Chapter 3 Biological Molecules: The Carbon Compounds of Life

A vocabulary-focused set of flashcards covering the key terms and concepts from the lecture notes on chapter 3 (Biological Molecules: The Carbon Compounds of Life), including chemistry of carbon, organic macromolecules, macromolecular structure, and nucleic acids.

Carbon

The essential element for life; tetravalent and forms stable bonds with many elements, including itself, making diverse organic macromolecules possible.

Organic molecules

Carbon-based compounds forming the backbone of life’s macromolecules: carbohydrates, lipids, proteins, and nucleic acids.

Functional group

A small reactive group of atoms attached to a molecule that largely determines its chemical properties and reactivity.

Isomer

Compounds with the same molecular formula but different structures or spatial arrangements; includes stereoisomers and chiral forms.

Dehydration synthesis (condensation)

A reaction that links monomers to form polymers with the loss of a water molecule.

Hydrolysis

A reaction that breaks polymers into monomers by adding water.

Monosaccharide

A simple sugar (e.g., glucose) with 3–7 carbon atoms; soluble in water and often forms ring structures.

Disaccharide

A carbohydrate formed by linking two monosaccharides via a glycosidic bond (e.g., maltose, sucrose, lactose).

Polysaccharide

Polymers of many monosaccharides; used for storage (starch, glycogen) or structure (cellulose, chitin).

Glycosidic linkage

Covalent bond joining carbohydrate monomers via dehydration synthesis.

Ring forms (α and β)

Cyclic forms of sugars (e.g., α- and β-glucose) that arise when linear monosaccharides cyclize in solution.

Chiral carbon

A carbon atom bonded to four different groups; gives rise to non-superimposable mirror images.

Stereoisomers

Isomers with the same molecular formula and connectivity but different spatial arrangement; includes enantiomers (L/D) and diastereomers.

Fischer projection

A diagrammatic method introduced by Emil Fischer to represent stereochemistry around chiral centers.

Glucose enantiomers (D- and L-)

Mirror-image forms of glucose; the D-form is more common in nature and in cells.

Structural isomer

Isomers with the same formula but different bond arrangement (e.g., glucose vs. fructose).

Monomer

The basic building block of a polymer (e.g., glucose, amino acid, nucleotide, glycerol).

Polymer

A large molecule built from repeating monomer units linked by covalent bonds.

Macromolecule

A very large polymer (carbohydrates, proteins, nucleic acids) generally exceeding 1,000 Da.

Carbohydrates (macro category)

Biomolecules that include monosaccharides, disaccharides, and polysaccharides; provide energy and structure.

Lipids

Hydrophobic, nonpolar biological molecules not true polymers; include triglycerides, phospholipids, and steroids.

Proteins

Macromolecules made of amino acids; perform structural, catalytic, transport, signaling, and other cellular functions.

Nucleic acids

Macromolecules (DNA and RNA) that store, transmit, and express genetic information.

Amino acid

Monomer of proteins; contains an amino group, a carboxyl group, a hydrogen, and a variable R-group.

Peptide bond

Covalent bond formed by a dehydration synthesis between the carboxyl group of one amino acid and the amino group of the next.

Primary structure

The linear sequence of amino acids in a protein.

Secondary structure

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

Tertiary structure

The overall three-dimensional shape of a single polypeptide, shaped by R-group interactions.

Quaternary structure

Arrangement of multiple polypeptide subunits in a protein; e.g., hemoglobin.

Disulfide bridge

Covalent S–S bond between cysteine residues that helps stabilize protein structure.

Chaperonins

Proteins that assist in the proper folding of other proteins.

Denaturation

Unfolding of a protein’s structure due to heat, pH, or chemicals, often destroying function.

Nucleic acids

DNA and RNA; polymers built from nucleotides that store and transfer genetic information.

Nucleotide

Monomer of nucleic acids; consists of a nitrogenous base, a five-carbon sugar, and one to three phosphate groups.

