BIOL 107 - Topic 6: The Plasma Membrane

Phospholipids (Plasma Membrane)

Forms the bilayer that faces water on both sides

• hydrophilic head (interact with polar heads and water at membrane surface)

• hydrophobic tail (interact with fatty acids in membrane interior)

Fluid Mosaic Model

The model of the plasma membrane which shows that proteins are embedded throughout the lipids

Cholesterol (Plasma Membrane)

Regulates and maintains the optimal fluidity in animal membranes

• at low temperatures, it prevents solidification (close packing)

• at high temperatures, it prevents disruption (retains movement)

• if cholesterol was removed, the cell membrane would be less tolerant of temperature changes

Membrane Carbohydrates

Short, branched chains of sugar monomers on the surface of the membrane attached to lipids and proteins that functions for cell-cell recognition

• glycoprotein

• glycolipid

• always face the outside of the cell

Glycoprotein (Membrane Carbohydrate)

A carbohydrate attached to an integral membrane protein

• present all throughout the membrane

Glycolipid (Membrane Carbohydrate)

A carbohydrate attached to a phospholipid

Diffusion (Passive Transport)

A passive transport method involving the tendency of molecules to move down a concentration gradient

• high to low concentration

• releases energy

Facilitated Diffusion (Passive Transport)

A passive transport method that involves the diffusion of substances aided by membrane transport proteins

• movement occurs down concentration gradient

• allows diffusion of molecules that can’t cross membrane on their own

• no energy is required

• NOT active transport

Channel Proteins (Facilitated Diffusion)

A protein used in facilitated diffusion that forms hydrophilic channels that allows specific molecules to pass

• different channel proteins for different molecules

• ex, aquaporins are specific for water molecules

Carrier Proteins (Facilitated Diffusion)

A protein used in facilitated diffusion that changes shape when specific molecules bind to carry them across the membrane

• opens on one side, then closes to release on the other side (always sealed in one direction)

• ex, glucose transport

Osmosis (Passive Transport)

A passive transport method that involves the diffusion of water across a selectively permeable membrane

• water can cross the membrane, but solutes can’t

• direction of water movement is affected by solute concentration

Hypertonic Solution

A comparison term used to describe a solution with a higher solute concentration

Hypotonic Solution

A comparison term used to describe a solution with a lower solute concentration

Isotonic Solution

A comparison term used to describe a solution with equal solute concentrations

Osmoregulation

The control of cell water balance

• used by organisms that live in hypotonic or hypertonic environments

Active Transport

Transport that causes a substance to move against the concentration gradient

• builds up concentration gradients

• impermeability of membrane allows gradients to form

• uptake of nutrients, removal of wastes, maintenance of ion gradients

• requires energy

Membrane Potential

A separation of charge across the cell membrane

• due to concentration gradient of ions

Electrochemical Gradient

Concentration gradient + membrane potential (electric gradient)

• determines movement of ions

Primary Active Transport

A type of active transport where the transport protein breaks down ATP to provide energy for transport

• transports positively-charged ions

• creates membrane potentials

Proton Pump

A protein that actively transports protons (H⁺) out of the cell

• establishes a concentration gradient of protons and a membrane potential

• Energy comes from ATP hydrolysis

Sodium-Potassium Pump

An active transport protein found in animal cells that establishes membrane potential and concentration gradients

• 3 Na⁺ out

• 2 K⁺ in

• energy comes from ATP hydrolysis

Secondary Active Transport

A type of active transport where the transport protein uses an ion gradient for energy

• ion gradient created by primary active transporter that uses ATP as energy

• transport of solute is coupled to diffusion of ions down the electrochemical gradient

• symport and antiport

Symport (Secondary Active Transport)

A type of secondary active transport where the transported solute moves in the same direction as the gradient of the driving ion

• ex, Sucrose-H⁺ Cotransporter

Antiport (Secondary Active Transport)

A type of secondary active transport where the transported solute moves in the direction opposite from the gradient of the driving ion

Vesicle

A small, membrane-bounded compartment in the cytoplasm used in bulk transport

• cells can fuse and form vesicles due to membrane fluidity

Exocytosis

A form of bulk transport where cells secrete proteins and other molecules by the fusion of vesicles with the plasma membrane

Endocytosis

A form of bulk transport where cells take in materials by forming new vesicles from the plasma membrane

Pinocytosis (Endocytosis)

A type of endocytosis where the cell non-specifically engulfs extracellular fluid

• takes up liquids and dissolved solutes

Receptor-Mediated Endocytosis (Endocytosis)

A type of endocytosis used for the uptake of a high concentration of specific molecules

• uses receptor proteins

• integral membrane proteins that bind to specific ligand (substrates)

Phagocytosis (Endocytosis)

A type of endocytosis where the cell engulfs entire particles using pseudopodia

• important for macrophage function