Cell Biology Reading Week 3
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Questions and Answers

Which type of molecules can easily diffuse across a lipid bilayer?

  • Large polar molecules
  • Polar molecules
  • Ions
  • Nonpolar molecules (correct)

    • What type of proteins are present in biological membranes to facilitate the transport of substances into and out of the cell?

  • Transport proteins (correct)
  • Enzymes
  • Cytoskeletal proteins
  • Structural proteins

    • What characterizes a transport protein in biological membranes?

  • It binds solutes on both sides of the membrane simultaneously
  • It undergoes a change in conformation to move solutes across the membrane (correct)
  • It is non-specific for molecules or ions
  • It can only serve as a channel through the membrane

    • What is a role of membranes in a cell?

    <p>To define the boundaries of the cell and internal compartments</p> Signup and view all the answers

    Which organelles are specifically mentioned as having membranes in Eukaryotic cells?

    <p>Nucleus, mitochondria, and chloroplasts</p> Signup and view all the answers

    What characterizes the presence of organelles in Eukaryotic cells?

    <p>Presence of membranes defining internal compartments</p> Signup and view all the answers

    Which type of proteins allow cells to recognize, transmit, and respond to specific signals in nearly all cell types?

    <p>Receptors</p> Signup and view all the answers

    What is the function of gap junctions in animal cells?

    <p>Allowing exchange of cellular components between cells</p> Signup and view all the answers

    What is the main function of plasmodesmata in plant cells?

    <p>Allowing exchange of cellular components between cells</p> Signup and view all the answers

    Who first proposed the fluid mosaic model of the membrane?

    <p>S. Jonathan Singer and Garth Nicolson</p> Signup and view all the answers

    What is a key characteristic of the membrane according to the Singer-Nicolson model?

    <p>Fluid nature</p> Signup and view all the answers

    In the Singer-Nicolson model, what is a significant feature of the lipid components of a membrane?

    <p>In constant motion with lateral mobility</p> Signup and view all the answers

    Who proposed the concept of the lipid bilayer in 1925?

    <p>Evert Gorter and François Grendel</p> Signup and view all the answers

    What are the main classes of membrane lipids?

    <p>Phospholipids, glycolipids, and sterols</p> Signup and view all the answers

    What components make up a phospholipid molecule?

    <p>Two fatty acids, a negatively charged phosphate group, and a charged or polar head group</p> Signup and view all the answers

    Which lipid is the most abundant in cell membranes?

    <p>Phospholipids</p> Signup and view all the answers

    What gives phospholipids their amphipathic character critical for membrane structure?

    <p>Highly polar head and two nonpolar tails</p> Signup and view all the answers

    Which molecule forms a hydrophobic barrier in phospholipids?

    <p>Glycerol</p> Signup and view all the answers

    What is the common head group found in phosphoglycerides like phosphatidylcholine?

    <p>Choline</p> Signup and view all the answers

    What is the main sterol found in animal cell membranes?

    <p>Cholesterol</p> Signup and view all the answers

    What type of fatty acids have higher transition temperatures and are considered less fluid in membranes?

    <p>Long-chain saturated fatty acids</p> Signup and view all the answers

    How do membrane lipids with saturated fatty acids differ from those with unsaturated fatty acids in terms of packing?

    <p>They pack together tightly</p> Signup and view all the answers

    What effect do sterols like cholesterol have on the permeability of a lipid bilayer to ions and small polar molecules?

    <p>Decrease permeability</p> Signup and view all the answers

    What is the primary mechanism by which organisms regulate membrane fluidity?

    <p>Changing lipid composition</p> Signup and view all the answers

    What do amphibians and reptiles do to adapt to lower temperatures in terms of their membrane lipid composition?

    <p>Increase unsaturated lipids</p> Signup and view all the answers

    What technique involves freezing a membrane quickly and then subjecting it to a sharp blow from a diamond knife?

    <p>Freeze fracturing</p> Signup and view all the answers

    Where are integral membrane proteins located within the lipid bilayer?

    <p>Embedded within the lipid bilayer</p> Signup and view all the answers

    What characterizes lipid-anchored proteins in membranes?

    <p>They are hydrophilic proteins located on membrane surfaces</p> Signup and view all the answers

    What is the main characteristic of transmembrane proteins?

