A1 Biology: Biological Molecules - Carbohydrates, Lipids, Proteins, and Enzymes

Comprehensive vocabulary flashcards covering monomers, polymers, carbohydrates, lipids, proteins, and enzyme kinetics and inhibition from Unit 1: Biological Molecules.

Monomer

A smaller unit or molecular sub-unit from which larger molecules are made.

Polymer

A large molecule formed from a large number of monomers joined together.

Condensation reaction

A chemical reaction that joins two molecules together with the formation of a chemical bond, accompanied by the elimination of a molecule of water.

Hydrolysis reaction

A chemical reaction that breaks a chemical bond between two molecules through the addition or use of a water molecule.

Monosaccharide

The basic monomer unit of carbohydrates (such as glucose, fructose, and galactose) with the molecular formula $C_6H_{12}O_6$.

Isomers of glucose

Molecules having identical molecular formulas ($C_6H_{12}O_6$) but distinct structural configurations; in $\alpha$-glucose the $-OH$ on carbon-1 lies below the ring, whereas in $\beta$-glucose it lies above the ring.

Disaccharide

A double sugar formed when two monosaccharides are joined by a glycosidic bond during a condensation reaction with the release of water.

Glycosidic bond

A covalent chemical bond formed between two monosaccharides during a condensation reaction.

Maltose

A disaccharide formed by the condensation reaction between two glucose molecules, linked by a 1,4-glycosidic bond.

Sucrose

A non-reducing disaccharide formed by the condensation of a glucose molecule and a fructose molecule.

Lactose

A disaccharide formed by the condensation of a glucose molecule and a galactose molecule.

Benedict's test for reducing sugars

A biochemical test where a sample is mixed with $2\,\text{cm}^3$ of Benedict's solution and heated in a water bath for 5 minutes; a positive result produces a brick red or orange precipitate of copper (I) oxide.

Test for non-reducing sugars

A biochemical test in which a non-reducing sugar (such as sucrose) is first boiled with dilute acid to hydrolyse it, neutralised with dilute sodium hydroxide ($\text{NaOH}$), and then heated with Benedict's solution to yield a brick red precipitate.

Polysaccharide

A large polymer formed by the condensation of many monosaccharide units joined by glycosidic bonds, which is relatively insoluble in water and non-reducing.

Cellulose

A structural fibrous polysaccharide in plant cell walls formed from long, straight, unbranched chains of $\beta$-glucose joined by $\beta$-1,4 glycosidic bonds, where every alternate monomer is inverted.

Microfibril

A three-dimensional structure consisting of straight, unbranched cellulose chains running parallel to each other and cross-linked by hydrogen bonds between hydroxyl ($-OH$) groups.

Macrofibrils

Large bundles of microfibrils ($50\,\text{nm}$ diameter) that are interwoven in differing directions and embedded in a matrix to provide rigidity and permeability in plant cell walls.

Starch

A plant storage carbohydrate composed of long, branched chains of $\alpha$-glucose, consisting of amylose and amylopectin, stored in amyloplasts and osmotically inactive.

Amylose

An unbranched polymer in starch formed solely by $\alpha$-1,4 glycosidic bonds, forming a compact helical chain.

Amylopectin

A branched polymer in starch formed by both $\alpha$-1,4 and $\alpha$-1,6 glycosidic bonds.

Iodine test

A biochemical test for starch involving the addition of 2-3 drops of iodine/potassium iodide solution, turning from orange/yellow to blue/black if starch is present.

Glycogen

The storage polysaccharide of $\alpha$-glucose found in animal cytoplasm (notably liver and muscle tissues), featuring many more branches than starch to enable rapid hydrolysis for respiration.

Glycerol

A 3-carbon alcohol molecule containing three hydroxyl ($-OH$) groups that bonds with fatty acids to form triglycerides and phospholipids.

Triglyceride

A lipid formed by the condensation of one glycerol molecule with three fatty acids, yielding three ester bonds and releasing three water molecules.

Ester bond

A chemical bond formed between a carboxylic acid group of a fatty acid ($R-COOH$) and a hydroxyl group of glycerol during a condensation reaction.

