biochem membrane structure, lipid bilayer
Ruptured biological membranes are "self-sealing" due to all of the following factors EXCEPT for __________.
covalent interactions among the lipids, Lipids found within membranes are amphiphathic, meaning these molecules contain hydrophobic tails and polar head groups. The polar head group forms favorable interactions with water, such as ion-dipole and hydrogen bonds. The hydrophobic tails associate in the core of the lipid bilayer via hydrophobic interaction (van der Waals). The hydrophobic effect drives the formation of the the lipid bilayer, where the entropy of the water molecules increases as the lipid bilayer surface area decreases. Covalent bonds are the only factor mentioned that does not affect the "self-sealing" property of ruptured biological membranes.
Which of the following populations of fatty acids will have the highest melting temperature?
18:0,The 18:0 fatty acid population will have the most intermolecular interactions occurring between the acyl tails of the fatty acids, causing them to be more stable and therefore have a higher melting temperature. Saturated fatty acids have more possible interactions than unsaturated fatty acids with the same number of carbons. Trans fatty acids have more possible interactions than cis fatty acids, assuming the number of carbons is the same, because the cis bond causes "kinks" in the acyl tail and impedes acyl tail interactions. Also longer-chain acyl tails have more interactions than shorter acyl tails.
Consider the following structure: fatty acid structure The symbolic notation for the fatty acid structure shown is __________.
18:1 (cis Δ9),In symbolic notation, the number before the colon represents the total number of carbons (including the carboxylate carbon). The number after the colon represents the number of double bonds. The superscript after the delta symbol indicates where the double bond is located. Cis and trans indicate the stereochemistry of the double bond. The fatty acid in the diagram has 18 carbons and 1 degree of unsaturation (which starts at carbon number 9). Its double bond is cis because the carbon groups are on the same side of the double bond. Thus, the symbolic notation for the fatty acid structure shown is 18:1 (cis Δ9).
Which of the following populations of fatty acids would most likely be a solid at room temperature?
A saturated fatty acid with 20 carbons, The saturated fatty acid population with 20 carbons will have the most intermolecular interactions occurring between acyl tails of fatty acids, causing them to be more stable and therefore more likely solid at room temperature. Saturated fatty acids have more interactions possible than unsaturated fatty acids with the same number of carbons. Trans fatty acids are unsaturated and have more possible interactions than cis fatty acids, assuming the number of carbons is the same. The omega fatty acids have a cis bond that causes "kinks" in the acyl tail and thus impedes acyl tail interactions. Also, longer-chain acyl tails have more interactions than shorter acyl tails.
Which of the following molecules is NOT classified as a lipid?
Glycerol is not a lipid because it is not an amphipathic molecule with a polar head group and a hydrophobic tail. All of the other choices belong to the lipid family. Testosterone is a steroid, prostaglandin is an eicosanoid, cholesterol is a sterol, and oleic and arachidonic acid are fatty acids.
Which of the following is NOT a class of lipid? glycoproteins, steroids, sterols, Eicosanoids, Phospholipids, Triacylglycerols
Glycoproteins consist of amino acids and monosaccharides. While present in lipid bilayers, they are not members of the lipid class. All of the other choices are lipids; even though they have differing structures and functions, they all contain a polar head group and hydrophobic tail.
Consider the following structure: Glycosylated membrane lipid Where in an animal cell would this molecule most likely be located?
In the outer leaflet of the cytoplasmic membrane, Glycosylation occurs on the outside of the cell, where monosaccharides and polysaccharides are covalently attached to proteins (glycoproteins) and membrane lipids (glycolipids). These carbohydrates are important for cell-cell recognition, antigen-antibody interactions, and other cellular signals. The molecule shown has a monosaccharide covalently attached to a diacylglycerol. The most likely cellular location for this glycoprotein is therefore the outer leaflet of the cytoplasmic membrane because the other membranes are contained within the cell. They are not important for cell signaling.
