Membrane Transport

Question 1

Examples of molecules that can freely diffuse through the cell membrane

Answer 1

Oxygen, CO2, urea, ethanol, and water

Small and nonpolar

Question 2

Simple diffusion that only applies to solvents. For the mcat, ALWAYS WATER!

Answer 2

Osmosis
*If both solutes and water can diffuse, then only the solutes will move to equalize the concentration through simple diffusion

Question 3

If the solution has a lower concentration of solutes than the cell, the solution is ?

Answer 3

Hypotonic

Question 4

Where does water move in a hypotonic solution

Answer 4

water moves to the inside of the cell, making it swell. Because there is a higher concentration of solute inside the cell than outside, water will move inside

Question 5

Where does water move in hypertonic solution?

Answer 5

The water moves from inside the cell to the outside of the cell, causing the cell to shrink. Because the outside solution has a higher concentration of solute than the inside.

Question 6

Equilibrium is reached when the hydrostatic pressure of the water becomes large enough that it prevents more net osmosis from occurring. This pressure is known as __________, and can be expressed in an equation according to _________. State the equation.

Answer 6

Osmotic pressure, van ’t Hoff’s law: pie = MRT

pie is osmotic pressure, M is total solute concentration, R is ideal gas constant, and T is temperature in Kelvin

Question 7

*MCAT Strategy

Answer 7

Isotonic, Hypertonic, and Hypotonic refer to properties of the solution relative to a cell placed in that solution.

Question 8

Osmotic pressure is a colligative property much like boiling point elevation/depression. What does it mean to be a colligative property?

Answer 8

It means that the osmotic pressure depends on the total quantity of the particles of solutes present, even if they are different chemically.
ex. Glucose counts as 1 molecule while NaCl counts as 2 molecules (1 Na+ and 1 Cl-)

Question 9

Facilitated diffusion is an active or passive transport?

Answer 9

Passive

Question 10

Refers to the process of spontaneous passive transport of ions or molecules across a membrane via specific transmembrane integral channels

Answer 10

Facilitated Diffusion

Question 11

T or F. Facilitated diffusion can sometimes move molecules against the osmotic gradient.

Answer 11

True.

Question 12

T or F. Larger molecules are transported by transmembrane carrier proteins that do not change their conformation as the molecules are carried across.

Answer 12

False. They change conformation.

Question 13

Transmembrane proteins that selectively conduct water molecules in and out of the cells hole preventing the passage of ions and other solutes. Also known as water channels

Answer 13

Aquaporins

Question 14

When does water move across cell membrane through osmosis and when do they use aquaporin?

Answer 14

They use aquaporins when they need to move large amounts of water into or out of cells.

Question 15

T or F. Ion channels are highly specific for a single ion.

Answer 15

True. Even though potassium and sodium have the same charge and differ only slightly in their radius, their selectivity ratio is 1000:1

Question 16

This type of transfer is a spontaneous process that is “powered“ by the increase in entropy associated with transport

Answer 16

Passive transport

Question 17

How is the rate of facilitated diffusion not linear?

Answer 17

The rate of facilitated diffusion depends in the enzyme activity of the carrier protein or channel

Question 18

*Important note about Facilitated Diffusion

Answer 18

Facilitated Diffusion is a form of passive transport and therefore, does not require the input of chemical energy, it is subject to regulation, unlike osmosis and simple diffusion. The gated carrier proteins open in response to a stimulus.

Question 19

This type of channel open and close in response to the binding of a ligand molecules, such as a neurotransmitter.

Answer 19

Ligand-gated channels

Question 20

This type of channel open and close in response to the voltage across the membrane

Answer 20

Voltage-gated channels

Question 21

In this type of active transport, energy is used directly to transport a solute against its gradient

Answer 21

Primary active transport

Question 22

In this type of active transport, the energy stored in an electrochemical gradient established via primary active transport is used to facilitate the movement of a solution

Answer 22

Secondary active transport

Question 23

Name of the enzyme family that perform primary active transport

Answer 23

Transmembrane ATPase family

Question 24

Sodium potassium pump ratio of sodium and potassium that goes in and out

Answer 24

3 Na+ are transported out of the cell and 2 K+ are transported into the cell

Question 25

Are there more potassium ions inside or out of the cell? How about sodium?

Answer 25

There are more potassium ions inside and more sodium ions outside of the cell

Question 26

These transporters can also be powered by redox reactions or by energy harnessed from the photons of incident light.

Answer 26

Primary active transporters.

Ex. Protons in the mitochondrial electron transport chain

Question 27

The subcategories of transporters involved in secondary active transport

Answer 27

Antiporters and symporters

Question 28

These transporters pump two species of ions or other solutes in opposite directions across a membrane. One of the species is allowed to flow from high to low concentration, which yields the entropic energy that drives the transport of the solute from a low concentration to high concentration.

Answer 28

Antiporters

Ex. 3 sodium ions flows down their concentration gradient (primary active transport), so calcium ion is transported out

Question 29

This transporter uses the “downhill” movement of one solute species from high to low [ ] to move another molecule in the same direction, but against its concentration gradient.

Answer 29

Symport

Ex. Glucose symporter SGLT-1 in kidneys, heart, and small intestine

Question 30

Energy-using prices by which cells absorb molecules by engulfing them

Answer 30

Endocytosis

Question 31

Pinocytosis vs Phagocytosis

Answer 31

Pinocytosis- engulf liquid substances

Phagocytosis- engulf solid particles

Question 32

Pathway of endocytosis

Answer 32

Recognition of a target molecule at the plasma membrane ——> invagination ——> formation a vesicle on the inside of the cell

Question 33

Endocytosis uptakes physiologically important molecules such as? This is accomplished via what kind of endocytosis?

Answer 33

Low-density lipoprotein (LDL), growth factors, antibodies, and proteins.
Via clarithin-mediated endocytosis

Question 34

The process by which cells bind and internalize larger materials, such as cellular debris, microorganisms, and in some specialized cell types, other apoptotic cells

Answer 34

Phagocytosis- uptake of large membrane areas than is possible in clarity in-mediated endocytosis

Question 35

Phagocytosis, pinocytosis, and receptor-mediated endocytosis

Answer 35

Phagocytosis- phagosome (food vacuole)
Pinocytosis- vesicle
Receptor-mediated endocytosis- coated vesicle
Pic in page 188 (biochemistry)

Question 36

Which are responsible for recycling molecules back to the surface?

Answer 36

Early endosomes

Question 37

Which are responsible for degradation?

Answer 37

Late endosomes and lysosomes

Question 38

The principal hydrolysis compartment of the cell, function to break down cellular waste products and macromolecules, and are highly acidic by physiological standards, with a pH of 4.8

Answer 38

Lysosomes

Question 39

This type of exocytosis is performed regularly by all cells to release material to the extracellular matrix or to deliver membrane proteins to the membrane

Answer 39

Constitutive exocytosis

Question 40

This type of exocytosis is mediated by Ca2+ signaling and is used to release vesicles with specific content into the extracellular space or synaptic cleft.

Answer 40

Non-constitutive or regulated exocytosis

Question 41

Give an example of constitutive and non-constitutive exocytosis

Answer 41

Constitutive- goblet cells of stomach

Non-constitutive- motor neuron terminal