Biochemistry Chapter on Lipid Metabolism

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Questions and Answers

What is produced in every turn of beta-oxidation?

  • 1 NADH and 1 FADH2 (correct)
  • 1 Propionyl CoA
  • 1 ATP
  • 2 Acetyl CoA

Every step in beta-oxidation produces 2 NADH.

False (B)

How many Acetyl CoA molecules are formed from the complete oxidation of palmitic acid?

8

During fatty acid synthesis, Acetyl CoA and _______ are used as starting materials.

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

Match the types of fatty acids with their characteristics:

<p>Palmitic acid = 16 carbons, produces 8 Acetyl CoA Margaric acid = 17 carbons, produces 7 Acetyl CoA and 1 Propionyl CoA Propionyl CoA = 3 carbons, contributes to Succinyl CoA formation Succinyl CoA = 4 carbons, yields less energy in TCA compared to Acetyl CoA</p> Signup and view all the answers

What is the primary function of bile acids in lipid digestion?

<p>Emulsify fats (A)</p> Signup and view all the answers

Chylomicrons are responsible for the transport of triacylglycerols in the lymphatic system.

<p>True (A)</p> Signup and view all the answers

Name two types of lipoproteins that transport lipids in the bloodstream.

<p>Very Low Density Lipoproteins (VLDL) and High Density Lipoproteins (HDL)</p> Signup and view all the answers

The products of lipase digestion form __________ for absorption by the intestinal cells.

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

Match the lipid pathway with its corresponding function:

<p>Digestion = Breakdown of lipids into fatty acids and glycerol Absorption = Formation of micelles in the intestinal cells Transportation = Packaging lipids into chylomicrons Catabolism = Decomposing fatty acids for energy</p> Signup and view all the answers

Which enzyme is primarily responsible for the digestion of triglycerides in the intestine?

<p>Pancreatic lipase (B)</p> Signup and view all the answers

Fatty acids with an odd number of carbon atoms are metabolized into Acetyl-CoA and Propionyl-CoA.

<p>True (A)</p> Signup and view all the answers

What type of bonds do sphingophospholipids contain, based on their structure?

<p>Amide bonds</p> Signup and view all the answers

What is the primary role of lipids in biological systems?

<p>Storing energy (B)</p> Signup and view all the answers

Phospholipids contain a hydrophobic tail and a hydrophilic head.

<p>True (A)</p> Signup and view all the answers

What are the three main components of a triacylglycerol?

<p>Three fatty acids and one glycerol molecule</p> Signup and view all the answers

Lipids that are widely used for energy storage are called ______.

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

Match the following lipid types with their descriptions:

<p>Phospholipids = Major components of cell membranes Fatty Acids = Building blocks of lipids Steroids = Hormonal signaling molecules Waxes = Water-repellent coatings</p> Signup and view all the answers

Which type of lipid serves as insulation and provides energy storage?

<p>Triacylglycerols (B)</p> Signup and view all the answers

Waxes are a type of lipid that is soluble in water.

<p>False (B)</p> Signup and view all the answers

What is the structural difference between saturated and unsaturated fatty acids?

<p>Saturated fatty acids have no double bonds between carbon atoms; unsaturated fatty acids have one or more double bonds.</p> Signup and view all the answers

Flashcards

Lipids

Molecules that are insoluble in water but highly soluble in organic solvents.

Hydrophobic

The property of a molecule that repels water.

Hydrophilic

The property of a molecule that attracts water.

Fatty Acids

Long chains of hydrocarbons with a carboxylic acid group at one end.

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Glycerol

A three-carbon alcohol that forms the backbone of many lipids, including triacylglycerols and phospholipids.

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Triacylglycerol

A type of lipid that stores energy in adipose tissue. Formed from glycerol and three fatty acids.

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Phospholipids

A type of lipid that forms the structural basis of cell membranes. They have a glycerol backbone, two fatty acid chains, and a phosphate group.

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Sphingosine

The molecule that forms the backbone of sphingolipids. It has a long hydrocarbon chain and an amino group.

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Beta-oxidation

A process where fatty acids are broken down into two-carbon units (acetyl-CoA) to generate energy. It occurs in the mitochondria and involves multiple steps, including activation, transport, and beta-oxidation.

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Fatty acid activation

The first step of fatty acid oxidation, where the fatty acid is activated by attaching it to coenzyme A (CoA) using energy from ATP.

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Beta-oxidation cycle

A series of repeating reactions that remove two-carbon units from the fatty acid chain in the form of acetyl-CoA. Each cycle produces NADH and FADH2, electron carriers used in oxidative phosphorylation to produce ATP.

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Odd-chain fatty acid oxidation

A type of fatty acid oxidation that occurs when the starting fatty acid has an odd number of carbons. It results in the production of propionyl-CoA, which is then converted into succinyl-CoA and enters the citric acid cycle.

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Fatty acid synthesis

The process of building fatty acids from smaller units, primarily acetyl-CoA. It occurs in the cytosol and requires NADPH and ATP.

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Lipid Digestion

Lipids are broken down into smaller components through a series of enzymatic reactions. This process is facilitated by enzymes like lingual lipase in the mouth, gastric lipase in the stomach, and pancreatic lipase in the intestine.

