Chemical Basis of Life Chapter 6

Lipids

• Lipids are a diverse group of organic compounds including fats, oils, phospholipids, and cholesterol.
• Composed primarily of carbon (C), hydrogen (H), and oxygen (O) with an H:O ratio greater than 2:1.
• Building blocks of lipids are fatty acids and glycerol.
• Lipids do not form polymers but consist of larger molecules made from smaller subunits.
• Fats and oils function in energy storage; fats provide thermal insulation while waxes and oils serve as protective coatings.
• Phospholipids compose cell membranes and are critical for cellular structure and recognition.
• Carotenoids assist in light absorption during photosynthesis, and steroids regulate functions as hormones and vitamins.
• Myelin, made of lipids, acts as electrical insulation around nerves.
• Fats are solid at room temperature, whereas oils are liquid due to the structure of their fatty acids.

Fatty Acid Structure

• Consist of a long hydrocarbon chain and a polar carboxyl group (COOH).
• Fatty acids can be saturated (no double bonds, solid at room temperature) or unsaturated (one or more double bonds, liquid at room temperature).
• Polyunsaturated fatty acids have multiple double bonds, contributing to lower melting points.

Triglycerides

• Formed by three fatty acids linked to glycerol through ester linkages (dehydration synthesis).
• Can consist of different types of fatty acids that do not need to be identical.
• Non-polar nature makes triglycerides insoluble in water, leading to clumping in aqueous environments.

Phospholipids

• Comprised of glycerol, two fatty acids, and a phosphate group, giving rise to hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
• Form bilayers in aqueous environments, crucial for cell membrane structure.

Steroids

• Signaling molecules that are integral to membrane structure and function.
• Include hormones like testosterone and estrogen, regulating sexual development.
• Cholesterol, produced in the liver, forms part of cell membranes and serves as a precursor for steroid hormones.

Nucleic Acids (DNA and RNA)

• Polymeric molecules responsible for genetic information storage, transmission, and usage.
• Two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), composed of nucleotides.
• Nucleotides contain a pentose sugar, a phosphate group, and a nitrogenous base.
• DNA contains deoxyribose; RNA contains ribose.

Differences Between DNA and RNA

• DNA bases: Adenine, Guanine, Cytosine, Thymine; RNA bases: Adenine, Guanine, Cytosine, Uracil.
• DNA is double-stranded; RNA is single-stranded, lacking base-pairing.
• Nucleotides in nucleic acids are linked by phosphodiester bond, growing in the 5' to 3' direction.

Chemical Basis of Life

• Life's essential elements are few and contribute to the same biological compounds across all living organisms.
• The biochemical differences arise from unique atomic compositions and bonding in various compounds.
• Both fats and carbohydrates serve as energy sources, with fats being more energy-dense.
• Starch (branched polymer) is digestible while cellulose (linear polymer) is not, due to structural differences.

This quiz focuses on the chemical basis of life, specifically examining organic molecules like lipids and nucleic acids. It covers the structure and assembly of proteins, providing insight into their primary, secondary, tertiary, and quaternary structures. Test your understanding of these essential biological components.