Biomembrane structure
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Which of the following correctly describes integral membrane proteins?

  • They can only exist as monomers within the membrane.
  • They lack any affinity for lipid environments.
  • They interact with both the hydrophobic and hydrophilic environments. (correct)
  • They are exclusively hydrophilic in nature.

    • Which components of biological membranes are considered amphipathic?

  • Both phospholipids and integral membrane proteins (correct)
  • Only phospholipids
  • Only glycolipids
  • Only integral membrane proteins

    • Which of the following statements about membrane lipids is accurate?

  • Flippases can only transfer lipid molecules from the inner to the outer leaflet.
  • All membrane lipids are fully hydrophilic.
  • Different lipid compositions can exist in the outer and inner leaflets. (correct)
  • Membrane lipids can move spontaneously between leaflets without any assistance.

    • Where are glycolipids primarily located within the plasma membrane?

    <p>Outer leaflet of the plasma membrane</p> Signup and view all the answers

    What is a characteristic feature of transmembrane proteins?

    <p>They can function as channels for specific ions or molecules.</p> Signup and view all the answers

    What is the primary function of fatty acid binding proteins (FABPs) in cells?

    <p>To bind and facilitate the movement of fatty acids within the cytoplasm</p> Signup and view all the answers

    Which step directly follows the conversion of mevalonate during cholesterol synthesis?

    <p>Conversion of mevalonate to isopentenyl pyrophosphate (IPP)</p> Signup and view all the answers

    What initiates the process that leads to atherosclerosis?

    <p>Damage to endothelial cells</p> Signup and view all the answers

    Which enzyme is primarily responsible for the conversion of HMG-CoA to mevalonate in cholesterol synthesis?

    <p>HMG-CoA reductase</p> Signup and view all the answers

    During phospholipid synthesis, which molecule is formed first from fatty acyl CoA and glycerol phosphate?

    <p>Phosphatidic acid</p> Signup and view all the answers

    What is a common mechanism for the transport of lipids between organelles?

    <p>Direct contact between organelle membranes mediated by proteins</p> Signup and view all the answers

    What happens to foam cells during the development of atherosclerosis?

    <p>They accumulate and contribute to plaque formation</p> Signup and view all the answers

    What regulates the levels of fatty acid binding proteins (FABPs) in cells?

    <p>Cellular requirements for free fatty acids</p> Signup and view all the answers

    What determines the blood type in individuals with the O Antigen?

    <p>The presence or absence of glycosyltransferases that add galactose or GalNAc.</p> Signup and view all the answers

    Which fatty acids are primarily synthesized in the cytosol from Acetyl CoA?

    <p>14C and 16C fatty acids.</p> Signup and view all the answers

    What is the role of ionic detergents in membrane studies?

    <p>They denature proteins, disrupting their structure.</p> Signup and view all the answers

    How are new bio membranes synthesized?

    <p>By expanding pre-existing membranes.</p> Signup and view all the answers

    What is the primary function of amphipathic molecules like detergents?

    <p>To disrupt membranes by intercalating into phospholipid bilayers.</p> Signup and view all the answers

    Which statement accurately describes the function of glycolipids in the plasma membrane?

    <p>They contain oligosaccharide chains that function in cell recognition.</p> Signup and view all the answers

    What is the significance of farnesyl and geranylgeranyl as acyl anchors?

    <p>They attach to cysteine residues at the C terminus of proteins.</p> Signup and view all the answers

    What pathways provide the building blocks for cholesterol synthesis?

    <p>Acetyl-CoA and acetate through HMG-CoA.</p> Signup and view all the answers

    What is the primary product of fatty acid synthesis that is synthesized in the cytosol?

    <p>Fatty acids.</p> Signup and view all the answers

    Which factor is crucial for the diversity of human ABO blood types?

    <p>The genetic variation in glycosyltransferases.</p> Signup and view all the answers

    Which statements accurately describe transmembrane proteins?

    <p>All transmembrane proteins contain a hydrophilic core.</p> Signup and view all the answers

    Which of the following lipid components are found in biological membranes?

    <p>Integral membrane proteins have both hydrophobic and hydrophilic regions.</p> Signup and view all the answers

    What is true regarding the movement of membrane lipids?

