Chapter 4- Cell membranes

Question 1

What side of the membrane is Na higher?

Answer 1

Outside

Question 2

What side of the membrane is K higher?

Answer 2

Inside

Question 3

What side of the membrane is Cl higher?

Answer 3

Outside

Question 4

What side of the membrane is Ca higher?

Answer 4

Outside

Question 5

What side of the membrane is HCO3 higher?

Answer 5

Outside

Question 6

What are channel proteins?

Answer 6

contain watery spaces all the way through the molecule and allow free movement of water, as well as selected ions or molecules

Question 7

What are carrier proteins?

Answer 7

bind with molecules or ions that are to be transported; conformational changes in the protein molecules then move the substances through the interstices of the protein to the other side of the membrane.

Question 8

What is diffusion?

Answer 8

random molecular movements of substances molecule by molecule, either through intermolecular spaces in the membrane or in combination with a carrier protein

Question 9

What is Active transport?

Answer 9

movement of ions or other substances across the membrane in combination with a carrier protein in such a way that the carrier protein causes the substance to move against an energy gradient; from a low-concentration to a high-concentration state

Question 10

What does active transport require that diffusion doesn’t require?

Answer 10

Energy

Question 11

What does it mean when we say a channel is “selectively permeable?”

Answer 11

many of the channels are highly selective for transport of one or more specific ions or molecules, this results from the characteristics of the channel itself: diameter, shape, nature of the electrical charges, and chemical bonds along its inside surfaces.

Question 12

What is an example of a selectively permeable channel?

Answer 12

Potassium channels permit the passage of K+ 1000 times more readily than they permit Na+

Question 13

What is voltage gating?

Answer 13

molecular conformation of the gate or of its chemical bonds responds to the electrical potential across the cell membrane (conducts current “all or none”)

Question 14

What are some examples of voltage gated channels?

Answer 14

Na+ or K+ channels; conformational changes in the protein molecules to open or close “gates” guarding the channels

Question 15

What are chemical/ligand gated channels?

Answer 15

gates that are opened by the binding of a chemical substance (a ligand) with the protein; this causes a conformational or chemical bonding change in the protein molecule or closes the gate.

Question 16

What is an example of a ligand gated channel?

Answer 16

Ach opens the gate of a Na+ channel

Question 17

What is simple diffusion?

Answer 17

kinetic movement of molecules or ions occurs through a membrane opening or through intermolecular spaces without any interaction with carrier proteins in the membrane

Question 18

What are the 4 things that determine the rate of simple diffusion?

Answer 18

o Rate of diffusion depends on the amount of substance available, velocity of kinetic motion, and number and sizes of openings in the membrane through which the molecules or ions can move

Question 19

What is facilitated diffusion?

Answer 19

requires interaction of a carrier protein; the protein aids in the passage of the molecules or ions through the membrane by binding chemically with them and shuttling them through the membrane in this form.

Question 20

What is the Fick’s diffusion equation?

Answer 20

J= -PA (C1- C2)

Question 21

What are the 3 variables that alter the flux of solutes across a cell membrane?

Answer 21

o Concentration of solutes on either side of the membrane (intracellular and extracellular)
o The amount/size of Surface of the Area of the membrane that is exposed to the solutes
o Permeability is the ease with which a solute diffuses through a membrane. This depends on the characteristics of the solute and the membrane.

Question 22

What are the 3 factors that increase the permeability?

Answer 22

o ↑ Oil/water partition coefficient of the solute increases solubility in the lipid of the membrane
o ↓ Radius (size) of the solute increases the speed of diffusion
o ↓ Membrane thickness decreases the diffusion distance

Question 23

What is the permeability of water across the membrane?

Answer 23

• Water is highly insoluble in the membrane lipids, however it readily passes through protein channels

Question 24

What is the permeability of urea across the membrane?

Answer 24

• Urea is a lipid-insoluble molecule that can pass through protein channels (same as water molecules); however its penetration is slow due to its larger diameter

Question 25

What is the permeability of Glucose and amino acids across the membrane?

Answer 25

Cannot pass- must use facilitated diffusion

Question 26

What is the permeability of charged ions across the cell membrane?

Answer 26

• Due to their charged state (Na+, Cl-, and K+) ions are impermeable to the lipid membrane therefore they must beable to pass through protein channels. These protein channels are highly specific to the diameter, shape/size, charge, and chemical bond of the molecule.

Question 27

What is the Vmax of facilitated diffusion?

Answer 27

• Rate of facilitated diffusion approaches a maximum (Vmax; look familiar) as the concentration of the diffusing substance increases, this is due to the fact that the rate of transport can never be greater than the rate at which the carrier protein molecule can undergo change back and forth between the two states.

Question 28

What is primary active transport?

Answer 28

the energy is derived directly from the breakdown of ATP (or some other high-energy phosphate)

Question 29

What is an example of primary active transport?

Answer 29

Na+/K+ Pump (ATPase)

Question 30

What is secondary active transport?

Answer 30

movement of ions via primary active transport generates energy for other ions and solutes to be transported. Therefore the energy is derived secondarily from energy that has been stored in the form of ionic concentration differences of secondary molecular or ionic substances between the 2 sides of a cell membrane, created originally by primary active transport.

Question 31

What is a symporter and give an example

Answer 31

carriers the 2 ions/molecules together to the same side

o Ex: Sodium-glucose transporter

Question 32

What is an antiporter and give an example

Answer 32

carriers the 2 ions/molecules in opposite directions

o Ex: Sodium-Calcium transporter and Sodium-Hydrogen transporter