Download Membrane structure, I

Lecture Cell
Chapters 5 and 6
Biological Membranes
and
Cell Communication
Membrane structure, I
 Selective permeability
 Amphipathic~
hydrophobic & hydrophilic
regions
 Singer-Nicolson:
fluid mosaic model
Carbohydrate
chains
Glycoprotein
Carbohydrate
chain
Extracellular
fluid
Hydrophobic
Hydrophilic
Glycolipid
Cholesterol
Hydrophilic
Cytosol
α-helix
Peripheral
protein
Integral
proteins
Fig. 5-6, p. 111
Membrane structure, II




Phospholipids~ membrane fluidity
Cholesterol~ membrane stabilization
“Mosaic” Structure~
Integral proteins~ transmembrane
proteins
 Peripheral proteins~ surface of
membrane
 Membrane carbohydrates ~ cell to
cell recognition;
oligosaccharides (cell markers);
glycolipids; glycoproteins
Hydrophilic
region of protein
Hydrophobic
region of protein
Phospholipid
bilayer
Peripheral
protein
Integral
(transmembrane)
protein
(b) Fluid mosaic model. According to this model, a cell
membrane is a fluid lipid bilayer with a constantly changing
“mosaic pattern“ of associated proteins.
Fig. 5-2b, p. 108
The Lipid Bilayer
Lipids of the bilayer

fluid or liquid-crystalline state
Proteins move within the membrane
Membrane Proteins
Functions of
Membrane Proteins
Membrane traffic
Diffusion~ tendency of
any molecule to spread out
into available space
Concentration gradient
Passive transport~
diffusion of a substance
across a biological
membrane without using
energy
Osmosis~ the diffusion of
water across a selectively
permeable membrane
Diffusion
Osmosis
Pressure applied
to piston to resist
upward movement
Water
plus
solute
Pure water
Selectively
permeable
membrane
Molecule
of solute
Water
molecule
Fig. 5-12, p. 117
Water balance
 Osmoregulation~ control
of water balance
 Hypertonic~ higher
concentration of solutes
 Hypotonic~ lower
concentration of solutes
 Isotonic~ equal
concentrations of solutes
 Cells with Walls:
 Turgid (very firm)
 Flaccid (limp)
 Plasmolysis~ plasma
membrane pulls away from
cell wall
Osmotic
Pressure
Outside
cell
Inside
cell
H20
molecules
Solute
No net water molecules
movement
(a) Isotonic solution.
When a cell is placed in an
isotonic solution, water
molecules pass in and out
of the cell, but the net
movement of water
molecules is zero.
Fig. 5-13a, p. 118
Outside
cell
Inside
cell
Net water movement
out of the cell
(b) Hypertonic solution.
When a cell is placed in a
hypertonic solution, there
is a net movement of
water molecules out of the
cell (blue arrow). The cell
becomes dehydrated and
shrunken.
Fig. 5-13b, p. 118
Outside
cell
Inside
cell
Net water movement
into the cell
(c) Hypotonic solution.
When a cell is placed in a
hypotonic solution, the net
movement of water
molecules into the cell
(blue arrow) causes the cell
to swell or even burst.
Fig. 5-13c, p. 118
Turgor and
Plasmolysis
Plasma
membrane
Nucleus
Cytoplasm
Plasma
membrane
Vacuole
Vacuole
Vacuolar
membrane
(tonoplast)
Fig. 5-14, p. 119
Specialized Transport
 Transport proteins
 Facilitated diffusion~
passage of molecules and
ions with transport
proteins across a
membrane down the
concentration gradient
 Active transport~
movement of a substance
against its concentration
gradient with the help of
cellular energy
Facilitated Diffusion
Outside cell
Glucose
High
concentration
of glucose
Low
concentration
of glucose
Glucose
transporter
(GLUT 1)
Cytosol
1
Glucose binds to GLUT 1.
Fig. 5-16a, p. 120
2 GLUT 1 changes shape and
glucose is released inside cell.
Fig. 5-16b, p. 120
3 GLUT 1 returns to its original
shape.
Fig. 5-16c, p. 120
Types of Active Transport
 Sodium-potassium pump
 Exocytosis~ secretion of
macromolecules by the fusion of
vesicles with the plasma
membrane
 Endocytosis~ import of
macromolecules by forming new
vesicles with the plasma
membrane
•phagocytosis
•pinocytosis
•receptor-mediated
endocytosis (ligands)
Higher
Outside
cell
Active
transport
channel
Sodium
concentration gradient
Lower
Lower
Cytosol
Higher
(a) The sodium–potassium pump is a carrier protein that requires
energy from ATP. In each complete pumping cycle, the energy of
one molecule of ATP is used to export three sodium ions (Na+)
and import two potassium ions (K+).
Fig. 5-17a, p. 121
2. Phosphate group is
transferred from ATP
to transport protein.
3. Phosphorylation
causes carrier protein
to change shape, releasing
3 Na+ outside cell.
1. Three Na+ bind
to transport protein.
4. Two K+ bind to
transport protein.
6. Phosphate release causes 5. Phosphate is released.
carrier protein to return
to its original shape. Two
K+ ions are released inside
cell.
Fig. 5-17b, p. 121
Phagocytosis
Large particles enter cell
Receptor-Mediated
Endocytosis
Intracellular junctions
 PLANTS:
 Plasmodesmata:
cell wall perforations; water and
solute passage in plants
 ANIMALS:
 Tight junctions~ fusion of
neighboring cells; prevents
leakage between cells
 Desmosomes~ riveted,
anchoring junction; strong
sheets of cells
 Gap junctions~ cytoplasmic
channels; allows passage of
materials or current between
cells
Tight Junctions
Gap Junctions
Cell Signaling
1. Synthesis, release, transport of signaling
molecules
-
neurotransmitters, hormones, etc
ligand binds to a specific receptor
2. Reception of information by target cells
Cell Signaling
3. Signal transduction
-
-
receptor converts extracellular signal into
intracellular signal
causes change in the cell
4. Response by the cell
Cell
Signaling
1 Cell sends
signal
Signaling
molecules
Receptor
2 Reception
Signaling
protein
3 Signal
transduction
Protein
4 Response
Altered
membrane
permeability
Enzyme
Altered
metabolism
Protein that
regulates a gene
Altered
gene activity
Fig. 6-2, p. 136
Local Regulators
Paracrine regulation


diffuse through interstitial fluid
act on nearby cells
Local regulators




histamine
growth factors
prostaglandins
nitric oxide
Local Signals
Neurotransmitters
Chemical signals

released by neurons (nerve cells)
Hormones
Chemical messengers

in plants and animals
Secreted by endocrine glands

in animals
Transported by blood

to target cells
Hormones