Phospholipids, Cholesterol, cell membranes and physiology
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Questions and Answers

What is the first step in phospholipid synthesis?

  • Synthesis of glycerol backbone (correct)
  • Exchange/modification of head group
  • Addition of head group
  • Attachment of fatty acids to backbone

    • What molecule is added to the glycerol-3-phosphate in steps 1 and 2 of phospholipid synthesis?

  • Fatty acyl CoAs (correct)
  • Cytosine diphosphate
  • Phosphate group
  • Nucleotide

    • What is the role of CDP in step 3 of phospholipid synthesis?

  • Translocates phospholipids
  • Displaces CMP
  • Activates one of the hydroxyl groups (correct)
  • Donates methyl groups

    • Which nucleotide is used to help with the addition of the head group to phosphatidic acid?

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

    What is the role of flippase in phospholipid synthesis?

    <p>Translocates phospholipids across the ER membrane</p> Signup and view all the answers

    Which of the following is NOT a step in phospholipid synthesis?

    <p>Exchange/modification of fatty acids</p> Signup and view all the answers

    Where does phospholipid synthesis primarily occur?

    <p>Luminal surface of the smooth ER</p> Signup and view all the answers

    What is the starting molecule for phospholipid synthesis?

    <p>Glycerol-3-phosphate</p> Signup and view all the answers

    What is the role of SAM in phospholipid synthesis?

    <p>Donates methyl groups</p> Signup and view all the answers

    What is the role of phosphatidylinositol in the cell membrane?

    <p>Plays an important role in cell signaling</p> Signup and view all the answers

    Which class of lipids can be broken down structurally into two main classes?

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

    What are the three components of a phospholipid?

    <p>Hydrocarbon chain, glycerol, and phosphate-alcohol head group</p> Signup and view all the answers

    Which phospholipid is much more common in the cell membrane?

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

    What is the basic structure of a phospholipid called?

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

    Which phosphoglyceride is not mentioned in the text?

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

    Which lipid contains a ceramide backbone?

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

    Which lipid can also be classified as a sphingolipid?

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

    What is the cellular location of phospholipid synthesis?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    How do phospholipids synthesized in the smooth ER reach the plasma membrane?

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

    What is the role of the transfer molecule CDP in phospholipid synthesis?

    <p>Catalyzes the synthesis of phospholipids</p> Signup and view all the answers

    Which step in cholesterol synthesis is catalyzed by HMG CoA reductase?

    <p>Step 1</p> Signup and view all the answers

    How many acetyl CoA molecules are needed to make squalene in cholesterol synthesis?

    <p>6 acetyl CoA</p> Signup and view all the answers

    Which enzyme is the main regulatory step of cholesterol synthesis?

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

    Which molecule inhibits HMG CoA reductase in cholesterol synthesis?

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

    Which molecule activates HMG CoA reductase in cholesterol synthesis?

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

    What happens to the transcription of HMG CoA reductase gene when intracellular cholesterol levels are high?

    <p>It decreases</p> Signup and view all the answers

    Which molecule promotes de-phosphorylation of HMG CoA reductase, activating the enzyme?

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

    Which molecule promotes phosphorylation of HMG CoA reductase, inhibiting the enzyme?

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

    What is the rate-limiting step in cholesterol synthesis?

    <p>Condensation of 3 acetyl CoA into Mevalonate</p> Signup and view all the answers

    What is the final step in cholesterol synthesis?

    <p>Ring closure</p> Signup and view all the answers

    Which of the following is NOT a step in cholesterol synthesis?

    <p>Conversion of squalene into cholesterol</p> Signup and view all the answers

    Which organs of the body contribute most significantly to cholesterol synthesis?

    <p>Liver and kidney</p> Signup and view all the answers

    Which structural group does cholesterol belong to?

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

    What is the role of the key regulatory enzyme HMG CoA reductase in cholesterol synthesis?

    <p>Condensation of 3 acetyl CoA into mevalonate</p> Signup and view all the answers

    What inhibits HMG CoA reductase in cholesterol synthesis?

    <p>High intracellular levels of cholesterol</p> Signup and view all the answers

    What is the cellular location of cholesterol synthesis?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    Which class of lipids can be broken down structurally into two main classes?

    <p>Sterols and isoprenoids</p> Signup and view all the answers

    What are the two main structural groups of lipids?

    <p>Sterols and isoprenoids</p> Signup and view all the answers

    What is the basic structure of a steroid called?

    <p>Fused rings</p> Signup and view all the answers

    What is the name for steroids with a hydroxy group at C3?

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

    Which cellular structure is formed from microtubules and rotates and moves in a whip-like fashion?

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

    Which molecular motors can move along microtubules and cause the whipping movements of cilia and flagella?

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

    Which type of intermediate filament confers stability and structure to muscle cells and some epithelial cells?

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

    Which type of filament is responsible for the shape of microvilli in an epithelial cell?

    <p>Actin filaments</p> Signup and view all the answers

    Which type of filament is more stable and does not dissociate as readily as actin or tubulin?

