Movement across membranes (Carriers)

Question 1

Facilitated diffusion

Answer 1

• Substrate binds specifically to integral membrane proteins called facilitative transporter

-Changes in transporter conformation allows compound to be released on other side of membrane

• Compound moves down a concentration gradient

Question 2

Glucose transporter

Answer 2

• Most animal cells import glucose from the blood into cells down a concentration gradient via this mechanism (facilitator)

Question 3

Steps of Glucose transporter

Answer 3

1. Transporter ready to accept glucose molecule
2. Glucose is accepted by transporter
3. Intracellular side of transporter opens
4. Glucose is released and cycle repeats

Question 4

Symporter

Answer 4

• Under certain circumstances, cells need to move substances from a lower concentration to a higher concentration

-Need to rely on the chemical gradient of another molecule that would not reach extracellular and intracellular equilibrium

Question 5

Na+ glucose symporter

Answer 5

1. Simultaneously binding of 2 Na+ and 1 glucose to the transporter with outward facing binding sites
2. This causes conformational change in the transporter
3. Eventually the transporter adopts an inwards facing confirmation that allows that dissociation of the two Na+ molecules in the cytosol
4. Glucose molecule gets pushed in as well
5. Returns to the outwards facing conformation to repeat the cycle

Question 6

Antiporter

Answer 6

-The concentration gradient of one molecule is used to transfer the second molecule in opposite directions
(exchange of molecules)

• Example: sodium - proton exchanger

Question 7

Active transport

Answer 7

• Carried out by protein carriers within the cell
• Have specific binding sites for the exact molecule they are transporting
• They then use ATP to move the molecule from low concentration to high concentration