MEMBRANE STRUCTURE AND FUNCTION

CHAPTER 7 PART 2

CELL-TO-CELL RECOGNITION

• Carbohydrates are often used for ID• Glycolipids – carbs

bound to lipids• Glycoproteins – carbs

bound to proteins (most)

• Important for:• Cell sorting in

embryo• Immune responses• Blood types

MEMBRANE SYNTHESIS

•Molecules on the inside of the ER end up on the outside of the membrane

MEMBRANE PERMEABILITY

Moves easily

• Nonpolar molecules (hydrophobic)• Hydrocarbons, CO2, O2

Doesn’t move easily

• Polar molecules (hydrophilic)• Glucose, water

• Charged molecules surrounded by water• Ions

AQUAPORINS

• 3 billion water molecules per second single file

• Without them, H2O would diffuse slowly through the membrane

DIFFUSION

• Passive Transport – requires no energy• Substances move from high to low concentration• Down the concentration gradient

OSMOSIS

• Diffusion of water across a selectively permeable membrane

• Difference in FREE WATER CONCENTRATION causes it to move

OSMOSIS

CELLS WITHOUT WALLS

• Tonicity – ability of cell to gain or lose water

• Isotonic• “iso” = same• No NET movement

of water• No change in cell

size

CELLS WITHOUT WALLS

• Hypertonic• Hyper = more

(solutes)• Water moves out

• Cell will shrink

CELLS WITHOUT WALLS

• Hypotonic• Hypo = “less”

(solute)• Water moves in• Cell size increases

• Cell will swell and burst

OSMOREGULATION

• Organisms that live in hyper or hypo tonic environments have special adaptations• Ex: Paramecium

contractile vacuole

CELLS WITH WALLS

• Hypotonic – turgid “very firm”• Isotonic – flaccid

“limp”• Hypertonic –

plasmolysis • Membrane pulls

away from wall• Plant wilts

FACILITATED DIFFUSION

• Passive transport with the help of proteins

• Channel proteins• Aquaporins• Ion Channels • Gated channels

open in response to a stimulus

ACTIVE TRANSPORT

• Move things against the concentration gradient• Uses energy

• Sodium-potassium pump

MEMBRANE POTENTIAL

• Voltage across the membrane• -50 to -200 mV

(inside negative)

• Energy source for all movement

• Favors cations in, anions out

ION DIFFUSION

• Electrochemical gradient• Chemical force – ions concentration gradient• Electrical force – membrane potential

COTRANSPORT

• Substance that was pumped across the membrane does work as it comes back

• Brings another molecule with it

BULK TRANSPORT

Exocytosis• Transport vesicle

from Golgi moves along microtubules toward plasma membrane

Endocytosis• Cell takes in

molecules and matter by forming new vesicles• Phagocytosis “eating”• Pinocytosis “drinking”• Receptor-Mediated

Endocytosis

BULK TRANSPORT

Exocytosis• Transport vesicle

from Golgi moves along microtubules toward plasma membrane

Endocytosis

BULK TRANSPORT

BULK TRANSPORT

• Endocytosis

LIGANDS

• A molecule that binds to a receptor site of another molecule

• Ex: LDL