Consider the following structure: Membrane lipid structure Which of the following statements about the molecule shown is FALSE?
It has the same composition in all types of cell membranes.
The complete hydrolysis of a lipid yields five components in a 1:1:1:1:1 molar ratio: glycerol, a 16:3 cis(Δ9,11,13) fatty acid, an omega-3,6 fatty acid (12:2), a phosphoric acid, and a monosaccharide. What is the name of this lipid?
Phosphatidylinositol,The hydrolysis of a lipid breaks the molecule into distinct pieces. In a 1:1:1:1:1 molar ratio, only one of each piece is present. The presence of two-acyl chains indicates that it is either a phospholipid or sphingolipid. The phosphate and glycerol molecules confirm that this is a phospholipid and not a sphingolipid. The last piece of evidence, the monosaccharide, means that it is a glycosylated phospholipid and thus the only option is phosphatidylinositol. Inositol is shown in the figure below, confirming that it is a monosaccharide. Serine, choline, and ethanolamine do not belong to the saccharide family; they all contain nitrogen and far fewer hydroxyls and chiral carbons than inositol.
Which of the following is NOT a membrane lipid? Testosterone, Cholesterol, Sphingolipid, Phosphatidylcholine
Testosterone is a steroid, an oxidized sterol. These more hydrophilic molecules can travel throughout the body via the bloodstream. These molecules are responsible for causing signals throughout the body, as they are the most water-soluble form of a lipid. Cholesterol is a membrane lipid whose primary function is structural support. Phosphatidylcholine is also useful for membrane support. It can also be a cellular signal. Sphingolipid is a membrane lipid commonly found in myelin.
Increasing the membrane composition of cholesterol will likely __________.
decrease the membrane fluidity, The steroid nucleus of sterols, like cholesterol, is almost planar and very rigid. These molecules are found inside of lipid bilayers to constrict the motion of phospholipids, thus decreasing membrane fluidity. Because of its function in membrane rigidity, cholesterol, does not cause the membrane to dissociate. Also, membrane proteins are synthesized inside of ER membrane, and eventually migrate to the cytoplasmic membrane through vesicles. There is no recruitment event.
All of the following are functions of lipids EXCEPT __________. facilitated transporters,signaling molecules, energy storage, membrane fluidity, membrane strength
facilitated transporters, Lipids have a variety of functions due to the fact that they have a variety of structures. Lipid bilayers are the "gate-keepers" and these membrane lipids do not transport molecules. Molecules that are small, non-polar, and uncharged can diffuse freely through a lipid bilayer, but this is not facilitated transport. Steroids and eicosanoids are signaling lipids, with steroids traveling throughout the body and eicosanoids being a localized signal. Triacylglycerols (TAGS) store excess energy. Sterols, phospholipids, and sphingolipids are membrane lipids responsible for the fluidity and strength of the membrane.
Consider the following structure: fatty acid structure The following molecule is a/an __________.
monounsaturated fatty acid,The molecule is a monounsaturated fatty acid, meaning it has an acyl tail (fatty) a carboxylic acid (acid), and one double bond. The double bond in this fatty acid is not trans but cis because the carbon groups are on the same side of the double bond. An omega-3 fatty acid has a double bond three carbons away from the end carbon or the omega carbon. (Omega is the last letter of the Greek alphabet.) Sterols have a steroid nucleus and no carboxylic acid functional group. Eicosanoids have a cyclic functional group.
The extracellular side of a transmembrane helix of an integral membrane protein does NOT contain __________.
mostly hydrophobic amino acids,the extracellular side of a transmembrane protein contains mostly hydrophilic, not hydrophobic, amino acids, as these are exposed to water and can make many favorable intermolecular interactions. This side of the membrane is also glycosylated, as mono/polysaccharides are important for cell-cell recognition, antigen-antibody interactions, etc. These saccharides are covalently bound to glycoproteins via the amino acids Ser, Thr, and Asn, and therefore the extracellular side of the transmembrane protein contains many of these specific residues.