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Role of Bile Salts

Bile salts, produced by the liver, act as detergents that emulsify fats. They increase surface area, making it easier for lipases to work.

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Lipid Absorption

The products of lipid digestion are absorbed in the small intestine. This includes free fatty acids, cholesterol, and 2-monoacylglycerol. Fat-soluble vitamins (A, D, E, and K) are also absorbed here.

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Lipid Transportation

After absorption, lipids are reassembled into triacylglycerols and packaged into lipoprotein particles called chylomicrons. These particles transport lipids through the lymphatic system and into the bloodstream.

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Lipoprotein Categories

Lipoproteins are complexes that transport lipids in the blood. They are classified into different categories based on their density: chylomicrons, VLDL, LDL, and HDL. Each type has a specific role in lipid metabolism.

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Fatty Acid Oxidation

The breakdown of fatty acids into acetyl-CoA through a series of steps. This process occurs in the mitochondria and generates energy in the form of ATP.

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Significance of Fatty Acid Oxidation

Fatty acid oxidation is a critical process for energy production, particularly during periods of fasting or when carbohydrate intake is limited. This pathway provides an alternative energy source for the body.

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Study Notes

Lipids

  • Lipids are defined as water-insoluble (hydrophobic) molecules, highly soluble in organic solvents.
  • They have both hydrophilic (polar) and hydrophobic (nonpolar) regions, making them amphipathic.
  • Lipids are crucial for energy storage, membrane structure, and signaling.

Learning Objectives

  • Explain structural properties of lipids.
  • Detail the roles of lipids.
  • Categorize lipids.
  • Identify fatty acids.
  • Describe lipid digestion and absorption.
  • Recognize steroids.
  • Classify lipoproteins.
  • Explain fatty acid catabolism (beta-oxidation).
  • Explain fatty acid synthesis.

Types of Lipids

  • Fatty acids
  • Waxes
  • Sphingolipids
  • Terpenes
  • Phospholipids
  • Ceramides
  • Steroids
  • Triacylglycerides
  • Eicosanoids

Roles of Lipids

  • Energy storage: Lipids store energy more efficiently than carbohydrates as they require less water for storage.
  • Membrane structure: Lipids are essential components of cell membranes, providing a barrier and facilitating communication.
  • Signaling: Lipids serve as hormones and other signaling molecules, regulating various bodily functions.
  • Thermal insulation: Lipids help maintain body temperature by acting as thermal insulators.

Triacylglycerols (TAGs)

  • Storage lipids, made of glycerol and three fatty acids.
  • Major energy storage form for the body, storing energy efficiently with less water.
  • Found in adipose tissue.

Phospholipids

  • Crucial component of cell membranes, featuring a glycerol backbone, two fatty acid chains, a phosphate group, and an additional polar group (e.g., choline, ethanolamine).
  • Formation of cell membrane bilayers through the self-assembly property of phospholipids.

Glycolipids

  • Lipids with carbohydrate groups attached, playing a crucial role in cell recognition and signaling in cell membranes.
  • Component of blood types, playing a role in cell-to-cell recognition.

Steroids

  • Four fused hydrocarbon rings structure, serving as hormones (e.g., estradiol, testosterone), bile acids, and cholesterol (structural component of cell membranes).
  • Steroid hormones regulate various physiological processes.

Lipid Digestion

  • Digestion begins in the mouth with lingual lipase activation.
  • Stomach continues lipid digestion with gastric lipase, aided by bile salts.
  • Pancreatic lipase in the small intestine further breaks down lipids into smaller molecules.
  • Mechanical mixing (peristalsis) and emulsifying agents (bile salts) are essential for proper lipid digestion.

Lipid Absorption

  • Lipids are absorbed by intestinal cells as fatty acids, monoglycerides, and cholesterol.
  • Absorption involves formation of micelles in the intestinal lumen.
  • Lipids pass directly through the cell membrane.
  • Fat-soluble vitamins are absorbed with lipids.

Lipid Transport

  • Absorbed lipids are packaged into lipoprotein particles (chylomicrons).
  • These lipoproteins transport lipids throughout the body via the lymphatic system to the blood.
  • Different lipoprotein types carry different lipid compositions (e.g., chylomicrons, VLDL, LDL, HDL) with different functions and density.

Lipoprotein Structure

  • Lipoproteins are amphipathic structures composed of a core of hydrophobic lipids (TAGs, cholesterol esters) surrounded by a hydrophilic coat of proteins, phospholipids, and cholesterol.

Fatty Acid Oxidation

  • Process where fatty acids are broken down to produce energy.
  • Involves activation, transport into mitochondria, and the beta-oxidation cycle.
  • Beta-oxidation removes two-carbon units from fatty acids, yielding acetyl CoA, NADH, and FADH2.
  • These products enter the citric acid cycle to generate ATP.
  • Odd-numbered fatty acids generate a different product, succinyl CoA, which is then processed in the citric acid cycle.

Fatty Acid Synthesis

  • Processes that produce fatty acid molecules from acetyl CoA.
  • The process involves cycles of adding two carbon units to a growing fatty acid chain.
  • Uses enzyme acetyl CoA carboxylase which uses biotin as a coenzyme.
  • Essential fatty acids are obtained solely through diet, and need desaturation and elongation in the body.

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