Biochem II Ch 12 practice questions

***23) 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.

B

**2) 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

C

***8) 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

D

**33) 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.

D

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

cerebroside

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

ω-3 Fatty acids

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

1 second

***3) 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.

A

***32) 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.

A

***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

A

***35) 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.

B

**1) 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.

B

**31) 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

B

*6) What protein polymerizes into a lattice network around a budding membrane? A) porin B) clathrin C) epsin D) G protein E) glycophorin

B

***28) 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.

C

***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.

C

***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.

C

**34) 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.

C

***22) 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.

D

***24) 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.

D

***25) 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.

D

***29) 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

D

***30) 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.

D

**4) 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.

D

***21) Membranes are primarily comprised of A) lipids. B) proteins. C) carbohydrates. D) All of the answers are correct. E) A and B.

E

***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.

E

***5) 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

E

**9) What membrane components contain carbohydrates? A) lipid-linked proteins B) cholesterol C) integral membrane proteins in contact with the cytoplasm D) phosphatidylserine E) glycolipids

E

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

Examples of head groups include serine, ethanolamine, choline, glycerol, and inositol.

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

Membrane potential plays a key role in transport, energy conversion, and excitability of neurons.

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

One system refers to the double bond relative to the last, or omega, carbon. (An example would be omega-3 fatty acids.) The other system uses notation that indicates the position of the double bond relative to the carboxyl carbon, and indicates if the bond is cis or trans. (An example would be cis-delta9.)

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

Peripheral

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

Phospholipids derived from glycerol are called phosphoglycerides and consist of a glycerol backbone to which are attached two fatty-acid chains and a phosphorylated alcohol. Sphingomyelin is a phospholipid derived from sphingosine, an amino alcohol. The sphingosine backbone is linked to a fatty acid by an amide bond and the primary hydroxy group of sphingosine is esterified to phosphorylcholine.

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

Tm, or melting temperature

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

cholesterol

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

ester

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

lipid vesicles, or liposomes

***Ionized fatty acids readily form ______________ in aqueous solutions.

micelles

*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.

palmitoyl