Proteins A, B, and C (either peripheral or integrated) are associated with an intact biological membrane. Suppose the membrane is exposed to a severe decrease in pH. If the only protein that remains associated with the membrane is protein A, then one can conclude that __________.
proteins B and C are likely peripheral proteins,Membrane proteins can be classified based on association with the membrane. Peripheral proteins associate with the membrane via electrostatic interactions and can be dissociated by altering ionic strength or pH. Integral membrane proteins span the membrane, are associated with hydrophobic interactions, and are dissociated using detergents. Since Proteins B and C are no longer associated with the membrane after the change in pH, these are likely peripheral proteins. Protein A is still associated with the membrane after the pH change, therefore it is likely an integral protein. Note that these classifications do not indicate the function of these proteins but only how they associate with the membrane.
Consider the following structure: Sterol structure The molecule's function is to __________.
provide structural support to the lipid bilayer,This structure is a sterol because it has a steroid nucleus and only one polar head group, a hydroxyl. Sterol's function is to provide membrane support. Steroids travel throughout the body, sending out global signals. Eicosanoids send out localized signals. Triacylglycerols (TAGS) store excess energy.
Bacteria that thrive in cooler growth temperatures compensate by __________ as compared to bacteria growing at warmer temperatures.
putting more unsaturated fatty acids into their membranes, Bacteria growing at cold temperatures need a membrane composition that facilitates increased membrane fluidity, because the cooler temperatures decrease molecular motion. Therefore, bacteria thriving in cool temperatures have increased populations of unsaturated fatty acids on phospholipids because the cis double bonds cause kinks or separations within the membrane. Saturated and long-chain fatty acids have an increased number of intermolecular interactions and they are more likely to become solid at cool temperatures. Testosterone is not a membrane lipid.
Consider the following structure: Steroid structure The molecule's function is to __________.
send out global cellular signals,The structure is a steroid because it has a steroid nucleus and a higher level of oxidation than a sterol. These molecules are more hydrophilic than sterols and therefore travel throughout the bloodstream readily. They bind to receptor proteins and initiate signaling cascades. Thus it's function is to send out global cellular signals. In contrast, eicosanoids are localized signaling molecules because they are less polar. Triacylglycerols are for energy storage. Sterols, phospholipids, sphingolipids are for membrane structure and fluidity.
Consider the following structure: Eicosanoid structure The molecule's function is to __________.
send out localized cellular signals,The structure is a prostaglandin, which is a type of eicosanoid. These lipids are derived from a polyunsaturated fatty acid and have a distinctive five-membered ring that is sometimes oxidized. These are local signaling molecules (sending out localized cellular signals) that can control pain, inflammation, and local housekeeping. They are less polar than steroids and therefore less soluble in the bloodstream, so they do not stray far from the cell that synthesized them. Triacylglycerols (TAGS) store excess energy. Sterols, phospholipids, and sphingolipids are membrane lipids responsible for the fluidity and strength of the membrane.
Consider the following structure: Triacylglycerol structure The molecule's function is to __________.
store energy, This structure is triacylglycerol because it contains three acyl chains covalently bound to a glycerol backbone. These acyl chains contain many reduced carbons (saturated with H atoms) that release energy upon oxidation that can be used to synthesize ATP. TAGs are therefore provide efficient energy storage. Sterols, phospholipids, and sphingolipids are membrane lipids responsible for the fluidity and strength of the membrane. Steroids and eicosanoids are signaling lipids, with steroids traveling throughout the body and eicosanoids being a localized signal.
The polar head group of a sterol is __________.
the hydroxyl group
Consider the following structure: Glycerol structure This molecule is a component of __________.
triacylglycerols, phospholipids, and glycoglycerolipids,The molecule shown is glycerol. Triacylglycerols, phospholipids, and glycoglycerolipids all have a glycerol backbone. Sphingolipids do not have a glycerol backbone, but instead one of the hydroxyl groups is an amine on the three-carbon backbone.