Selective BarrierSelective Barrier

Transport Systems

Transport Systems

Cell Signaling

Cell Signaling

Membrane FunctionsMembrane Functions

Enzyme Systems for Energy Metabolism

Enzyme Systems for Energy Metabolism

Membranes create cell compartments through selective permeability. Cell compartments can have individually controlled pH, molecular concentrations, and charge differential.

Receptor proteins allow: Cell-cell recognition. Cell signaling.

Membranes can control reaction sequences.

Charge differences across membranes can send nerve impulses and drive cell reactions.

Membranes create cell compartments through selective permeability. Cell compartments can have individually controlled pH, molecular concentrations, and charge differential.

Receptor proteins allow: Cell-cell recognition. Cell signaling.

Membranes can control reaction sequences.

Charge differences across membranes can send nerve impulses and drive cell reactions.

Membrane FunctionsMembrane Functions

Membranes are composed of lipids and proteins.

Lipids provide the structure and proteins provide the function.

Membrane ComponentsMembrane

Components

Electron micrograph ofmyelin inner membrane.

Myelin insulatesthe charge on nervefibers.

Electron micrograph ofmyelin inner membrane.

Myelin insulatesthe charge on nervefibers.

Phospholipidscholesterolphospholipid bilayerfluid mosaic modelglycolipidsglycoproteins

Phospholipidscholesterolphospholipid bilayerfluid mosaic modelglycolipidsglycoproteins

MembraneComponen

ts

MembraneComponen

ts

Membrane PropertiesMembrane Properties

FluidityPermiabilityInside vs OutsideTransport PropertiesCharge and pH

FluidityPermiabilityInside vs OutsideTransport PropertiesCharge and pH

Membrane PropertiesMembrane Properties

In general, the phospholipids and proteins in membranes are free tomove laterally but, only very rarelyflip.

In general, the phospholipids and proteins in membranes are free tomove laterally but, only very rarelyflip.

How do we know that?How do we know that?

One way is from making mouse-human hybrid cells.One way is from making mouse-human hybrid cells.

Add PEG or Sendai virus

Freeze fracture lets you “cut” membranes in half and see each phospholipid leaflet.

Freeze fracture lets you “cut” membranes in half and see each phospholipid leaflet.

Membrane FluidityMembrane Fluidity

Which part of a membrane gives it its fluid characteristics?

Which part of a membrane gives it its fluid characteristics?

Membranes must remain fluid for assembly and biological functions

Bacteria and yeast adapt to varying temperatures by changing the lengths and the unsaturation of their tails more unsaturation = more fluid

Animal cells regulate fluidity with cholesterol

Membranes must remain fluid for assembly and biological functions

Bacteria and yeast adapt to varying temperatures by changing the lengths and the unsaturation of their tails more unsaturation = more fluid

Animal cells regulate fluidity with cholesterol

The most common fatty acid is palmitate.The most common fatty acid is palmitate.

CholesterolCholesterolPlasma

membranes have nearly one

cholesterol per phospholipid molecule.

Plasma membranes have

nearly one cholesterol per phospholipid molecule.

Cholesterol makes the lipid bilayer lessdeformable and decreases its permeability to small water-soluble molecules by partially immobilizing the phospholipid molecules next to each cholesterol molecule.

Without cholesterol, animal cells would need cell walls.

Cholesterol makes the lipid bilayer lessdeformable and decreases its permeability to small water-soluble molecules by partially immobilizing the phospholipid molecules next to each cholesterol molecule.

Without cholesterol, animal cells would need cell walls.

What feature in a membrane helps to prevent freezing?

What feature in a membrane helps to prevent freezing?

Short chainfatty acids melt at a lower temperature thanlong chains.

Unsaturated fatty acidsremain fluid at lower temperaturesthan saturated fatty acids.

Short chainfatty acids melt at a lower temperature thanlong chains.

Unsaturated fatty acidsremain fluid at lower temperaturesthan saturated fatty acids.

Permeabili

ty

Permeabili

ty

Membranes are impermeable to certain molecules.

How do these molecules enter the cell?

Protein Glycosylation

Protein Glycosylation

Oligosaccharide side chains (sugars) are added to many proteins in the ER and are then modified in the Golgi apparatus.

Glycosylation serves various functions including protection from degradation, transport and packaging signals, and cell communication when displayed on the outer membrane.

In glycolipids, as with glycoproteins, the sugar portions of the molecule are facing the extracellular space.

In glycolipids, as with glycoproteins, the sugar portions of the molecule are facing the extracellular space.

Membrane Structure Review

Describe the fluid mosaic model of membrane structure.

What is the most abundant lipid in membranes?

How do bacteria and yeast modulate membrane fluidity?

How do animal cells modulate fluidity?

Describe the fluid mosaic model of membrane structure.

What is the most abundant lipid in membranes?

How do bacteria and yeast modulate membrane fluidity?

How do animal cells modulate fluidity?

Cell Membran

e Function

Cell Membran

e Function Transport

Recognition

Cell Signaling

Transport

Recognition

Cell Signaling

Bulk Transport

Endocytosis

Exocytosis

Pinocytosis

Bulk Transport

Endocytosis

Exocytosis

Pinocytosis

(figure adapted from Alberts et al.,1994, Molecular Biology of the Cell)

The role of clathrin, adaptin and yolk protein receptors in the internalization of yolk proteins by developing oocytes.

(figure adapted from Alberts et al.,1994, Molecular Biology of the Cell)

Adaptin binds cytoplasmic tail of receptor.

Adaptin binds cytoplasmic tail of receptor.

(figure adapted from Alberts et al.,1994, Molecular Biology of the Cell)

Clathrin binds adaptin deforming membrane to form bud.

Clathrin binds adaptin deforming membrane to form bud.

FROM GENE TO DNA TECHNOLOGY

FROM GENE TO DNA TECHNOLOGY

Case Study: Familial HYPERCHOLESTEROLEMIACase Study: Familial HYPERCHOLESTEROLEMIA

References:

The information about “FH” on these slides is excerpted from Online MendelianInheritance in Manhttp://www.ncbi.nlm.nih.gov/Omim/

RFLPgene mappingcDNAPCRin-situ hybridizationgene cloning“knock-out” genesgene therapy

RFLPgene mappingcDNAPCRin-situ hybridizationgene cloning“knock-out” genesgene therapy

Familial HYPERCHOLESTEROLEMIAFamilial HYPERCHOLESTEROLEMIA

BackgroundBackground

an autosomal dominant disorder characterized by elevation of serum cholesterol bound to low-density lipoprotein (LDL), resulting in markedly increased cholesterol level and an increased incidence of early onset of atherosclerosis and its complications.

Mutations in the LDL receptor (LDLR) gene on chromosome 19 cause this disorder.

Occurance: about 7 out of 1000 people.

The LDL receptor was discovered through an extraordinary collaboration between two extraordinary scientists, Michael S. Brown and Joseph L. Goldstein.

The LDL receptor was discovered through an extraordinary collaboration between two extraordinary scientists, Michael S. Brown and Joseph L. Goldstein.

Cells that need cholesterol synthesize LDL receptors. Cells that need cholesterol synthesize LDL receptors.

from Alberts et al. Molecular Biology of the Cell, Garland Publishing, Third edition, 1994.

Clathrin PitsClathrin Pits

Molecular Transport

Passive DiffusionFacilitated DiffusionActive Transport

Molecular Transport

Passive DiffusionFacilitated DiffusionActive Transport

Gap Junctions allow

communication between cells.

Small molecules and ions can pass

through.

Gap Junctions allow

communication between cells.

Small molecules and ions can pass

through.