Cell Biology: exam 2

How does the inclusion of cholesterol affect animal cell membranes? Choose one: It makes the lipid bilayer more permeable. It tends to make the lipid bilayer more fluid. It makes the lipid bilayer wider. It tends to make the lipid bilayer less fluid. It has little effect on the properties of the lipid bilayer.

It tends to make the lipid bilayer less fluid. This stiffening makes the bilayer less flexible as well as less permeable.

Why do phospholipids form bilayers in water? Choose one: The hydrophilic head is insoluble in water. The hydrophilic head is attracted to water, while the hydrophobic tail shuns water. The hydrophobic tail is attracted to water, while the hydrophilic head shuns water. The hydrophobic head is attracted to water, while the hydrophilic tail shuns water. The hydrophobic head shuns water, while the hydrophilic tail is attracted to water.

The hydrophilic head is attracted to water, while the hydrophobic tail shuns water. The hydrophilic head can form electrostatic attractions and hydrogen bonds with water, while the hydrophobic tails are insoluble in water.

Which term correctly describes the entire phospholipid molecule? Choose one: apathetic hydrophobic hydrophilic hydropathic amphipathic

amphipathic Phospholipids contain both a hydrophilic and hydrophobic component and are therefore amphipathic. This property allows them to form bilayers in water, where the hydrophilic portions interact with the aqueous environment on either side of the membrane, while the hydrophobic portions are shielded from water in the bilayer's interior.

One of the grand challenges in biology is understanding how the first cells formed on Earth. Since all cells are bound by a cell membrane, origin of life researchers are interested in modeling what the first membranes may have been like. What types of molecules might these researchers consider to be the original building blocks of cell membranes? Choose one: A. hydrophilic molecules B. amphipathic molecules C. hydrophobic molecules D. carbohydrate molecules

amphipathic molecules Amphipathic molecules, with both hydrophilic and hydrophobic regions, spontaneously form bilayers in aqueous solutions. A 2012 Chem. Soc. Rev. article discusses the different amphipathic molecules researchers use to model early cells.

Multipass transmembrane proteins can form pores across the lipid bilayer. The structure of one such channel is shown in the diagram. In this figure, what do the areas shown in red represent? Choose one: the hydrophobic side chains of the transmembrane β barrel the hydrophilic side chains of the transmembrane β barrel the hydrophilic side chains of the transmembrane α helices the hydrophobic side chains of the transmembrane α helices the amphipathic side chains of the transmembrane α helices the hydrophobic lipid tails of the bilayer

the hydrophilic side chains of the transmembrane α helices Small water-soluble molecules can pass through the water-filled pore formed by the hydrophilic side chains of the transmembrane helices, shown in red.

In the α helices of transmembrane proteins, the hydrophobic side chains face which direction? Choose one: the inside of the membrane-spanning helix the external or lumenal side of the membrane the cytosolic side of the membrane the outside of the membrane-spanning helix

the outside of the membrane-spanning helix This arrangement allows the exposed hydrophobic side chains of the α helix to interact with the hydrophobic tails of the lipid bilayer.

In a lipid bilayer, where do lipids rapidly diffuse? Choose one: not at all, because they remain in place within the bilayer within the plane of one monolayer and back and forth between the monolayers in and out of the bilayer within the plane of their own monolayer back and forth from one monolayer to the other in the bilayer

within the plane of their own monolayer The lipid bilayer is a two-dimensional fluid in which phospholipids rapidly diffuse within the plane of their own monolayer.

Which characteristic describes the tails of phospholipids? Choose one: stiff amphipathic coated with sugars hydrophobic hydrophilic

hydrophobic The hydrocarbon tails of phospholipids tend to avoid contact with water, which helps drive the formation of the lipid bilayer.

Porin proteins—which form large, water-filled pores in mitochondrial and bacterial outer membranes—fold into β-barrel structures. The amino acids that face the outside of the barrel have what kind of side chains? Choose one: hydrophobic charged polar hydrophilic amphipathic

hydrophobic These hydrophobic side chains interact with the hydrophobic tails within the lipid bilayer. This arrangement allows the protein, which also contains hydrophilic amino acids and a hydrophilic peptide backbone, to penetrate the hydrophobic environment of the membrane.

What is a functionally specialized region of a cell membrane, typically characterized by the presence of specific proteins, called? Choose one: glycocalyx membrane domain cell cortex sphingomyelin domain carbohydrate layer

membrane domain Membrane domains are generated when cells restrict the movement of certain membrane proteins to localized areas within a cell membrane.

