Membrane Transport

Question 1

Phospholipid bilayer is permeable to:

Answer 1

small molecules and gases (O2, CO2, N2, H2O, glycerol, ethanol, benzene)

Question 2

Phospholipid bilayer is impermeable to:

Answer 2

Large, uncharged or polar molecules (amino acids, glucose, nucleosides) and ions (Na+, K+, H+, Cl-, etc)

Question 3

Overcoming the permeability barrier of the cell

Answer 3

It is crucial to proper functioning of the cell

Question 4

Key components of transport:

Answer 4

Energy requirements
Selectivity/specificity
Specialized proteins involved
Size of transported molecule

Question 5

Energy requirements

Answer 5

No energy required for transport - passive transport

Energy required for transport - active transport

Question 6

Solutes cross membranes by:

Answer 6

Simple diffusion, facilitated diffusion, or active transport

Question 7

Two categories of Passive Transport:

Answer 7

Simple diffusion and facilitated diffusion

Question 8

Simple Diffusion

Answer 8

no specialized proteins required; rate of diffusion depends on concentration gradient, size of molecule, and hydrophobicity; limiting factor is hydrophobicity of the molecule; non-selective
flow of solute = concentration gradient x permeability coefficient
Unassisted diffusion down concentration gradient; typically only for gases and nonpolar molecules

Question 9

Facilitated Diffusion

Answer 9

Transporters and channels; no energy required; solutes move down their concentration gradients; specialized proteins required to provide a path through the lipid bilayer; highly specific

Question 10

Transporters

Answer 10

Carrier proteins; substrates binds to a specific binding site; protein and solute for an intermediate; conformational change occurs and solute is released on other side of membrane; regulated by external factors; saturation can occur

Question 11

Alternating Conformation Model

Answer 11

Carrier proteins are constantly alternating their conformations regardless of the presence of the solute; increased concentration gradient drives solute transport

Question 12

Types of Carrier Proteins

Answer 12

uniport, symport, or antiport

Question 13

Glucose Transporter

Answer 13

Transports glucose across the membrane; uniport; transports via alternating conformation mechanism; GLUT1 (10 different glucose transporters in humans); glucose phosphorylated inside cell to prevent glucose being taken out of cell

Question 14

Channels

Answer 14

Proteins which form a hydrophilic transmembrane channel that allows for specific solutes to cross the membrane; no energy required - solutes travel down concentration gradient

Question 15

Types of Channels

Answer 15

Ion channels, porins, and aquaporins

Question 16

Porins

Answer 16

Transmembrane proteins that allow rapid passage of various solutes (large); nonspecific; beta sheets form porins

Question 17

Aquaporins

Answer 17

Transmembrane channels that allow rapid passage of water; tetramers formed from alpha helices; hydrophilic amino acid side chains form channel

Question 18

Ion Channels

Answer 18

Transmembrane proteins that allow the rapid passage of specific ions; tiny pores; high selective; ion gradients important in cell function, therefore gradients are maintained through gates - voltage, ligand, mechanical;

Question 19

Electrochemical gradient

Answer 19

Chemical/potential gradient; ions are charged, therefore ion concentration gradients are both chemical and electrical/potential;

Question 20

Gated Ion Channels

Answer 20

Most ion channels are gated and open in response to some stimulus; opening and closing is an “all-or-none” response

Question 21

Ion Channel Specificity

Answer 21

The size of the pore and the groups that interact with the solute determines what ions can cross through; specific amino acid side chains determine what ions can cross through pore

Question 22

Active Transport

Answer 22

Protein-mediated movement of a solute up its concentration gradient; requires energy input; unidirectional; primary (direct) and secondary (indirect)

Question 23

Three ways cells drive active transport:

Answer 23

Coupled transporter, ATP-driven pump, light-driven pump

Question 24

Indirect Active Transport

Answer 24

Depends on the simultaneous transport of two solutes; favorable movement of one solute down its gradient drives the unfavorable movement of the other solute up its gradient; symport or antiport

Question 25

Direct Active Transport

Answer 25

Direct hydrolysis of ATP drives the movement of solutes up their gradient;
Three types: V-type, F-type, P-type

Question 26

V-type ATPase

Answer 26

Pump protons into organelles (vacuoles, vesicles, lysosomes, Golgi, etc)

Question 27

F-type ATPase

Answer 27

Two components: transmembrane pore and peripheral membrane component which contains ATP binding site
Reverse process: ATP synthase
Present in bacteria, mitochondria, chloroplasts

Question 28

P-type ATPase

Answer 28

Transport ions or phospholipids; reversibly phosphorylated by ATP on aspartate residue
Na+/K+ pump

Question 29

Na+/K+ Pump

Answer 29

Maintains electrochemical ion gradients; allosteric protein; two alternating conformations with different affinities for Na+ and K+

Question 30

ABC Transporters

Answer 30

Hydrolyze 2 ATPs to move larger, hydrophobic molecules; large class of proteins; two domains; important medically because some are used by cells to pump antibiotics or drugs out of the cells rendering the cell resistent to the drug

Question 31

Na+ Symport

Answer 31

Drives the uptake of glucose by the cell