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Questions and Answers
Which of the following correctly describes integral membrane proteins?
Which of the following correctly describes integral membrane proteins?
Which components of biological membranes are considered amphipathic?
Which components of biological membranes are considered amphipathic?
Which of the following statements about membrane lipids is accurate?
Which of the following statements about membrane lipids is accurate?
Where are glycolipids primarily located within the plasma membrane?
Where are glycolipids primarily located within the plasma membrane?
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What is a characteristic feature of transmembrane proteins?
What is a characteristic feature of transmembrane proteins?
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What is the primary function of fatty acid binding proteins (FABPs) in cells?
What is the primary function of fatty acid binding proteins (FABPs) in cells?
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Which step directly follows the conversion of mevalonate during cholesterol synthesis?
Which step directly follows the conversion of mevalonate during cholesterol synthesis?
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What initiates the process that leads to atherosclerosis?
What initiates the process that leads to atherosclerosis?
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Which enzyme is primarily responsible for the conversion of HMG-CoA to mevalonate in cholesterol synthesis?
Which enzyme is primarily responsible for the conversion of HMG-CoA to mevalonate in cholesterol synthesis?
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During phospholipid synthesis, which molecule is formed first from fatty acyl CoA and glycerol phosphate?
During phospholipid synthesis, which molecule is formed first from fatty acyl CoA and glycerol phosphate?
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What is a common mechanism for the transport of lipids between organelles?
What is a common mechanism for the transport of lipids between organelles?
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What happens to foam cells during the development of atherosclerosis?
What happens to foam cells during the development of atherosclerosis?
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What regulates the levels of fatty acid binding proteins (FABPs) in cells?
What regulates the levels of fatty acid binding proteins (FABPs) in cells?
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What determines the blood type in individuals with the O Antigen?
What determines the blood type in individuals with the O Antigen?
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Which fatty acids are primarily synthesized in the cytosol from Acetyl CoA?
Which fatty acids are primarily synthesized in the cytosol from Acetyl CoA?
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What is the role of ionic detergents in membrane studies?
What is the role of ionic detergents in membrane studies?
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How are new bio membranes synthesized?
How are new bio membranes synthesized?
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What is the primary function of amphipathic molecules like detergents?
What is the primary function of amphipathic molecules like detergents?
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Which statement accurately describes the function of glycolipids in the plasma membrane?
Which statement accurately describes the function of glycolipids in the plasma membrane?
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What is the significance of farnesyl and geranylgeranyl as acyl anchors?
What is the significance of farnesyl and geranylgeranyl as acyl anchors?
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What pathways provide the building blocks for cholesterol synthesis?
What pathways provide the building blocks for cholesterol synthesis?
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What is the primary product of fatty acid synthesis that is synthesized in the cytosol?
What is the primary product of fatty acid synthesis that is synthesized in the cytosol?
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Which factor is crucial for the diversity of human ABO blood types?
Which factor is crucial for the diversity of human ABO blood types?
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Which statements accurately describe transmembrane proteins?
Which statements accurately describe transmembrane proteins?
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Which of the following lipid components are found in biological membranes?
Which of the following lipid components are found in biological membranes?
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What is true regarding the movement of membrane lipids?
What is true regarding the movement of membrane lipids?
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Where are glycolipids typically located in the plasma membrane?
Where are glycolipids typically located in the plasma membrane?
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Which of the following biological membrane components can be classified as amphipathic?
Which of the following biological membrane components can be classified as amphipathic?
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What primarily determines the blood type of an individual with type O Antigen?
What primarily determines the blood type of an individual with type O Antigen?
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What is the role of myristate and palmitate in membrane proteins?
What is the role of myristate and palmitate in membrane proteins?
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Which statement correctly describes the composition of biological membranes?
Which statement correctly describes the composition of biological membranes?
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What distinguishes B and AB blood types from type O?
What distinguishes B and AB blood types from type O?
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Which process leads to the solubilization of membrane proteins using detergents?
Which process leads to the solubilization of membrane proteins using detergents?
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What type of fatty acids are primarily synthesized by Acetyl-CoA carboxylase in the cytosol?
What type of fatty acids are primarily synthesized by Acetyl-CoA carboxylase in the cytosol?
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Which characteristic is true of non-ionic detergents when used in membrane studies?
Which characteristic is true of non-ionic detergents when used in membrane studies?
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In the context of membrane biosynthesis, where are final steps of lipid synthesis typically completed?
In the context of membrane biosynthesis, where are final steps of lipid synthesis typically completed?
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What characterizes the amphipathic nature of detergents?
What characterizes the amphipathic nature of detergents?
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Which enzyme is responsible for the conversion of Acetyl-CoA to fatty acids in the cytosol?
Which enzyme is responsible for the conversion of Acetyl-CoA to fatty acids in the cytosol?
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What function do fatty acid binding proteins (FABPs) serve in cells?
What function do fatty acid binding proteins (FABPs) serve in cells?
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Which process converts phosphatidic acid into diacylglycerol during phospholipid synthesis?
Which process converts phosphatidic acid into diacylglycerol during phospholipid synthesis?
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What is the role of HMG-CoA reductase in cholesterol synthesis?
What is the role of HMG-CoA reductase in cholesterol synthesis?
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Which step follows the significant accumulation of foam cells in atherosclerosis?
Which step follows the significant accumulation of foam cells in atherosclerosis?
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What is primarily responsible for the elongation of palmitoyl CoA to longer fatty acids?
What is primarily responsible for the elongation of palmitoyl CoA to longer fatty acids?
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How do anti-atherosclerosis medications work?
How do anti-atherosclerosis medications work?
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Which lipid transport mechanism is NOT Golgi-dependent?
Which lipid transport mechanism is NOT Golgi-dependent?
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Which lipid is the final product of the cholesterol synthesis pathway?
Which lipid is the final product of the cholesterol synthesis pathway?
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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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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.
