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Membrane Proteins quiz #1

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  • What are the four main types of membrane proteins, and how do they differ in their association with the lipid bilayer?
    The four main types of membrane proteins are transmembrane, integral, peripheral, and lipid-anchored proteins. Transmembrane proteins span the entire lipid bilayer. Integral proteins are directly attached to the bilayer but may not span it completely. Peripheral proteins are attached to membrane proteins but do not directly interact with the lipid bilayer. Lipid-anchored proteins are covalently bonded to lipids within the membrane.
  • Describe the two main structural motifs found in transmembrane proteins and their functional significance.
    Transmembrane proteins commonly form alpha helices, which allow hydrophobic amino acids to interact with the membrane's hydrophobic core, and beta barrels, which are typically found in channel proteins that allow molecules to pass through the membrane.
  • How does the asymmetric distribution of membrane proteins contribute to cellular function?
    The asymmetric distribution of membrane proteins allows different sides of the membrane to have distinct functions, such as nutrient absorption on one side and transport on the other, and enables specific modifications like glycosylation that protect the cell and mediate interactions.
  • What laboratory techniques are commonly used to study membrane proteins, and what does each technique reveal?
    Common techniques include using detergents to isolate membrane proteins, freeze fracturing to examine membrane structure and protein distribution, and FRAP (Fluorescent Recovery After Photobleaching) to study membrane fluidity and protein mobility.
  • What are the four main types of membrane proteins and how do they differ in their association with the lipid bilayer?
    The four main types are transmembrane, integral, peripheral, and lipid-anchored proteins. Transmembrane span the bilayer, integral are directly attached but may not span it, peripheral bind to other proteins not the bilayer, and lipid-anchored are covalently bonded to lipids.
  • What are the two main structural motifs found in transmembrane proteins and what is their functional significance?
    Transmembrane proteins commonly form alpha helices, which interact with the hydrophobic core, and beta barrels, which are often found in channel proteins allowing molecules to pass through the membrane.
  • How does the asymmetric distribution of membrane proteins contribute to cellular function?
    Asymmetric distribution allows different sides of the membrane to have specialized functions, such as nutrient absorption on one side and transport on the other, and enables specific modifications like glycosylation for protection and cell interactions.
  • What is the main difference between peripheral and lipid-anchored membrane proteins?
    Peripheral proteins attach to membrane proteins but do not directly interact with the lipid bilayer, while lipid-anchored proteins are covalently bonded to lipids within the membrane.
  • What laboratory techniques are commonly used to study membrane proteins and what does each reveal?
    Detergents are used to isolate membrane proteins, freeze fracturing examines membrane structure and protein distribution, and FRAP studies membrane fluidity and protein mobility.
  • What is the function of the cell cortex and how does it relate to membrane proteins?
    The cell cortex is a structure on the inner surface of the plasma membrane that interacts with the cytoskeleton, helping to anchor the membrane, support cell shape, and limit membrane protein movement.
  • What are three functions of proteins in the cell membrane?
    Three functions of proteins in the cell membrane are: (1) forming channels and pumps to transport molecules across the membrane, (2) providing structural support and shape to the cell through interactions with the cell cortex and extracellular matrix, and (3) facilitating cell signaling and recognition through glycoproteins and other surface modifications.
  • What roles do proteins play in the cell membrane?
    Proteins in the cell membrane serve as transporters (channels and pumps), structural components (supporting cell shape and anchoring to the cytoskeleton), and mediators of cell communication and recognition (such as glycoproteins involved in signaling and protection).
  • Which molecules form the channels and pumps in the phospholipid bilayer?
    Transmembrane proteins form the channels and pumps in the phospholipid bilayer, often adopting structures like alpha helices or beta barrels to span the membrane and facilitate the movement of molecules.