Membrane

Question 1

What do membranes do?

Answer 1

Receive info, import and export small molecules, and have the capacity for movement and expansion.

Question 2

What is the membrane structure?

Answer 2

Lipid bilayer with lipids and proteins interacting noncovalently.

Question 3

What are the different types of membrane lipids and what characteristic do they share?

Answer 3

Glycolipid, cholesterol, phospholipid, all are amphiphilic.

Question 4

Describe cholesterol and its role

Answer 4

reduces membrane permeability to small molecules. Role in fluidity is temperature dependent .

Question 5

How do monolayers in plasma membrane move?

Answer 5

Monolayers (leaflets) commonly diffuse laterally but transverse movement (flip flop) is rare.

Question 6

How is saturation related to fluidity?

Answer 6

Unsaturated hydrocarbon chains reduce membrane thickness and Shorter hydrocarbon chains makes membrane more fluid due to fewer interactions.

Question 7

How did experiment between mouse and human cells show diffusion of proteins in membrane?

Answer 7

When they were mixed, the labeled proteins mixed and moved around.

Question 8

Describe FRAP

Answer 8

Used to measure the rate of diffusion of lipids and proteins in the membrane
Higher rate of diffusion means a quicker rate of fluorescence return

Question 9

How is mobility of proteins restricted in cell?

Answer 9

• Protein aggregation •
Tethering to a protein inside the cell •
Tethering to a protein outside the cell •
Cell-cell interactions •
Tight junctions •
Cytoskeletal Network

Question 10

Where does phospholipid synthase occur?

Answer 10

In the ER

Question 11

What do scramblases do?

Answer 11

They randomly distribute phospholipids in either direction toward equilibrium.

Question 12

What do flippases and floppases do?

Answer 12

Move phospholipids from outer to cytosolic leaflet or vice versa, requires ATP unlike scramblase

Question 13

What do membrane proteins do and what are their types.

Answer 13

They perform the tasks of the membrane. Integral and Peripheral Membrane Proteins.

Question 14

Describe single vs multipass transmembrane alpha helices.

Answer 14

Single pass are mostly nonpolar with no proline. Multipass may have a mix of hydrophobic and hydrophilic, or be entirely hydrophobic depending on structure.

Question 15

How many amino acids needed to span membrane as a helix?

Answer 15

20-30

Question 16

Describe beta barrels.

Answer 16

H bonding between B strands, can’t be identified by hydropathy plot since only 10 amino acids required for B strand to cross membrane.

Question 17

Where are oligosaccharides added in membrane?

Answer 17

Non cytosolic side of lipids and proteins.

Question 18

Describe permeability of the lipid bilayer.

Answer 18

Small hydrophobic molecules like CO2 easily diffuse. Small uncharged polar molecules like H2O diffuse but with more difficulty. Large uncharged polar molecules like glucose hard to diffuse. Ions can not diffuse.

Question 19

Describe diffusion and the difference between passive and active transport.

Answer 19

Diffusion is the movement down a gradient.
Passive uses a channel or transporter but no energy needed.
Active transport requires energy.

Question 20

What are channel proteins?

Answer 20

Water filled pores through which solutes can diffuse.

Question 21

How do transporters work?

Answer 21

They alternate between two conformations to mediate transport.

Question 22

What are the types of transporters?

Answer 22

Uniport (One transported molecule), Symport (two molecules together), Antiport(one molecule on each opposite side.)

Question 23

What is glut1-glucose transporter?

Answer 23

A passive transport uniporter that transports glucose to the cytosol.

Question 24

What is the chloride bicarbonate exchanger?

Answer 24

A passive transport antiporter that uses Cl- and other molecules to cause exhalation and movement of CO2.

Question 25

What are the steps of the CBE?

Answer 25

1. CO2 reacts with H2O, through carbonic anhydrase to from HCO3- and H+
2. HCO3- moved out, Cl- moved in
3. HCO3- moves into erythrocyte, Cl- out, CO2, and H2O formed
4. CO2 leaves erythrocyte and is exhaled.

Question 26

What are the different types of active transporters?

Answer 26

Coupled transporters that move multiple molecules across membrane and ATP driven pumps.

Question 27

What does the Ca2+ pump do?

Answer 27

Functions in muscle cells to sequester Ca2+ in the Sarcoplasmic Reticulum, so it can be released during muscle contraction, Uses ATP as energy source.

Question 28

What is the Na+/K+ pump?

Answer 28

An antiporter that uses ATP as an energy source and maintains concentration gradient and contributes to difference in charge across membrane.

Question 29

How does Na+ /K+ pumping work?

Answer 29

Phosphorylation causes pump to hydrolyze ATP, triggering a conformational change that ejects Na+ and causes K+ to move in.
The pump then dephosphorylates itself, causing it to return to its original conformation and K+ is ejected.

Question 30

What is the Na+/ Glucose transporter?

Answer 30

A symporter and gradient driven pump that uses the Na+ electrochemical gradient as an energy source for the pump, both molecules move in same direction.

Question 31

What occurs in transcellular transport?

Answer 31

Intestinal cells transport glucose from the gut to extracellular fluid first, using sodium gradient to transport it against concentration gradient.
Then passive transport moves it from high to low concentration. Na+ moves out of cell through Na+/K+ pump.

Question 32

What are the characteristics of ion channels?

Answer 32

They exist in open/closed states, can be regulated by gating and/or phosphorylation.

Question 33

What types of ion channels are there?

Answer 33

Voltage gated, ligand gated (extracellular/intracellular ligand), mechanically gated.

Question 34

How does the bacterial/k+ channel work?

Answer 34

Amino acids affect what goes through pore, number of interactions ion makes based on pore size and charge of amino acids surrounding the pore.