Deck 12: Lipids and Cell Membranes

Question 1

The temperature at which a phospholipid membrane transitions from a rigid to a fluid state is referred to as _______________.

Answer 1

T_m,or melting temperature

Question 2

What important property is conferred on membranes by transport systems?

A) asymmetry
B) selective permeability
C) bilayer
D) amphipathic nature
E) None of the answers is correct.

Answer 2

B

Question 3

In phosphoglycerides,the fatty acids are linked to the glycerol backbone by ______________ linkages.

Answer 3

ester

Question 4

___________________ membrane proteins are bound to membranes primarily by electrostatic and hydrogen bond interactions with the head groups of lipids.

Question 5

What membrane components contain carbohydrates?

A) lipid-linked proteins
B) cholesterol
C) integral membrane proteins in contact with the cytoplasm
D) phosphatidylserine
E) glycolipids

Question 6

What complex is observed between cholesterol and membrane phospholipids?

A) salt bridge
B) clathrate
C) lipid raft
D) phospholipid domain
E) None of the answers is correct.

Question 7

What property is used to determine the probability that a segment of a protein will be found embedded in a membrane?

A) hydropathy
B) polarity
C) acidity
D) entropy
E) solvation

Question 8

What substance inhibits prostaglandin H₂ synthase-1 by blocking the channel through which the substrate,arachidonate,travels?

A) acetaminophen
B) Celebrex
C) ibuprofen
D) Vioxx
E) acetylsalicylic acid

Question 9

What term describes molecules that have both hydrophilic and hydrophobic moieties?

A) amphoteric
B) amphiprotic
C) amphibian
D) amphipathic
E) None of the answers is correct.

Question 10

__________________ contain a double bond three carbons from the distal end of the fatty acid.

Question 11

The rate of diffusion is such that a phospholipid molecule can travel from one end of a bacterium to the other in _______________ of time.

Question 12

In animals,________________ is the key regulator of membrane fluidity.

Question 13

What is the most common process by which lipids and proteins move in the membrane bilayer?

A) kinesin-mediated movement
B) flip-flopping
C) translocation
D) lateral diffusion
E) asymmetric longitudinal flipping

Question 14

Some proteins are anchored to the membrane by being covalently attached to a _______________ group by a thioester linkage to a specific (non-C-terminal)cysteine residue.

Question 15

___________________ are aqueous compartments enclosed by a lipid bilayer which can be created in a laboratory.

Question 16

Ionized fatty acids readily form ______________ in aqueous solutions.

Question 17

What is the number of carbons found in the most commonly observed fatty acids?

A) 12 or 14
B) 14 or 16
C) 16 or 18
D) 18 or 20
E) 20 or 22

Question 18

What protein polymerizes into a lattice network around a budding membrane?

A) porin
B) clathrin
C) epsin
D) G protein
E) glycophorin

Question 19

________________ is a membrane lipid composed of sphingosine,fatty acid,and a simple sugar like glucose or galactose.

Question 20

In addition to phospholipids and glycolipids,which of the following is a major type of membrane lipid?

A) cholesterol
B) vitamin E
C) triacylglycerol
D) free fatty acids
E) None of the answers is correct.

Question 21

What are the primary structural differences between phospholipids constructed from a glycerol platform and those from sphingosine?

Question 22

Membranes are primarily comprised of

A) lipids.
B) proteins.
C) carbohydrates.
D) All of the answers are correct.
E) A and B.

Question 23

Draw a cross-section of a micelle and a membrane bilayer.

Question 24

The most common motif found in membrane spanning proteins is

A) $\alpha$ helices of nonpolar amino acids that pass through the membrane.
B) $\alpha$ helices of charged amino acids that form channels via extensive hydrogen bonding.
C) a triple helix of $\alpha$ helices.
D) a helix-turn-helix arrangement of the peptide strands.
E) None of the answers is correct.

Question 25

Which of the following is NOT correct concerning the structure given?

A) It is a component of biological membranes.
B) It is amphipathic.
C) It is a sphingolipid.
D) It is a phosphoglyceride.
E) It is phosphatidyl choline.

Question 26

What force(s)stabilize(s)the lipid bilayers?