Imagine you collected bacteria from the sediment in a frozen lake in Minnesota in January and compared the membranes to membranes from bacteria collected from a lake in Texas in June. Consider how the membranes would likely differ.The membranes in bacteria from the Minnesota lake would most likely have which of the following? Choose one: A. phospholipids with more negatively charged phosphate groups than membranes in Texas bacteria B. more unsaturated lipid tails than membranes in Texas bacteria C. more saturated lipid tails than membranes in Texas bacteria D. fewer lipid tails with cis double bonds than membranes in Texas bacteria

more unsaturated lipid tails than membranes in Texas bacteria Unsaturated lipid tails with cis double bonds are kinked and pack less tightly than saturated lipids. The bacteria in a cold environment will have more of the unsaturated lipid tails to maintain fluidity even in cold temperatures.

Which of the following would produce the most fluid lipid bilayer? Choose one: A. phospholipids with tails of 18 carbon atoms and two double bonds B. phospholipids with fully saturated tails of 18 carbon atoms C. phospholipids with fully saturated tails of 20 carbon atoms D. phospholipids with tails of 20 carbon atoms and two double bonds E. large amounts of cholesterol

phospholipids with tails of 18 carbon atoms and two double bonds A shorter chain length and double bonds both reduce the tendency of the phospholipid tails to interact with one another, thereby increasing the fluidity of the membrane.

In eukaryotic cells, phospholipids are synthesized by enzymes bound to which of the following? Choose one: the cytosolic face of the Golgi apparatus the inside of the endoplasmic reticulum the cytosolic face of the endoplasmic reticulum both monolayers of the endoplasmic reticulum the cytosolic face of the plasma membrane

the cytosolic face of the endoplasmic reticulum New phospholipids are added to the ER membrane asymmetrically. Some of the newly made phospholipids are subsequently moved from the cytosolic monolayer to the other half of the bilayer so that the membrane can grow evenly.

On what side of the plasma membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located? Choose one: the inside the underside both sides the cytosolic side the extracellular side

the extracellular side The sugars on plasma membrane glycolipids, glycoproteins, and proteoglycans all face the cell exterior, where they form a carbohydrate layer or glycocalyx that coats the surface of the cell.

Which statements are true about the differences between phospholipids and detergents? Choose one or more: Phospholipids are amphipathic, whereas detergents are hydrophobic. Detergents are shaped like cones, whereas phospholipids are more cylindrical. Phospholipids form bilayers in water, whereas detergents tend to form micelles. Phospholipids have two hydrocarbon tails, whereas detergents have just one. Phospholipids are hydrophobic, whereas detergents are amphipathic.

Detergents are shaped like cones, whereas phospholipids are more cylindrical. Phospholipids form bilayers in water, whereas detergents tend to form micelles. Phospholipids have two hydrocarbon tails, whereas detergents have just one. Detergents differ from membrane phospholipids in that they have only a single hydrophobic tail. Because they have one tail, detergent molecules are shaped like cones; in water, this shape drives these amphipathic molecules to form small clusters called micelles, rather than forming a bilayer as do the phospholipids, which—with their two tails—are more cylindrical.

Which of the following would be most likely to disrupt lipid bilayer formation? Choose one: A. addition of a methyl group to the end of the lipid tail B. addition of cholesterol to the membrane C. addition of a phosphate to the end of the lipid tail D. addition of a hydroxyl group to the head group of the lipid

addition of a phosphate to the end of the lipid tail Addition of a negatively charged phosphate to the hydrophobic lipid tail would likely disrupt the formation of the lipid bilayer.

The shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called what? Choose one: glycocalyx basal lamina tight junction cell cortex lamellipodium

cell cortex This meshwork of protein filaments is attached to the underside of the plasma membrane.

The plasma membrane is involved in which activities? Choose one or more: DNA replication and repair cell recognition cell signaling cell growth and motility RNA interference import and export of nutrients and wastes

cell recognition cell signaling cell growth and motility import and export of nutrients and wastes The cell membrane is indeed involved in cell signaling and recognition, growth and motility, and the import of nutrients and export of wastes.The plasma membrane is not involved in DNA replication and repair or in the gene-silencing technique of RNA interference.

Which of the following is a function of proteins in the plasma membrane? Choose one or more: serve as anchors to attach the cell to the extracellular matrix transmit extracellular signals to the cell interior generate the energy required for lipids to diffuse within the membrane transport molecules across the membrane allow specific ions to cross the plasma membrane, thereby controlling its electrical properties

serve as anchors to attach the cell to the extracellular matrix transmit extracellular signals to the cell interior transport molecules across the membrane allow specific ions to cross the plasma membrane, thereby controlling its electrical properties Membrane proteins serve many functions. Some transport particular nutrients, metabolites, and ions across the lipid bilayer. Others anchor the membrane to macromolecules on either side. Still others function as receptors that detect chemical signals in the cell's environment and relay them into the cell interior, or work as enzymes to catalyze specific reactions at the membrane. Each type of cell membrane contains a different set of proteins, reflecting the specialized functions of the particular membrane.