Lecture 7 Block 2

Question 1

What is the defining characteristic of all types of active transport?

Answer 1

A net movement of a substrate against its electrochemical (EC) gradient

Question 2

What are two sources of energy that can be used to support movement of a substrate against its gradient?

Answer 2

1. Metabolic energy (from direct hydrolysis of ATP - used to support Primary Active Transport)
2. Gradient Energy (Secondary Active Transport)

Question 3

Where does the energy for Primary Active Transport come from?

Answer 3

Energy derived from the direct hydrolysis of ATP by the transporter - Metabolic Energy

Question 4

Where does the energy for Secondary Active Transport come from?

Answer 4

Energy obtained through dissipation of energy in the EC gradient of a different substrate - Gradient Energy… uses the energy derived from the gradient of one substrate to move a second substrate against its EC gradient

Question 5

What are the two descriptive categories of Primary Active Transport?

Answer 5

1. ABC transporters

2. Ion pumps

Question 6

What are ABC transporters?

Answer 6

ABC refers to ATP Binding Cassette - describes a conserves structural amino acid sequence (motif) found in all members of this very large family of carrier proteins. 
In mammals this class of transport process is (almost always) used to transport potentially toxic compounds out of the cell.

Question 7

Why are several classes of ABC transporters referred to as MDRs? (Multidrug resistance transporters)

Answer 7

B/C they can pump out drugs from the cell reducing the effectiveness of the drug which can lead to resistance (of whichever pathogen the drug was targeting) over multiple drug types

Question 8

What are some ions that ion pumps use ATP to move against their EC gradients?

Answer 8

Na, K, Ca, and/or H

Question 9

T/F Ion pumps are saturable and selective?

Answer 9

True

Question 10

T/F Ion pumps transport Na, K, Ca, and/or H

Answer 10

True

Question 11

T/F Because all their activity involves hydrolysis of ATP ion pumps are all ATPases?

Answer 11

True

Question 12

T/F Ion pumps are all “P-type” ATPases b/c during the overall reaction the transport protein itself is transiently phosphorylated then dephosphorylated?

Answer 12

True - this phosphorylation/dephosphorylation cycle catalyzes the conformational changes that result in translocation of their substrate(s) across the membrane

Question 13

List the 4 “P-type” ATPases

Answer 13

1. Na,K-ATPase
2. Plasma membrane Ca-ATPase (PMCA)
3. Sarco/Endoplasmic Reticulum Ca-ATPase (SERCA)
4. H,K-ATPase

Question 14

What does the plasma membrane Ca-ATPase pump do? (PMCA)

Answer 14

Pumps Ca2+ out of the cell. Works constantly using ATP energy to keep the cytoplasmic Ca2+ concentration in the vicinity of 50-100nM (depending on cell type).
By keeping the cytoplsamic Ca2+ so low, small ‘absolute’ increases in Ca2+ content can represent a large % change.

Question 15

What does the sarco/endoplasmic reticulum Ca-ATPase pump do? (SERCA)

Answer 15

Pumps Ca2+ into the smooth endoplasmic reticulum (in muscle referred to as the sarcoplasmic reticulum).
Smooth ER is storage site for Ca2+. Once released SERCA uses ATP to pump the Ca2+ back into the ER.