unit 1 - biological molecules

Condensation reaction

A chemical reaction in which two molecules join together with the formation of a chemical bond, accompanied by the elimination of a molecule of water ($H_2O$).

Hydrolysis reaction

A chemical reaction that breaks a covalent bond between two molecules, requiring the addition of a water molecule ($H_2O$).

Biochemical test for reducing sugars

Add Benedict's reagent and heat in a water bath to at least $80\,^\circ\text{C}$; an observed color change from blue to green, yellow, orange, or brick-red precipitate indicates presence.

Glycosidic bond

The covalent bond formed between two monosaccharides during a condensation reaction.

Biochemical test for starch

Add iodine dissolved in potassium iodide solution to the sample; a color shift from orange-brown to blue-black indicates presence.

Emulsion test

Shake the test substance with ethanol, mix with water, and observe; the appearance of a cloudy, milky-white layer confirms the presence of lipids.

Biuret test

Add sodium hydroxide followed by dilute copper(II) sulfate solution; a color change from blue to lilac or purple indicates the presence of peptide bonds.

Primary structure of a protein

The unique linear sequence of amino acids in a polypeptide chain, determined by genetic code and joined by peptide bonds.

Induced-fit model

The mechanism of enzyme action in which the active site undergoes conformational changes to mold snugly around the substrate upon binding, placing strain on chemical bonds.

Phosphodiester bond

The covalent link connecting the $5'$ phosphate group of one nucleotide to the $3'$ hydroxyl group of the adjacent pentose sugar in a polynucleotide strand.

High specific heat capacity of water

The thermal buffering property resulting from extensive hydrogen bonding between molecules, preventing rapid internal temperature fluctuations in aquatic organisms and cells.

Secondary structure of a protein

The regular local folding pattern of a polypeptide chain into $\alpha$-helices or $\beta$-pleated sheets, stabilized by hydrogen bonds between peptide backbone components.

Tertiary structure of a protein

The overall three-dimensional conformation of a single polypeptide chain, maintained by disulfide bridges, ionic bonds, and hydrophobic interactions between R-groups.

Biochemical test for non-reducing sugars

Boil the sample with dilute hydrochloric acid, neutralize with sodium hydrogencarbonate, and then heat with Benedict's reagent to produce a brick-red precipitate.

Ester bond

The covalent link formed by a condensation reaction between a glycerol hydroxyl group and the carboxyl group of a fatty acid.

Competitive inhibitor

A substance with a complementary shape to an enzyme's active site that directly binds to it, blocking substrate molecules from entering.

High latent heat of vaporization of water

The large quantity of thermal energy needed to evaporate a unit mass of liquid, providing a significant cooling mechanism for organisms via sweating or transpiration.

Quaternary structure of a protein

The association of two or more individual polypeptide chains and any non-protein prosthetic groups into a functional macromolecular complex.

Non-competitive inhibitor

A molecule that binds to an allosteric site rather than the active site, altering the tertiary structure of an enzyme and preventing catalysis regardless of substrate concentration.

Structure of cellulose

A linear, unbranched polymer of $\beta$-glucose molecules joined by $1,4$-glycosidic bonds, forming parallel chains cross-linked by hydrogen bonds into strong microfibrils.

Structure of glycogen

A compact, highly branched polysaccharide of $\alpha$-glucose units linked by $1,4$- and $1,6$-glycosidic bonds, functioning as an energy reserve in animals.

Phospholipid

An amphipathic molecule composed of a glycerol molecule bonded to two fatty acid chains and a phosphate group, forming a hydrophilic head and two hydrophobic tails.

Peptide bond

The covalent bond formed between the amine group of one amino acid and the carboxyl group of another during a condensation reaction.

Cohesion of water molecules

The sticking together of identical polar molecules via extensive hydrogen bonding, facilitating the transport of continuous fluid columns under tension through plant xylem vessels.

DNA helicase

An enzyme that catalyzes the disruption of hydrogen bonds between complementary base pairs, unwinding and separating the two polynucleotide strands during replication.

DNA polymerase

An enzyme that catalyzes the formation of phosphodiester bonds between adjacent nucleotides in a $5'$ to $3'$ direction during DNA synthesis.

Structure of a triglyceride

A lipid composed of one glycerol molecule bonded to three fatty acid chains via three ester bonds formed during condensation reactions.

Structure of starch

A plant storage polysaccharide composed of $\alpha$-glucose units, consisting of unbranched helical amylose with $1,4$-glycosidic bonds and branched amylopectin with $1,4$- and $1,6$-glycosidic bonds.

Semi-conservative replication

The mechanism of DNA synthesis yielding two daughter molecules, each retaining one intact original parental strand paired with one newly synthesized strand.

Adenosine triphosphate

A phosphorylated nucleotide derivative composed of ribose, adenine, and three phosphate groups, hydrolyzed to yield an immediate source of energy for cellular processes.

Activation energy

The minimum kinetic energy required by colliding reactant molecules for a chemical reaction to take place.

Structure of an amino acid

A monomer consisting of a central carbon atom covalently bonded to a hydrogen atom, an amine group ($-\text{NH}_2$), a carboxyl group ($-\text{COOH}$), and a variable side chain ($\text{R}$).

ATP hydrolase

An enzyme that catalyzes the breakdown of adenosine triphosphate into adenosine diphosphate and an inorganic phosphate group, releasing energy for cellular work.

ATP synthase

An enzyme that catalyzes the condensation of adenosine diphosphate and an inorganic phosphate group to reform adenosine triphosphate during respiration or photosynthesis.

Saturated fatty acid

A hydrocarbon chain containing no carbon-carbon double bonds, maximizing the number of bonded hydrogen atoms along the carbon skeleton.

Unsaturated fatty acid

A hydrocarbon chain containing one or more carbon-carbon double bonds ($\text{C}=\text{C}$), creating bends or kinks in the tail.

Water as a metabolite

A biological property whereby molecules directly participate as reactants or products in chemical reactions, including hydrolysis and condensation.

Water as a solvent

A property resulting from dipolarity that allows the dissolution and transport of charged mineral ions and polar solutes for metabolic reactions.

Role of iron ions

Inorganic cations ($\text{Fe}^{2+}$) that bind molecular oxygen within the haem prosthetic group of haemoglobin for systemic transport.

Role of phosphate ions

Inorganic anions ($\text{PO}_4^{3-}$) that join nucleotides in phosphodiester backbones, phosphorylate molecules to increase reactivity, and store chemical energy.

Complementary base pairing in DNA

The specific hydrogen bonding pattern where adenine joins thymine via two hydrogen bonds, and cytosine joins guanine via three hydrogen bonds.