A) van der Waals interactions
B) electrostatic and hydrogen bonding between the polar heads and surrounding water
C) covalent bonds between the lipids and membrane proteins
D) van der Waals interactions and electrostatic and hydrogen bonding between the polar heads and surrounding water
E) electrostatic and hydrogen bonding between the polar heads and surrounding water and covalent bonds between the lipids and membrane proteins

Question 27

How do the membranes of archaea differ from bacteria and eukaryotes?

A) The lipids do not contain a carboxylic acid ester, but instead have an ether link to the glycerol.
B) The alkyl chains are branched.
C) The stereochemistry of the central carbon of glycerol is inverted.
D) A and C are correct.
E) All the answers are correct.

Question 28

Which of the following is true?

A) Membranes are lipid bilayers.
B) Membrane lipids have both hydrophobic and hydrophilic properties.
C) Many membranes are electrically polarized.
D) All of the answers are correct.
E) A and B.

Question 29

The low incidence of protein or lipid flip-flop in a membrane preserves

A) membrane fluidity.
B) membrane melting temperatures.
C) membrane asymmetry.
D) membrane fluidity and membrane melting temperatures.
E) All of the answers are correct.

Question 30

Membranes carry out what functions due to their electrically polarized structure?

Question 31

The degree of membrane fluidity in bacteria depends mainly on the percentage of

A) lipids that contain sphingosine.
B) glycolipids.
C) free fatty acids.
D) unsaturated fatty acids.
E) None of the answers is correct.

Question 32

What are the two systems for naming the positions of the double bonds? Provide examples.

Question 33

Which of the following statements is consistent with the structure of biological membranes?

A) All membrane proteins are integral and associate with the hydrophobic region of the membrane.
B) Both proteins and lipids readily undergo transverse ("flip-flop") diffusion from the inside to the outside of the membrane.
C) Membranes are symmetric.
D) The membrane lipids self-assemble to form the lipid bilayer.
E) A biological membrane consists of proteins sandwiched between two layers of lipids, which are referred to as a lipid bilayer.

Question 34

Which of the following membranes would be the most fluid?

A) a bilayer made of lipids with polyunsaturated 18 carbon-fatty acids
B) a bilayer made of lipids with saturated 18 carbon-fatty acids
C) a bilayer made of lipids with saturated 16 carbon-fatty acids
D) a bilayer made of lipids with polyunsaturated 16 carbon-fatty acids
E) All of the above are equivalent in fluidity.

Question 35

Carbohydrate residues attached to the membrane lipids are almost always

A) positioned on the intracellular side of the membrane.
B) positioned on the inside center of the bilayer.
C) positioned on the extracellular side of the membrane.
D) positioned equally on both sides of the membrane.
E) also covalently attached to membrane proteins.

Question 36

How many molecules thick are membranes?

A) one
B) two
C) infinite
D) varying thickness, depending on structure
E) None of the answers is correct.

Question 37

Which of the following membrane-bound organelles is thought to have evolved from bacteria by endosymbosis?

A) peroxisomes
B) mitochondria
C) cell walls
D) nuclei
E) endoplasmic reticulum

Question 38

Hydrophobic molecules can be covalently attached to proteins to increase membrane association.Type(s)of group(s)include

A) palmitoyl groups attached via Cys residues.
B) glycolipid structures attached to the carboxy terminus.
C) farnesyl groups attached via Cys residues.
D) All of the answers are correct.
E) None of the answers is correct.

Question 39

What are some molecules that form the polar head group of a phospholipid (bound to the phosphate)? Provide several examples.

Question 40

Which of the following helps regulate membrane fluidity in animals?

A) proteins
B) cholesterol
C) ATP
D) magnesium ions
E) None of the answers is correct.

Question 41

Explain the relationship between the endoplasmic reticulum and the nuclear membrane and one additional characteristic about the nuclear membrane that sets it apart from other membranes.

Question 42

Why do most phospholipids preferentially form sheets instead of micelles?

Question 43

What is the function of prostaglandin H₂ synthase-1? How does its position in the membrane facilitate its activity?

Question 44

Draw and label a typical phospholipid.

Question 45

How are lipid bilayers formed? What is/are the driving forces?

Question 46

Draw the structure of sphingomyelin,and label the linkages in this structure.

Question 47

Draw a bilayer membrane that has both an integral and peripheral protein present.

Question 48

What is receptor-mediated endocytosis?

Question 49

Eukaryotic cells are distinguished from prokaryotic cells by the presence of membranes inside the cell that form internal compartments.What are some examples?

Question 50

What are liposomes? What are some of the current commercial applications?