Saturated fatty acid

A fatty acid whose hydrocarbon chain has no double bonds between carbon atoms, allowing its straight tail to pack tightly at lower temperatures.

Unsaturated fatty acid

A fatty acid that contains one or more double bonds ($C=C$) between carbon atoms in its hydrocarbon chain, introducing kinks that reduce packing density.

Phospholipid

A lipid composed of one glycerol molecule bonded to two fatty acid tails and one negatively charged, polar phosphate group.

Phospholipid bilayer

A double layer of phospholipids forming cell membranes, with hydrophilic phosphate heads interacting with water and hydrophobic fatty acid tails pointing inward toward each other.

Emulsion test

A biochemical test for lipids where the sample is dissolved in $2\,\text{cm}^3$ of ethanol, poured into water, and shaken; the appearance of a milky white emulsion confirms the presence of lipid.

Amino acid

The monomer of proteins, containing an amine group ($-NH_2$), a carboxyl group ($-COOH$), and a variable side chain ($R$ group) attached to a central carbon atom.

Peptide bond

A covalent bond ($-CONH-$) formed between the amine group of one amino acid and the carboxyl group of another through a condensation reaction.

Dipeptide

A molecule formed by the condensation of two amino acids joined by a single peptide bond.

Polypeptide

A polymer chain consisting of many amino acids linked together by peptide bonds.

Primary structure of a protein

The specific sequence of amino acids joined by peptide bonds in a polypeptide chain, which determines its final shape.

$\alpha$-helix

A coiled secondary protein structure formed by hydrogen bonds between the $-NH$ group of one amino acid and the $C=O$ group of another.

$\beta$-pleated sheet

A folded, sheet-like secondary protein structure stabilised by regular hydrogen bonding across parallel or antiparallel polypeptide backbones.

Tertiary structure of a protein

The overall three-dimensional folding and coiling of a polypeptide chain stabilised by hydrogen bonds, ionic bonds, and disulfide bridges between $R$ groups.

Quaternary structure of a protein

A protein structure formed by the association of two or more polypeptide chains held together by ionic bonds, hydrogen bonds, disulfide bridges, and hydrophobic interactions (e.g., haemoglobin).

Globular proteins

Soluble proteins with compact, coiled, and spherical tertiary structures that perform metabolic functions, including enzymes and antibodies.

Fibrous proteins

Long, thin, insoluble proteins that perform structural functions in organisms, such as collagen in connective tissues and keratin in hair.

Protein denaturation

An alteration in the three-dimensional tertiary structure of a protein caused by high temperatures, extreme pH, or heavy metals, breaking hydrogen and ionic bonds and permanently destroying function.

Biuret test

A chemical test for detecting proteins; the addition of Biuret reagent produces a purple, lilac, or mauve colour when peptide bonds are present.

Enzyme

A tertiary globular protein that acts as a biological catalyst, speeding up biological reactions without being altered itself.

Activation energy

The minimum energy required for a chemical reaction to occur; lowered by enzymes through the formation of enzyme-substrate complexes.

Active site

The specific region of an enzyme molecule shaped by its tertiary structure with complementary configuration and charge to bind a substrate.

Lock and key model

A historical model of enzyme specificity proposing that the enzyme possesses a rigid active site that perfectly fits the complementary shape of the substrate.

Induced-fit model

A model of enzyme action stating that the active site is flexible and molds its shape around the substrate upon binding, creating strain on bonds to lower activation energy.

$$V_{\text{max}}$$

The constant maximum rate of an enzyme-controlled reaction reached when all enzyme active sites are occupied or saturated by substrate.

Optimum temperature

The temperature at which an enzyme-controlled reaction reaches its maximum rate before thermal energy causes denaturation.

Optimum pH

The specific pH value at which the tertiary structure and ionic charges of an enzyme's active site are optimal, resulting in the maximum rate of reaction.

Competitive inhibitor

A substance with a molecular shape similar to the normal substrate that competes for the active site of an enzyme; its inhibition can be overcome by increasing substrate concentration.

Non-competitive inhibitor

A substance that binds to an enzyme at an allosteric site (a site other than the active site), altering the tertiary structure and active site shape so the reaction cannot proceed even with excess substrate.