Membrane Structure

Question 1

What is the function of the plasma membrane?

Answer 1

Forms the boundary of the cell, and separates the cytosol from the extracellular environment.

Question 2

What organelles have a membrane separating them from the cytosol?

Answer 2

Organelles in the endomembrane system: nucleus, ER, Golgi, mitochondria, chloroplast, lysosome, peroxisome

Question 3

How thick is a phospholipid membrane?

Answer 3

about 5 nm thick

Question 4

What percent of the mass of the membrane is attributed to lipids?

Answer 4

~50%

Question 5

How many carbons are typically found in a fatty acid tail?

Answer 5

14-24

Question 6

What are the three most common phosphoglycerides in membranes?

Answer 6

phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS)

Question 7

Which main phosphoglyceride has a negative charge in the head?

Answer 7

phosphatidylserine (PS)

Question 8

What are sphingolipids?

Answer 8

Phospholipids that use sphingosine rather than glycerol as a backbone, and contains a long fatty acid chain with a double carbon bond. At one end there is two hydroxyl groups and an amine group.

Question 9

What is the most abundant sphingosine?

Answer 9

Sphingomyelin

Question 10

What are glycolipids?

Answer 10

Like phospholipids but have sugar attached instead of a phosphate group.

Question 11

Describe cholesterol

Answer 11

steroid with a 4-C ring structure attached to a polar hydroxyl group and a short nonpolar hydrocarbon chain.

Question 12

How many times a second does a membrane component move laterally?

Answer 12

1 * 10^7 times per second

Question 13

What kind of movement rarely happens in membranes

Answer 13

A flipping of phospholipids

Question 14

What catalyzes the flip-flop between monolayers?

Answer 14

phospholipid translocators (AKA flippases)

Question 15

What is different about the plasma membrane of bacteria cells?

Answer 15

They commonly only have one phospholipid and no cholesterol in their cell membrane.

Question 16

A myelinated section of membrane would have greater or smaller glycolipid concentration?

Answer 16

Greater

Question 17

What is a micelle?

Answer 17

aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid

Question 18

Why are tears in membranes spontaneously fixed?

Answer 18

It is energetically favorable for the phospholipid bilayer to form a sealed compartment.

Question 19

What properties will a membrane have if the fatty acid tails are shorter, with more doubly bonded carbons?

Answer 19

The phospholipids will be less tightly packed, resulting in a more fluid membrane with a lower transition temperature.

Question 20

What is the function of the steroid rings of cholesterol?

Answer 20

To prevent the side chains of lipids from approaching each other, which prevents crystallization.

Question 21

What are lipid rafts?

Answer 21

Microdomains of the plasma membrane with a higher concentration of cholesterol, sphingomyelin, and glycosphingolipids.

Question 22

What is one theorized function of lipid rafts?

Answer 22

Cell signalling

Question 23

Which phospholipids are found mainly in the outer monolayer?

Answer 23

phosphatidylcholine and sphingomyelin, both of which have a choline in the head group

Question 24

Which phospholipids are found mainly in the inner monolayer?

Answer 24

Phosphatidylethanolamine and phosphatidylserine

Question 25

On the cytosolic side of the plasma membrane, what does protein kinase C (PKC) need to bind to to become activated?

Answer 25

phosphatidylserine (PS)

Question 26

What is the third main phospholipid found primarily on the cytosolic layer?

Answer 26

phosphatidylinositol (PI)

Question 27

What does phosphatidylinositol (PI) result in?

Answer 27

phosphoinositide 3- kinase (PI3K), a signaling molecule

Question 28

What happens to phosphatidylserine when a cell is undergoing apoptosis?

Answer 28

It will be translocated to the extracellular monolayer, which targets the cell for phagocytosis

Question 29

Where are glycolipids found?

Answer 29

Extracellular monolayer of plasma membrane, and inner monolayer of organelles

Question 30

Approximately how much is the protein concentration in myelin membranes?

Answer 30

25%

Question 31

About how much is the protein concentration in the inner membranes of chloroplasts and mitochondria?

Answer 31

75%

Question 32

What is the difference between an integral protein and a transmembrane protein?

Answer 32

an integral protein enters the plasma membrane but does not pass through the entire lipid bilayer

Question 33

What are peripheral proteins?

Answer 33

Proteins attached to the plasma membrane but do not enter the lipid bilayer. They can be attached by covalently linked lipid chains.

Question 34

What is a GPI?

Answer 34

composed of a phosphatidylinositol group linked through a carbohydrate-containing linker

Question 35

What are membrane-associated proteins?

Answer 35

proteins that interact with other membrane proteins via noncovalent interactions

Question 36

What characteristic, other than shape, determines a protein’s function?

Answer 36

Its location on the membrane

Question 37

What are glycosylated membrane proteins?

Answer 37

proteins that have sugar moieties added to them.

Question 38

what are the functions of the glycocalyx AKA sugar coat?

Answer 38

1. Protects cell against mechanical and chemical insults
2. Keeps unwanted cells away
3. prevents unwanted cell-cell interactions

Question 39

what is rotational diffusion?

Answer 39

a compound’s rotation on an axis perpendicular to the plane of the bilayer

Question 40

what is lateral diffusion?

Answer 40

movements of compounds from side to side

Question 41

Where are Major Histocompatibility Complex (MHC) molecules synthesized?

Answer 41

RER and Golgi

Question 42

What is the function of MHC molecules?

Answer 42

To act as a “clear” tag, and also to be a marker for destruction when a cell is infected