Biochem Chapter 12

Ionized fatty acids readily form ___________ in aqueous solutions.

Micelles

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

Micelles are spherical arrangements in which the tails are on the inside of the sphere, and the heads are on the outside surface. Bilayers have two lipid layers, in which the heads are on the outside, and the tails are arranged on the inside in two rows. Figures 12.9 and 12.10 in the textbook provide an example of this.

This is the number of carbons in most common fatty acids.

16 or 18

Which of the following membrane-bound organelles is thought to have evolved from bacteria by endosymbosis? A) Mitochondria B) Peroxisomes C) Nucleus D) Endoplasmic reticulum E) Cell walls

A) Mitochondria

How does the presence of cis double bonds in fatty acids affect membrane fluidity? A) They tend to increase the fluidity. B) They tend to decrease the fluidity. C) They don't have any specific effect on fluidity.

A) They tend to increase the fluidity.

Facilitated diffusion requires A) a channel protein through which the transported substance passes without binding B) a carrier protein to which the transported substance binds C) a receptor protein D) expenditure of energy by the cell

A) a channel protein through which the transported substance passes without binding

In the operation of the sodium-potassium pump A) a membrane protein is phosphorylated with ATP as the source of the phosphate group B) conformational changes in membrane proteins are inhibited C) the ions involved bind to the lipid portion of the membrane D) a membrane protein is phosphorylated with ADP as the source of the phosphate group

A) a membrane protein is phosphorylated with ATP as the source of the phosphate group (Guess)

Unsaturated fatty acids usually have ____ double bonds. A) cis B) trans

A) cis

With what compound are fatty acids reacted to make a fat or oil? A) glycerol B) sphinganine C) cholesterol D)ceramide

A) glycerol

Which of the following lipids is not found in biological membranes? A) triacylglycerols B) phosphoacylglycerols C) glycolipids

A) triacylglycerols

The most common motif found in membrane spanning proteins is A) α-helices of nonpolar amino acids that pass through the membrane. B) α helices of charged amino acids that form channels via extensive hydrogen bonding. C) a triple helix of α helices. D) A helix-turn-helix arrangement of the peptide strands. E) None of the above.

A) α-helices of nonpolar amino acids that pass through the membrane

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

Acetylsalicylic Acid (Aspirin)

This is a term applied to molecules that have both hydrophilic and hydrophobic moieties.

Amphipathic

Which of the following membranes would be the most rigid? 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

B) A bilayer made of lipids with saturated 18 carbon-fatty acids (Guess)

Which of the following treatments would be most useful in separating an integral membrane protein from the lipid component of a cell membrane? A) Change the pH. B) Add a detergent. C) Add a salt. D) Add a mixture of proteases. E) None of these. You can't separate an integral membrane protein from the lipid.

B) Add a detergent.

How does cholesterol affect membrane fluidity? A) It tends to increase the fluidity. B) It tends to decrease the fluidity. C) It doesn't have any specific effect on fluidity.

B) It tends to decrease the fluidity.

Which of the following is true? A) Most fatty acids have an odd number of carbons B) Most fatty acids have an even number of carbons C) Fatty acids with an even number of carbons are more rare than those with an odd number D) Fatty acids are equally likely to have an even number of carbons as they are an odd number

B) Most fatty acids have an even number of carbons

Glycolipids are characterized by containing the following non-lipid component: A) Glycerol B) Sugars C) Phosphate D) Sphingosine E) More than one of these characterize glycolipids.

B) Sugars

How many molecules thick are membranes? A) One B) Two C) Infinite D) Varying thickness, depending on structure E) None of the above

B) Two

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

B) always positioned on the extracellular side of the membrane.

Liposomes are A) single-layered membranes. B) artificial membrane-bounded structures used to deliver medications. C) mixed micelles involved in cholesterol transport among cells. D) bilayers with the hydrophobic regions on the outside.

