8.26.16 Lecture

Question 1

Lipid bilayers exhibit differential ___ to certain molecules.

Answer 1

Permeability

Question 2

Which molecules are most permeable to a lipid bilayer?

Answer 2

Hydrophobic molecules (O2, N2, CO2, steroid hormones)

Question 3

Which molecules are moderately permeable to a lipid bilayer?

Answer 3

Small uncharged polar molecules (water, urea, glycerol) and large uncharged polar molecules (glucose and sucrose)

Question 4

Which molecules are least permeable to a lipid bilayer?

Answer 4

Ions (H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+)

Question 5

What three methods can be utilized to cross the lipid bilayer?

Answer 5

1. Simple diffusion - no energy required
2. Passive transport - with concentration gradient, no energy required
3. Active transport - against concentration gradient, requires energy

Question 6

15-30% of all membrane proteins are ___ proteins.

Answer 6

Transport

Question 7

Passive transport can occur via ___ proteins or ___ proteins.

Answer 7

Channel; transport

Question 8

What is the electrochemical gradient?

Answer 8

The combinatorial gradient generated by both the concentration (chemical) and electrical gradients across a lipid bilayer.

Question 9

Channel proteins allow for ___ of a molecule ___ its electrochemical gradient through an ___ pore.

Answer 9

Diffusion; down; aqueous

Question 10

What are ion channels?

Answer 10

Regulated, conditional facilitators of diffusion (passive transport)

Question 11

What are the three types of ion channels?

Answer 11

Voltage-gated, ligand-gated (extracellular and intracellular), and mechanically gated

Question 12

Transporter proteins utilize ___ changes to transport solutes.

Answer 12

Conformational

Question 13

True or false - transporter proteins are only utilized in passive transport.

Answer 13

False - can be utilized in both active and pasive transport

Question 14

What are the three major types of active transport mechanisms?

Answer 14

1. Coupled transporter
2. ATP-driven pumps
3. Light-driven pumps

Question 15

What are the two types of coupled transporters?

Answer 15

Symport (2 molecules move in the same direction) and Antiport (2 molecules move in opposite directions)

Question 16

Describe the difference between primary and secondary active transport.

Answer 16

Primary: uses the energy of ATP hydrolysis to drive cargo against its electrochemical gradient
Secondary: uses energy stored in an electrochemical gradient (usually Na+) to drive cargo against its gradient.

Question 17

___ transport can be driven by a sodium gradient. Explain.

Answer 17

Glucose; sodium flows down its electrochemical gradient into the cytosol of the cell. Glucose is found at high concentrations in the cell and low concentrations outside the cell; however, it utilizes the energy of the sodium gradient through a secondary active transport process to move glucose against its gradient (into the cell).

Question 18

What are the 4 classes of ATP-driven pumps and what do they do?

Answer 18

1. P-type: phosphorylate themselves during transport; transport ions.
2. F-type: ATP synthases, make ATP from gradient
3. V-type: hydrolyze ATP, pump hydrogen ions
4. ABC pumps: pumps molecules rather than ions while hydrolyzing ATP (can still pump ions)

Question 19

What establishes the sodium gradient?

Answer 19

Sodium/potassium pump

Question 20

An average animal cell devotes ___ of its energy to the sodium/potassium pump.

Answer 20

1/3

Question 21

Describe the cycle of the sodium/potassium pump.

Answer 21

Initially, there is a high Na+ concentration outside the cell and a high K+ concentration inside the cell. The goal is to move 3 Na+ out (against its gradient) and 2 K+ in (against its gradient).

1. Na+ binds to the pump. ATP hydrolysis occurs. Phosphorylation of cytoplasmic residues occurs.
2. This induces conformation changes that transfer Na+ out of the cell.
3. K+ binds on the extracellular face of the pump. Dephosphorylation occurs.
4. K+ is transferred to the inside of the cell due to dephosphorylation induced conformation changes.

Question 22

What are ABC transports?

Answer 22

ATP Binding Cassetes; transport all things “non-ionic,” though some also transport ions

Question 23

Name three diseases in which ABC transporters are important.

Answer 23

1. Multi-drug resistance (MDR)
2. CF
3. Malaria

Question 24

What does MDR protein do?

Answer 24

Pumps numerous drugs out of the cytosol; its expression is increased in many cancers, making them drug resistant.

Question 25

What happens in CF?

Answer 25

The CFTR (transmembrane conductance regulator protein) is not functioning correctly. The Cl- channel that removes Cl- from the cell is not working. Cl- ions are trapped the cell. This attracts more cations. There are more ions in the cytoplasm, which induces water to enter the cell via osmosis. This induces thick pathological mucus.

Question 26

What is plasmodium falciparum?

Answer 26

A malaria agent that uses ABC transporter to pump chloroquine, an anti-malarial drug, out of disease-causing protists.

Question 27

What is cystinuria?

Answer 27

Genetic defect in an amino acid transporter responsible for removing cystine (Cys dimer) from urine and intestine; leads to development of cystine stones in bladder and kidneys

Question 28

Describe the mathematical characteristics of transport proteins.

Answer 28

vmax = maximum rate of transport; occurs when all transporter binding sites are occupied.
Km = concentration of 1/2 maximal transport; reflects affinity of transporter for solute

Question 29

What allows the transcellular transport of molecules and is important in nutrient absorption?

Answer 29

Spatial regulation of specific transporters

Question 30

What are the general concentrations of ions in a typical cell (intracellular, extracellular)?

Answer 30

Na+: (low, high)
K+: (high, low)
Mg2+: (low, high)
Ca2+: (low, high)
Cl-: (low, high)

Question 31

What is the Nernst Potential?

Answer 31

Vx = RT/Fz * ln([Ko]/[Ki])

Question 32

If the Nernst Potential is positive…

Answer 32

…there is a positive current. There is either a positive ion leaving the cell or a negative ion entering the cell.

Question 33

If the Nernst Potential is negative…

Answer 33

…there is a negative current. There is either a negative ion leaving the cell or a positive ion entering the cell.