Plasma Membrane 1

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Questions and Answers

Which technique is necessary to study the details of the organization of cell membranes?

  • Spectrophotometry
  • Microscopy
  • Centrifugation
  • X-ray diffraction (correct)

According to the fluid mosaic model, cell membranes are described as:

  • Fluid, dynamic structures with molecules able to move in the plane of the membrane (correct)
  • Completely impermeable structures
  • Static, rigid structures with fixed molecules
  • Lacking a lipid bilayer structure

What is the typical thickness of a plasma membrane as viewed in cross-section?

  • 0.5-0.8 nm
  • 10-15 nm
  • 50-80 nm
  • 5-8 nm (correct)

In an electron micrograph of an E.coli cell, what is denoted by the red circle in the schematic of the lipid bilayer?

<p>Hydrophilic head with a polar phosphoglycerol group (B)</p> Signup and view all the answers

Which type of structures exclude water as well as polar or charged compounds?

<p>Hydrophobic barriers (A)</p> Signup and view all the answers

What is the main characteristic shared by all cell membranes when viewed in cross-section?

<p>Trilaminar appearance (A)</p> Signup and view all the answers

What is the main function of cell membranes?

<p>Regulate movement of materials into and out of the cell (A)</p> Signup and view all the answers

Which statement best describes the structure of a cell membrane?

<p>Selectively permeable to polar solutes (C)</p> Signup and view all the answers

What is the significance of the cell membrane in cell-to-cell communication?

<p>Facilitates electrical signaling between cells (C)</p> Signup and view all the answers

Which function is NOT attributed to cell membranes?

<p>Producing genetic mutations (D)</p> Signup and view all the answers

Why are cell membranes described as 'selectively permeable'?

<p>They regulate which molecules can pass based on size and polarity (A)</p> Signup and view all the answers

In what way do cell membranes contribute to compartmentalization in eukaryotic cells?

<p>Help separate processes and compartments within the cell (D)</p> Signup and view all the answers

What is the main function of compartmentalization in cell membranes?

<p>Separate anabolic and catabolic processes (D)</p> Signup and view all the answers

Which organelles are involved in fatty acid oxidation for energy production?

<p>Mitochondria (D)</p> Signup and view all the answers

What is the main role of proteins in cell membranes?

<p>Facilitate transport across the membrane (A)</p> Signup and view all the answers

Which component makes up about 50% of the mass of most animal cell membranes?

<p>Lipids (C)</p> Signup and view all the answers

Where are the TCA cycle and electron transport chain located in a cell?

<p>Mitochondria (A)</p> Signup and view all the answers

Which type of cations are commonly found associated with cell membranes?

<p>$Ca^{2+}$ and $Mg^{2+}$ (A)</p> Signup and view all the answers

What is the main difference between prokaryotic and eukaryotic plasma membranes?

<p>Eukaryotic membranes are composed of different types of phospholipids, while prokaryotic membranes are composed of a single type. (D)</p> Signup and view all the answers

What role do sterols like cholesterol play in the stability and fluidity of cell membranes?

<p>Increase both mechanical stability and fluidity. (C)</p> Signup and view all the answers

What is the purpose of membrane fusion in cellular processes?

<p>To allow for the transport of material between organelles and the plasma membrane. (C)</p> Signup and view all the answers

How do lipid molecules assemble in aqueous environments?

<p>With hydrophobic tails in the interior and hydrophilic heads outside to water. (D)</p> Signup and view all the answers

What is the significance of membrane fission in cellular processes?

<p>To enable the splitting of a membrane into two parts for transport purposes. (C)</p> Signup and view all the answers

How do hydrophilic molecules behave in aqueous environments?

<p>They dissolve readily in water due to uncharged polar groups that interact favorably with water molecules. (D)</p> Signup and view all the answers

Why does phospholipid bilayer closure to form a sealed compartment represent an energetically favorable process?

<p>The closed structure prevents the exposure of hydrophobic tails to water, which is energetically unfavorable. (B)</p> Signup and view all the answers

In an aqueous environment, which type of molecules form micelles according to the text?

<p>Fatty acids (B)</p> Signup and view all the answers

What is the main difference between vesicles and liposomes as outlined in the text?

<p>Vesicles are naturally occurring, while liposomes are artificial structures created in laboratories. (D)</p> Signup and view all the answers

What is the function of vesicles within cells as described in the text?

<p>Metabolism (C)</p> Signup and view all the answers

Which technique directly produces a three-dimensional image of the surface of a specimen according to the text?

<p>Scanning electron microscopy (SEM) (C)</p> Signup and view all the answers

Why do phospholipids form bilayers or liposomes according to the text?

