M 1-2 Membrane Dynamics

Aquaporins

Proteins that allow H2O to move through ion channels and special H2O channels

Active transport

A process that moves molecules against their concentration gradient, using energy (ATP) to move from areas of lower concentration to areas to higher concentrations

Antiport

2 solutes moving in opposite directions across a membrane (typically using pumps/carriers)

Amphiphilic

molecules possessing both hydrophilic and hydrophobic properties, crucial for forming membranes.

ATPase

Enzymes that hydrolyze ATP to ADP and inorganic phosphate (Pi), releasing usable energy in the process

Carriers

• Proteins that perform facilitated diffusion and secondary active transport

• only open to one side of the membrane

• never form a continuous connection between the intracellular and extracellular fluid

• bind to substate then change conformation

Channels

• hydrophilic “pore” through membrane

• able to open and close, regulating the movement of small molecules and ions through them

• proteins form water-filled channels that link the intracellular and extracellular compartment

• can only perform facilitated diffusion

• higher rate of conformational change

• open to both sides of membrane allowing for faster transport of materials

Diffusion

Movement of molecules from higher concentration of molecules to lower concentration of molecules down a concentration gradient without the need for energy input

Electrochemical disequilibrium

An unequal distribution of large uncharged polar compounds and ions across a membrane, resulting in a difference in electric potential.

Extracellular fluid (ECF)

Watery-internal environment that surrounds the cells

• serves as a buffer zone between the organism’s external environment and their cells

• contains interstitial fluid and plasma

Facilitated Diffusion

Type of passive transport where free water moves from a higher concentration to a lower concentration down via specific transmembrane proteins its concentration gradient without energy input (NOT solutes moving down)

Fatty acid/hydrocarbon chain

A long glycerophospholipid tail that is hydrophobic and nonpolar, typically found in lipids and essential for the structure of membranes.

Gated channels

Generally closed, allowing these channels to regulate the movement of ions through them in response to specific stimuli.

• open or closed channels from chemical, mechanical, and voltage forces

Glucose transporter (GLUT)

family of uniport carrier proteins move glucose and related hexose sugars across membranes

• performs facilitated diffusion of glucose with no added energy required

• glucose binding triggers conformational change (phosphorylation into glucose-6-phosphate (G6P)

Glycerophospholipids

A class of lipids that are a major component of all biological cell membranes, composed of a glycerol backbone, two fatty acid/hydrocarbon carbon tails, different hydrophilic/polar head groups, and a phosphate group.

Hydrophillic/polar

“water loving,” dissolve in water easily; composed of phospholipid head groups that interact with the aqueous environment.

Hydrophobic/nonpolar

"water fearing," do not dissolve in water easily'; composed of phospholipid tails that turn away from the aqueous environment

Hydrostatic pressure

Pressure exerted by a fluid within a chamber (e.g. blood within vessels)

Hyperosmotic

Solution A has a higher solute concentration than Solution B

• higher osmolarity (more particles/unit volume, more concentrated solution A

• Solution A ≥ Solution B

Hypertonic

Describes the cell losing water and shrinking at equilibrium in a solution with a higher concentration of non-penetrating solutes, leading to the movement of water out of cells and resulting in cell shrinkage.

Hyposmotic

• Solution B has a lower solute concentration than Solution A

• Solution B has a lower osmolarity (fewer solute particles/unit volume, more dilute solution B)

Hypotonic

Describes a solution with a lower concentration of non-penetrating solutes compared to the inside (cytoplasm) of a cell, causing water to enter the cell and resulting in cell swelling.

Interstitial fluid

Fluid that surrounds the cells and in between the tissues outside of the cell membrane

Intracellular fluid (ICF)

Fluid that surrounds inside the cell

Isosmotic

Describes two solutions having the same number of solute particles/unit volume

Isotonic

Describes a solution having the same non-penetrating solute concentration in the cell and the solution, resulting in no net water movement at equilibrium

Ligand-gated channel

Signaling molecules from either the extracellular and intracellular environment that binds to the protein, triggering the opening of the channel to transport the solute across the membrane.

Lymphatic system

A network of capillaries that collects excess interstitial fluid and return it to plasma in venous circulation

Mechanically-gated channel

A type of ion channel that opens in response to physical forces, such as increased temp or pressure that puts tension on the membrane, triggering the opening of the gate

Na+/K-ATPase/pump

A pump that performs primary active transport to maintain high intracellular [K+] and higher extracellular [Na+] by using ATP.

• in the cell membrane 1 ATP molecules requires to move 3 Na+ out of the cell and 2 K+ into the cell

Non-penetrating solutes

Solute particles that cannot cross the cell membrane

Open channels

Ion channels that generally have open gates, allowing the passage of ions across the membrane without gating mechanisms, facilitating passive transport.

• typically behave as if there is no gates

• sometimes called either leak channels or pores (water pores)

Osmolarity

The measure of a solute concentrating, describing the number of osmotically active “particles” (ions or intact molecules) in a solution per liter of solution

Osmosis

The movement of water across a membrane (using faciliated diffusion of water via aquaporins) in response to a solute concentration gradient

• membrane is impermeable to solute, permeable to water

• high [free water] → low [free water]

• low [solute] → high [solute]

Osmotic equilibrium

The state where the free movement of water between cells and the extracellular fluids in the cell membrane occurs until the fluid concentrations are equal, NOT fluid volumes

Osmotic pressure

• The pressure created by the movement of water across a semi-permeable membrane (alternatively, the pressure needed to oppose osmosis)

• how molecules get absorbed and how solutes get drawn into cells

Passive transport

The process of moving substances across a cell membrane without the use of energy, moving down/with its concentration gradients, resulting in equilibrium

• processes using facilitated diffusion, simple diffusion, or osmosis

Penetrating solute

A solute that can cross the cell membrane and behaves as the cell membrane dividing the ECF and ICF doesn’t exist

Plasma

• The fluid component with heavy blood cells; apart of the ECF

• Contains high protein, Na+ and CI- concentrations but low K+ concentrations

Primary active transport

Using energy directly from ATP to push molecules against the concentration gradient (active transport) from high energy phosphate bond of ATP

Pumps

• Analogous to carriers

• a protein that transports ions or molecules across the cell membrane against their concentration gradient by utilizing energy from ATP.

• performs primary active transport, using energy from ATP to drive a solute up its concentration gradient

Secondary active transport

• Indirect use of ATP that uses potential energy stored in the concentration gradient of one molecule to push other molecules against their concentration gradient

• also depends on the primary active transport bc it creates the concentration gradients that drive secondary active transport

Simple diffusion

The movement of molecules from an area of high concentration to an area of low concentration without the use of energy from protein transporters