Lecture 13

Question 1

T or F, lipids are structurally and functionally diverse group of molecules

Answer 1

True

Question 2

Describe the amphipathic properties of membrane lipids.

Answer 2

• • Apolar tail (hydrophobic)
• • Polar head (hydrophilic)
• • polar head associates with water and nonpolar tail hides from water

– don’t form large covalent polymers instead they ten to associate w/ each other through noncovalent interactions

– stabilized through the hydrophobic effect

– also stabilized through van Der Waals interactions between hydrocarbon regions of molecules

Question 3

What are primary components of membranes?

Answer 3

lipids

Question 4

What are key components of lipids?

Answer 4

– fatty acids –> long hydrocarbon chains (14-24 C) with carboxyl group

Question 5

What is an oleate ion?

Answer 5

– an unsaturated fatty acid with one cis double bond

Question 6

What is a stearate ion?

Answer 6

Stearate (the anionic deprotonated form of stearic acid) it is a saturated fatty acid

Question 7

In most naturally occurring unsaturated fatty acids what is the orientation?

Answer 7

• • Orientation is about double bonds is cis rather than trans
• • this has an important effect on molecular structure bc each cis double bond inserts a bend into the hydrocarbon chain

Question 8

What is the difference between saturated and unsaturated fatty acids

Answer 8

• • unsaturated –> liquid at room temp
• • Saturated –> solid

– usually an even number of carbons

Question 9

Why is unsaturation important?

Answer 9

• • because it keeps membranes fluid instead of solid

- - helps with movement and conformation changes of transmembrane proteins

Question 10

What is the importance of straight fatty acid tails?

Answer 10

– they can pack together and interact

– increasing number of van der Waals contacts to form regular semi crystalline structures

Question 11

What is the nomenclature of a double vs saturated fatty acid

Answer 11

double is enonated whereas saturated is anoate

Question 12

What makes up a triaglycerol?

Answer 12

Fatty acids + glycerol

– a glycerol molecule, which is a 3 carbon with OH at each carbon and a three carboxylic acids esterified to the

– water-insoluble, so must have a specific mechanism of transport in the body

Question 13

What are the effects of the amphipathic nature of membrane lipids?

Answer 13

They will preferentially arrange into micelles or bilayers to bury phobic tails away from the aqueous environment

– self assembly process driven by hydrophobic interactions between fatty acid cahins

– close packing is directed by van der Waals interactions between hydrocarbon chains

Question 14

What is the most abundant lipid in membranes?

Answer 14

– Glycerophospholipids

Question 15

What is the general structure of glycerophospholipids?

Answer 15

carbon one and to have an acyl group and carbon three has an orthophosphate group attached with a philic group attached

Question 16

What is the general structure of a sphingolipid? What is this basic structure called?

Answer 16

it is a C15 on the C1, an amine on C2, and C3 containing a hydroxyl group. Called a sphingosine unit

Question 17

What is the structure of glycosphingolipids? What category do these lipids fall under?

Answer 17

contains a C15 on C1, an amide on C2, and a sugar on C3. Categorized as glycolipids

Question 18

What is the non-sugar portion of glycosphingolipids generally referred to as?

Answer 18

Ceramide

Question 19

True or false. glycolipids can have many carb residues and are oriented asymmetrically in the plasma and are always facing the extracellular side.

Answer 19

True

Question 20

True or false.

glycolipids can be components of RBC membranes

Answer 20

True

Question 21

What is the general function of cholesterols in the membrane?

Answer 21

act as a fluidity buffer

Question 22

What does cholesterol due at each extreme in temperature?

Answer 22

it cold temps it prevents close packing and increases fluidity whereas at high temps it prevents excessive movement and decreases movement.

Question 23

What is the general structure and characteristic of cholesterol

Answer 23

tetracyclic molecule that has a weak ampihatic nature, polar groups, rigid ring system, and a flexible tail.

Question 24

True or false. Brain cells commonly have cerebrosides and ganliosides

Answer 24

True

Question 25

True or false | axons are rich in glycosphingolipids

Answer 25

True

Question 26

What maintains glycolipids in the rigid aqueous face configuration?

Answer 26

the inability of these lipids to move from these positions maintained by the limited flip flip ability of proteins

Question 27

What are the typical ratios of lipid:protein?

Answer 27

1:4 or 4:1

Question 28

What type of proteins exist in RBC membrane, retinal rod cells, vs SAR muscle cells in terms of size?

Answer 28

larger exist in RBC + SAR and smaller size exist in Retinal rod cells

Question 29

What differentiated anchored proteins from peripheral and integral proteins?

Answer 29

anchored protein are covalently linked to fatty acids chains or glycolipids at surface whereas the other types are associated by non-covalent interactions

Question 30

True or false | Diffusion is mainly lateral and rapid and rarely transverse.

Answer 30

True

Question 31

What factors of membranes increase fluidity?

Answer 31

short fatty acid tails, unsaturated fatty acids, and cholesterol

Question 32

True or false. | Saturated fatty acids decrease the Tm of the membrane

Answer 32

false they increase by increasing number of hydrogen bonds

Question 33

true or false | outer and inner membrane differ in lipid composition and in types of associated proteins

Answer 33

true

Question 34

What enzyme is responsbile for flipping lipids between inner and outer membranes?

Answer 34

flippase

Question 35

True or false | orientation of transmembrane proteins does not change over time

Answer 35

true

Question 36

true or false. | outer plasma membrane is rich in cholesterol

Answer 36

false. it is rich in glycosylated protein and lipids

Question 37

true or false | fats tend to be saturated in animals and unsaturated in plants

Answer 37

true

Question 38

Integral proteins are held by noncovalent forces. True or false?

Answer 38

true

Question 39

What are the characteristics of the glycophorin integral protein?

Answer 39

ampihphatic with extracelluar portion that is rich in phillic AA Ser Thr Asp and a phobic alpha helix in the membrane that has phobic amino acid. It is also a glycoprotein meaning it has sugars attached to its structure

Question 40

What are common characteristics of protein/membrane interactions in integral protein?

Answer 40

typically 7 alpha helices that span the membrane with 20aa/helix with extensive H bonding there are the typical 3.6aa/turn and 1 turn=0.54nm bilayer core is about 3nm

Question 41

What characteristic does bacteriorhodopsin have?

Answer 41

has a light absorbing pigment at its center that captures light energy and pumps protons from cell to outside -- acts as a proton pump

Question 42

If a phobic index is positive, does it mean it is phobic or phillic?

Answer 42

phobic. negative values are phillic.

Question 43

What information can you get from a phobic index?

Answer 43

it can help you see which sections of the protein is in the membrane/ specific AA involved at teach section. The groups let you see how many helices the protein has in the membrane

Question 44

What is the structure of a transmembrane porin?

Answer 44

it is made of an amphiphatic b barrel structure. Hydrophillic residues on the inside of the channel and phobic residues on the outside facing the lipid bilayer.

Question 45

What is the general function of membranes?

Answer 45

``` transport of substance in and out of cell ion transport and nerve cell conductance cell signaling maintaining shape cell-cell interaction ```