<p>Their cylinder-shaped form leads to bilayer or liposome formation. (D)</p> Signup and view all the answers

What is the main function of the cell membrane in facilitating electrical signaling between cells?

<p>Serving as an attachment surface (B)</p> Signup and view all the answers

Which type of cells break and re-seal their cell membranes for fusion or fission?

<p>Eukaryotic cells (A)</p> Signup and view all the answers

How do cell membranes contribute to the regulation of molecular traffic across the boundary?

<p>By being selectively permeable (C)</p> Signup and view all the answers

What is the primary role of the lipid bilayer structure in the cell membrane?

<p>Providing a barrier to separate cellular compartments (B)</p> Signup and view all the answers

Which visualization technique is commonly used to study the details of the organization of cell membranes?

<p>Electron microscopy (B)</p> Signup and view all the answers

What is the significance of the compartmentalization provided by cell membranes in eukaryotic cells?

<p>Segregating processes and compartments (A)</p> Signup and view all the answers

What type of structures are cell membranes, as described in the text?

<p>Fluid and dynamic (A)</p> Signup and view all the answers

Which component makes up the central region in the trilaminar appearance of cell membranes when viewed in cross-section?

<p>Hydrophilic heads (C)</p> Signup and view all the answers

What does the red circle in the schematic of the lipid bilayer denote?

<p>Hydrophilic head (A)</p> Signup and view all the answers

Why is membrane thickness important in influencing the rate of diffusion across cell membranes?

<p>Thinner membranes allow for faster diffusion. (A)</p> Signup and view all the answers

What characteristic appearance do all cell membranes share when viewed in cross-section?

<p>Trilaminar appearance (C)</p> Signup and view all the answers

Which technique is necessary to study the details of the organization of cell membranes as implied in the text?

<p>Freezefracture (C)</p> Signup and view all the answers

Why does the spontaneous closure of a phospholipid bilayer to form a sealed compartment represent an energetically favorable process?

<p>It prevents the exposure of the hydrophobic hydrocarbon tails to water, which is energetically unfavorable. (C)</p> Signup and view all the answers

Which type of molecules form micelles in an aqueous environment according to the text?

<p>Amphipathic molecules (C)</p> Signup and view all the answers

What is the main difference between vesicles and liposomes?

<p>Vesicles consist of liquid enclosed by a lipid bilayer, while liposomes consist of cytoplasm enclosed by a lipid bilayer. (A)</p> Signup and view all the answers

What is the role of lipids in forming vesicles and bilayers?

<p>Lipids spontaneously form vesicles and bilayers due to their amphipathic nature. (B)</p> Signup and view all the answers

What is the significance of vesicles in cellular processes?

<p>Vesicles are involved in temporary storage, transport, and metabolic processes within cells. (D)</p> Signup and view all the answers

How do liposomes differ from vesicles?

<p>Liposomes consist of liquid enclosed by a lipid bilayer, while vesicles consist of cytoplasm enclosed by a lipid bilayer. (C)</p> Signup and view all the answers

What does the freeze-fracture technique involve?

<p>Breaking apart a frozen biological sample to study the membrane (B)</p> Signup and view all the answers

How do differences in the length and saturation of fatty acid tails affect phospholipid molecules?

<p>Enhance the ability to pack together and influence membrane fluidity (D)</p> Signup and view all the answers

What is the main structural difference between saturated and unsaturated fatty acids in cell membranes?

<p>The presence of double bonds in unsaturated fatty acids (C)</p> Signup and view all the answers

Which major phospholipids predominate in the plasma membrane of many mammalian cells?

<p>Phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine, sphingomyelin (A)</p> Signup and view all the answers

Why is the freeze-fracture technique important for studying cell membranes?

<p>It reveals internal membrane organization by fracturing frozen samples (C)</p> Signup and view all the answers

How does the freeze-etch electron microscopy technique differ from freeze-fracture?

<p>It creates a 3D view of surfaces inside cells by etching frozen samples (B)</p> Signup and view all the answers

What is the main purpose of compartmentalization in cell membranes?

<p>Avoiding interference in reactions (A)</p> Signup and view all the answers

Where are fatty acid oxidation for energy production and fatty acid synthesis held to avoid competition?

<p>Mitochondria and ER (C)</p> Signup and view all the answers

Which component makes up approximately 50% of the mass of most animal cell membranes?

<p>Lipids (C)</p> Signup and view all the answers

Where are the TCA cycle and electron transport chain located to ensure energy efficiency?

<p>Mitochondria (C)</p> Signup and view all the answers

How do cell membranes contribute to cell-to-cell communication?

<p>By facilitating the exchange of signaling molecules (D)</p> Signup and view all the answers

What is the significance of proteins in biological membranes?

