Lecture 18- Membrane Protein Transporters

Question 1

How does glucose transport?

What type of glucose is quickly metabolized or stored?

What type of protein-lipid interaction is it?

Answer 1

• Facilitated Diffusion: down the concentration gradient into the cell
• Intracellular glucose
• Type III: 12 TM helices

Question 2

Hallmarks of Facilitated Diffusion:

• ____ rates of diffusion _____ a concentration gradient
• __________ kinetics
• Susceptible to __________ inhibition

Answer 2

• High rates of diffusion down a concentration gradient
• Saturation kinetics
• Susceptible to competitive inhibition

Question 3

Modeling Facilitated Diffusion as an Enzyme Rxn:

• “________” = glucose outside the cell (__out)
• “________” = glucose inside the cell (__in)
• “______” = transporter (_)

Answer 3

• “Substrate” = glucose outside the cell (S_out)
• “Product” = glucose inside the cell (S_in)
• “Enzyme” = transporter (T)

Question 4

What is the transport constant for glucose and what is it similar to?

Relationship to affinity?

Answer 4

K_t

K_m

K_t increases & affinity increases

Question 5

Eukaryotic Cells Express a Number of Glucose Transporters:

• Transporter GLUT 3:
  
  • Tissues expressed?
• Transporter GLUT 4:
  
  • Tissues expressed?

Answer 5

Eukaryotic Cells Express a Number of Glucose Transporters:

• Transporter GLUT 3:
  
  • Brain (neuronal), Testis (Sperm)
• Transporter GLUT 4:
  
  • Muscle, fat, heart

Question 6

Glucose uptake by muscle and fat cells is regulated through ________-sensitive _________/_________ of glucose transporters (GLUT 4)

Answer 6

Glucose uptake by muscle and fat cells is regulated through insulin-sensitive exocytosis/endocytosis of glucose transporters (GLUT 4)

Question 7

3 General Classes of Transport Systems:

• Transporters that carry only 1 substance?
• Transporters that carry 2 substances w/ 1 protein transport?
  
  • Same direction
  • Opposite direction

Answer 7

• Transporters that carry only 1 substance: Uniport
• Transporters that carry 2 substances w/ 1 protein transport: Cotransport
  
  • Same direction: Symport
  • Opposite direction: Antiport