Glyco-

proteinCarbohydrate

Glycolipid

Microfilaments

of cytoskeleton

EXTRACELLULAR

SIDE OF

MEMBRANE

CYTOPLASMIC SIDE

OF MEMBRANE

Integral

protein

Peripheral

proteins

Cholesterol

Fibers of extra-

cellular matrix (ECM)

Ch 5. Cell Membrane• Phospholipid bilayer• Cholesterol• Protein• Carbohydrates (on lipid or protein)

• Cell boundary• 8 ƞm thick• Selective permeable• Hydrophobic interaction• 1972 Singer & Nicholson

• Fluid mosaic model

Membrane Structure

•

Which of the following best describes the structure of a biological

membrane?

a) two layers of phospholipids with proteins embedded between the two layers

b) a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot

c) two layers of phospholipids with proteins either crossing the layers or on the surface of the layers

d) a fluid structure in which phospholipids and proteins move freely between sides of the membrane

e) two layers of phospholipids (with opposite orientations of the phospholipids in each layer) with each layer covered on the outside with proteins

Figure 7.4

Knife

Plasma membrane Cytoplasmic layer

Proteins

Extracellular

layer

Inside of extracellular layer Inside of cytoplasmic layer

TECHNIQUE

RESULTS

Freeze Fracturing

• 1972 Singer & Nicholson Fluid mosaic model confirmation

• 1935 Davson & Danielli

Figure 7.3

Phospholipid

bilayer

Hydrophobic regions

of proteinHydrophilic

regions of protein

1972 Fluid Mosaic Model• Amphipatic phospholipids & proteins

Figure 7.2Hydrophilic

head

Hydrophobic

tail

WATER

WATER

Fluid Mosaic Model1) Phospholipids

• Amphipatic

• hydrophilic & hydrophobic

Figure 7.6

Lateral movement occurs

107 times per second.

Flip-flopping across the membrane

is rare ( once per month).

Fluid Mosaic Model

1) Phospholipids

• Amphipatic

• Movement

• Lateral

• Flip-flopping

Figure 7.8Fluid

Unsaturated hydrocarbon

tails

Viscous

Saturated hydrocarbon tails

(a) Unsaturated versus saturated hydrocarbon tails

(b) Cholesterol within the animal

cell membrane

Cholesterol

Fluid Mosaic Model

1) Phospholipids

• Amphipatic

• Movement

• Fatty Acid Tails

• Saturated vs Unsaturated

2) Cholesterol

• Warm vs cold

Membrane Lipids and Fluidity

An animal cell membrane will be

more fluid at room temperature if it

contains

a) more cholesterol.

b) longer chain fatty acids.

c) more cis-unsaturated and polyunsaturated fatty acids.

d) more trans-unsaturated fatty acids.

e) any of the above

Glyco-

proteinCarbohydrate

Glycolipid

Microfilaments

of cytoskeleton

EXTRACELLULAR

SIDE OF

MEMBRANE

CYTOPLASMIC SIDE

OF MEMBRANE

Integral

protein

Peripheral

proteins

Cholesterol

Fibers of extra-

cellular matrix (ECM)

Cell Membrane

Fluid Mosaic Model• Phospholipid bilayer

• Cholesterol

Fluid Mosaic Model• Protein (integral & peripheral)

• Carbohydrates (on lipid or protein)

Figure 7.9

N-terminus

helix

C-terminus

EXTRACELLULAR

SIDE

CYTOPLASMIC

SIDE

Fluid Mosaic Model

3. Proteins

• Intergral proteins

• amphipatic

Figure 7.7

Membrane proteins

Mouse cellHuman cell

Hybrid cell

Mixed proteins

after 1 hour

RESULTS

Membrane Proteins

Membrane Protein Functions

1) Transport• Uniport: 1 in 1 direction

• Symport: 2 in same direction

• Antiport: 2 in opposite directions

• Carrier proteins• Pumps

• Facilitated diffusion

• Ion channels• Na+, K+, Ca++, Cl-.

Membrane Protein Functions

2) Receptor site

• For chemical messengers

• Cellular recognition

3) Signal transduction

Glyco-

protein

Membrane Protein Functions

4) Enzymatic• Chemical rxn

• Energy production

• Signal transduction

Figure 7.11

Receptor(CD4)

Co-receptor(CCR5)

HIV

Receptor (CD4)but no CCR5 Plasma

membrane

HIV can infect a cell thathas CCR5 on its surface,as in most people.

HIV cannot infect a cell lackingCCR5 on its surface, as in resistant individuals.