    <p>Membrane lipids can spontaneously move between the inner and outer leaflets.</p> Signup and view all the answers

    Where are glycolipids typically located in the plasma membrane?

    <p>Concentrated in the outer leaflet of the plasma membrane.</p> Signup and view all the answers

    Which of the following biological membrane components can be classified as amphipathic?

    <p>Integral membrane proteins exhibit amphipathic characteristics.</p> Signup and view all the answers

    What primarily determines the blood type of an individual with type O Antigen?

    <p>Presence or absence of glycosyltransferases</p> Signup and view all the answers

    What is the role of myristate and palmitate in membrane proteins?

    <p>They act as acyl anchors to proteins</p> Signup and view all the answers

    Which statement correctly describes the composition of biological membranes?

    <p>They consist of a phospholipid bilayer embedded with proteins</p> Signup and view all the answers

    What distinguishes B and AB blood types from type O?

    <p>Presence of terminal oligosaccharide sugars</p> Signup and view all the answers

    Which process leads to the solubilization of membrane proteins using detergents?

    <p>Intercalation into phospholipid bilayers</p> Signup and view all the answers

    What type of fatty acids are primarily synthesized by Acetyl-CoA carboxylase in the cytosol?

    <p>14 and 16 carbon fatty acids</p> Signup and view all the answers

    Which characteristic is true of non-ionic detergents when used in membrane studies?

    <p>They maintain the structure of integral membrane proteins</p> Signup and view all the answers

    In the context of membrane biosynthesis, where are final steps of lipid synthesis typically completed?

    <p>On the destination membranes</p> Signup and view all the answers

    What characterizes the amphipathic nature of detergents?

    <p>They have both hydrophilic and hydrophobic regions</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of Acetyl-CoA to fatty acids in the cytosol?

    <p>Fatty acid synthase</p> Signup and view all the answers

    What function do fatty acid binding proteins (FABPs) serve in cells?

    <p>They facilitate the movement of fatty acids within the cytoplasm.</p> Signup and view all the answers

    Which process converts phosphatidic acid into diacylglycerol during phospholipid synthesis?

    <p>Membrane phosphatase activity.</p> Signup and view all the answers

    What is the role of HMG-CoA reductase in cholesterol synthesis?

    <p>It catalyzes the reduction of HMG-CoA to mevalonate.</p> Signup and view all the answers

    Which step follows the significant accumulation of foam cells in atherosclerosis?

    <p>Plaque formation in arterial walls.</p> Signup and view all the answers

    What is primarily responsible for the elongation of palmitoyl CoA to longer fatty acids?

    <p>Smooth ER membrane enzymes.</p> Signup and view all the answers

    How do anti-atherosclerosis medications work?

    <p>By directly inhibiting HMG-CoA reductase activity.</p> Signup and view all the answers

    Which lipid transport mechanism is NOT Golgi-dependent?

    <p>Transport through the nuclear pore complex.</p> Signup and view all the answers

    Which lipid is the final product of the cholesterol synthesis pathway?

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

    Study Notes

    Fatty Acid Metabolism

    • Palmitoyl CoA (16C) can be elongated to 18-24C in the smooth ER membrane.
    • All newly synthesized fatty acids are saturated.
    • Addition of double bonds occurs in the ER membrane by desaturase enzymes.
    • Fatty acids move within cells bound to cytosolic proteins called fatty acid binding proteins (FABPs).
    • FABPs bind to hydrophobic pockets with which a long fatty acid chain can interact.
    • FABPs are up-regulated and down-regulated depending on the cellular requirements for the uptake and release of free fatty acids.
    • A cell using fatty acids for respiration, or an adipocyte releasing fatty acids, contains large numbers of FABPs within the cytosol.

    Phospholipid Synthesis

    • Fatty acids are converted into fatty acyl CoAs (CoA esters).
    • Fatty acyl CoA + glycerol phosphate are converted to phosphatidic acid by acyl transferases (esterases) on the smooth ER membrane.
    • Membrane phosphatase converts phosphatidic acid to diacylglycerol.
    • Choline phosphotransferase transfers phosphocholine to diacylglycerol to form the phospholipid.
    • Flippase transfers lipids from the cytosolic leaflet to the exoplasmic leaflet.