    <p>Intermediate filaments</p> Signup and view all the answers

    Which protein monomers are responsible for the formation of microtubules?

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

    What is the role of nucleating factors in the formation of F-actin?

    <p>To stimulate the formation of F-actin</p> Signup and view all the answers

    Which cellular structures are actin filaments strongly anchored to in a muscle cell?

    <p>Cell membrane and other proteins</p> Signup and view all the answers

    What is the main function of microfilaments in a fibroblast?

    <p>To deposit collagen/ECM</p> Signup and view all the answers

    What is the role of G-actin hydrolyzing ATP to ADP in the stability of F-actin?

    <p>To prevent the disassembly of F-actin</p> Signup and view all the answers

    Which type of membrane protein is responsible for separating cells into apical and basal compartments?

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

    Which type of membrane protein is involved in providing structural integrity for a wide range of cells and tissues?

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

    Which type of membrane protein connects the cell membrane to important extracellular structures?

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

    Which type of junction contains a plaque and connects to microfilaments formed from actin?

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

    Which component of the cytoskeleton is responsible for cellular movement and organization of organelles?

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

    Which lipid component has an unbranched fatty acid tail with usually 16-18 carbons?

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

    What is the most common molecule linked to the phosphate head of glycerophospholipids?

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

    Which lipid intercalates between phospholipids and can impact membrane fluidity?

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

    Which lipid component has a sphingosine backbone and can decrease membrane fluidity due to its slightly different shape?

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

    Which membrane-bound components might have more cholesterol and/or sphingolipids, and why?

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

    Which of the following is a characteristic of a semi-permeable membrane?

    <p>It allows water to pass through, but is impermeable to at least one solute</p> Signup and view all the answers

    What is the most-used model of osmosis discussed in the text?

    <p>The U-tube model</p> Signup and view all the answers

    What is the role of the Na+/K+ ATPase in the cell membrane?

    <p>All of the above</p> Signup and view all the answers

    What is the concentration of Na+ in the extracellular fluid (ECF)?

    <p>142 mM</p> Signup and view all the answers

    What is the main difference between passive transport and active transport?

    <p>Passive transport moves molecules from low to high concentration, while active transport moves molecules from high to low concentration</p> Signup and view all the answers

    Which of the following is NOT a lipid component of the cell membrane?

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

    What is the function of the plasma membrane?

    <p>To regulate the movement of molecules in and out of the cell</p> Signup and view all the answers

    What are the three main components of the cytoskeleton?

    <p>Microfilaments, microtubules, and intermediate filaments</p> Signup and view all the answers

    What is the role of the Na+/K+ ATPase in maintaining cellular integrity?

    <p>It maintains the balance of sodium and potassium ions inside and outside the cell</p> Signup and view all the answers

    What is the function of the cell membrane in cell signaling?

    <p>To transmit signals between cells</p> Signup and view all the answers

    Study Notes

    Phospholipid Synthesis

    • The first step in phospholipid synthesis is the attachment of two fatty acids to glycerol-3-phosphate.
    • In steps 1 and 2 of phospholipid synthesis, fatty acids are added to the glycerol-3-phosphate.
    • CDP acts as a carrier molecule in step 3 of phospholipid synthesis, facilitating the transfer of the activated diacylglycerol to the head group.
    • CTP (cytidine triphosphate) is used to add the head group to phosphatidic acid.
    • Flippase helps move phospholipids from the cytosolic leaflet to the luminal leaflet of the endoplasmic reticulum membrane.
    • The synthesis of a glycerol-3-phosphate molecule is not a step in phospholipid synthesis.
    • Phospholipid synthesis primarily occurs in the smooth endoplasmic reticulum.
    • Glycerol-3-phosphate is the starting molecule for phospholipid synthesis.
    • SAM (S-adenosyl methionine) is involved in the methylation of some phospholipids, contributing to their final structure and function.
    • Phosphatidylinositol is involved in cell signaling, acting as a precursor to second messengers.

    Lipid Classification

    • Lipids can be categorized into two main classes: those with a glycerol backbone and those with a sphingosine backbone.
    • Phospholipids consist of three components: a glycerol backbone, two fatty acid tails, and a phosphate head group.
    • Phosphatidylcholine is the more common type of phospholipid found in the cell membrane.
    • Phospholipids have a basic structure called a "glycerophospholipid" or "phosphoglyceride."
    • Phosphatidylserine is not mentioned in the text as being a phosphoglyceride.
    • Sphingomyelin contains a ceramide backbone, which is formed from sphingosine and a fatty acid.
    • Sphingomyelin can also be classified as a sphingolipid.

    Phospholipid Transport

    • Phospholipid synthesis occurs in the smooth endoplasmic reticulum.
    • Phospholipids synthesized in the smooth ER reach the plasma membrane through vesicular transport.
    • CDP acts as a transfer molecule in phospholipid synthesis, activating diacylglycerol and facilitating its movement to the appropriate head group.

