Movement Across Membranes

Question 1

what molecules is the membrane permeable to?

Answer 1

Gases and small uncharged polar molecules

Question 2

what molecules are impermeable to the membrane?

Answer 2

large uncharged polar molecules, ions, charged moleucles

Question 3

what are the membrane channels like?

Answer 3

narrow aqueous pores, (size or charge selective)

passive - may be gated by either voltage or ligand - usually ions or water.

Question 4

what are the carrier proteins like?

Answer 4

have a specific binding site, under go a conformational change to move molecules
passive or active

Question 5

what are the 3 types of carrier proteins?

Answer 5

unipolar - single substance
symport - two substances in the same direction
antiport - twi substances in opposite directions

Question 6

what are the 3 driving forces that move substances in or out of cells?

Answer 6

chemical, electrical, electrochemical

Question 7

how does the chemical driving force work?

Answer 7

based on concentration gradients

force directly proportional to concentration gradient

Question 8

how does the electrical driving force work (also called membrane potential)?

Answer 8

based on charge across membrane
Na+ and K+ ions (out and inside the cell)
force depends on size of membrane potential and ion charge

Question 9

how does primary active transport work?

Answer 9

Na+/K+ ATPase pumps 3Na+ out and 2K+ in

uses ATP

Question 10

how does secondary active transport work?

Answer 10

transport of a substance coupled to the transport of an ion down its gradient.
uses energy from generation of ions electrochemical gradient.

Question 11

what signalling molecules bind to intracellular receptors?

Answer 11

steroid hormones

Question 12

what signalling molecules bind to extracellular receptors?

Answer 12

peptide hormones

Question 13

what is GLUT1 deficiency syndrome?

Answer 13

very rare, mutations in a gene that encodes GLUT1, less functional so reduces the amount of glucose available to brain cells.

Question 14

what is Wilsons Disease?

Answer 14

rare disorder, mutation of ATP7B, results in deposition of copper in the liver and other tissues
when primary active transport goes wrong.

Question 15

what is Glucose-Galactose Malabsorption?

Answer 15

very rare, mutations in SGTL1 - less functional, inability to transport glucose and galactose resulting in malabsorption

Question 16

what causes cystic fibrosis?

Answer 16

mutation in CFTR protein, Chloride channel, found in many tissues, leads to sticky mucus