The Chemical Basis of Life II: Organic Molecules

Vocabulary flashcards covering the key concepts of organic molecules, their structures, and their functions from Chapter 3.

Organic chemistry

The science of carbon-containing molecules, which are found in living organisms.

Carbon’s four covalent bonds

A key property of carbon enabling diverse organic molecules by allowing four bonds with other atoms (including carbon).

Functional group

A group of atoms with characteristic chemical properties that influences reactivity (examples include -NH2, -OH, -COOH, -PO4^3-, -SH).

Isomer

Molecules with the same chemical formula but different structures and properties.

Structural isomer

Isomers with the same atoms arranged differently by bonding relationships.

Stereoisomer

Isomers with the same bonding pattern but different spatial arrangement.

Enantiomer

A non-superimposable mirror-image stereoisomer; often has different biological activity.

Dehydration (condensation) reaction

A reaction that links monomers to form polymers by removing a water molecule.

Hydrolysis

A reaction that breaks polymers into monomers by adding water.

Monomer

A small molecule that can join with others to form a polymer.

Polymer

A large molecule built from many monomers via dehydration reactions.

Monosaccharide

The simplest carbohydrate; a single sugar (e.g., glucose, fructose).

Pentose

A five-carbon sugar (e.g., ribose, deoxyribose).

Hexose

A six-carbon sugar (e.g., glucose).

Glycosidic bond

The covalent bond linking two sugar molecules in a disaccharide.

Disaccharide

A carbohydrate composed of two monosaccharides (e.g., sucrose, maltose, lactose).

Sucrose

Glucose and fructose linked together; major transport sugar in plants.

Maltose

A disaccharide made of two glucose units.

Lactose

A disaccharide consisting of galactose and glucose.

Polysaccharide

A carbohydrate polymer formed by many monosaccharides (e.g., starch, glycogen, cellulose).

Starch

Polysaccharide of α-D-glucose; energy storage in plants; branched structure.

Glycogen

Highly branched polysaccharide of α-D-glucose; energy storage in animals; highly soluble.

Cellulose

Polysaccharide of β-D-glucose; linear, unbranched; structural component in plant cell walls; not digestible by most animals.

Chitin

Structural polysaccharide with nitrogen-containing groups; forms exoskeletons and fungal walls.

Glycosaminoglycans

Large polysaccharides contributing to structure in animals, especially in cartilage and extracellular matrix.

Lipids

Hydrophobic, nonpolar molecules mainly composed of carbon and hydrogen; include fats, phospholipids, steroids, and waxes.

Triglyceride

Fat formed when glycerol binds to three fatty acids via ester bonds; primary energy storage.

Fatty acid

Hydrocarbon chain with a terminal carboxyl group; can be saturated or unsaturated.

Saturated fatty acid

Fatty acid with only single C–C bonds; packs tightly; typically solid at room temperature.

Unsaturated fatty acid

Fatty acid with one or more C=C double bonds; introduces kinks; typically liquid at room temperature.

Cis isomer

Configuration where hydrogens around a C=C are on the same side; common in natural fatty acids.

Trans fatty acid

Fatty acid with trans double bonds; more linear; higher melting point and health concerns.

Essential fatty acids

Fatty acids that must be obtained from the diet because they cannot be synthesized.

Phospholipid

Lipid with glycerol, a phosphate group, and two fatty acids; amphipathic and forms membranes.

Amphipathic

Molecule containing both hydrophilic (polar) and hydrophobic (nonpolar) regions.

Steroid

Lipids with four fused carbon rings; include cholesterol and steroid hormones.

Cholesterol

A sterol essential in membranes and precursor to steroid hormones.

Waxes

Nonpolar lipids that repel water and form protective coatings.

Protein

Macromolecule made of amino acids; performs a wide range of cellular functions.

Amino acid

Building block of proteins; contains an α-carbon attached to an amino group, a carboxyl group, a hydrogen, and an R side chain.

Side chain (R group)

Variable group attached to the α-carbon of an amino acid; determines properties.

Peptide bond

Covalent bond between the carboxyl group of one amino acid and the amino group of another (via dehydration).

Polypeptide

Linear chain of amino acids; a protein may consist of one or more polypeptides.

Primary structure

Linear sequence of amino acids in a polypeptide; determined by genes.

Secondary structure

Local folding patterns—α-helix and β-pleated sheet—stabilized by hydrogen bonds.

Tertiary structure

Three-dimensional shape of a single polypeptide, driven by side-chain interactions.

Quaternary structure

Arrangement of multiple polypeptides into a functional protein.

Domain

A modular region within a protein with a specific structure and function; found across related proteins.

Nucleic acids

DNA and RNA; store, express, and transmit genetic information.

Nucleotide

Building block of nucleic acids; consists of a phosphate, a five-carbon sugar, and a base.

DNA

Deoxyribonucleic acid; two strands form a double helix; sugar is deoxyribose; stores genetic information.

RNA

Ribonucleic acid; usually single-stranded; sugar is ribose; uses uracil instead of thymine.

Base pairing (A–T, G–C)

Specific hydrogen bonding between bases in DNA: A pairs with T (two H-bonds), G pairs with C (three H-bonds). In RNA, A pairs with U.

Double helix

Two DNA strands wound around each other in a helical shape, stabilized by base pairing.

Adenine

Purine base that pairs with thymine in DNA and with uracil in RNA.

Cytosine

Pyrimidine base that pairs with guanine in DNA and RNA.

Guanine

Purine base that pairs with cytosine.

Thymine

Pyrimidine base in DNA, pairs with adenine.

Uracil

Pyrimidine base in RNA, replaces thymine and pairs with adenine.

Phosphodiester bond

Covalent bond linking nucleotides in DNA/RNA backbones (3'–5' sugar-phosphate linkage).

Sugar type (DNA vs RNA)

DNA contains deoxyribose; RNA contains ribose.

Base

Nitrogen-containing component of a nucleotide; purines (A, G) and pyrimidines (C, T/U).

Amino acid L‑form

Most proteins contain amino acids in the L‑configuration; D‑forms are rare in cells.

Anfinsen experiment

showed that a protein’s primary sequence contains information to fold into its native structure; demonstrated by ribonuclease refolding after denaturation.