Chapter 3: Carbon and the Molecular Diversity of Life

Vocabulary flashcards covering key terms and concepts from Chapter 3: Carbon and the Molecular Diversity of Life.

Organic compound

A chemical compound that contains carbon; the basis of most biological molecules.

Inorganic compound

A chemical compound that does not include carbon.

Carbon

The element that forms the backbone of organic molecules and can form up to four covalent bonds.

Valence

The number of covalent bonds an atom can form.

Carbon skeleton

The chain or ring structure of carbon atoms in an organic molecule; variations create diversity.

Straight chain

A carbon skeleton arranged linearly without branches.

Branched chain

A carbon skeleton with one or more side chains branching off the main chain.

Double bond

A covalent bond formed by sharing two pairs of electrons between atoms, often restricting rotation.

Closed ring

A carbon skeleton arranged in a ring.

Functional group

A specific group of atoms attached to a carbon skeleton that influences reactivity and function.

Hydroxyl group

The -OH functional group found in alcohols; increases polarity.

Amino group

The -NH2 functional group; acts as a base and is part of amino acids.

Carboxyl group

The -COOH functional group; acidic and found in organic acids and amino acids.

Phosphate group

A phosphorus-containing group (-O-P=O and related structures) involved in energy transfer and phosphorylation.

Methyl group

The -CH3 group; nonpolar and influences molecule properties.

Carbonyl group

The C=O functional group found in aldehydes and ketones.

Alcohol

An organic compound containing a hydroxyl group (-OH).

Hydrocarbon

An organic molecule consisting only of carbon and hydrogen.

Hydrophobic

Not mixing well with water; nonpolar regions or molecules.

Macromolecule

A very large, complex molecule built from many monomers (e.g., proteins, nucleic acids, polysaccharides).

Monomer

A small molecule that can join with others to form polymers.

Nucleotide

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

Polymer

A large molecule made by linking many monomers covalently.

Dehydration synthesis

A chemical reaction that forms a covalent bond by removing a molecule of water.

Hydrolysis

A chemical reaction that breaks bonds between monomers by adding water.

Amino acid

The monomer of proteins; contains an amino group, a carboxyl group, and a side chain.

Enzyme

A protein that acts as a catalyst to speed up chemical reactions without being consumed.

Substrate

The molecule that binds to an enzyme at the active site.

Active site

The region of the enzyme where the substrate binds.

Enzyme-substrate complex

The temporary state formed when a substrate binds to an enzyme.

Carbohydrate

An organic molecule class including sugars and polysaccharides; a major energy source.

Monosaccharide

A simple sugar; the monomer of carbohydrates.

Disaccharide

A sugar formed from two monosaccharides linked by a glycosidic linkage.

Glycosidic linkage

Covalent bond joining two sugar units.

Glucose

A hexose monosaccharide (C6H12O6) used as a primary energy source.

Fructose

A hexose sugar, isomer of glucose.

Sucrose

A disaccharide formed from glucose and fructose; common table sugar.

Lactose

A disaccharide formed from glucose and galactose; digested by lactase.

Lactase

The enzyme that breaks down lactose.

Starch

Storage polysaccharide in plants made of glucose.

Glycogen

Storage polysaccharide in animals, stored mainly in liver and muscles.

Cellulose

Structural polysaccharide in plant cell walls; linear and unbranched.

Chitin

Structural polysaccharide used by arthropods and fungi to build exoskeletons.

Lipid

A group of hydrophobic molecules (fats, phospholipids, steroids); not a true polymer.

Fat

A triglyceride; storage form of energy made of glycerol linked to three fatty acids.

Fatty acid

A long hydrocarbon chain with a terminal carboxyl group; nonpolar.

Triglyceride

A glycerol molecule bound to three fatty acids; major dietary fat.

Ester linkage

Bond formed between glycerol's hydroxyl and a fatty acid's carboxyl group.

Saturated fat

Fatty acids with no double bonds between carbons; straight chains; solid at room temperature.

Unsaturated fat

Fatty acids with one or more double bonds; kinks in the chain; liquid at room temperature.

