Chapter 03 The Chemical Basis of Life II: Organic Molecules

Vocabulary flashcards covering key terms from the lecture notes on organic molecules (Biology 2025).

Carbon atom

The element that forms the backbone of organic molecules; tetravalent and capable of forming up to four bonds; bonds can be polar or nonpolar.

Organic molecule

A carbon-containing molecule found in living organisms; abundant in life; macromolecules are large organic molecules.

Macromolecule

A large, complex organic molecule made of many atoms; typically formed by polymerization of monomers.

Monomer

A single subunit that links to form polymers.

Polymer

A large molecule formed by linking many monomer units.

Condensation reaction

Chemical reaction that joins monomers by releasing a water molecule.

Dehydration reaction

Another term for condensation reaction; water is removed during bond formation.

Hydrolysis

Reaction that breaks polymers into monomers by adding water; catalyzed by enzymes.

Carbohydrate

Molecule class composed of carbon, hydrogen, and oxygen; often in rings; includes sugars and starches.

Monosaccharide

Simplest sugar; usually 5 or 6 carbons; examples: ribose, deoxyribose, glucose.

Pentose

Five-carbon sugar; examples: ribose, deoxyribose.

Hexose

Six-carbon sugar; example: glucose.

Glucose

A hexose sugar and primary energy source for many cells; exists in linear and ring forms and in α/β anomers.

Isomer

Compound with the same molecular formula as another but different structure or arrangement.

Structural isomer

Isomers that differ in the covalent arrangement of atoms.

Stereoisomer

Isomers with the same covalent bonds but different spatial arrangement.

Cis-trans isomer

A type of stereoisomer around double bonds or ring systems; cis means same side, trans opposite.

Enantiomer

Mirror-image isomer that cannot be superimposed; often different in biological activity.

Glycosidic bond

Covalent bond linking two monosaccharides via dehydration in carbohydrates.

Disaccharide

Carbohydrate formed by two monosaccharides connected by a glycosidic bond.

Sucrose

Disaccharide formed from glucose and fructose; common table sugar.

Glycogen

Highly branched polysaccharide used for energy storage in animals.

Starch

Plant storage polysaccharide with mostly linear chains of glucose linked by α-1,4 bonds and branches via α-1,6 bonds.

Cellulose

Structural polysaccharide of plants with unbranched chains connected by β-1,4 glycosidic bonds.

Chitin

Structural polysaccharide found in arthropod exoskeletons; similar to cellulose with different monomer.

Lipids

Hydrophobic, nonpolar molecules including fats, phospholipids, steroids, and waxes; insoluble in water.

Fat

Triglyceride; glycerol backbone with three fatty acids; formed by dehydration; forms ester bonds.

Fatty acid

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

Saturated fatty acid

Fatty acid with no double bonds; typically solid at room temperature.

Unsaturated fatty acid

Fatty acid with one or more double bonds; typically liquid at room temperature; natural cis form.

Phospholipid

Glycerol plus two fatty acids and a phosphate group; amphipathic with polar head and nonpolar tails; forms membranes.

Steroid

Lipid with four fused carbon rings; includes cholesterol and hormones like estrogen and testosterone.

Cholesterol

Steroid molecule; precursor to other steroids; component of cell membranes.

Waxes

Nonpolar lipids secreted on surfaces; barrier to water loss.

Proteins

Macromolecules made of carbon, hydrogen, oxygen, nitrogen (and sometimes sulfur); built from amino acids.

Amino acid

Building blocks of proteins; contain an amino group, a carboxyl group, a hydrogen, and an R side chain; 20 standard.

Peptide bond

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

Polypeptide

Chain of many amino acids linked by peptide bonds; forms proteins; has an N-terminus and a C-terminus.

Primary structure

Linear sequence of amino acids in a protein; encoded by genes.

Secondary structure

Local folding patterns (α-helix, β-pleated sheet) stabilized by hydrogen bonds.

Tertiary structure

Three-dimensional shape of a single polypeptide; folding driven by various interactions.

Quaternary structure

Assembly of two or more polypeptide chains into a functional protein.

Hydrogen bond

Bond between electronegative atoms and hydrogens; stabilizes protein structure and nucleic acid pairs.

Ionic bond

Bond between oppositely charged side chains or groups in proteins.

Hydrophobic effect

Nonpolar amino acids cluster away from water, helping protein folding.

Van der Waals forces

Weak attractions between atoms at optimal distances; contribute to stability.

Disulfide bridge

Covalent bond between two cysteine sulfur atoms; stabilizes protein structure.

Anfinsen

Idea that a protein’s primary sequence contains information to fold into its native structure; supported by ribonuclease experiments.

Nucleic acids

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

Nucleotide

Monomer of nucleic acids; composed of a sugar, a phosphate, and a nitrogenous base.

Purine

Double-ring bases; adenine (A) and guanine (G).

Pyrimidine

Single-ring bases; cytosine (C), thymine (T), and uracil (U).

Deoxyribose

Five-carbon sugar in DNA; lacks 2' hydroxyl group.

Ribose

Five-carbon sugar in RNA; contains a 2' hydroxyl group.

DNA

Deoxyribonucleic acid; stores genetic information; double-stranded; A pairs with T; C pairs with G; uses deoxyribose.

RNA

Ribonucleic acid; decodes DNA to synthesize proteins; usually single-stranded; uses ribose and uracil.

Adenine

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

Thymine

Pyrimidine base in DNA; pairs with adenine.

Uracil

Pyrimidine base in RNA; replaces thymine; pairs with adenine.

Cytosine

Pyrimidine base; pairs with guanine.

Guanine

Purine base; pairs with cytosine.

Base pair

Adenine–thymine (DNA) or cytosine–guanine (DNA); stabilized by hydrogen bonds.

Double helix

Two complementary DNA strands wound around each other.

5' to 3' direction

Directionality of nucleic acid synthesis; phosphate group attaches to 5' carbon; synthesis occurs at the 3' end.

Sugar-phosphate backbone

The repeating pattern of sugars and phosphate groups forming the sides of a DNA/RNA strand.

Functional domain

A distinct region of a protein with a specific function, such as a DNA-binding or ligand-binding domain.

Glycosidic bond (reprise)

Covalent linkage between two monosaccharides formed during dehydration reactions.