Fluid Mosaic model, membrane proteins, and movement across membranes

Question 1

What are the components of a cell membrane [3]?

Answer 1

1) Lipids
2) Proteins
3) Carbohydrates (Attached to glycolipids and glycoproteins)

Question 2

Phospholipids:

Answer 2

• Head is a polar hydrophilic and tail is a nonpolar fatty acid (amphipathic molecule)
• Shape of a structure is determined by ratio of head to tail
• Forms a bilayer in water because of polarity

Question 3

How do liposomes form?

Answer 3

Phospholipids in water with a neutral pH form a spherical bilayer that surround whatever potential macromolecule was captured from the system.

Question 4

How does cholesterol impact the fluidity of a membrane?

Answer 4

Can increase or decrease depending on the temperature:

At typical cell temperatures, cholesterol decreases fluidity.

At low temperatures, it increases fluidity.

Question 5

Functions of membrane proteins [4]:

Answer 5

1) Transporters (moves ions across membrane)
2) Receptors (receives signals from the environment)
3) Enzymes (catalyze chemical reactions)
4) Anchors (attach to other proteins)

Question 6

What are the two groups of membrane proteins?

Answer 6

1) Integral membrane proteins
2) Peripheral membrane proteins

Question 7

What is an integral membrane protein?

Answer 7

Proteins that are permanently associated with the cell membranes.

Question 8

What are peripheral membrane proteins?

Answer 8

Temporarily associated with the lipid bilayer or with integral membrane proteins through weak covalent forces.

Question 9

How do transmembrane proteins work?

Answer 9

They span the entire lipid layer with a hydrophobic section that spans the membrane and two hydrophilic sections on either side.

Question 10

What is FRAP?

Answer 10

Fluorescent Recovery After Photobleaching. This process was used to prove that proteins move in the membrane plane.
->Area of membrane is bleached
->Fluorescent dye is attached to proteins
-> Bleach spot becomes fluorescent indicating proteins moved

Question 11

What is the fluid mosaic model?

Answer 11

Idea that lipids and proteins coexist in the plane of the plasma membrane moving laterally.

Question 12

How is homeostasis maintained within a cell?

Answer 12

The plasma membrane is selectively permeable, meaning it lets certain molecules in and out under certain conditions.

Question 13

What is passive transport?

Answer 13

This is when something enters the cell through diffusion. Oxygen and carbon dioxide move in this way.

Question 14

Types of membrane transports [2]:

Answer 14

1) Channel
2) Carrier

Question 15

How does a channel transport work?

Answer 15

It provides a channel for molecules of certain shape and size to pass through.

Question 16

How do carrier transporters work?

Answer 16

This binds to and then transports specific molecules. They can either be open to the inside or outside of the cell.

Question 17

What is osmosis?

Answer 17

Solvent like water moving across a selectively permeable membrane from a region of lower solute concentration to a region with higher solute concentration.

Question 18

What is osmotic pressure?

Answer 18

The tendency of a solution to draw in solvent by osmosis

Question 19

What is active transport

Answer 19

When molecules that cells need are not highly concentrated in its environment, it needs to be actively transported which requires energy.

Question 20

How does the sodium-potassium pump work?

Answer 20

Sodium has to move out of the cell and potassium needs to move in–both against gradients. The antiporter transport proteins use energy from adenosine triphosphate to do this.

Question 21

Where do phospholipids come from?

Answer 21

Fatty acids are activated in the cytosol, then they bond to glycerol-phosphate and are inserted into the ER. From there enzymes and protein work together to synthesize.

Question 22

Factors affecting membrane fluidity [3]:

Answer 22

1) Temperature
2) type of lipid (saturated increases, unsaturated decreases)
3) Cholesterol

Question 23

Types of ion channels [2]:

Answer 23

1) Voltage-gated: open/close in response to changes in membrane charge
2) Ligand-gated: open when molecule binds to channel

Question 24

Toxins on ion channels [2]:

Answer 24

1) Tetrodotoxin blocks voltage gated channels stopping nerve signals
2) Curare blocks acetylcholine receptors causing muscle paralysis

Question 25

Whats a symporter

Answer 25

Moves two molecules in the same direction

Question 26

What’s and antiporter

Answer 26

Moves two molecules in opposite directions

Question 27

How does a gated ion channel work?

Answer 27

Turns on/off in response to signals

Question 28

How does Na-Glucose symporter work?

Answer 28

Uses the higher concentration of Na+ to drive glucose against a concentration gradient