play important roles
on the plasma membrane. Covalently
bonded to lipids (forming glycolipids) or
more commonly to proteins (forming
glycoproteins)
___________________________________ (f) Attachment to
the cytoskeleton
and extracellular
matrix (ECM)
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 12 Fig. 7-10
___________________________________ ER
1
Membranes
have
distinct
inside and
outside
faces
Transmembrane
glycoproteins
Secretory
protein
Glycolipid
Golgi
2
apparatus
Vesicle
3
4
Secreted
protein
Plasma membrane:
Cytoplasmic face
Extracellular face
Transmembrane
glycoprotein
The
asymmetrical
distribution of
proteins, lipids,
and
carbohydrates
is determined
when the
membrane is
built by the ER
and Golgi
apparatus
___________________________________ ___________________________________ ___________________________________ Membrane glycolipid
___________________________________ ___________________________________ ___________________________________ Slide 13 ___________________________________ Selective Permeability
• A cell must exchange materials with its
surroundings and compartmentalize its interior.
___________________________________ • This process is controlled by the membranes.
• Membranes are selectively permeable,
regulating the cell’s molecular traffic
___________________________________ • What does “Selective Permeability” mean?
___________________________________ _______________________________________
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 14 ___________________________________ The Permeability of the Lipid Bilayer
Hydrophobic (nonpolar) molecules, such as hydrocarbons,
can dissolve in the lipid bilayer and pass through the
membrane rapidly
___________________________________ estradiol
___________________________________ Charged or strongly polar
molecules, such as ions,
sugars and proteins, do
not cross the membrane easily
testosterone
___________________________________ glucose
proteins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 15 Some small molecules, even if
polar, can pass through the lipid
bilayer - very slowly......
___________________________________ -oxygen
-carbon dioxide
-urea
___________________________________ -water
___________________________________ H2O
___________________________________ ___________________________________ ___________________________________ Slide 16 ___________________________________ Diffusion: True or False
1. Diffusion requires that the membrane be permeable to the substance
that is diffusing
___________________________________ 2. Diffusion is spontaneous and passive – requiring no Energy
3. A substance moves against its concentration gradient during diffusion
4. The concentration of one substance can affect the diffusion of another
5. Diffusion occurs because populations of molecules move randomly,
but individual molecules can be directional (moving in a particular
direction across a membrane)
___________________________________ 6. Diffusion results from thermal motion (heat)
7. Osmosis is the diffusion of a solute across a selectively-permeable
membrane.
___________________________________ 8. At dynamic equilibrium, as many molecules cross in one direction
across the membrane as in the other direction
___________________________________ ___________________________________ ___________________________________ Slide 17 Fig. 7-11
___________________________________ Membrane (cross section)
one
solute
WATER
___________________________________ Net diffusion
Net diffusion
Equilibrium
Net diffusion
___________________________________ two
solutes
Net diffusion
Net diffusion
Net diffusion
Net diffusion
___________________________________ Equilibrium
Equilibrium
Net diffusion
___________________________________ ___________________________________ ___________________________________ Slide 18 Fig. 7-12
Lower
concentration
of solute (sugar)
Higher
concentration
of sugar
___________________________________ Same concentration
of sugar
___________________________________ H2O
Selectively
permeable
membrane
___________________________________ Water bound to sugar
creates less “free” water
OSMOSIS: the special
case of water (solvent)
diffusion.
