Lecture 8 Block 2

Question 1

Is secondary active transport selective and saturable?

Answer 1

Yes, b/c it’s carrier mediated

Question 2

What is the energy source for secondary active transport (it’s not ATP)?

Answer 2

In secondary active transport the potential energy available in the transmembrane gradient in one (or more) of the solutes is used. For example, “uphill” movement of an ion could be supported by “downhill” movement of another ion

Question 3

What is coupled transport?

Answer 3

The coupling of the downhill movement of one substrate that serves to drive uphill the movement of another

Question 4

What direction do coupled gradients move in?

Answer 4

They move in opposite directions - One is going uphill and the other is going downhill… this is GRADIENTS.

Question 5

When gradient coupling moves substrates in the same direction what is it called?

Answer 5

Cotransport (or symport)

Question 6

When substrates are moving in opposite directions what is this called?

Answer 6

Countertransport (or antiport)…

Question 7

Which direction are the gradients in countertransport?

Answer 7

In countertransport the ‘coupled gradients’ are in the same direction - one is moving down its concentration gradient while simultaneously bringing the other substrate in the same direction UP its concentration gradient

Question 8

What is the most commonly used solute gradient used to drive secondary active transport in mammalian cells?

Answer 8

The inwardly directed Na+ gradient

Question 9

In the Na-D-Glucose cotransport mechanism the active transport of glucose involves a direct physical coupling of the flows of Na+ and glucose… where does the energy for this transport come from? Because the transport event includes a NET movement of charge the driving force for this uptake includes what two things?

Answer 9

The inwardly directed Na+ gradient provides the energy.
The driving force includes:
1. the chemical gradient for Na+
2. the electrical potential difference across the membrane