<p>To interact with other molecules and transport materials (C)</p> Signup and view all the answers

What type of model describes cell membranes as fluid, dynamic structures where most molecules can move?

<p>Fluid mosaic model (B)</p> Signup and view all the answers

In the trilaminar appearance of all cell membranes, what do the two electron-dense layers consist of?

<p>Proteins (C)</p> Signup and view all the answers

What is the main function of the hydrophilic head denoted by the red circle in the schematic of the lipid bilayer?

<p>Attract water and charged compounds (C)</p> Signup and view all the answers

What is the significance of the less dense central region in the trilaminar appearance of cell membranes?

<p>Facilitates movement of transmembrane proteins (A)</p> Signup and view all the answers

What technique is necessary to study the detailed organization of cell membranes and involves breaking them to reveal their inner structures?

<p>Freezefracture (C)</p> Signup and view all the answers

In what way does membrane thickness influence the rate of diffusion across cell membranes?

<p>Thicker membranes impede diffusion (C)</p> Signup and view all the answers

What is the main function of the plasma membrane in a cell according to the text?

<p>Facilitating electrical signaling between cells (D)</p> Signup and view all the answers

Why are cell membranes described as 'selectively permeable'?

<p>To only permit certain molecules to cross while blocking others (C)</p> Signup and view all the answers

Which component plays a central role in defining the external boundaries of a cell?

<p>Membrane lipids (A)</p> Signup and view all the answers

How do cell membranes contribute to biological energy conservation?

<p>By facilitating electron transport chain reactions (B)</p> Signup and view all the answers

What is a key feature of the lipid bilayer structure in cell membranes?

<p>Providing flexibility and selective permeability (C)</p> Signup and view all the answers

Which major function of cell membranes involves serving as an attachment surface for extracellular structures?

<p>Providing attachment points for cytoskeleton proteins (C)</p> Signup and view all the answers

Why is the closure of a phospholipid bilayer to form a sealed compartment energetically favorable?

<p>It stabilizes the closed structure by avoiding exposure of hydrophobic tails to water. (D)</p> Signup and view all the answers

What is the main difference between micelles and bilayers according to the text?

<p>Micelles are cone-shaped, while bilayers are cylinder-shaped. (C)</p> Signup and view all the answers

In cell membranes, what provides the self-healing property to the bilayer?

<p>Free edges (C)</p> Signup and view all the answers

What is the purpose of vesicles within cells as described in the text?

<p>To have cytoplasm with different composition from the cytosol (A)</p> Signup and view all the answers

How do liposomes differ from vesicles according to the text?

<p>Liposomes consist of liquid/cytoplasm enclosed by a lipid bilayer, while vesicles are intra or extra cellular structures. (D)</p> Signup and view all the answers

What is the main function of lipids in forming vesicles and bilayers?

<p>To provide stability and enclosure (B)</p> Signup and view all the answers

What is the main function of transmembrane proteins in cell membranes?

<p>Serve as structural links between the cytoskeleton and the extracellular matrix (B)</p> Signup and view all the answers

Which statement accurately describes the lipid bilayer in cell membranes?

<p>Consists of amphipathic lipid molecules (B)</p> Signup and view all the answers

What is the significance of membrane proteins in drug development?

<p>They serve as targets for over 50% of modern medicinal drugs (C)</p> Signup and view all the answers

Which lipid molecule is the most abundant in cell membranes?

<p>Phospholipids (D)</p> Signup and view all the answers

What is the primary reason for the bilayer structure of cell membranes?

<p>Due to special properties of lipids that cause spontaneous assemblage into bilayers (C)</p> Signup and view all the answers

Why are over 30% of human genome's proteins classified as membrane proteins?

<p>To facilitate signal transduction and proper cell function (B)</p> Signup and view all the answers

How does the freeze-fracture technique help in studying cell membranes?

<p>It physically breaks apart frozen biological samples to expose structural detail (C)</p> Signup and view all the answers

What is the function of the polar head group in phospholipids?

<p>To anchor the phospholipid in the membrane (B)</p> Signup and view all the answers

How do differences in the length and saturation of fatty acid tails affect membrane fluidity?

<p>They affect the ability of phospholipid molecules to pack together and guarantee membrane fluidity (C)</p> Signup and view all the answers

What is the significance of coating the fractured surface with a metal layer in freeze-fracture electron microscopy?

<p>To provide contrast for electron microscopy (C)</p> Signup and view all the answers

What makes up more than half of the lipid mass in most cell membranes?

<p>Phospholipids (C)</p> Signup and view all the answers

What role do unsaturated fatty acids play in phospholipids compared to saturated fatty acids?

<p>Create small kinks in the fatty acid tails (D)</p> Signup and view all the answers

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