Chapter 10: Membrane Transport

Question 1

what is membrane transport? what can’t pass through

Answer 1

the movement of particles (solute) across or through a membranous barrier of ions, such as Na+, K+, Ca2+, and Cl−, as well as metabolites such as pyruvate, amino acids, sugars, and nucleotides, and even water.
Biological membranes present formidable barriers to the passage of ionic and polar substances,

Question 2

2 types of transport? What do they mean

Answer 2

mediated transport and non mediated transport
-non mediated transport occurs through simple diffusion.
-mediated transport occurs through the action of specific carrier proteins.

two types of mediated transport: passive transport/facilitated diffusion and active transport

Question 3

what is simple diffusion

Answer 3

Transport across a membrane without the assistance of membrane proteins.

Question 4

What kind of molecules can and cannot move across the cell membrane and why? what do they require?Which transport

Answer 4

CAN:
-Nonpolar molecules such as steroids and O 2readily diffuse through biological membranes
-must be small and nonpolar like oxygen,CO2, and H2O move freely
-the concentration of the molecule is higher on one side of the membrane than the other
* Continues untill equilibrium is achieved.
non-polar molecules can easily dissolve in a hydrophobic nonpolar solution so if a small non polar molecule wants to make its way across the cell membrane all it has to do is dissolve inside that cell membrane and this process by which a small nonpolar molecule will move down its concentration gradient from a high to low potential through the core of that membrane by dissolving in that cell membrane
CANNOT: ions that contain positive or negative charges and molecules that are very polar and large cannot move across the cell membrane because they cannot dissolve inside the hydrophobic non polar region of the membrane
-they require assistance from a protein called a Chanels and carrier proteins

Question 5

What is Passive transport/facillitated difusion

Answer 5

transports large and polar molecule
Proteins change shape to allow molecules for transport.
molecule flows from high concentration to low concentration.

Question 6

difference between passive transport and active transport

Answer 6

-passive transport doesn’t use any energy molecules/ATP to carry out the process while active does. uses channels
-passive transport always moves down their concentration gradient from a high to low potential while
-Active transport uses energy to move the molecules against the concentration gradient from a low to high potential. uses pumps

Question 7

Substances that are too large or too polar to diffuse across lipid bilayers on their own may be conveyed across membranes via proteins or other molecules that are variously called

Answer 7

ionophores (carrier), porins (permeases), ion channels, aquaporins, and transport proteins.

All differ in sleectivity

Question 8

what are channels

Answer 8

passageways that allow these ions and molecule to move and bypass the nonpolar core of that membrane so that they can pass without ever interacting with that hydrophobic core

Remove the hydrophobic core
part of passive transport

Question 9

What are Ionophopres? What are the two types? How fast?

Answer 9

Ionophores facilitate ion diffusion by binding an ion, diffusing through the membrane, and then releasing the ion; or by forming a channels
Carry ions across membrane

Ionophores are organic molecules of diverse types, usually of bacterial origin, that increase the permeability of membranes to ions. These molecules often exert an antibiotic effect by discharging the vital ion concentration gradients that cells actively maintain.
Two types
1. Carrier ionophores, which increase the permeabilities of membranes to their selected ion by binding it, diffusing through the membrane, and releasing the ion on the other side
2. Channel-forming ionophores, which form transmembrane channels or pores through which their selected ions can diffuse
. (a) Carrier ionophores transport ions by diffusing through the lipid bilayer. (b) Channel-forming ionophores span the membrane with a channel through which ions can diffuse.

Both types of ionophores transport ions at a remarkable rate.

Question 10

one of the best characterized ionophores

Answer 10

Valinomycin

Question 11

What are Porins

Answer 11

are β barrel protein structures with a central aqueous channel
forms a water-filled open channel and allows the passive transport of hydrophilic compound
In general, the size of the channel and the residues that form its walls determine what types of substances can pass through.
Porins form β barrel structures about a central channel that is selective for anions, cations, or certain small molecules.

provide a passageway for ions or non polar solutes

beta barrel. The amino acid composition of the porin beta sheets is unique in that polar and nonpolar residues alternate along them. This means the nonpolar residues face outwards so as to interact with the nonpolar lipid membrane, while the polar residues face inwards into the center of the beta barrel to interact with the aqueous channel.

Question 12

difference between channel and carrier proteins

Answer 12

Channel proteins provide an open channel or passageway through the cell membrane for molecules to move across
for ions and nonpolar solutes
Carrier proteins bind and carry the molecules across the cell membrane. These proteins bind a molecule on one side of the membrane, change shape as they carry the molecule across the membrane, and deposit the molecule on the other side of the membrane.
neither require energy

Question 13

What are Ion channels? Ion Channels are highly ? Due to what?

Answer 13

Highly Selective and Rapid, may be gated
Gates- being able to selectively open and close ion channels
Due to charge repulsion, structural features, and gates are the driving force for rapid ion movement

allowing only certain ions to pass through. Some channels conduct only one type of ion (e.g., potassium), whereas other channels exhibit relative selectivity—for example, allowing positively charged cations to pass through while excluding negatively charged anions.

The Structure of the KcsA K+ Channel Explains Its Selectivity and Speed.

Ion channels mediate changes in membrane potential by allowing the rapid and spontaneous transport of ions. Ion channels are highly soluteselective and open and close (gate) in response to various stimuli. Nerve impulses involve ion channels.

Question 14

How are channels activated?