Phospholipid

Lipid with two fatty acids and a phosphate-containing head; amphipathic.

Amphipathic

A molecule containing both hydrophobic and hydrophilic regions.

Phospholipid bilayer

Two-layer membrane formed by phospholipids, with hydrophilic heads outward and hydrophobic tails inward.

Steroid

Lipid with four fused carbon rings; differentiates by attached groups.

Cholesterol

A crucial animal steroid; component of cell membranes and precursor to other steroids.

HDL

High-density lipoprotein; transports cholesterol to the liver for removal; 'good' cholesterol.

LDL

Low-density lipoprotein; carries cholesterol to cells and can deposit in arteries; 'bad' cholesterol.

Protein

A polymer of amino acids that carries out a wide range of cellular functions.

Amino acid

Monomer of proteins; contains an amino group, a carboxyl group, and a side chain.

Side chain (R group)

The variable group attached to the alpha carbon that determines amino acid properties.

Non-polar (hydrophobic) side chain

A side chain that is nonpolar and tends to avoid water.

Polar (hydrophilic) side chain

A side chain that is polar and interacts with water.

Acidic (negatively charged) amino acid

Amino acids with negatively charged side chains (e.g., Asp, Glu) under physiological conditions.

Basic (positively charged) amino acid

Amino acids with positively charged side chains (e.g., Lys, Arg, His).

Peptide bond

A covalent bond formed by condensation between the carboxyl group of one amino acid and the amino group of another.

Polypeptide

A chain of amino acids linked by peptide bonds; a protein before folding.

Primary structure

The linear sequence of amino acids in a polypeptide; held by covalent bonds along the backbone.

Secondary structure

Local folding stabilized by hydrogen bonds; includes alpha helices and beta sheets.

Alpha helix

A right-handed coil stabilized by hydrogen bonds every fourth amino acid.

Beta pleated sheet

A sheet-like arrangement stabilized by hydrogen bonds between strands.

Tertiary structure

The three-dimensional shape of a protein due to interactions among side chains.

Hydrophobic interactions

Clustering of nonpolar side chains in the protein interior away from water.

Hydrogen bonds (protein structure)

Hydrogen bonds between polar side chains or backbone that help stabilize structure.

Ionic bonds

Electrostatic attractions between positively and negatively charged side chains.

Disulfide bridges

Covalent bonds between cysteine residues (–S–S–) that stabilize structure.

Quaternary structure

Association of two or more polypeptide subunits into a functional protein.

Denaturation

Unfolding of a protein’s 3D structure due to heat, pH, salt, or other factors; loss of function.

DNA

Deoxyribonucleic acid; double-stranded polymer that stores genetic information; uses deoxyribose and thymine.

RNA

Ribonucleic acid; usually single-stranded; uses ribose and uracil.

Nucleotide

Monomer of nucleic acids consisting of a phosphate, a five-carbon sugar, and a nitrogenous base.

Purine

Nitrogenous base family with two rings (adenine and guanine).

Pyrimidine

Nitrogenous base family with one ring (cytosine, thymine, uracil).

Adenine

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

Thymine

Pyrimidine base that pairs with adenine in DNA.

Cytosine

Pyrimidine base that pairs with guanine.

Guanine

Purine base that pairs with cytosine.

Uracil

Pyrimidine base that pairs with adenine in RNA.

Complementary base pairing

A pairs with T (or U in RNA) and G pairs with C through hydrogen bonds.

Anti-parallel

The two strands of DNA run in opposite directions.

Sugar-phosphate backbone

The alternating sugar and phosphate groups forming the structural framework of nucleic acids.

Deoxyribose

Five-carbon sugar in DNA lacking an oxygen on the 2' carbon.

Ribose

Five-carbon sugar in RNA with a hydroxyl group on the 2' carbon.

Phosphodiester bond

Bond linking nucleotides to form the sugar-phosphate backbone of nucleic acids.

Nucleic acid

Biomolecule (DNA or RNA) that stores, transmits, and expresses genetic information.