B) artificial membrane-bounded structures used to deliver medications. (Guess)

What does amphipathic mean? A) having both positive and negative charges B) having both hydrophilic and hydrophobic regions C) having both acid and base properties D) having two stereoisomers

B) having both hydrophilic and hydrophobic regions

What characteristic is most used to define lipids? A) ionic charge B) solubility C) melting point D) ability to bind metal ions

B) solubility

The degree of membrane fluidity depends on A) the percentage of glycolipids. B) the percentage of unsaturated fatty acids. C) the percentage of lipids that contain sphingosine. D) the percentage of free fatty acids. E) None of the above.

B) the percentage of unsaturated fatty acids.

How are lipid bilayers formed? What is the driving force?

Bimolecular sheets of lipids form spontaneously by self-assembly. Hydrophobic interactions are the driving force. Van der Waals attractive forces between the hydrocarbon tails favor the close packing of the tails. The polar heads are attracted to each other by electrostatic and hydrogen-bonding attractions.

Which of the following statements concerning active transport is true? A) It requires no expenditure of energy by the cell. B) It takes place in the same direction as a concentration gradient. C) A membrane-associate protein must be involved. D) It can be compared to water running downhill

C) A membrane-associate protein must be involved.

Which of the following groups is not present in a phosphatidic acid? A) Fatty acids B) Glycerol C) Choline D) Phosphate E) All of these are components of phosphatidic acid.

C) Choline

Which of the following is not a characteristic of most fatty acids? A) Even number of carbon atoms. B) Presence of cis double bonds. C) Two carboxyl (-COOH) groups, one at each end. D) Absence of conjugated double bonds. E) All of these characterize lipids.

C) Two carboxyl (-COOH) groups, one at each end.

The low incidence of protein or lipid flip-flop in a membrane preserves A) membrane fluidity. B) membrane melting temperatures. C) membrane asymmetry. D) All of the above. E) None of the above.

C) membrane asymmetry.

The difference between active transport and passive transport is that A) concentration gradients are involved in one and not in the other. B) glycolipids play a role in one and not in the other. C) one requires expenditure of energy by the cell and the other does not. D) ions are transported into and out of the cell by one process and not by the other.

C) one requires expenditure of energy by the cell and the other does not.

The distribution of lipids in membranes is A) distinguished by the absence of cholesterol B) characterized by even distribution of molecules C) uneven, with bulkier molecules on the exterior D) not well understood

C) uneven, with bulkier molecules on the exterior

___________ is a membrane lipid composed of sphingosine, fatty acid, and a simple sugar.

Cerebroside

In addition to phospholipids and glycolipids, this is a major type of membrane lipid

Cholesterol

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

Cholesterol

A protein that polymerizes into a lattice network around a budding membrane.

Clathrin

How many hydroxyl groups does a molecule of glycerol have? A) none B) 1 C) 2 D) 3 E) 4

D) 3

Which of the following four fatty acids has the lowest melting point? 1. CH3CH2CH2CH2CH2COOH 2. CH3CH2CH2CH2CH2CH2CH2CH2CH2COOH 3. CH3CH2CH2CH2CH2CH2CH2COOH 4. CH3CH=CHCH2CH2COOH A) 1 B) 2 C) 3 D) 4

D) 4

Membranes are primarily comprised of A) lipids. B) proteins. C) collagen. D) A and B. E) A, B, and C.

D) A and B

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 above. E) None of the above.

D) All of the above.

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 above. E) None of the above.

D) All of the above.

Which of the following lipid molecules possess a different fundamental structural make-up from the others? A) Fatty acids B) Sphingolipids C) Triglycerides D) Cholesterol E) Glycolipids

D) Cholesterol

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 lipid tails D) Covalent bonds between the lipids and membrane proteins E) A and B

D) Covalent bonds between the lipids and membrane proteins

Which of the following groups is not present in a cerebroside? A) Fatty acid B) Sugar C) Sphingosine D) Phosphate E) All of these can be components of cerebrosides.

