Membranes• Everything in life is variable

– Chaotic

• Membranes organize the chaos of cellular metabolism– E.g. houses & stores with doors & gates– E.g. streets organize traffic

• Selectively permeable– Allows some things in & blocks some

things

• Plasma membrane (cell) – Takes up what cell needs & takes out the

trash

• Thin, requires EM at 200,000x

• 3 zones– Construction of Phospolipids

Phospholipid

• Polar, hydrophilic head– Phosphate group– React and interact with

the environment

• Non-polar, hydrophobic tail– Two-tailed fatty acid

• Relation w/ water = Phospholipid Bi-layer– Non-polar, hydrophobic molecules move more freely

through the membrane (soluble in lipids)• E.g. vessicles and vacuoles transporting packages

throughout membrane system• E.g. soap to clean (breakdown) grease

– Polar molecules & ions not soluble

• Membrane = Fluid mosaic of phospholipids and proteins

• Mosaic– Made up of

many small pieces

• Mosaic = diverse proteins embedded in phospholipids

• Fluid = proteins can drift laterally within bi-layer

• Cholesterol – helps stabilize at body temperature & maintains fluidity at lowered temperatures

• Glycolipids & glycoprotiens– Carbohydrate ID tags

• E.g. immune system recognizes good cells from bacterial cells• E.g. embryonic development – cells differentiate (tissues & organs)

• Proteins – do most of the work

Membrane Proteins• Very diverse

– E.g. >50 different proteins in plasma membrane of human blood cells

• Enzymes – catalyze molecule assembly (e.g. modify by increasing rate)

• Receptors – messengers from other cells (e.g. hormones)

• Transport – allows large molecules to pass

Passive Transport = diffusion

• Diffusion = natural tendency of particles to spread evenly (from high concentration to low concentration) to reach balance

• No energy required

• Many smaller molecules simultaneously

• E.g. O2 and CO2 move in & out of rbc’s

Facilitated Diffusion

• Size or polarity prevents diffusion?

• Protein creates a channel or pore for passage– E.g. sugars, amino

acids, ions, & water

• Down concentration gradient (high conc. to low conc.)

• Passive transport– No energy required

Active Transport

• Spends energy to push solutes against conc. gradient• Passive transport down a gradient is “as easy as falling

in a hole”• But, how do you climb back up/out?• Use the notches/cracks/crevices, but takes energy - ATP

Transport of LARGE molecules

• Exocytosis – transport out of cell– Vesicle (membrane package) fuses with

plasma membrane, opens, releases outside– E.g. salty tears from tear glands

• Endocytosis – reverse of exocytosis– bringing in macromolecules from outside of

plasma membrane– Pinching of membrane to form vesicle

• Phagocytosis – cellular eating– Engulfs food molecules forming a vacuole, fuses with lysosomes

for digestion• E.g. Amoeba

• Pinocytosis – cellular drinking– Vesicles of non-specific liquid

• Receptor mediated endocytosis– Pit forms in plasma membrane that is lined with specific

receptors, pinches closed, releases molecules inside cytoplasm