Answer 14

by changes in the voltage across a membrane (voltage-activated channels) or by binding of specific molecules to the channels (ligand activated channels)

Question 15

what are the four ion channel gates

Answer 15

1. Mechanosensitive channels open in response to local deformations in the lipid bilayer. Consequently, they respond to direct physical stimuli such as touch, sound, and changes in osmotic pressure.
2. Ligand-gated channels open in response to an extracellular chemical stimulus such as a neurotransmitter.
3. Signal-gated channels open on intracellularly binding a Ca 2+ ion or some other signaling molecule (Section 13-4B).
4. Voltage-gated channels open in response to a change in membrane potential. Multicellular organisms contain numerous varieties of voltage-gated channels, including those responsible for generating nerve impulses.

Question 16

The coordinated opening and closing of ion channels generates an ?

Answer 16

action potential in nerve cells.

Question 17

Aquaporins?

Answer 17

Mediate the Transmembrane Movement of Water
protein pores that conduct water through biological membranes.

allow water to move readily across their membrane

Question 18

What are transport proteins?

Answer 18

Two Conformations
Transport proteins such as GLUT1 alternate between two conformational states that expose the ligand-binding site to opposite sides of the membrane.

Question 19

What are transport proteins?

Answer 19

Transport proteins such as GLUT1 alternate between two conformational states that expose the ligand-binding site to opposite sides of the membrane.

Question 20

Transport proteins may mediate what kinds of transport?

Answer 20

uniport, symport, and antiport transport.
A uniport involves the movement of a single molecule at a time. GLUT1 is a uniport system.

2. A symport simultaneously transports two different molecules in the same direction.
3. An antiport simultaneously transports two different molecules in opposite directions.

Question 21

What is active transport?

Answer 21

When pumps utilize ATP to transport ions against their gradient

Question 22

In what situation is active transport used?

Answer 22

Many substances, however, are available on one side of a membrane in lower concentrations than are required on the other side of the membrane. Such substances must be actively and selectively transported across the membrane against their concentration gradients.

Passive-mediated transporters, including porins, ion channels, and proteins such as GLUT1, facilitate the transmembrane movement of substances according to the relative concentrations of the substance on the two sides of the membrane.

Question 23

What are the three pumps discussed?

Answer 23

(Na+−K+)–ATPase/(Na+−K+) pump

Ca2+–ATPase

ABC transporters

Question 24

What is the (Na+−K+)–ATPase/(Na+−K+) pump?

Answer 24

it pumps Na + out of and K + into the cell with the concomitant hydrolysis of intracellular ATP.

One of the most thoroughly studied active transport systems in the plasma membranes of higher eukaryotes

Antiport

Transports Ions in Opposite Directions

Question 25

How does (Na+−K+)–ATPase work? Why is it important?

Answer 25

Na+ and K+ transport is electrogenic meaning 3 Na+ ions are pumped out of/exit the cell per ATP hydrolyzed and only 2 K+ are pumped back/entered, making the outside of the cell positively charger.
-Important in neurons to restore the original ion distribution to allow a new nerve impulse

Question 26

Both (Na+–K+)–ATPase and Ca2+–ATPase form

Answer 26

a phorlylated intermediate
ATP Binds to the asparte residue

Question 27

(Na+–K+)–ATPase steps

Answer 27

1. Na+ binding
2. formation of high energy aspartyl phosphate intermediate
3. Na+ transport
4. K+ binding
5. Phosphate hydrolysis
6. K+ transport and ATP binding

Question 28

What is Ca2+–ATPase? Main function +example

Answer 28

Pumps Ca 2+Out of the Cytosol/cell
example: a muscle cell where removal of Ca2+ allows the muscle to relax

Question 29

Ca2+ transport by Ca2+–ATPase is electrogenic meaning

Answer 29

as 2 CA2+ ions are pumped out of the cell per ATP hydrolyzed and 2-3 H+ are pumped back, making the outside of the cell positively charged

Question 30

Steps of Ca2+–ATPase

Answer 30

1. Ca2+ binding and formation of high energy intermediate
2. Ca2+ transport
3. Phosphate hydrolysis
4. ATP binding

Question 31

what are ABC transporters responsible for ?

Answer 31

Move amphipathic substances from one side of the members to the other

drug resistance and genetic disease (cystic fibrosis)
one of the largest family of membrane transport proteins

Question 32

The inability of anticancer drugs to kill cancer cells is frequently traced to the overexpression of a membrane protein known as ?

Answer 32

P-glycoprotein
This member of the ABC family of transporters pumps a variety of amphiphilic substancesincluding many drugs—out of the cell, so that it is also called a multidrug resistance (MDR) transporter.

function is to protect the organism from toxic xenobiotics and secretion of metabolites

Question 33

another member of the ABC transporters?

Answer 33

CFTR Is an ABC Transporter. Only one of the thousands of known ABC transporters (48 in humans) functions as an ion channel rather than a pump: the cystic fibrosis transmembrane conductance regulator (CFTR). This 1480-residue protein, which is defective in individuals with the inherited disease cystic fibrosis (Box 3-1), allows Cl − ions to flow out of the cell, following their concentration gradient.

the cystic fibrosis transmembrane conductance regulator (CFTR), which acts as a chloride ion channel rather than a pump. Mutations in this protein prevent the transport of CL- resulting In abnormally thick mucus and leads to cystic fibrosis

Question 34

What gave ABC transporters their name?

Answer 34

because they contain a domain that binds ATP, called the ATP-binding cassette

Question 35

secondary active transport?

Answer 35

Active Transport May Be Driven by Ion Gradients

In secondary active transport, an ion gradient maintained by an ATPase or other free energy-capturing cellular process drives the transport of another substance. For example, the transport of lactose into a cell by lactose permease is driven by the cotransport of H+ , whose gradient is maintained by oxidative metabolism.