Lipids: Structure and Clinical Relevance

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Questions and Answers

What is the first step in the synthesis of triacylglycerols (TAGs)?

Formation of glycerol 3-phosphate from glycolysis (correct)

Conversion of diacylglycerol to TAG by DGAT

Storage of TAG in lipid droplets

Addition of fatty acids to diacylglycerol

What role does hormone-sensitive lipase (HSL) play in energy metabolism?

Stimulates the storage of fat

Catalyzes the lipolysis of TAGs (correct)

Inhibits the absorption of cholesterol

Converts cholesterol to bile acids

Which position of glycerol in phospholipids typically contains a phosphate ester?

Sn3 (correct)

Sn2

Sn1

All positions are occupied by fatty acids

What is the function of perilipin in TAG storage?

Coats lipid droplets to protect TAGs Signup and view all the answers

What is the key regulatory step in the biosynthesis of cholesterol?

Reduction of HMG CoA to mevalonate by HMG CoA reductase Signup and view all the answers

Where does the absorption of dietary cholesterol primarily occur?

Duodenum and jejunum Signup and view all the answers

What happens to plant sterols during cholesterol absorption?

They are returned to the gastrointestinal lumen Signup and view all the answers

Which enzyme is targeted by statins to lower cholesterol levels?

HMG CoA reductase Signup and view all the answers

What is one primary function of lipids in cells?

Major components of biological membranes Signup and view all the answers

Which type of lipids are characterized by their hydrolysis products consisting of alcohol and fatty acids?

Simple lipids Signup and view all the answers

What type of lipids includes phospholipids and glycolipids?

Compound (Complex) lipids Signup and view all the answers

How do trans fatty acids differ from cis fatty acids?

Trans fatty acids have hydrogens on opposite sides of the double bond Signup and view all the answers

What is the role of cholesterol in the context of cardiovascular disease?

Elevated levels contribute to cardiovascular disease Signup and view all the answers

Which of the following correctly describes triacylglycerols (TAGs)?

They are stored in adipose tissue for energy Signup and view all the answers

What distinguishes derived lipids from other types of lipids?

They are non-hydrolysable and derivatives of isoprene Signup and view all the answers

What is a characteristic of unsaturated fatty acids?

They can have one or more double bonds Signup and view all the answers

Study Notes

Lipids: Structure, Function, and Clinical Relevance

Lipids are fatty, water-insoluble substances with diverse roles in cells.
They are crucial components of biological membranes.
Lipids are used as metabolic fuels, precursor to hormones, and participate in cell signaling.

Classification of Lipids

Simple Lipids: Hydrolysis yields alcohol and fatty acids (e.g., waxes, triglycerides).
Compound/Complex Lipids: Hydrolysis yields alcohol, fatty acids, and other components like phosphate groups or sugars (e.g., phospholipids, glycolipids).
Derived/Polyprenyl Lipids: Non-hydrolysable, derivatives of isoprene (e.g., fat-soluble vitamins A, D, steroids like cholesterol, aldosterone, testosterone, and estrogen).

Cholesterol and Cardiovascular Disease

High cholesterol contributes to cardiovascular disease (CVD).
Cholesterol metabolism is linked to fat (triglyceride) metabolism influencing the effect of diet.
Atheroma formation involves cholesterol-rich deposits in artery walls.
Lipids are transported as lipoproteins in the blood, their uptake in artery walls leading to atheroma development.
Key components of a lipid profile include total cholesterol, triglycerides, HDL-C, LDL-C, and non-HDL-C.

Fatty Acids (FAs)

Structure: Even-numbered carbon chain with a carboxyl group.
Saturation: Saturated FAs (no double bonds), Unsaturated FAs (one or more double bonds, including polyunsaturated FAs with multiple double bonds).
Configuration: Naturally occurring FAs are usually cis (hydrogens on the same side of the double bond), whereas trans FAs are typically harmful (hydrogens on opposite sides).

Triacylglycerols (TAGs)

Structure: Three fatty acid (FA) residues esterified to a glycerol backbone.
Synthesis: Occurs in adipocytes, utilizing glycerol 3-phosphate from glycolysis, and fatty acid acyl transferases in the smooth endoplasmic reticulum.
Storage: Stored as lipid droplets within adipocytes, coated with perilipin protein.

TAGs – Energy Storage and Regulation

TAGs are the major energy reserve in adipocytes.
Lipolysis (breakdown of TAGs) is regulated by hormone-sensitive lipase (HSL). Insulin inhibits lipolysis by preventing HSL action; fasting hormones (catecholamines, glucagon, growth hormone) stimulate it.

Phospholipids (PLs) and Cholesterol

Structure: Similar to TAGs, but with a phosphate ester at the Sn3 position (e.g., phosphatidylcholine).
Function: Major components in biological membranes (40-50% of membrane lipids)
Cholesterol: A sterol with a hydroxyl group at C-3; can be esterified to form cholesterol ester.
Functions: Precursor of steroid hormones, vitamins D, bile acids; crucial component of biological membranes.

Cholesterol Biosynthesis and Absorption

Biosynthesis: Involves the reduction of HMG-CoA to mevalonate. HMG-CoA reductase is a key regulatory enzyme (target of statins).
Absorption: Dietary cholesterol is solubilized by bile salts and fats to form mixed micelles in the duodenum and jejunum. Cholesterol esters are hydrolyzed into free cholesterol, then absorbed via NPC1L1. Plant sterols are returned to the gut lumen, with cholesterol being transported as CEs in chylomicrons.

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Description

This quiz explores the structure, function, and clinical importance of lipids, focusing on their roles in biological membranes and metabolic processes. It also covers the classification of lipids and their connection to cardiovascular disease, particularly cholesterol's impact on health.