    Cholesterol Synthesis

    • Cytosolic acetyl CoA combines with acetoacetyl CoA forming HMG-CoA
    • HMG-CoA is converted to 6C mevalonate by HMG-CoA reductase.
    • HMG-CoA reductase is embedded in the SER membrane but has a catalytic domain in the cytosol.
    • Cytosolic enzymes convert mevalonate to IPP, Farnesyl pyrophosphate, and squalene.
    • Squalene is converted to cholesterol on the SER membrane.

    Atherosclerosis

    • Hardening of the arteries caused by blockage of the arterial lumen.
    • Major cause of heart disease in the industrialized West.
    • Steps:
      • damage to endothelial cells
      • monocyte entry & conversion to macrophages
      • uptake of LDL
      • conversion to foam cells
      • foam cells accumulate
      • plaque formation
    • Anti-atherosclerosis medications include statins.
    • Statins bind to HMG-CoA reductase and directly inhibit its activity, reducing cholesterol biosynthesis.

    Transport of Lipids between Organelles

    • Some cholesterol & phospholipids are transported via Golgi-dependent processes, especially if lipids are bound to proteins.
    • Three Golgi-independent mechanisms have been proposed for most lipid transport between organelles:
      • via vesicles
      • direct contact between membranes mediated by integral proteins
      • mediated by soluble lipid-transfer proteins

    Anchored Membrane Proteins by Covalently Linked Hydrocarbons

    • Fatty acyl group attaches to N-term glycine. Anchors: Myristate(C14) and palmitate (C16) are common acyl anchors.
    • Hydrocarbon chain attaches to a cysteine residue at the C terminus. Anchors: farnesyl(C15) and geranylgeranyl(C20).
    • Exoplasmic face to GPI (glycolipids) – Glycosylphosphatidylinositol

    Human ABO Blood Group Antigens

    • Oligosaccharide chains covalently attached to glycolipids or glycoproteins in the PM.
    • Terminal oligosaccharide sugars distinguish 3 antigens.
    • Presence or absence of glycosyltransferases that add galactose or GalNAc to the O antigen determine blood type.

    Different Blood Types in US & Canadian Populations

    • O+ is the most common blood type in North America, followed by A+ and O-.

    Detergents

    • Detergents are amphipathic molecules that disrupt membranes by intercalating into phospholipid bilayers and solubilize lipids and many membrane proteins.
    • Proteins can be removed from membranes with detergents.
      • Ionic detergents denature proteins.
      • Non-ionic solubilize integral membrane proteins.

    Principles of Membrane Biosynthesis

    • New bio membranes are synthesized by expanding preexisting membranes.
    • Many lipids are synthesized on the membranes of the smooth ER.
    • The final steps of membrane lipid synthesis take place on destination membranes.
    • After synthesis, membrane lipids must be distributed to the appropriate leaflet and organellar membranes.

    Fatty Acid Synthesis

    • Fatty acids can be synthesized from:
      • the enzymatic hydrolysis of triacylglycerol, which is stored in adipocytes in mammals and other vertebrates
      • or de novo from Acetyl CoA.
    • 14 and 16C fatty acids are synthesized in the cytosol by Acetyl-CoA carboxylase and fatty acid synthase.

    Q1: Which statements accurately describe membrane proteins?

    • All integral membrane proteins are amphipathic.
    • All transmembrane proteins are also integral membrane proteins.

    Q2: Which of the following components of biological membranes are amphipathic?

    • Integral membrane proteins.
    • Phospholipids.
    • Glycolipids.
    • Membrane steroids such as cholesterol, sitosterol, and ergosterol.

    Q3: Which of the following applies to membrane lipids?

    • Membrane lipids are composed of hydrophobic molecules.
    • Flippases are able to catalyze the transfer of lipid molecules between the outer and inner leaflets.
    • Different lipid compositions are found in the two leaflets of a membrane.

    Q4: In the plasma membrane, Glycolipids are usually situated in:

    • The outer leaflet of the plasma membrane.