___________________________________ Osmosis
___________________________________ ___________________________________ ___________________________________ Slide 19 ___________________________________ Water Balance of Cells
• Tonicity is the ability of a solution to cause a cell to gain or
lose water (e.g., potato in lab)
–
Considers both solute concentration, and
–
Membrane permeability
–
Depends on concentration of non-penetrating solutes
___________________________________ ___________________________________ • Isotonic solution: Solute concentration is the same as that
inside the cell; no net water movement across the plasma
membrane
• Hypertonic solution: Solute concentration is greater than
that inside the cell; cell loses water
___________________________________ • Hypotonic solution: Solute concentration is less than that
inside the cell; cell gains water
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
___________________________________ ___________________________________ ___________________________________ Slide 20 Fig. 7-13
Hypotonic solution
H2O
Isotonic solution
H2O
H2O
___________________________________ Hypertonic solution
H2O
___________________________________ (a) Animal
cell
Lysed
H2O
Normal
H2O
Shriveled
H2O
___________________________________ H2O
(b) Plant
cell
Turgid (normal)
Flaccid
___________________________________ Plasmolyzed
___________________________________ ___________________________________ ___________________________________ Slide 21 ___________________________________ Water Balance of Cells with Walls
• Cell walls help maintain water balance
___________________________________ • A plant cell in a hypotonic solution swells until the
wall opposes uptake; the cell is now turgid (firm)
• If a plant cell and its surroundings are isotonic,
there is no net movement of water into the cell; the
cell becomes flaccid (limp), and the plant may wilt
___________________________________ • In a hypertonic environment, plant cells lose
water; eventually, the membrane pulls away from
the wall, a usually lethal effect called plasmolysis
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 22 • Hypertonic or hypotonic environments can
create osmotic problems
___________________________________ • Osmoregulation, the control of water balance,
is a necessary adaptation for life in such
environments
___________________________________ • The protist Paramecium, which is hypertonic to
its pond water environment, has a contractile
vacuole that acts as a pump
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
___________________________________ ___________________________________ ___________________________________ Slide 23 Fig. 7-14
Filling vacuole
___________________________________ 50 µm
___________________________________ (a) A contractile vacuole fills with fluid that enters from
a system of canals radiating throughout the cytoplasm.
___________________________________ Contracting vacuole
___________________________________ (b) When full, the vacuole and canals contract, expelling
fluid from the cell.
___________________________________ ___________________________________ ___________________________________ Slide 24 ___________________________________ Transmembrane ‘Transport Proteins’ can help
hydrophilic substances cross the membrane
1. Facilitated Diffusion
___________________________________ 1. Aqueous channels for charged or polar molecules to diffuse
through
- or 2. Passive carrier mechanisms that move molecules from higher to
lower concentration – usually in either direction
___________________________________ 2. Active Transport
1. ATP-dependent carrier that can move charged or polar molecules
against their concentration gradient
___________________________________ 3. All Transport Proteins are very specific for their molecules
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 25 Fig. 7-17
Passive transport
___________________________________ Active transport
___________________________________ ___________________________________ ATP
Diffusion
Facilitated diffusion
___________________________________ Both passive and active carrier
proteins undergo a change in shape
that opens the solute-binding site on
the pother side of the membrane
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 26 • Channel proteins include
___________________________________ – Aquaporins, for facilitated diffusion of water
– Ion channels that open or close in response to a
stimulus (gated channels)
___________________________________ What kind of “gating” have you heard about?
_____________________________________________
___________________________________ _____________________________________________
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 27 • Active transport allows cells to maintain concentrations of
things different from what would occur naturally
–
We have calcium pumps, hydrogen ion pumps and
sodium-potassium pumps, among others
–
We also have glucose transporters and amino acid
transporters – even large protein transporters
___________________________________ ___________________________________ Why do you think a cell would want to do that?
___________________________________ ion pumps?_____________________________________
transporters?____________________________________
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 28 • What other way have we already learned that
big molecules, like proteins, lipids and
carbohydrates, can be moved in or out or
around within a cell?
___________________________________ _____________________________________
___________________________________ _____________________________________
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 29 Bulk transport across the plasma membrane
occurs by exocytosis and endocytosis
___________________________________ • Small molecules and water enter or leave the
cell through the lipid bilayer or by transport
proteins
___________________________________ • Large molecules, such as polysaccharides and
proteins, cross the membrane in bulk via
vesicles
___________________________________ • Bulk transport requires energy
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings
___________________________________ ___________________________________ ___________________________________ Slide 30 Fig. 7-16-1
___________________________________ EXTRACELLULAR FLUID
Example:
Active
Transport
[Na+]
high
[K+] low
___________________________________ Na+
Na+
- natural
gradients?
___________________________________ CYTOPLASM
Na+
[Na+] low
[K+] high
1
Cytoplasmic Na+ binds to
the sodium-potassium pump.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 31 Fig. 7-16-2
___________________________________ ___________________________________ Na+
Na+
Na+
P
ADP
___________________________________ ATP
2 Na+ binding stimulates
phosphorylation by ATP.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 32 Fig. 7-16-3
___________________________________ Na+
Na+
___________________________________ Na+
___________________________________ P
3 Phosphorylation causes
the protein to change its
shape. Na+ is expelled to
the outside.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 33 Fig. 7-16-4
___________________________________ ___________________________________ ___________________________________ P
P
4 K+ binds on the
extracellular side and
triggers release of the
phosphate group.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 34 Fig. 7-16-5
___________________________________ ___________________________________ ___________________________________ 5 Loss of the phosphate
restores the protein’s original
shape.
