Chapter 6.3.2 (Exam 1) Facilitated Diffusion Flashcards
Substances Can Cross Membranes by Passive Processes
What is facilitated diffusion?
polar and charged molecules diffuse with concentration gradients, but facilitated by protein channels or carriers
What are channel proteins?
Integral membrane proteins that form a tunnel
Inside of the tunnel is lined with hydrophilic molecules
What are carrier proteins?
Membrane proteins that bind some substances and speed their diffusion through the bilayer
What are ion channels?
Channel proteins with hydrophilic pores
Most are gated—can be closed or open to ion passage
When do gated ion channels open?
When the protein is stimulated to change shape by:
Chemical signal (ligand-gated)
Mechanical stimulus
Electrical charge difference (voltage-gated)
What are aquaporins?
Special channels where water can cross membranes but ions cannot
How was the function of aquaporins identified?
By injecting aquaporin proteins into a frog oocyte, aquaporins were formed, and when the oocyte was placed into a hypotonic solution, water flowed into it
What is the function of carrier proteins?
Transport polar molecules, such as glucose, across membranes in both directions
A glucose transporter is a type of carrier protein. How does it function?
Glucose binds to the glucose transporter, causing it to change shape and release the glucose on the other side
What does the rate of diffusion depend on?
Concentration gradient
Number of carrier proteins in the cell membrane
What does it mean if a diffusion system is saturated?
All of the carrier proteins are loaded, and the rate of diffusion is being limited by the number of transporters
How do cells that need lots of energy increase their rate of diffusion for glucose?
Cells that need lots of energy (e.g., muscle cells) have many glucose transporters