Receptor protein & binding HIV+ & Leukemia

Membrane Protein Functions

5) Cytoskeleton attachment• Cell shape

• Coordinate extracellular & intracellular changes

Membrane Protein Functions

6) Cell adhesion

Figure 7.10

Enzymes

Signaling molecule

Receptor

Signal transduction

Glyco-

protein

ATP

(a) Transport (b) Enzymatic activity (c) Signal transduction

(d) Cell-cell recognition (e) Intercellular joining (f) Attachment to

the cytoskeleton

and extracellular

matrix (ECM)

Fluid Mosaic Model

4) Carbohydrates

Glycoproteins

Glycolipids

• Function:

Cell-cell recognition

Organ donor/blood type

Glyco-

protein

Transmembrane Domains

Which of the following amino acids

would most likely be present in the

transmembrane domain of an integral

membrane protein?

a) a charged amino acid like lysine

b) a polar amino acid like serine

c) a special amino acid like glycine or proline

d) a hydrophobic amino acid like valine

e) any of the above, with no preference

Figure 7.12

Transmembraneglycoproteins

ER

ER lumen

Glycolipid

Plasma membrane:

Cytoplasmic face

Extracellular face

Secretoryprotein

Golgiapparatus

Vesicle

Transmembraneglycoprotein Secreted

protein

Membraneglycolipid

Endomembrane System & sidedness

Membrane Synthesis and Sidedness

An oligosaccharide covalently linked to a

lipid in the lumen of the rough ER may

end up on the

a) cytoplasmic face of the plasma membrane.

b) extracellular face of the plasma membrane.

c) cytoplasmic face of a secretory vesicle.

d) any of the above

Membrane Permeability & Transport• Size:

– Small molecules

• Charge:

– Uncharged easy

– Charged: can not

• Lipid solubility

– Hydrophobic molecules

• Carrier proteins

– Assist small charged

– Assist non-soluble

Glyco-

proteinCarbohydrate

Glycolipid

Microfilaments

of cytoskeleton

EXTRACELLULAR

SIDE OF

MEMBRANE

CYTOPLASMIC SIDE

OF MEMBRANE

Integral

protein

Peripheral

proteins

Cholesterol

Fibers of extra-

cellular matrix (ECM)

Molecules of dyeMembrane (cross section)

WATER

(a) Diffusion of one solute

Net diffusion Net diffusion Equilibrium

Membrane Transport

Simple Diffusion (single molecule):• [High] [Low]

• Down its [gradient]

• Passive no energy

Figure 5.8 – Diffusion through membranes

(b) Diffusion of two solutes

Net diffusion Net diffusion

Net diffusion Net diffusion

Equilibrium

Equilibrium

Membrane Transport

Simple Diffusion (two molecules):• [High] [Low]

• Down its [gradient]

• Passive no energy

• Facilitated diffusion• Carrier protein

• Channel protein

• Passive no energy

• Ions, water

Passive transport:Facilitated diffusion

Channelprotein

Carrierprotein

Membrane Transport

Figure 7.17

EXTRACELLULARFLUID

CYTOPLASM

Channel proteinSolute

SoluteCarrier protein

(a) A channelprotein

(b) A carrier protein

Membrane Transport

• Osmosis• Diffusion of water

• Across a selectively permeable

membrane

• Passive

• Hypotonic• Lower [solute] & High [H2O]

• Isotonic• Equal/same [solute] &

equal/same [H2O]

• Hypertonic• Higher [solute] & Low [H2O]

Hypotonic hypertonic

Membrane Transport

Figure 7.14

Lowerconcentrationof solute (sugar)

Higher concentrationof solute

Sugarmolecule

H2O

Same concentrationof solute

Selectivelypermeablemembrane

Osmosis

MembraneTransportFigure 5.11

• Isotonic solution

Equal/same [solute]

Inside cell: 3% NaCl, 97% H2O

Beaker: 3% NaCl, 97% H2O

Animal cells = Normal

Plant cells = Normal

3% NaCl

97% H2O

Membrane Transport - Osmosis

• Hypotonic solution

Lower [solute] Inside cell: 3% NaCl, 97% H2O

Beaker: 3% NaCl, 97% H2O

H2O: more IN than out

Plant cells turgid

Animal cells burst/lyse

Why? 1% NaCl

99% H2O

Membrane Transport - Osmosis

• Hypertonic solution

Higher [solute]

Inside cell: 3% NaCl, 97% H2O

Beaker: 5% NaCl, 95% H2O

H2O: more OUT than in

Animal cells shrinks

Plant cells plasmolysis 5% NaCl

95% H2O

Membrane Transport - Osmosis

Osmosis – hypertonic solutions

• Animal cells

Shrinks/shrivels

• Plant cells

Plasmolysis

• Cell membrane separates from

cell wall

5% NaCl

95% H2O

Figure 7.15

Hypotonicsolution

Osmosis

Isotonicsolution

Hypertonicsolution

(a) Animal cell

(b) Plant cell

H2O H2O H2O H2O

H2O H2O H2O H2OCell wall

Lysed Normal Shriveled

Turgid (normal) Flaccid Plasmolyzed

Membrane Transport - Osmosis

Figure 5.12

Figure 5.13

Osmosis

If a marine algal cell is suddenly

transferred from seawater to freshwater,

the algal cell will initially

a) lose water and decrease in volume.

b) stay the same: neither absorb nor lose water.

c) absorb water and increase in volume.

