Chapter 9

Question 1

What roles do membranes play in the cell?

Answer 1

membranes serve as a barrier/checkpoint for all things going in or out of the cell

Question 2

what is passive diffusion? thermodynamics?

Answer 2

transported species move across membranes in a thermodynamically favorable direction without the help of a specific transport protein. High -> low concentration, - Delta G

Question 3

what is facilitated diffusion? thermodynamics?

Answer 3

transported species move across membranes in a thermodynamically favorable direction with the help of a specific transport protein. high -> low concentration, - delta G

Question 4

what is active transport? thermodynamics?

Answer 4

transported species move across membrane in thermodynamically unfavorable direction with the help of a specific transport protein and energy input. low->high concentration + delta G

Question 5

why is saturation behavior seen in facilitated diffusion and not with passive diffusion?

Answer 5

saturation behavior is seen in facilitated diffusion because it uses a specific transport protein, whereas passive diffusion doesn’t use a protein so it displays 1st order kinetics

Question 6

what are the general themes of ion channels that transport ions by facilitated diffusion?

Answer 6

quaternary structure with 3 subunits, selectivity filter that is typically charge based, can be gated using ligand, voltage, or pH, and width with smaller being more selective

Question 7

what are the structural features of the KcsA potassium channel?

Answer 7

4 subunits with 3 alpha helices each, wide water-filled central pore (10 angstroms), selectivity filter (3 angstroms) containing 4 pentapeptide sequences, C=O backbone and Thr-OH facing center of the selectivity filter

Question 8

describe the mechanism of transport for the KcsA potassium channel?

Answer 8

facilitated diffusion, transports K at high rates and is highly selective for K over Na

Question 9

what is the chemical and thermodynamic bases for selectivity and rapid transmission of KcsA channel?

Answer 9

2 K ions are typically bound in the filter at positions 1 & 3 or 2 & 4. Inbound K repels bound K ions out of the other side of the filter. K ions are attracted to the filter by the potential to bind 8 O’s.
it is thermodynamically favorable for K to move through the filter, it is unfavorable for Na and other small molecules

Question 10

What are the three sources of energy used in active transport processes?

Answer 10

ATP, light, Ion gradient

Question 11

what are the structural features of the NA+, K+ - ATPase?

Answer 11

quaternary structure, 3 subunits

Question 12

What is the transport stoichiometry of the NA+, K+ - ATPase?

Answer 12

ATP + 3 NA (in) + 2 K (out) => ADP + 3 NA (out) + 2 K (in)

Question 13

Describe the mechanism of transport of NA+, K+ - ATPase?

Answer 13

active transport using ATP and conformational changes