4 & 5 Human Physiology

sodium potassium ATPase pump

A(n) ________ is an example of Primary Active Transport.

Diffusion

________ does not require energy nor binding to a transporter protein.

Larger surface area

________ makes more opportunity for substances to permeate.

Ions

________ can only move down a concentration gradient if channels are present in the plasma membrane.

Polar

________ or charged molecules can not readily cross a cell membrane via simple diffusion.

Ion channels

________ do not require binding.

Ion channels

________ allow downhill movement of ions.

Simple diffusion

Random movement of molecules due to thermal motion

Net diffusion

Always occurs down a concentration gradient

Flux

The amount of a substance crossing a membrane per unit time

Net flux

The difference between two one-way fluxes

Lipid bilayer

The limiting factor for diffusion across cell membranes

Simple diffusion

The type of diffusion by while non-polar molecules readily move

Electrochemical gradient

The net flux in and out of a cell is ultimately determined by this gradient

Ligand-gated

Cell membrane channels that open on one side of the cell membrane to open or close to passage

Voltage-gated

Channels that rely on electrical signals to move open or closed

Mechanically-gated channels

Channels of a cell membrane that must move themselves open or closed using energy

Leak

Non-gated cell membrane channels

Osmosis

Net diffusion of water from a region of higher water concentration to a region of lower concentration

Osmolarity

total moles of solute divided by Liters of solution

Aquaporins

Channels that allow the rapid passage of water through the cell membrane, necessary because water is polar

Permeable

If a membrane is fully to water and solute, both will eventually reach equilibrium

Semi-permeable

If membrane is (only permeable to water), water will move to area of higher solute concentration

Mediated transport

The process by which the solute moves by binding to a transmembrane protein known as a transporter

Facilitated diffusion, active transport

Two broad categories of mediated transport

Facilitated diffusion

A type of mediated transport that involves downhill movement, no energy required

Active transport

A type of mediated transport that involves uphill movement and requires energy (ATP)

Primary

This Active Transport type occurs when energy comes directly from ATP hydrolysis

Secondary

This Active Transport type occurs when energy comes from an existing ion gradient

Cotransport

A type of secondary active transport; Transported substance can move in same direction as Na+ and it kinda hitches a ride

Countertransport

A type of secondary active transport; Transported substance can move in opposite direction as Na+ where it kinda sneaks against the sodium flow

Endocytosis

Cell membrane folds in from the outside to create a baby pocket, losing some cell membrane and requiring ATP, and is generally used for bulk movement

Exocytosis

Vesicle fuses to te cell membrane to release stuff outside of the cell; replaces the membrane it lost during endocytosis; most secreted substances come from the Golgi apparatus