D) Phosphate

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) The membrane lipids self-assemble to form the lipid bilayer.

A major difficulty in extracting receptor proteins from membranes is that A) it is difficult to remove the proteins from the membrane without denaturation B) there may be very few molecules of the protein in a cell C) receptor proteins tend to have high molecular weights D) all of these

D) all of these (Guess)

Which of the following molecules is not amphipathic? A) cholesterol B) phosphatidylcholine C) oleic acid D) glucose

D) glucose

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) A, B, and C are correct.

E) A, B, and C are correct.

The mechanism of membrane transport may involve the following: A) ATP hydrolysis. B) Conformation change of membrane proteins. C) Phosphorylation or dephosphorylation of membrane proteins. D) ATP hydrolysis and conformation change of membrane proteins. E) All of these are correct.

E) All of these are correct.

Glycoproteins on the cell surface are involved in this type of function: A) Cell identification B) Receptor sites C) Immune function D) Cell identification and receptor sites E) All of these are correct.

E) All of these are correct. (Guess)

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 phosphatidyl choline. D) It is a sphingolipid. E) It is a phosphoglyceride.

E) It is a phosphoglyceride. (Guess)

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

Ester

What are some molecules that form the polar head group of a phospholipid? Provide several examples.

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

These membrane components contain carbohydrates.

Glycolipids

This procedure is used to determine the probability that a segment of a protein will be found embedded in a membrane.

Hydropathy

This is the process by which lipids and proteins move in the membrane bilayer.

Lateral Diffusion

This is a complex between cholesterol and membrane phospholipids

Lipid Raft

_______________ are aqueous compartments enclosed by a lipid bilayer.

Liposomes

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

Liposomes are spherical structures of lipid bilayers, similar to miniature organelles. They are extremely useful as models of cell systems. They can be used to contain or transport molecules such as drugs for therapy, DNA for gene therapy, and are commonly used in cosmetics such as skin creams.

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

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

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

One Second

Some proteins are anchored to the membrane by being covalently attached to a _________ group by a thioester linkage to a specific cysteine residue.

Palmitoyl

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

Peripheral

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

Peroxisomes play a major role in the oxidation of fatty acids. Mitochondria are organelles in which ATP is synthesized. The nucleus is a double membrane that consists of a set of closed membranes that come together at nuclear pores. The endoplasmic reticulum's roles include drug detoxification and modification of proteins for secretion.

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 is 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 phorphorylcholine

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

Prostaglandin H2 synthase-1 converts arachidonic acid into prostaglandin H2. The protein is embedded in the membrane, with a hydrophobic channel submerged about halfway through the bilayer. The arachidonic acid is a product of membrane lipid hydrolysis and enters the protein channel from within the membrane, successfully avoiding any interaction with aqueous environments.

What is receptor-mediated endocytosis?

Receptor-mediated endocytosis is a transport process in which a protein is recognized by a receptor on the cell surface and then that region of the membrane invaginates into the cell.

Transport systems confer this important property on membranes.

Selective Permeability

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

The membrane should be depicted as a bilayer, with the head groups indicated by small balls, and the alkyl chains represented by long tails. The peripheral membrane proteins would be loosely attached to the outside of the membrane, and the integral proteins would be shown traversing the membrane.

How is the nuclear membrane different from other membranes?

The nuclear membrane is not continuous. It is a set of closed membranes that comes together at pores.

Draw and label a typical phospholipid.

The phospholipid drawn should resemble Figure 12.5 in the textbook. It should contain a central glycerol molecule, to which two fatty acids are attached in ester linkages at the center and an end. The other end should be linked to a phosphor alcohol group. The phosphate should be shown negatively charged at pH 7.

Why do most phospholipids preferentially form sheets instead of micelles?

The two tails in phospholipids makes it sterically unstable for them to form micelles.

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

Tm or Melting Temperature

True or false? Cholesterol is particularly important as a component of animal membranes.

True

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

w-3 Fatty Acids