Lecture 16

Question 1

Ion channel structure

Answer 1

• formed by integral membranes proteins
• multiple subunits
• line aqueous pores

Question 2

What is a transmembrane protein domain?

Answer 2

• peptide sequence largely hydrophobic and spans across PM

- permanently attached to PM

Question 3

What is an antiporter?

Answer 3

• concentration gradient of 1 molecule is used to transfer a 2nd in opposite directions

Question 4

What can and can’t cross membranes

Answer 4

• small, uncharged molecules CAN CROSS membranes like O2

- large, charged, polar molecules CANT CROSS membranes like cholesterol

Question 5

What is an a helice?

Answer 5

• most common protein structure that can cross biological membranes

Question 6

How do ion channels work?

Answer 6

• often are gated, can turn ON and OFF to respond to different stimuli

Question 7

Types of gated ion channles?

Answer 7

Voltage: channels respond to charge changes across membranes
- looks at neurons and action potentials
Ligand: channel responds by binding specific molecules on the surface
- binding ligands produces a conformational change in the structure of receptor/channel

Question 8

What are the 4 basic mechanism for moving molecules across membranes?

Answer 8

1) Simple Diffusion
2) Active Transport
3) Diffusion through channels
4) Facilitated diffusion

Question 9

How do glucose transporters work?

Answer 9

1) transport ready to accept glucose molecule
2) glucose accepted by the transport
3) intracellular side of the transporter opens
4) glucose= released and the cycle repeats

Question 10

What do Tetraspanins play a role in?

Answer 10

• play a role in cell adhesion, motility, proliferation, and more

Question 11

What is are Tetraspanins?

Answer 11

• a family of membrane proteins found in all multicellular eukaryotes
• 4 transmembrane alpha-helices
• 2 extracellular domains- 1 short and 1 long

Question 12

What are channels?

Answer 12

• provide another form of passive transport
• selective only some ions can pass
• effective for small, CHARGED molecules like Na+
• down concentration gradient

Question 13

What is facilitated diffusion?

Answer 13

• compounds bind to integral membrane protein- facilitated transporter
• change in transport conformation allows release of compounds on other side of the membrane
• moves down a concentration gradient

Question 14

what are passive mechanisms

Answer 14

• passive movement of substances across membranes rely on molecular concentrations
• Does NOT needed NRG

Question 15

What is a symporter?

Answer 15

• sometimes cells need to move substances from higher concentrations to lower concentrations
• they can’t rely on gradients so they rely on ANOTHER molecules chemical gradient that would NOT REACH extracellular and intracellular equilibrium

Question 16

What are glucose transporters?

Answer 16

• animal cells import glucose from blood to cells DOWN concentration gradient

Question 17

What is active transport?

Answer 17

• compound binds to an integral protein called ACTIVE TRANSPORTER
• Change in the conformation of transporter caused by hydrolysis of ATP molecule allows molecules to be released on other side of the membrane
• compounds move AGAINST concentration gradient
• needs NRG and ATP to form

Question 18

What is simple diffusion?

Answer 18

• Down concentration gradient

- works for very small, uncharged molecules like O2

Question 19

What property of integral membrane proteins allows them to

remain embedded in a lipid bilayer?

Answer 19

They have a Transmembrane Domain made up of hydrophobic amino acids

Question 20

What do Tetrodotoxin (TTX) and curare toxins interfere with?

Answer 20

movement through ion channels.

Question 21

What mechanisms do Molecules move across membranes through?

Answer 21

Passive and active