GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Membrane Structure
Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Example Questions
Example Question #1 : Cell Biology
Which type of membrane protein spans the entire width of the membrane?
Glycolipid
Peripheral protein
Glycoprotein
Carrier protein
Carrier protein
Integral proteins are proteins that connect the inside of the cell to the outside by traversing the phospholipid bilayer. Carrier proteins, for example, allow substances to pass the membrane by letting them cross through channels.
Example Question #1 : Cellular Structures And Functions
Which of the following typically describes molecules that easily diffuse through the plasma membrane (lipid bilayer) of animal cells?
Nonpolar, small in size, and have a large lipid solubility coefficient
Polarity, size, and lipid solubility coefficient do not affect a molecule's ability to diffuse through a lipid bilayer
Polar, small in size and have a large lipid solubility coefficient
Nonpolar, large in size, and have a large lipid solubility coefficient
Small in size, have a small lipid solubility coefficient, but polarity does not affect diffusion rates
Nonpolar, small in size, and have a large lipid solubility coefficient
The correct answer is nonpolar, small in size, and have a large lipid solubility coefficient. The center of the lipid bilayer is nonpolar and composed of fatty acid chains; therefore, nonpolar molecules diffuse through more easily. Diffusion does not use transport proteins to shuttle molecules through the lipid bilayer, so smaller molecules are able to diffuse more easily between the phospholipids that comprise the bilayer. Finally, a higher lipid solubility coefficient means that the molecule is more soluble in lipids and less soluble in aqueous solutions. A low lipid solubility means that the molecule is more aqueous-soluble than lipid-soluble.
Example Question #1 : Cellular Structures And Functions
Dense specialized plasma membrane microdomains that cluster cholesterol, sphingolipids, and protein receptors, and are also sites of receptor trafficking and assembly of signal molecules, are called __________.
lipid rafts
micelles
phosphoinositides
None of the other answers
integrins
lipid rafts
The correct answer is lipid rafts. Lipid rafts are more dense, less fluid domains of the plasma membrane. In addition to clustering cholesterol and sphingolipids, large transmembrane-domain proteins also localize here.
Integrins are transmembrane receptors, micelles are small lipid spheres, and phosphoinositides are a family of lipid molecules.
Example Question #1 : Cellular Structures And Functions
Many retroviruses, including (human immunodeficiency virus) HIV and other lentiviruses, generally bind what structure on the plasma membrane of vertebrate cells?
Lipopolysaccharides
Cholesterol
Phosphatidylcholine
Oligosaccharides
Glycoproteins
Glycoproteins
The correct answer is glycoprotein. HIV and many lentiviruses, which are also retroviruses, bind the CD4 glycoprotein. Lipopolysaccharides are found in bacteria, not vertebrates. Oligosaccharides are sugar polymers and generally function in cell-cell signaling. Cholesterol and phosphatidylcholine are components of the plasma membrane, not necessarily extracellularly exposed. The latter two help define the shape and rigidity of the plasma membrane.
Example Question #2 : Cellular Structures And Functions
What is the name for dense microdomains of the plasma membrane that are enriched in cholesterol and sphingolipids and are centers for signal molecule assembly and receptor trafficking?
Phospholipid bilayer
Micelles
Lipid rafts
None of these
Endosomes
Lipid rafts
The correct answer is lipid rafts. These are dense portions of the phospholipid bilayer that are slightly thicker due to the increased presence of cholesterols and sphingolipids and are hubs for many processes. Micelles are single layer phospholipids that form spheres. Endosomes are intracellular compartments that are often important for transport of materials to the plasma membrane.
All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