Nucleoside

Nucleotide without the phosphate group; base linked to a sugar.

Phosphodiester bond

Bond linking nucleotides in nucleic acids, forming the sugar–phosphate backbone.

DNA

Deoxyribonucleic acid; stores genetic information; usually double-stranded; bases A, T, C, G; sugar is deoxyribose.

RNA

Ribonucleic acid; involved in protein synthesis and other roles; usually single-stranded; bases A, U, C, G; sugar is ribose.

Base pairing (A–T, G–C)

Complementary hydrogen-bonding rules in DNA: A pairs with T, G pairs with C.

Antiparallel

DNA strands run in opposite 5' to 3' directions in the double helix.

DNA double helix

Two polynucleotide strands wound around each other; sugar–phosphate backbones on outside, bases paired inside.

Watson–Crick pairing

A–T and G–C base-pairing rules that stabilize the DNA double helix.

R/S absolute configuration

A system to designate the three-dimensional arrangement around a chiral center; R and S describe the orientation.

Glycosidic linkage

Bond connecting carbohydrates between monosaccharides; examples include α-1,4 and α-1,6 linkages.

Amylose

Linear, unbranched component of starch made of glucose units.

Amylopectin

Branched component of starch; highly branched glucose polymer.

Starch

Storage polysaccharide in plants; mixture of amylose and amylopectin.

Glycogen

Storage polysaccharide in animals; highly branched glucose polymer stored mainly in liver and muscle.

Cellulose

Structural polysaccharide in plants; β-1,4 linkages cause a straight, rigid, glucose polymer that forms plant cell walls.

Chitin

Structural polysaccharide in arthropods and fungi; polymer of N-acetylglucosamine with β linkages.

Hydrocarbon

Organics made up solely of carbon and hydrogen; the backbone of many organic molecules.

Saturated fatty acid

Fatty acid with only single bonds; maximum hydrogen; typically solid at room temperature.

Unsaturated fatty acid

Fatty acid with one or more double bonds; introduces kinks, usually liquid at room temperature.

Trans fat

Hydrogenated unsaturated fats with trans double bonds; associated with cardiovascular risk.

Triglyceride

A fat molecule: glycerol + three fatty acids linked by ester bonds; major energy storage form.

Phospholipid

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

Phospholipid bilayer

Two-layer membrane structure formed by phospholipids in water; hydrophilic heads face outward, tails inward.

Micelle

Spherical arrangement of amphipathic lipids in water, with tails inward and heads outward.

Steroid

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

Cholesterol

A sterol component of animal cell membranes and a precursor to steroids.

Steroid hormones

Hormones derived from steroids that regulate development, behavior, and metabolism.

Amino acid polarity and charge

R-group properties determine whether the amino acid is hydrophobic, hydrophilic, acidic, or basic.

Disulfide bond (S–S)

Covalent bond between cysteine residues that stabilizes protein structure.

Intrinsically disordered proteins (IDPs)

Proteins or regions lacking fixed 3D structure; often functional and dynamic.

Glycoprotein

Protein with carbohydrate groups attached; many enzymes and receptors are glycoproteins.

Lipoprotein

Protein–lipid complexes that transport lipids in the bloodstream and in membranes.

Nucleoside vs nucleotide

Nucleoside = base + sugar; nucleotide = nucleoside with one to three phosphate groups.

RNA polymerization (phosphodiester linkage)

Formation of RNA via condensation with phosphodiester bonds between ribonucleotides.

5′ to 3′ direction

Direction of nucleotide linkage in nucleic acids; backbone runs 5′ to 3′.

A–T and G–C base pairing strength

A–T forms two hydrogen bonds; G–C forms three hydrogen bonds, contributing to duplex stability.

Abiogenesis (chemical evolution)

Nonliving precursors transformed into complex organic molecules and, eventually, life; explored via Miller–Urey experiments and Oparin–Haldane theory.

Miller–Urey experiment

Classic experiment simulating early Earth conditions to synthesize amino acids and other organics from simple gases.