Carrier Proteins and Channel Proteins Facilitate Diffusion by Different Mechanisms

Question 1

What is the role of carrier proteins?

Answer 1

Carrier proteins bind solute molecules on one side of the membrane, undergo a conformation change, and release the solute on the other side of the membrane.

Question 2

What does the Alternating conformation model state? What happens at the two conformational states? (2 steps)

Answer 2

that a carrier protein i an allosteric protein and alternates between two conformational states.

• (1) in one state, the solute binding site of the protein is accessible on one side of the membrane
• (2) the protein shifts to the alternate conformation, with the solute binding site on the other side of the membrane, triggering solute release

Question 3

Carrier proteins are analogous to enzymes (4)

Answer 3

(1) facilitated diffusion involves binding a substrate on a specific solute binding site
(2) The carrier protein and solute form an intermediate
(3) after conformational change, the “product” is released (the transported solute)
(4) Carrier proteins are regulated by external factors

Question 4

Specificity of carrier proteins

(1) relationship to enzymes?
(2) transport proteins?

Answer 4

• Carrier proteins share the property of high specificity with enzymes too
• transport proteins are often highly specific for a single compound or small group of closely related compounds

Question 5

Kinetics of carrier protein function: Carrier proteins and saturation

Answer 5

carrier proteins can become saturated as the concentration of the solute rises - this is b/c the number of carrier proteins is limited and each functions as a finite maximum velocity (like enzyme catalysts) exhibits saturation kinetics

Question 6

What do channel proteins do?

Answer 6

Form hydrophobic channels through the membrane to provide a passage route for solutes

Question 7

Not all channels are the same… some are…?

Answer 7

some channels are large and nonspecific such as pores on the outer membranes of bacteria, mitochondria, and chloroplasts

Question 8

Channel proteins: How are pores formed?

Answer 8

pores are formed by transmembrane proteins called porins that allow passage of solutes up to a certain size to pass (600D)

Question 9

Most channels are? such as?

Answer 9

small and highly selective, such as ion channels

Question 10

Most of the smaller channels are involved in what?

Answer 10

ion transport (ion channels)

Question 11

Movement of solutes through ion transport vs carrier proteins?

Answer 11

the movement of solute through ion channels is much faster than transport by carrier proteins (likely b/c conformational changes does not occur)