Membrane Transport• Active Transport

• [lower] [higher]

• Against [gradient]

• Carrier protein

• REQUIRES energy

Figure 7.18-6

EXTRACELLULAR

FLUID[Na] high

[K] low

[Na] low

[K] highCYTOPLASM

Na

Na

Na

1 2 3

456

Na

Na

Na

Na

Na

Na

K

K

K

K

K

K

PP

PP i

ATP

ADP

Active transport – Na+/K+ pump

Figure 7.19

3 types of Passive transport Active transport

Diffusion Facilitated diffusion ATP

Figure 5.18 – Active Transport

• Primary active transport moves ions across a membrane, creating an electrochemical

gradient (electrogenic transport). (credit: modification of work by Mariana Ruiz Villareal)

Resting Membrane Potential

• Unequal distribution of

ions (Na+/K+/Cl-/A-)

• Separation of ions

• Movement of ions due

to leak channels• Concentration gradient

• Electrical charge

• Electrochemical gradient

• Excitable cells (nerve &

muscle)

Figure 5.16 – Electrochemical gradient

Active transport & electrochemical gradient

Ion distribution across the membrane

Figure 48.7KeyNa

K

Sodium-potassiumpump

Potassiumchannel

Sodiumchannel

OUTSIDEOF CELL

INSIDEOF CELL

Resting Membrane Potential

For a nerve cell at its resting

potential, the forces acting on

potassium ions (K+) area) none: K+ ions do not move at the resting potential.

b) an electrical gradient, pulling K+ inward, and a

chemical gradient, pushing K+ outward.

c) an electrical gradient, pushing K+ outward, and a

chemical gradient, pulling K+ inward.

d) an electrical gradient, pulling K+ inward, and a

chemical gradient, pushing K+ outward.

e) an electrical gradient, pushing K+ outward, and a

chemical gradient, pushing K+ outward.

Figure 7.20

CYTOPLASM

ATP EXTRACELLULAR

FLUID

Proton pumpH

H

H

H

H

H

Type of transporter?

What’s a “pump?”

Figure 7.21

ATP

H

H

HH

H

H

H

H

Proton pump

Sucrose-H

cotransporter

SucroseSucrose

Diffusion of H

Co-transportType of transporters?

Solutes

Pseudopodium

“Food” or

other particle

Food

vacuole

CYTOPLASM

Plasma

membrane

Vesicle

Receptor

Ligand

Coat proteins

Coated

pit

Coated

vesicle

EXTRACELLULAR

FLUID

Phagocytosis Pinocytosis Receptor-Mediated Endocytosis

3 types of Bulk Transport for large molecules (Endocytosis)

Figure 5.22

Figure 5.22

Pseudopodium

Solutes

“Food”

or other

particle

Food

vacuole

CYTOPLASM

EXTRACELLULAR

FLUID

Pseudopodium

of amoeba

Bacterium

Food vacuole

An amoeba engulfing a bacterium

via phagocytosis (TEM).

1) Phagocytosis

1

m

Phagocytosis1

Phagocytosis2 = cell eating

Pinocytosis vesicles forming

in a cell lining a small blood

vessel (TEM).

Plasma

membrane

Vesicle

0.5

m

2) Pinocytosis

Pinocytosis = cell drinking

Figure 5.22

Top: A coated pit. Bottom: Acoated vesicle forming duringreceptor-mediated endocytosis(TEMs).

Receptor

0.2

5

m

3) Receptor-Mediated Endocytosis

Ligand

Coat proteins

Coated

pit

Coated

vesicle

Coat

proteins

Plasma

membrane

Receptor mediatedSubstance triggers receptor protein

Figure 5.22

• Large molecules• Endocytosis = in take

1. Phagocytosis = cell eating

2. Pinocytosis = cell drinking

3. Receptor mediatedSubstance triggers receptor protein

Membrane Transport

• Bulk Transport Large molecules out

• Exocytosis – Figure 5.23 Getting rid of substances

Transport vessicle fuses w/ cell membrane

Contractile

vacuole

Membrane Transport

Figure 7.16

Contractile vacuole50 m

Membrane Transport – Contractile Vacuole

c) Photomicrograph showingvarious stages of endocytosis.

a) Endocytosis. In endocytosis, material is surrounded bythe cell membrane and brought into the cell.

Extracellular environment

Plasma membrane

Cytoplasm

Vesicle

b) Exocytosis. In exocytosis, a membranous vesicle fuseswith the plasma membrane, expelling its contents outsidethe cell.

Comparison of endocytosis & exocytosis

Insulin results in the uptake

and lowering of blood sugar

would be an example of?

a) Endocytosis

b) Receptor mediated endocytosis

c) Phagocytosis

d) Pinocytosis

e) exocytosis

The resting membrane potential

results from:

a) An unequal distribution of ions across the cell membrane

b) Separation of ions

c) Osmosis

d) Diffusion

e) Aren’t there two correct answers?