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 35 Fig. 7-16-6
___________________________________ ___________________________________ ___________________________________ K+
is released, and the
cycle repeats.
___________________________________ Why do we want Na+ outside of the cell and K+ inside?
___________________________________ ___________________________________ ___________________________________ Slide 36 Neurons and muscle cells in animals and phloem
cells in plants rely on electrical signaling.
___________________________________ • Electricity is the energy created by the movement of
charged particles – it’s named for the example of electrons
___________________________________ • When a cell uses electricity it does it by allowing ions that it
has concentrated by active transport to rush from one side
of the membrane to the other through channel proteins
___________________________________ • The opening and closing of the channels determines when
the electrical current is flowing
• Voltage is a measure of how many ions are on the move
___________________________________ • Membrane potential is a measure of how many ions have
been actively concentrated across a membrane
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 37 • Concentrated ions diffuse faster than
uncharged molecules
___________________________________ • Two combined forces, collectively called the
electrochemical gradient, drive the diffusion
of ions across a membrane:
___________________________________ – A chemical force (the ion’s concentration
gradient)
– An electrical force (the effect of the membrane
potential on the ion’s movement)
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 38 • An electrogenic pump is a transport protein
that generates voltage across a membrane
___________________________________ • The sodium-potassium pump is the major
electrogenic pump of animal cells
___________________________________ • The main electrogenic pump of plants, fungi,
and bacteria is a proton pump
• Mitochondria and chloroplasts use a proton
pump to help make ATP
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 39 Fig. 7-18
___________________________________ –
ATP
EXTRACELLULAR
FLUID
+
–
+
___________________________________ H+
H+
Proton pump
H+
–
+
___________________________________ H+
H+
–
+
CYTOPLASM
–
___________________________________ H+
+
Where else have you heard of a proton pump?
___________________________________ ___________________________________ ___________________________________ Slide 40 Cotransport: Coupled Transport by a Membrane
Protein
___________________________________ • Cotransport occurs when active transport of a
solute indirectly drives transport of another
solute
___________________________________ • Plants commonly use the gradient of hydrogen
ions generated by proton pumps to drive active
transport of nutrients into the cell
___________________________________ ___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 41 Fig. 7-19
–
+
–
___________________________________ H+
ATP
H+
+
H+
Proton pump
___________________________________ H+
–
H+
+
–
H+
+
___________________________________ H+ Diffusion
of H+
Sucrose-H+
cotransporter
H+
Sucrose
–
–
___________________________________ +
+
Sucrose
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 42 • In receptor-mediated endocytosis, binding of
ligands to receptors triggers vesicle formation
___________________________________ • A ligand is any molecule that binds specifically
to a receptor site of another molecule
___________________________________ ___________________________________ Animation: Receptor-Mediated Endocytosis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ Slide 43 Fig. 7-20c
___________________________________ RECEPTOR-MEDIATED ENDOCYTOSIS
Coat protein
Receptor
Coated
vesicle
___________________________________ Coated
pit
Ligand
___________________________________ A coated pit
and a coated
vesicle formed
during
receptormediated
endocytosis
(TEMs)
Coat
protein
___________________________________ Plasma
membrane
0.25 µm
___________________________________ ___________________________________ ___________________________________ Slide 44 Fig. 7-UN3
___________________________________ What will happen?
“Cell”
0.03 M sucrose
0.02 M glucose
___________________________________ Environment:
0.01 M sucrose
0.01 M glucose
___________________________________ 0.01 M fructose
___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 45 ___________________________________ You should now be able to:
1. Define the following terms: amphipathic
molecules, aquaporins, diffusion
___________________________________ 2. Explain how membrane fluidity is influenced
by temperature and membrane composition
___________________________________ 3. Distinguish between the following pairs or
sets of terms: peripheral and integral
membrane proteins; channel and carrier
proteins; osmosis, facilitated diffusion, and
active transport; hypertonic, hypotonic, and
isotonic solutions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Slide 46 4. Explain how transport proteins facilitate
diffusion
___________________________________ 5. Explain how an electrogenic pump creates
voltage across a membrane, and name two
electrogenic pumps
___________________________________ 6. Explain how large molecules are transported
across a cell membrane
___________________________________ Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
___________________________________ ___________________________________ ___________________________________