Membranes and Proteins

Question 1

What is the function of the cell membrane?

Answer 1

Communication, regulating transport, transmitting signals

Question 2

What types of biological molecules are found in cell membranes?

Answer 2

Carbohydrates, proteins, and lipids

Question 3

Why does the membrane form a bilayer?

Answer 3

The hydrophobic tails of the phospholipids interact with each other and the hydrophilic heads interact with the water on the outside and inside of the cell

Question 4

Why are membranes asymmetrical? What causes it?

Answer 4

The outside has different functions than the inside. The asymmetry comes from the proteins and the different types of phospholipids

Question 5

What is a membrane’s TM?

Answer 5

The temperature where a membrane freezes or becomes fluid

Question 6

What characteristics of the phospholipid tails contribute to their fluidity?

Answer 6

Unsaturation and chain length

Question 7

What makes a membrane more fluid?

Answer 7

Phospholipids with shorter carbon chains and more double bonds

Question 8

What are integral membrane proteins?

Answer 8

Proteins with a hydrophobic regions that goes into (monotopic) or through (transmembrane) the membrane

Question 9

What are multipass proteins?

Answer 9

Proteins that have hydrophobic regions separated by hydrophilic regions. The hydrophobic regions pass through the membrane and the hydrophilic regions form loops

Question 10

What are peripheral membrane proteins?

Answer 10

Proteins on one side of the membrane that have no hydrophobic regions and don’t go into the membrane

Question 11

What is glycosylation and what is it used for?

Answer 11

Adding a sugar to something, usually a membrane protein for signaling or recognition purposes?

Question 12

What kinds of molecules can easily get through the membrane?

Answer 12

Small hydrophobic molecules, gases, small uncharged polar molecules

Question 13

What kinds of molecules can’t get through the membrane at all without help?

Answer 13

Large uncharged polar molecules, ions, charged polar molecules

Question 14

What is passive transport?

Answer 14

Solutes moving down their concentration gradient, no energy input is needed

Question 15

What is active transport?

Answer 15

Solutes move against their concentration gradient, requires energy input

Question 16

What are carrier proteins? How do they work?

Answer 16

They are used in facilitated diffusion to get certain molecules across the membrane that can’t diffuse across on their own. They bind to their specific solute, change shape, and the solute detaches on the other side of the membrane because its still moving down its concentration gradient

Question 17

What are channels? How do they work and how are they regulated?

Answer 17

Multiple proteins forming a hollow tube that allows ions through. The channels are specific for one particular ion, and the ion diffuses down its concentration gradient through the channel. They are regulated by gating

Question 18

What are the three types of ion channel gating?

Answer 18

Voltage, ligand, and mechanical

Question 19

What triggers voltage gated channels to open or close?

Answer 19

A change in the membrane potential will make the charged amino acids in the S4 domain of the channel move around and open the channel, and go back to their original positions when at resting voltage.

Question 20

What triggers ligand gated channels to open or close?

Answer 20

When the ligand binds, the channel opens. When the ligand detaches, the channel closes

Question 21

What triggers mechanical gated channels to open or close?

Answer 21

Physical stretching of the membrane

Question 22

How does the Na+/K+ ATPase pump work? What is the purpose?

Answer 22

ATP is hydrolyzed and 3 sodium are pumped out of the cell and 2 potassium are pumped in. It sets up membrane potential

Question 23

What are cotransporters? How do they work?

Answer 23

Transport proteins that move 2 things at once. They work through indirect active transport. One thing moves down its concentration gradient and powers the other thing moving against its concentration gradient. ATP is still used up, but not directly by the cotransporter

Question 24

What are symporters?

Answer 24

Both things move in the same direction

Question 25

What are antiporters?

Answer 25

Both things move in opposite directions

Question 26

In intestinal epithelial cells, which transporters are present and how do they move glucose from the intestinal lumen to the bloodstream?

Answer 26

The Na+/glucose symporter transports 2 Na+ into the cell and uses that energy to get a glucose into the cell. The concentration gradient for this was built up by the Na+/K+ ATPase pump through ATP hydrolysis. The GLUT2 transporter then moves the glucose into the bloodstream through facilitated diffusion.