    Anchored Membrane Proteins

    • Membrane proteins can be anchored by covalently linked hydrocarbons on either the exoplasmic or cytosolic face of the membrane.
    • Exoplasmic face: Glycosylphosphatidylinositol (GPI) anchors proteins to the exoplasmic face of the membrane.
    • Cytosolic face:
      • Fatty acyl groups (like myristate and palmitate) attach to the N-terminal glycine of a protein.
      • Hydrocarbon chains (like farnesyl and geranylgeranyl) attach to a cysteine residue at the C-terminus of a protein.

    Human ABO Blood Group Antigens

    • The human ABO blood group antigens are determined by oligosaccharide chains attached to glycolipids or glycoproteins in the plasma membrane.
    • The terminal oligosaccharide sugars distinguish the three antigens (A, B, and O).
    • The presence or absence of specific glycosyltransferases determines blood type. These enzymes add either galactose or GalNAc to the O antigen.

    Detergents

    • Detergents are amphipathic molecules that disrupt membranes by intercalating into phospholipid bilayers.
    • They solubilize lipids and many membrane proteins.
    • Ionic detergents denature proteins, while non-ionic detergents solubilize integral membrane proteins.

    Principles of Membrane Biosynthesis

    • New biomembranes are synthesized by expanding pre-existing membranes.
    • Many lipids are synthesized on the membranes of the smooth endoplasmic reticulum (ER).
    • The final steps of membrane lipid synthesis occur on the destination membranes.
    • After synthesis, membrane lipids must be distributed to the appropriate leaflet and organellar membranes.

    Fatty Acid Synthesis

    • Fatty acids can be synthesized from the enzymatic hydrolysis of triacylglycerol or de novo from acetyl CoA.
    • 14 and 16 carbon fatty acids are synthesized in the cytosol by acetyl-CoA carboxylase and fatty acid synthase.
    • Palmitoyl CoA (16C) can be elongated to 18-24 carbons in the smooth ER membrane.
    • Newly synthesized fatty acids are saturated.
    • Double bonds are added in the ER membrane by desaturase enzymes.

    Intracellular Movement of Fatty Acids

    • Fatty acids move within cells bound to cytosolic proteins called fatty acid binding proteins (FABPs).
    • FABPs are upregulated or downregulated depending on the cellular requirements for the uptake and release of free fatty acids.

    Synthesis of Phospholipids

    • Fatty acids are converted into fatty acyl CoAs.
    • Fatty acyl CoA and glycerol phosphate are converted to phosphatidic acid by acyl transferases on the smooth ER membrane.
    • Membrane phosphatase converts phosphatidic acid to diacylglycerol.
    • Choline phosphotransferase transfers phosphocholine to diacylglycerol to form the phospholipid.
    • Flippases transfer lipids from the cytosolic leaflet to the exoplasmic leaflet.

    Cholesterol Synthesis

    • Cytosolic acetyl CoA combines with acetoacetyl CoA to form HMG-CoA.
    • HMG-CoA is converted to mevalonate by HMG-CoA reductase.
    • HMG-CoA reductase is embedded in the SER membrane but has a catalytic domain in the cytosol.
    • Cytosolic enzymes convert mevalonate to IPP, farnesyl pyrophosphate, and squalene.
    • Squalene is converted to cholesterol on the SER membrane.

    Atherosclerosis

    • Hardening of the arteries caused by blockage of the arterial lumen.
    • A major cause of heart disease in the industrialized West.
    • Steps: damage to endothelial cells, monocyte entry, conversion to macrophages, uptake of LDL, conversion to foam cells, foam cell accumulation, plaque formation.
    • Statins are anti-atherosclerosis medications that bind to HMG-CoA reductase and inhibit its activity, reducing cholesterol biosynthesis.

    Transport of Lipids between Organelles

    • Some cholesterol and phospholipids are transported via Golgi-dependent processes, especially if the lipids are bound to proteins.
    • Three Golgi-independent mechanisms have been proposed for most lipid transport between organelles:
      • Via vesicles
      • Direct contact between membranes mediated by integral proteins
      • Mediated by soluble lipid-transfer proteins

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    Biomembrane Structure 2024

    Description

    This quiz explores the biochemical pathways involved in fatty acid metabolism and phospholipid synthesis. Learn about the role of palmitoyl CoA, fatty acid binding proteins, and the transformation processes that occur in the smooth ER. Test your knowledge on these essential metabolic processes.

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