Essentials of Biology: Chapter 3 – The Organic Molecules of Life

Comprehensive vocabulary flashcards covering the structure, properties, reactions, and biological roles of carbon, carbohydrates, lipids, proteins, and nucleic acids.

Gluten

A type of protein commonly found in wheat, rye, and barley.

Celiac Disease

A disorder that affects the small intestine by causing inflammation and loss of the intestinal lining in response to gluten.

Organic Molecule

A molecule that contains atoms of carbon and hydrogen.

Inorganic Molecule

A molecule that does not contain a combination of carbon and hydrogen atoms (such as $H_2O$ and $NaCl$).

Hydrocarbon

A chain or ring composed exclusively of carbon atoms bonded to hydrogen atoms.

Isomers

Molecules that share the same number and kinds of atoms (identical molecular formula) but possess different structural arrangements and properties.

Functional Group

A specific combination of bonded atoms that always has the same chemical properties and always reacts in the same way.

Hydroxyl Group

A functional group with the formula $-\text{OH}$, found in alcohols and sugars.

Carboxyl Group

A functional group with the formula $-\text{COOH}$, found in amino acids and fatty acids.

Amino Group

A functional group with the formula $-\text{NH}_2$, found in amino acids and proteins.

Sulfhydryl Group

A functional group with the formula $-\text{SH}$, found in the amino acid cysteine and in proteins.

Phosphate Group

A functional group with the formula $-\text{PO}_4^{3-}$, found in ATP and nucleic acids.

Hydrophobic Molecule

A nonpolar molecule that is not soluble in water.

Hydrophilic Molecule

A polar molecule that is water-soluble.

Monomer

A small molecular subunit that serves as the repeatable building block for larger biological macromolecules.

Polymer

A large macromolecule composed of multiple monomers joined together.

Dehydration Synthesis Reaction

A chemical reaction (condensation reaction) that links monomers into a polymer by removing the equivalent of a water molecule ($H_2O$).

Hydrolysis Reaction

A chemical reaction that breaks bonds within a polymer by adding water, attaching an $-\text{OH}$ group to one monomer and an $-\text{H}$ atom to the other.

Carbohydrates

Biological molecules classified into monosaccharides, disaccharides, and polysaccharides that function mainly as an immediate energy source and as structural components.

Monosaccharide

A simple single sugar molecule having a 3- to 7-carbon backbone (such as glucose, fructose, or galactose).

Glucose

A six-carbon monosaccharide with the molecular formula $C_6H_{12}O_6$, utilized by cells as the preferred immediate energy source.

Disaccharide

A carbohydrate composed of two monosaccharides linked together by a dehydration reaction.

Maltose

A disaccharide composed of two glucose subunits, commonly broken down by yeast during fermentation to yield ethanol.

Sucrose

A disaccharide acquired from sugar beets and sugarcane, commonly used as table sugar.

Lactose

A disaccharide commonly found in milk.

Polysaccharide

A carbohydrate polymer formed from long chains of monosaccharide subunits, serving energy storage or structural roles.

Starch

A slightly branched storage polysaccharide made of glucose chains, used by plants (such as in potato cells) for energy storage.

Glycogen

A highly branched storage polysaccharide composed of glucose chains, used by animals to store energy in liver and muscle cells.

Cellulose

An unbranched structural polysaccharide composed of glucose chains joined by hydrogen bonds in plant cell walls; the most abundant of all organic molecules.

Chitin

A structural polysaccharide polymer of glucose found in fungal cell walls and the exoskeletons of insects, crabs, and lobsters.

Lipids

A diverse class of nonpolar, water-insoluble biological molecules containing long hydrocarbon chains, used for long-term energy storage, insulation, protection, and waterproofing.

Triglycerides

Primary long-term energy storage lipids (fats and oils) composed of one glycerol molecule bonded to three fatty acids.

Glycerol

A three-carbon subunit of fats and phospholipids containing three polar, water-soluble $-\text{OH}$ (hydroxyl) groups.

Fatty Acid

A long chain of carbon atoms bonded only to hydrogen with a carboxyl group ($-\text{COOH}$) at one end.

Saturated Fatty Acid

A fatty acid chain that has no double bonds between carbon atoms and holds the maximum possible number of hydrogen atoms.

Unsaturated Fatty Acid

A fatty acid chain that contains one or more double bonds where the number of hydrogens is less than two per carbon atom, producing bends in the chain.

Trans Fat

An unsaturated fat containing double bonds in the trans orientation with hydrogen atoms on opposite sides, creating a straight carbon chain.

Phospholipid

A membrane lipid consisting of a polar, hydrophilic phosphate head and two nonpolar, hydrophobic fatty acid tails linked to a glycerol backbone.

Steroids

Lipids characterized by a carbon skeleton composed of four fused rings without fatty acids, derived from cholesterol.

Cholesterol

A fundamental steroid lipid consisting of four fused rings that serves as an essential component of animal plasma membranes and a precursor to other steroids.

Anabolic Steroids

Synthetic derivatives of the male sex hormone testosterone that promote muscle growth and secondary male sexual characteristics.

Protein

A biological macromolecule composed of amino acid monomers that performs critical functions including support, metabolism, transport, defense, regulation, and motion.

Amino Acid

The monomer of proteins, composed of a central carbon atom bonded to a hydrogen atom, an amino group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), and a variable $R$ group.

R Group

The variable side chain attached to the central carbon of an amino acid that makes each of the 20 amino acids unique and dictates its chemical properties.

Peptide Bond

A covalent bond formed by a dehydration synthesis reaction linking the carboxyl group of one amino acid to the amino group of another.

Peptide

A short chain of two or more amino acids linked together by peptide bonds.

Polypeptide

A long chain of many amino acids joined together by peptide bonds.

Conformation

The final three-dimensional shape of a protein determined by its specific linear sequence of amino acids.

Denaturation

The loss of a protein's natural three-dimensional shape and biological function, typically caused by disruptions in temperature or pH.

Primary Structure

The first level of protein organization, defined as the linear sequence of amino acids in a polypeptide chain.

Secondary Structure

The second level of protein organization, consisting of alpha ($\alpha$) helices and pleated ($\beta$) sheets held together by hydrogen bonds along the polypeptide backbone.

Tertiary Structure

The overall three-dimensional globular shape of a single polypeptide, formed by the interaction of its secondary structures.

Quaternary Structure

The structural level of a protein formed by the interaction and assembly of two or more polypeptide chains.

Sickle-Cell Disease

An inherited blood disorder caused by a genetic mutation changing a single amino acid (valine replacing glutamate) in hemoglobin, causing red blood cells to stiffen into an abnormal crescent shape.

Nucleic Acids

Biological polymers of nucleotide monomers (DNA and RNA) that store and transmit genetic information to direct cell activities and build proteins.

Nucleotide

The monomer subunit of nucleic acids, consisting of a phosphate group ($-\text{PO}_4^{3-}$), a 5-carbon sugar, and a nitrogen-containing base.

DNA (Deoxyribonucleic Acid)

A double-stranded nucleic acid arranged in a double helix, containing deoxyribose sugar and the nitrogenous bases adenine, thymine, cytosine, and guanine.

RNA (Ribonucleic Acid)

A single-stranded nucleic acid containing ribose sugar and the nitrogenous bases adenine, uracil, cytosine, and guanine, functioning in protein synthesis.

Complementary Base Pairing

The specific hydrogen bonding pattern between nitrogenous bases in DNA, where adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

ATP (Adenosine Triphosphate)

A high-energy nucleotide derivative that acts as the primary energy currency of the cell, storing and transporting chemical energy for cellular work.