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 cell
Hydrophilichead
Hydrophobictail
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 Transport
Animal 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 Osmosis
Higher solute concentration
Lower solute concentration
Higher water concentration(lower solute concentration)
Lower water concentration(higher solute concentration)
Solute
Higher soluteconcentration
Lower soluteconcentration
ATP
So
lute
So
lute
Wat
er
So
lute
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: