Chapter 2: Biological molecules

Water

A polar molecule with hydrogen bonds; has high specific heat capacity

Hydrogen Bond

A weak electrostatic attraction between a slightly positive hydrogen atom and a slightly negative atom

Cohesion

The attraction between water molecules due to hydrogen bonding

Adhesion

The attraction between water molecules and other polar surfaces

Polarity

Unequal charge distribution within a molecule; polar molecules like water interact with other charged or polar substances.

Inorganic Ion

Charged atoms or molecules involved in biological functions

Monosaccharide

Simple sugar and monomer of carbohydrates

α-glucose

Isomer of glucose with the -OH group on carbon 1 below the ring; forms starch and glycogen.

β-glucose

Isomer of glucose with the -OH group on carbon 1 above the ring; forms cellulose.

Disaccharide

Two monosaccharides joined by a glycosidic bond

Polysaccharide

Polymer of many monosaccharides; used for storage (starch

Glycosidic Bond

Covalent bond between two monosaccharides formed by a condensation reaction.

Condensation Reaction

A reaction where two molecules join together with the removal of a water molecule.

Hydrolysis

A reaction where a molecule is broken down by the addition of water.

Benedict’s Test

Test for reducing sugars; positive result turns brick-red after heating with Benedict’s reagent.

Lipid

Non-polar biological molecule used for energy storage

Triglyceride

A lipid made from one glycerol and three fatty acids joined by ester bonds.

Fatty Acid

Long hydrocarbon chain with a carboxyl group; can be saturated (no double bonds) or unsaturated (has double bonds).

Glycerol

A three-carbon alcohol that forms the backbone of triglycerides and phospholipids.

Hydrophobic

Repelled by water; non-polar molecules or parts of molecules.

Hydrophilic

Attracted to water; polar molecules or groups.

Emulsion Test

Test for lipids; positive result is a cloudy white emulsion after mixing with ethanol and water.

Amino Acid

Monomer of proteins; contains an amine group

Peptide Bond

Covalent bond between amino acids formed by condensation.

Polypeptide

Chain of amino acids joined by peptide bonds.

Primary Structure (Protein)

The specific sequence of amino acids in a polypeptide chain.

Secondary Structure (Protein)

Folding of polypeptide into α-helices and β-pleated sheets via hydrogen bonding.

Tertiary Structure (Protein)

3D shape of a polypeptide due to interactions between R groups

Quaternary Structure (Protein)

Structure formed when two or more polypeptides join

Globular Protein

Compact, circular and carry out functions

Fibrous Protein

Long, string like and provide structural support. Not soluble in water

Hydrogen Bond (Protein)

Weak bond between polar groups that stabilises protein structure.

Ionic Bond (Protein)

Attraction between oppositely charged R groups in protein structure.

Disulfide Bridge

Strong covalent bond between sulfur atoms in cysteine amino acids.

Biuret Test

Test for proteins; turns purple in presence of peptide bonds.

Enzyme

Biological catalyst that speeds up reactions by lowering activation energy.

Active Site

Region on an enzyme where the substrate binds and the reaction occurs.

Substrate

Molecule that fits into an enzyme’s active site to be transformed.

Enzyme-Substrate Complex

Temporary combination of enzyme and substrate during catalysis.

Induced Fit Model

Model where the enzyme changes shape slightly to better fit the substrate.

Lock and Key Model

Model where enzyme active site fits substrate exactly.

Activation Energy

Minimum energy needed for a chemical reaction to occur; lowered by enzymes.

Denaturation

Loss of enzyme structure and function due to changes in temperature or pH.

Optimum Temperature / pH

The temperature or pH at which an enzyme’s activity is highest.

Competitive Inhibitor

Molecule that competes with the substrate for the active site.

Non-Competitive Inhibitor

Molecule that binds elsewhere on the enzyme

pyranose sugar

A sugar with a six-membered ring structure made of five carbons and one oxygen, formed when the sugar cyclizes. Common in glucose and galactose, pyranose forms exist as α or β isomers.

ribose

A five-carbon (pentose) sugar with the formula C₅H₁₀O₅, found in RNA. It forms a furanose (five-membered) ring and is essential for nucleotides like ATP and RNA structure.

deoxyribose

A five-carbon (pentose) sugar with the formula C₅H₁₀O₄, found in DNA. It is similar to ribose but lacks one oxygen atom at carbon 2, making DNA more chemically stable than RNA.

glycosidic bond

A covalent bond that links two monosaccharides by joining the anomeric carbon of one sugar to a hydroxyl group of another, forming disaccharides or polysaccharides. It forms through a condensation reaction (removal of water).

Organic molecules

Molecules primarily made of carbon and hydrogen, often containing oxygen, nitrogen, or other elements. They form the basis of life and include carbohydrates, lipids, proteins, and nucleic acids.

micromolecules

Small, simple molecules with low molecular weight, such as water, oxygen, carbon dioxide, and mineral ions. They are essential for basic biological processes but are not polymers like macromolecules.

macromolecules

Large, complex molecules made of repeating smaller units (monomers) linked by covalent bonds. Key biological macromolecules include carbohydrates, proteins, lipids, and nucleic acids, essential for structure and function in living organisms.

cellular respiration

A metabolic process where cells break down glucose (or other fuels) to produce ATP, the main energy currency of the cell. It typically involves glycolysis, the Krebs cycle, and oxidative phosphorylation, releasing energy, water, and carbon dioxide.

metabolic reactions

Chemical reactions in living organisms that convert molecules to sustain life, including catabolic reactions (breaking down molecules for energy) and anabolic reactions (building complex molecules).

triglycerides

Lipid molecules made of one glycerol molecule bonded to three fatty acids. They store energy efficiently and provide insulation and protection in organisms.

Oligosaccharides

Short chains of 3 to 10 monosaccharide units linked by glycosidic bonds. They often function in cell recognition and signaling.

lipids

A diverse group of hydrophobic organic molecules, including fats, oils, and steroids, that store energy, make up cell membranes, and act as signaling molecules.

protein

Large molecules made of amino acid chains folded into specific shapes, essential for structure, enzymes, transport, and regulation in living organisms.

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carboxyl group

A functional group (–COOH) consisting of a carbon double-bonded to oxygen and single-bonded to a hydroxyl group; it gives molecules acidic properties and is found in amino acids and fatty acids.

non polar

Describes molecules or parts of molecules with an even distribution of electrical charge, making them hydrophobic (water-repellent) and unable to dissolve well in water.

polar

Describes molecules with an uneven distribution of electrical charge, creating partial positive and negative ends, making them hydrophilic (water-attracting) and soluble in water.

inorganic ion

Charged atoms or molecules not containing carbon, such as Na⁺, Cl⁻, or Ca²⁺, that play vital roles in cell function and biochemical processes.

starch

A plant carbohydrate made of glucose units linked mainly by α-1,4 and α-1,6 glycosidic bonds; it serves as an energy storage molecule.

cellulose

A structural carbohydrate in plant cell walls made of β-glucose units linked by β-1,4 glycosidic bonds, forming strong, fibrous chains that humans cannot digest.

reducing sugar

A sugar that can donate electrons to another chemical, usually because it has a free aldehyde or ketone group; examples include glucose and maltose.

non reducing sugar

A sugar that cannot donate electrons or reduce other chemicals because its reactive aldehyde or ketone group is involved in a glycosidic bond; examples include sucrose.

phospholipid

A lipid molecule with two fatty acid tails and a phosphate-containing head, forming the main component of cell membranes with a hydrophobic tail and hydrophilic head.

glycogen

A highly branched polysaccharide made of glucose units, serving as the main energy storage molecule in animals and fungi. The bonds in glycogen are mainly α-1,4 glycosidic bonds linking glucose units in a chain, with α-1,6 glycosidic bonds at branch points that create its highly branched structure.

unsaturated fatty acid

A fatty acid with one or more double bonds between carbon atoms, causing kinks in the chain and making the fat liquid at room temperature.

saturated fatty acid

A fatty acid with no double bonds between carbon atoms, meaning all carbons are fully "saturated" with hydrogen atoms; usually solid at room temperature.

Monounsaturated Fatty Acid

A fatty acid with exactly one double bond in its carbon chain, which introduces a slight bend and usually makes it liquid at room temperature.

Polyunsaturated Fatty Acid

A fatty acid with two or more double bonds in its carbon chain, causing multiple bends and typically remaining liquid at room temperature.

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Ester Bond

A covalent bond formed between a hydroxyl group (–OH) of glycerol and the carboxyl group (–COOH) of a fatty acid during lipid formation, releasing water (condensation reaction).

specific heat capacity

The amount of heat energy needed to raise the temperature of 1 gram of a substance by 1°C.

high latent heat of vaporization

The large amount of energy required to change 1 gram of a liquid into a gas without changing its temperature.