    <p>They span both sides of the lipid bilayer</p> Signup and view all the answers

    What is the function of GPI-anchored membrane proteins?

    <p>Released from the membrane by the enzyme phospholipase C</p> Signup and view all the answers

    What is a common feature of glycoproteins in membranes?

    <p>Covalently linked to amino acid side chains</p> Signup and view all the answers

    Where does glycosylation, the addition of a carbohydrate side chain to a molecule, occur for proteins?

    <p>Endoplasmic Reticulum and Golgi compartments</p> Signup and view all the answers

    In terms of diffusion, how do membrane proteins typically compare to lipids?

    <p>Membrane proteins are much more variable in their diffusion rates than lipids</p> Signup and view all the answers

    Why are some membrane proteins constrained in their movement within the lipid bilayer?

    <p>Due to being anchored to protein complexes adjacent to the membrane</p> Signup and view all the answers

    What role do glycoproteins, which have undergone glycosylation, play in plasma membranes?

    <p>Cell-cell recognition</p> Signup and view all the answers

    What structures do animal cells use for joining cells in long-term associations to form tissues and organs?

    <p>Adhesive junctions</p> Signup and view all the answers

    Which type of junctions in plants carry out functions similar to cell-cell junctions in animal cells?

    <p>Plasmodesmata</p> Signup and view all the answers

    What is the main function of adhesive junctions in multicellular organisms?

    <p>Maintain tissue integrity</p> Signup and view all the answers

    What type of interactions occur when cells interact with identical molecules on the surface of the cell to which they adhere?

    <p>Homophilic interactions</p> Signup and view all the answers

    What type of proteins are predominantly involved in forming adherens junctions between cells?

    <p>Cadherins</p> Signup and view all the answers

    Which feature is common between desmosomes and adherens junctions in terms of the type of proteins they rely on for adhesion?

    <p>Cadherins</p> Signup and view all the answers

    What is the key function of tight junctions in epithelial tissue?

    <p>Blocking lateral movement of lipids and proteins</p> Signup and view all the answers

    What is the main role of lectins in cell adhesion?

    <p>Secreting carbohydrate-binding proteins</p> Signup and view all the answers

    How do gap junctions facilitate communication between adjacent cells?

    <p>By allowing the passage of ions and small molecules</p> Signup and view all the answers

    What is the primary constituent of stretchable elastic fibres providing elasticity?

    <p>Elastins</p> Signup and view all the answers

    Which family of proteins primarily binds proteoglycans and collagen molecules to receptors on the plasma membrane surface?

    <p>Fibronectins</p> Signup and view all the answers

    What is the main function of laminins in the basal lamina beneath epithelial cells?

    <p>Maintain tissue organization</p> Signup and view all the answers

    Which component is the most abundant in the extracellular matrix of animal cells?

    <p>Collagens</p> Signup and view all the answers

    What is a defining characteristic shared by all collagens in animal tissues?

    <p>Rigid triple helix structure</p> Signup and view all the answers

    Where are fibronectins primarily located in relation to the lamina?

    <p>On either side of the lamina</p> Signup and view all the answers

    How do integrins link the cytoskeleton with the extracellular matrix?

    <p>By interacting with proteins in the cytosol</p> Signup and view all the answers

    Where do epithelial cells attach to laminin in the basal lamina?

    <p>Through hemidesmosomes</p> Signup and view all the answers

    What family of transmembrane proteins do integrins belong to?

    <p>Integrin family</p> Signup and view all the answers

    Which plant cell wall component is most abundant in tissues providing mechanical support?

    <p>Extensins</p> Signup and view all the answers

    What is the primary constituent of the secondary cell wall that makes it significantly stronger and more rigid than the primary wall?

    <p>Lignin</p> Signup and view all the answers

    Which structure is synthesized first in the plant cell wall and holds adjacent cells together?

    <p>Middle lamella</p> Signup and view all the answers

    In some plant cells, which type of wall creates a relatively thin and flexible structure?

    <p>Primary cell wall</p> Signup and view all the answers

    What do plasmodesmata provide in plant cells through their channels between adjacent cells?

    <p>Plasma membrane continuity</p> Signup and view all the answers

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