Cell Membrane & Transport

Is sodium (Na +) concentration higher inside or outside of the cell?

outside

Is calcium (Ca 2+) concentration higher inside or outside of the cell?

outside

Is chloride (Cl -) concentration higher inside or outside of the cell?

outside

Is protein concentration higher inside or outside of the cell?

inside

Is phosphate concentration (PO4 3-) higher inside or outside of the cell?

inside

Is potassium (K+) concentration higher inside or outside of the cell?

inside

The cell membrane acts as the barrier between intracellular and extracellular fluid, but some permeable substances pass through via what two kinds of proteins?

channels, carriers

proteins that are always open for free movement of solutes back and forth in and out of the cell

**important for maintaining resting membrane potential since things cross to reach a balance on both sides

(leak) channels

proteins that are open on one side of the cell membrane until a specific solute binds, then it changes conformation to open to the other side

carriers

True or false: The plasma membrane is not permeable to everything at all times.

true

(this is why we call it selectively permeable)

two terms for type of transport in which NO energy is needed for particles to move from an area of higher concentration to an area of lower concentration (until equilibrium is reached)

diffusion, passive transport

specific type of diffusion in which a solute moves freely across the membrane via a channel, or by just crossing the plasma membrane directly, from high concentration to low concentration

simple (diffusion)

What are three factors that affect the rate of simple diffusion?

concentration, electrical, pressure gradients

What are four examples of lipid-soluble substances that can cross the plasma membrane directly since phospholipid tails are hydrophobic?

oxygen, carbon dioxide, alcohol, cholesterol derivatives

What are two examples of minerals that utilize channels to cross the plasma membrane?

sodium, potassium

Even though leak channels are always open, they are still selective as to what can move through them. What are three factors that determine what can move through these channels?

size, shape, electrical charge

Does the sodium channel have a positive or negative charge?

negative

Does the potassium channel have a positive or negative charge?

none

refers to channels that are not leak channels and instead open upon response to certain stimuli (e.g., electrical or chemical); however, once they are open, they act as leak channels

gated

What are two types of gated channels?

voltage gated, ligand gated

specific type of diffusion in which the solute moves via a carrier protein down its gradient from high to low concentration (thus carrier-mediated)

facilitated (diffusion)

What are two examples of substances that utilize facilitated diffusion?

glucose, amino acids

What drives facilitated diffusion?

concentration gradient

Are transporters in facilitated diffusion selective? Why?

yes because certain solutes bind to carriers to trigger conformational changes

threshold in facilitated diffusion at which all carriers are used up (saturated) and at their transport maximum, so nothing else can be transported since they are basically full

V max

With the concept of V-max, we can say that facilitated diffusion is limited by what key factor?

number of transporter proteins

diffusion of water down its concentration gradient from lower solute concentration to higher (it dilutes the solute concentration)

osmosis

water channels used in osmosis to transport water

aquaporins

True or false: Membranes may be permeable to just water or to both water and solutes.

true

Does water move from lower to higher or higher to lower water concentration?

higher to lower

Does water move from lower to higher or higher to lower solute concentration?

lower to higher

refers to the pressure exerted by water due to gravity; the physical pushing of water on the membrane

hydrostatic pressure

refers to the pressure exerted by particles as determined by number of solutes per unit volume (NOT weight/mass); tendency of water to move into a solution because of the concentration of non-penetrating solutes

(colloid) osmotic pressure

There can be situations where there is just water on one side of a membrane and water + solute on the other side, but the membrane is impermeable to solutes. What stops the water on the water-only side from moving to where there is a higher solute concentration?

hydrostatic pressure is enough to make up for lack of osmotic balance

(osmotic and hydrostatic pressures are equal)

unit of measure of number of particles of a molecule in a solution; used in place of grams, so one of these is 1 g molecular weight of an undissociated solute

Example: 180 g of glucose = 1 ___ of glucose

58.5 g of NaCl = 2 ___ of NaCl (because it dissociates into 2 ions)

osmole

number of osmoles per kg of water (not used frequently)

osmolality

number of osmoles per liter of water (used frequently)

osmolarity

refers to things on both sides of a membrane having the same osmolarity (concentration)

isosmotic (isotonic)

refers to a side of the membrane having a higher osmolarity than normal

hyperosmotic (hypertonic)

refers to a side of the membrane having a lower osmolarity than normal

hypoosmotic (hypotonic)

Is water drawn to higher or lower osmolarity?

higher

(goes from hypo to hyper)

type of transport in which energy IS needed and it is mediated by carriers because you are moving a solute AGAINST its gradient

active

specific type of active transport that requires ATP as an energy source (via pumps, or ATPases)

primary

proteins that are specific to certain things and undergo a conformation change to drive solutes against their concentration gradient; also called ATPases

pumps

specific example of a protein pump that is involved in primary active transport

sodium potassium pump (NaK ATPase)

What is the trade off in the sodium potassium pump? (i.e. how many of each ion)

3 sodium out, 2 potassium in

(moving both against their gradients)

specific type of active transport that does not utilize ATP as its energy source and instead uses another solute's chemical gradient (typically sodium)

secondary

refers to solutes moving in the SAME direction in secondary active transport

symport

refers to solutes moving in OPPOSITE directions in secondary active transport

antiport

What are two examples of co-transported substance pairs in secondary active transport?

sodium and glucose, sodium and amino acids

Example of secondary active transport: In the intestines, the Na-K pump uses energy to drive sodium out of the cell, which establishes a sodium concentration gradient from the intestinal lumen to the cell.

This drives what co-transporter protein to take glucose from the lumen (where glucose is low) to the inside of the cell (where glucose is high)?

SGLT

(subsequently creates glucose concentration gradient from inside of cell to blood via passive facilitated diffusion with GLUT)

Which of the following requires ATP?

A. facilitated diffusion

B. movement of oxygen into cell

C. Na+/glucose cotransport

D. movement of Na+ out of the cell

D

Which of the following does NOT require a carrier protein?

A. facilitated diffusion

B. movement of oxygen into cell

C. Na+/glucose cotransport

D. movement of Na+ out of the cell

B

Which of these statements about the facilitated diffusion of glucose is true?

A. there is a net movement from the region of lower to the region of higher concentration

B. carrier proteins in the plasma membrane are required for this transport

C. this transport requires the energy obtained from ATP

D. this is an example of co-transport

B

Selective permeability of the membrane is primarily determined by...

A. membrane phospholipids

B. how much cholesterol is present

C. the number and type of membrane proteins

D. the charge of the membrane

E. none of these

C

Which of the following does not directly or indirectly require an energy source?

A. primary active transport

B. operation of the Na/K-ATPase

C. facilitated transport of glucose across the plasma membrane

D. secondary active transport

C