Lecture 4

Question 1

What are the functions of the biological membranes?

Answer 1

Defines boundaries and compartmentalizes organelles; compartmenst allow for localization of specific proteins, so unique functions for organelles; regulate the movement of molecules; contains receptors for signals allowing cell-cell communication

Question 2

What are phospholipids made from?

Answer 2

Two fatty acids attached to a glycerol backbone with a phosphate head

Question 3

What are fatty acids?

Answer 3

Hydrocarbon chains with a COO- (carboxylic acid) at one end

Question 4

What is the difference between saturated and unsaturated fatty acids?

Answer 4

Saturated has no C=C double bonds, unsaturated does (causes kinks)

Question 5

Name the three important properties of the biological membrane

Answer 5

Hydrophobic core acting as permeability barrier, stable and self-healing, provides sealed and closed compartments

Question 6

Name the classes of amphipathic lipids

Answer 6

Phosphoglycerides, Sphingolipids, Cholesterol, and Membrane Glycolipids

Question 7

What are phosphoglycerides?

Answer 7

Derivatives of glycerol-3-phosphate with two fatty acyl chains esterified to a glycerol backbone and polar head attached to a phosphate group

Question 8

What are the four head groups that can attach to the phosphate?

Answer 8

Phosphatidyl-ethanolamine (PE), phosphatidyl-serine (PS), phosphatidyl-choline (PC-most common) and sphingomyelin. (And inisitol- PI)

Question 9

What is sphingomyelin?

Answer 9

It is a specialized membrane lipid

Question 10

What is a sphingolipid?

Answer 10

Has a phosphate head where the lipid is derived from sphingosine

Question 11

What is a common sphingolipid and where is it found?

Answer 11

Sphingomyelin; it makes up myelin sheaths around axons in the brain

Question 12

What are lipid rafts?

Answer 12

Microdomains in membranes made of sphingolipids

Question 13

What is the function of cholesterol?

Answer 13

It modulates membrane fluidity

Question 14

What is cholesterol made of?

Answer 14

It is mostly hydrogen and carbon with a small polar OH

Question 15

How are membrane glycolipids formed?

Answer 15

By adding carbohydrate (sugar) groups to the lipids- occurs in the golgi.

Question 16

What determines blood type?

Answer 16

The sugar of the glycosphingolipid (either A or B) that is expressed on the surface of red blood cells

Question 17

What are the functions of glycolipids?

Answer 17

Cell-cell adhesion, cell-cell recognition, and the alteration of electrical gradients (sugars are often charged and always polar)

Question 18

What are the methods of movement of the phospholipids in the bilayer?

Answer 18

Lateral (side to side- rapid and frequent) and flip flop (switches sides of the bilayer- rare because polar head group does not cross hydrophobic core)

Question 19

What does FRAP stand for?

Answer 19

Fluorescence recovery after photobleaching

Question 20

What is FRAP used for?

Answer 20

To study membrane fluidity

Question 21

What factors influence membrane fluidity?

Answer 21

Lipid composition, structure of phopholipid tails, and temperature

Question 22

Which phospholipids are present in the extracellular leaflet?

Answer 22

PC and sphingomyelin

Question 23

Which phospholipids are present in the intracellular leaflet?

Answer 23

PE and PS

Question 24

How is membrane asymmetry accomplished?

Answer 24

Phospholipids are synthesized in the smooth ER and inserted into a bilayer at a lumenal face

Question 25

How are phospholipids transferred to the cytoplasmic face?

Answer 25

Enzymes called flipases move them.

Question 26

What are integral membrane proteins?

Answer 26

Amphipathic proteins that span the core of the membrane

Question 27

What are peripheral membrane proteins?

Answer 27

Proteins that do not contact the hydrophobic core of the membrane but associate with integral or lipid- anchored proteins or have direct interactions with lipid head groups

Question 28

What are lipid anchored membrane proteins?

Answer 28

Proteins bound covalently to one or more lipid molecules

Question 29

What are outer leaflet proteins linked to?

Answer 29

Covalently linked to GPI (glycosylated inisitol)

Question 30

What are inner leaflet proteins linked to?

Answer 30

The #5 protein is linked to a fatty acid tail or isoprene derivative

Question 31

What is myristalation/palmilation?

Answer 31

The attachment of inner leaflet proteins to a fatty acid

Question 32

Why do membrane proteins have asymmetric topology?

Answer 32

So that the membrane can have different functions on either side.

Question 33

How do you freeze fracture a membrane?

Answer 33

The membrane is quickly frozen and sliced with a "diamond knife" so it splits down the hydrophobic middle

Question 34

What is the purpose of freeze fracturing a membrane?

Answer 34

It allows us to view the membrane proteins

Question 35

How does trypsin allow us to study membrane proteins?

Answer 35

It is a non-specific protease, so by digesting proteins under certain conditions, it can help us differentiate intra and extracellular membrane proteins

Question 36

Describe the permeability of the bilayer to different types of molecules

Answer 36

Permeable to small, uncharged or hydrophobic molecules; relatively permeable to small uncharged polar molecules; mostly impermeable to large uncharged and polar molecules; and impermeable to charged molecules )(ions)

Question 37

How do impermeable molecules cross the bilayer?

Answer 37

Simple diffusion, facilitated diffusion, and active transport

Question 38

What do carrier proteins do?

Answer 38

They bind solutes on one side of the membrane, undergo a conformational change, and transfer solutes to the other side of the membrane

Question 39

What do channel proteins do?

Answer 39

Form hydrophilic channels through the membrane to allow the passage of solutes without a change in the protein's conformation

Question 40

What are gated channels?

Answer 40

Channel proteins that open only under certain conditions

Question 41

How do gated channels open?

Answer 41

The channel can undergo a depolarization event or a chemical-gated channel can rely on the binding of a particular substance

Question 42

What are the three ways energy can be supplied for active carriers?

Answer 42

ATP hydrolysis, coupled transport, and light driven

Question 43

Describe a Na/K pump

Answer 43

3 Na are pumped out and 2 K are pumped in against the concentration gradient for each ATP consumed

Question 44

What is coupled active transport?

Answer 44

The movement of two molecules simultaneously, where one molecule moves using the energy gradient from the other molecule

Question 45

What is the difference between symport and antiport?

Answer 45

Symport- molecules move together | Antiport- molecules move in opposite directions