    Cholesterol Synthesis

    • The formation of mevalonate from HMG CoA is the step in cholesterol synthesis catalyzed by HMG CoA reductase.
    • Six acetyl CoA molecules are required to produce squalene in cholesterol synthesis.
    • HMG CoA reductase is the key regulatory enzyme in cholesterol synthesis.
    • Cholesterol inhibits HMG CoA reductase activity in cholesterol synthesis, acting as a negative feedback mechanism.
    • Insulin activates HMG CoA reductase in cholesterol synthesis.
    • When intracellular cholesterol levels are high, the transcription of the HMG CoA reductase gene is suppressed.
    • Insulin promotes dephosphorylation of HMG CoA reductase, activating the enzyme.
    • Phosphorylation of HMG CoA reductase by AMPK inhibits the enzyme.
    • The formation of mevalonate from HMG CoA is the rate-limiting step in cholesterol synthesis.
    • The conversion of lanosterol to cholesterol is the final step in cholesterol synthesis.
    • The synthesis of cholesterol from acetyl CoA is not a step in cholesterol synthesis.
    • The liver and intestines contribute significantly to cholesterol synthesis in the body.
    • Cholesterol belongs to the steroid structural group.
    • HMG CoA reductase is the key regulatory enzyme in cholesterol synthesis, catalyzing the rate-limiting step.
    • Cholesterol inhibits HMG CoA reductase activity, providing negative feedback in cholesterol synthesis.
    • Cholesterol synthesis occurs in the smooth endoplasmic reticulum.

    Lipid Classification

    • Lipids can be categorized into two main classes: those with a glycerol backbone and those with a sphingosine backbone.
    • The two main structural groups of lipids are those with a glycerol backbone and those containing a sphingosine backbone.
    • The basic structure of a steroid is characterized by a four-ring system with branched alkyl groups attached to the rings.
    • Steroids with a hydroxy group at C3 are called sterols.

    Cytoskeleton

    • Cilia are formed from microtubules and move in a whip-like fashion.
    • Dynein motor proteins move along microtubules, driving the whipping movements of cilia and flagella.
    • Intermediate filaments of the vimentin type provide stability and structure to muscle cells and some epithelial cells.
    • Actin filaments are responsible for the shape of microvilli in an epithelial cell.
    • Intermediate filaments are more stable and do not dissociate as readily as actin or tubulin.
    • Tubulin protein monomers form microtubules.
    • Nucleating factors help initiate the formation of F-actin (filamentous actin) by providing a site for actin monomers to assemble.
    • Actin filaments in a muscle cell are strongly anchored to the Z-disc and sarcomere.
    • The main function of microfilaments in a fibroblast is to assist with cell movement and facilitate the changing shape of the cell.
    • G-actin (globular actin) hydrolyzing ATP to ADP contributes to the stability of F-actin, promoting a conformational change in the actin filament.

    Membrane Proteins

    • Integral membrane proteins are responsible for separating cells into apical and basal compartments.
    • Structural proteins provide structural integrity for a wide range of cells and tissues.
    • Anchoring proteins connect the cell membrane to important extracellular structures.
    • Adherens junctions contain a plaque and connect to microfilaments formed from actin.

    Cytoskeletal Components & Cell Membrane

    • Microtubules, part of the cytoskeleton, are responsible for cellular movement and organization of organelles.
    • Fatty acid tails of phospholipids are unbranched and typically contain 16-18 carbons.
    • Phosphatidylcholine is the most common molecule linked to the phosphate head of glycerophospholipids.
    • Cholesterol intercalates between phospholipids in the membrane, influencing membrane fluidity.
    • Sphingolipids, containing a sphingosine backbone, can decrease membrane fluidity due to their slightly different shape.
    • Membrane components like the lipid rafts might have more cholesterol and/or sphingolipids to maintain their structural integrity and function.

    Membrane Properties & Transport

    • A semi-permeable membrane allows certain molecules to pass through while restricting others.
    • The fluid mosaic model is the most-used model of osmosis discussed in the text.
    • The Na+/K+ ATPase pumps sodium ions out of the cell and potassium ions into the cell, contributing to the electrochemical gradient.
    • The concentration of Na+ in the extracellular fluid (ECF) is higher compared to the intracellular fluid (ICF).
    • Active transport requires energy to move molecules against their concentration gradients, while passive transport does not.
    • Carbohydrates are not a lipid component of the cell membrane.
    • The plasma membrane acts as a selective barrier, regulating the passage of molecules into and out of the cell.
    • The three main components of the cytoskeleton are microfilaments, microtubules, and intermediate filaments.
    • The Na+/K+ ATPase helps maintain cellular integrity by contributing to the electrochemical gradient across the cell membrane.
    • The cell membrane plays a crucial role in signal transduction and cell signaling, receiving signals from the environment and relaying them inside the cell.

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    Description

    Test your knowledge of phospholipids with this quiz! Learn about the classification, components, and synthesis of phospholipids found in the cell membrane.

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