Origin of Eukaryotes

Membrane Structure● The plasma membrane separates the living cell from its nonliving surroundings.

(a) Phospholipid bilayer ofmembrane

(b) Fluid mosaic model ofmembrane

Outside of cell Outside of cellHydrophilicheadHydrophobictail

Hydrophilicregion ofprotein

Hydrophilichead

Hydrophobictail

Hydrophobicregions ofprotein

Phospholipidbilayer

Phospholipid

Proteins

Cytoplasm (inside of cell)

Cytoplasm (inside of cell)

Membrane Structure

Membrane Structure● Phospholipid structure

Phospholipids are amphipathic molecules

Membrane Structure

Membrane Models:

1935 Today

*Membranes are fluid

Membrane Structure

Membranes are fluid

Membrane Structure

Membrane Structure

Fibers ofextracellularmatrix

Cytoskeleton Cytoplasm

Attachment tocytoskeleton andextracellularmatrix

a

b Cell signaling

c

d

Enzymatic activity

Transport

e Intercellularjoining f Cell-cell

recognition

Cytoplasm

● Some functions of membrane proteins

● Cell surface – Extracellular Matrix

Membrane Structure

Membrane Transport

Membrane Transport• Diffusion – a process in which molecules move from an

area of high concentration to an area of low concentration Molecules of dye Membrane

(a) Passive transport of one type of molecule

Net diffusion Net diffusion Equilibrium

Membrane TransportAnimal cell

Plant cell

Normal

Flaccid (wilts)

Lysing

Turgid

Shriveled

Shriveled

Plasmamembrane

H2OH2O H2O H2O

H2OH2OH2O H2O

(a) Isotonicsolution

(b) Hypotonicsolution

(c) Hypertonicsolution

Facilitated diffusion

Membrane Transport

Membrane Transport–Active transport requires energy to move molecules across a membrane.

Lower solute concentration

Higher solute concentration

ATP

Solute

*Active transport

Example: sodium-potassium pump

Membrane Transport

Electrogenic pump:

*Some ion pumps generate voltage across membranes

*Voltage*Membrane potential

Membrane Transport

*Each cell membrane has characteristic set of carrier proteins

Membrane Transport

Passive Transport(requires no energy)

Active Transport(requires energy)

Diffusion Facilitated diffusion OsmosisHigher solute concentration

Lower solute concentration

Higher water concentration(lower solute concentration)

Lower water concentration(higher solute concentration)

Solute

Higher soluteconcentration

Lower soluteconcentration

ATP

Solu

te

Solu

te

Wat

er

Solu

te

MEMBRANE TRANSPORT

Traffic of Large Molecules–Exocytosis is the secretion of large molecules within vesicles.

Outside of cell

Cytoplasm

Plasmamembrane

Traffic of Large Molecules–Endocytosis takes material into a cell within vesicles that bud inward from the plasma membrane.

*Phagocytosis

Exocytosis

*Pinocytosis

*Receptor-mediated endocytosis

Endocytosis

Transport of large moleculesTypes of endocytosis found in animal cells: