Biomolecules - Lipids Overview

Biomolecules - Lipids

• Lipids are a diverse group of fat-like substances, acting as concentrated energy stores.
• They are water-insoluble but soluble in organic solvents like ether, benzene, and chloroform.
• Lipids are esters of long-chain fatty acids and alcohols.
• They function as fuel, signaling molecules, and components of membranes, hormones and intracellular messengers.
• Lipids insulate, protect internal organs, and contribute to the body's shape and smoothness.
• Phospholipids prevent fat accumulation in the liver.

Lipid Function in Cells

• Lipids build cell membranes, regulating permeability.
• Vitamins K and Q are coenzymes crucial for blood clotting and ATP production respectively in cells.
• Paracrine hormones act locally affecting specific cellular processes.
• Steroid hormones affect the whole body.
• Growth factor molecules stimulate cell division and growth.
• Pigments like those in tomatoes, carrots, pumpkins and some birds impart color.
• Some lipids act as antioxidants.

Classification of Lipids

• Storage Lipids: These include fats and oils (triacylglycerols), the body's primary energy source. Waxes also fall under this category.
• Structural Lipids: Building blocks of biological membranes (phospholipids, sphingolipids).
• Derived Lipids: Formed through hydrolysis of simple and complex lipids like alcohols, fatty acids, and steroid hormones. They also include ketone bodies and hydrocarbons.
• Miscellaneous Lipids: These encompass compounds with varied characteristics, including squalene, terpenes, hydrocarbons, and carotenoids.

Triacylglycerol (TAG)

• TAGs are esters of glycerol with three fatty acids.
• They are hydrophobic and insoluble in water.
• TAGs function as energy storage molecules.
• Adipocytes (fat cells) store TAGs in animals, and endosperm and cotyledon cells in plants.
• Mammals store approximately 85-95% of their dietary storage lipids as TAGs.

Basic Phospholipid Structure

• Phospholipids form a bilayer structure critical to cell membranes.
• The hydrophilic head groups face the aqueous environment.
• The hydrophobic tails are positioned inwards, facing each other.
• These components are essential for the fluidity of the membrane.

Wax

• Waxes are esters of long-chain fatty acids with long-chain alcohols.
• They act as storage compounds, preventing water loss in plants, and as protective coatings for skin and hair in various organisms.

Fatty Acids

• Fatty acids consist of carbon, hydrogen, and oxygen atoms.
• They are carboxylic acids with hydrocarbon chains varying in length (4 to 36 carbons).
• Fatty acids are categorized into saturated and unsaturated.
• Saturated fatty acids lack double bonds and have higher melting points; unsaturated fatty acids have one or more double bonds and have lower melting points.

Physical Properties of Fatty Acids

• The length and unsaturation of the hydrocarbon chain determine their physical properties like melting point and water solubility.
• Longer chains, lower unsaturation, and higher melting points; shorter chains, higher unsaturation and lower melting points.
• The presence of double bonds lowers the melting point of fatty acids.
• Trivial names of fatty acids link them to natural sources like seed oils.

Nomenclature of Fatty Acids

• Fatty acids are named according to the number of carbon atoms and the presence of double bonds.
• No double bonds are marked with a ':0'.
• One double bond is marked as ':1'.
• Multiple double bonds are indicated thusly '20:4'.

Types of Compound Lipids

• Phosphoglycerides: This class includes phosphatidylcholine (lecithin), phosphatidylethanolamine (cephalin), phosphatidylinositol, and phosphatidylserine.
• Sphingolipids: Sphingomyelins, cerebrosides, and gangliosides are major examples.
• Cholesterol: A crucial component of animal cell membranes, precursor for steroid hormones, and involved in bile acid synthesis.

Lipoproteins

• HDL (High-Density Lipoproteins): Transport cholesterol from tissues to the liver. Often referred to as 'good' cholesterol.
• LDL (Low-Density Lipoproteins): Transport cholesterol from the liver to the tissues. Often referred to as 'bad' cholesterol.
• VLDL (Very Low-Density Lipoproteins): Transport triglycerides from the liver to the tissues. Often referred to as a type of chylomicron.

Effect of Fats on Blood

• Saturated fats raise total and LDL ('bad') cholesterol levels.
• Polyunsaturated fats lower total and LDL cholesterol, but might slightly reduce HDL cholesterol ('good').
• Monounsaturated fats are often linked to lower LDL cholesterol while raising HDL cholesterol.
• Trans fats raise total and LDL ('bad') cholesterol, and lower HDL ('good') cholesterol.
• Omega-3 fats lower total and LDL cholesterol and increase HDL cholesterol.

Atherosclerosis

• The build-up of plaque (cholesterol and other substances) in the arteries causing gradual narrowing.
• Leads to increased risk of heart attack or stroke.

This quiz covers the essential functions and characteristics of lipids, a vital class of biomolecules. Explore their roles in energy storage, cell membrane composition, and hormonal signaling. Understand how lipids contribute to various cellular processes and overall body functions.