cell and molec chapter 12

What do specialized transport proteins allow for?

specificity with what is transported

What are liposomes impermeable to?

most water-soluble molecules except a few solutes such as CO2, O2, and H2O

What do ions need to pass through a membrane?

a transport protein

What are the most plentiful solutes inside a cell?

Groups 1 and 2 + chlorine

What are two examples of the function of ion movement across a membrane?

the activity of nerve cells and ATP production by all cells

What is the most plentiful cation inside a cell?

K+

What is the most plentiful cation outside a cell?

Na+

What is the high Na+ outside a cell balanced by?

extracellular high Cl- (electrostatic attraction)

What does the diffusion rate of a molecule depend on?

its size and solubility

What kind of molecule is most soluble in oil and quickest to diffuse?

smaller molecules

What two molecule types diffuse quickest across the membrane?

hydrophobic molecules and small uncharged polar molecules

What does the hydrophobic interior of the lipid
bilayer create?

a barrier to the passage of ions and larger uncharged polar molecules

What is a characteristic of synthetic bilayers?

they are a billion times more permeable to
H2O than they are to ions like Na+ or K+

Which two substances rarely diffuse across a membrane?

amino acids and glucose

What is a transporter?

a membrane protein that undergoes a series of conformational changes

What is a channel?

a hydrophilic pore that allows specific ions or small molecules to diffuse

What kind of membrane transport protein can transfer molecules the fastest?

Channels

What conformations can an ion channel exist in?

an open or closed conformation

What does it mean for a molecule to move down its concentration gradient?

when a molecule moves from an area of high concentration to an area of low
concentration

What are the two types of passive transport?

Simple diffusion and facilitated diffusion

What is the difference between simple diffusion and facilitated diffusion?

Facilitated diffusion requires a transport protein

What does active transport require that passive transport does not?

energy

What is a membrane potential?

the difference in charge across a membrane

What is a high driving force?

moving down both a concentration and electrical gradient

What type of gradient wins over an electrical gradient?

A concentration gradient

What is a low driving force?

when charge and concentration gradients work in opposite directions

What are the three different types of active transport?

Coupled transport, ATP-driven pumps, light-driven pumps

What is coupled transport?

When the downward movement of one molecule provides the energy for another to move upwards

What is an ATP-driven pump?

an active transport protein that moves a molecule against its concentration gradient using the energy from ATP hydrolysis

What is a light-driven pump?

an active transport protein that moves a molecule up its concentration gradient using light energy

Where does most of the ATP in the body go to?

The sodium potassium pump

What is the goal of the sodium potassium pump?

To maintain the membrane potential

What is the overall net charge inside of a cell?

negative

What is ATPase?

an enzyme that converts ATP to ADP

Why must the intracellular
concentration of Ca2+ be kept low?

Because intracellular signaling often involves an increase of intracellular (cytosolic) Ca2+

What is transported in and out of the sodium potassium pump?

2 K+ in and 3 Na+ out

What kind of cell is the Ca2+ pump important for?

muscle cells and their contraction

What are the 2 different types of coupled transport?

symport and antiport

What is symport?

when 2 molecules are transported in the same direction across the membrane

What is antiport?

when 2 molecules are transported in the opposite directions across the
membrane

What is uniport?

only one molecule is transferred across the membrane

What uses the electrochemical Na+ gradient to drive the import of glucose?

The glucose-Na+ symport protein

What is the sarcoplasmic reticulum?

a specialized smooth ER that stores and pumps Ca2+ ions

Where is H+ pumped in animal vs plant cells?

lysosomes and vacuoles

What is osmosis?

the diffusion of water

What will cause cell lysis?

If the concentration of solutes in a cell is higher than the outside

What will cause a cell to crenate?

if the cell is placed in a high salt solution

During osmosis which direction does water go?

from low to high solute

What is a hypotonic solution?

A solution with a lower solute concentration than the cell

What is a hypertonic solution?

A solution with a higher solute concentration than the cell

What do aquaporins do?

they allow the selective passage of water molecules across a membrane

What is the biologically active form of the aquaporin protein?

the tetramer form

What causes a red blood cell to look spikey when it bursts?

spectrin dimers

What does the K+ channel use to control ion transport?

a selectivity filter

What is the main type of channel in animals and plants?

ion channels

What does ion channel selectivity depend on?

the size and shape of the ion and the amino acids lining the channel

What is ion channel jamming?

Interactions with water molecules can slow ion flow through a channel

What is a gated ion channel?

An ion channel that switches between open and closed conformations in response to stimuli

What are the 3 types of gated ion channels?

voltage-gated, ligand-gated, stress-activated

What controls voltage-gated channels?

the membrane potential

What detects changes in membrane potential in voltage-gated channels?

Charged protein domains called voltage sensors

What causes voltage-gated channels to open or close?

Changes in membrane potential beyond a threshold value

What are ligand-gated channels controlled by?

the binding of a ligand (such as neurotransmitters) to the channel protein (receptor)

Where are bindings sites in ligand-gated channels?

could be on either side of the cell

What are stress activated channels controlled by?

mechanical force

What is an example of a stress activated channel response?

sounds trigger the opening of ion channels in ear hair cells

What decides the membrane potential?

ions on each side of the membrane

When does the membrane potential = 0?

when both sides of the membrane have the same charge

What is the typical resting membrane potential for an animal cell?

-60 mV inside the cell

What is the role of K⁺ leak channels in resting cells?

Allow K⁺ to move across the plasma membrane down its electrochemical gradient

What type of channel is the most important to cell signaling between neurons?

gated ion channels

What allows nervous system signals to travel long distances without fading?

action potentials

What triggers an action potential?

A local stimulus that causes a large change in membrane potential

What do ligand-gated channels do to initiate depolarization?

Open temporarily in response to a ligand, allowing ions to flow across the membrane

What is depolarization?

A change in membrane potential that makes the inside of the cell less negative

What type of channel opens temporarily to cause depolarization of the plasma membrane?

ligand gated channels

What does further depolarization trigger?

Opening of voltage-gated Na⁺ channels

What are the 3 conformations of a voltage-gated Na+ channel?

closed, open, inactivated

What dictates the rise and fall of an action potential?

ion flow

What is repolarization?

when the plasma membrane returns to its resting membrane potential after
experiencing an action potential

What causes repolarization?

inactivation of the Na+ channels and opening of the voltage-gated K+ channels

What occurs at the nerve terminal?

an electrical signal is converted into a chemical one

What triggers neurotransmitter release at the nerve terminal?

the increased Ca2+ which stimulates the synaptic vesicles

How do neurotransmitters trigger an electrical signal in a postsynaptic cell?

They bind to and open transmitter-gated ion channels

What do excitatory neurotransmitters activate?

ion channels that allow the passage of Na+

What do inhibitory neurotransmitters activate?

ion channels that allow the passage of Cl-

What ions pass through the acetylcholine receptor channel?

Na⁺ and K⁺