Biological Molecules: Water, Carbohydrates, Lipids, Proteins, and Nucleic Acids

Vocabulary practice flashcards covering water characteristics, carbohydrates, lipids, protein structure, types of proteins, and nucleic acid biochemistry.

Polar molecule

A molecule with regions of negativity and regions of positivity resulting from the unequal sharing of electrons across covalent bonds.

Hydrogen bond

A relatively weak chemical interaction formed when the slightly positive region of one polar molecule attracts the slightly negative region of another polar molecule.

Cohesion

The property of water molecules sticking together and moving as one mass due to mutual attraction between polar molecules.

Adhesion

The attraction of water molecules to other materials and polar surfaces.

Capillary action

The process by which water rises up a narrow tube against the force of gravity, resulting from the combined effects of cohesion and adhesion.

Carbohydrate

A biological molecule containing only carbon, hydrogen, and oxygen, usually occurring in the ratio $C_x(H_2O)_y$.

Monosaccharide

A single sugar unit that serves as a monomer for larger carbohydrates (e.g., glucose, fructose, and ribose).

Disaccharide

A sugar formed when two monosaccharides join together by a glycosidic bond via a condensation reaction (e.g., maltose, lactose, and sucrose).

Polysaccharide

A large carbohydrate polymer formed from many monosaccharide subunits linked together (e.g., glycogen, cellulose, and starch).

Hexose monosaccharide

A monosaccharide sugar composed of six carbon atoms, having the molecular formula $C_6H_{12}O_6$, such as glucose, fructose, or galactose.

Alpha ($\alpha$) and Beta ($\beta$) glucose

Two structural isomers of hexose glucose that differ in the orientation of the hydroxyl ($-OH$) group attached to carbon 1.

Condensation reaction

A chemical reaction in which two molecules join together through covalent bond formation with the elimination of a water molecule.

Glycosidic bond

A covalent bond formed between two monosaccharides in a condensation reaction.

Amylose

An unbranched starch polysaccharide composed of $\alpha$-glucose monomers joined solely by $1,4$-glycosidic bonds that twists into a compact helix stabilised by hydrogen bonds.

Amylopectin

A branched starch polysaccharide composed of $\alpha$-glucose molecules joined by $1,4$-glycosidic bonds with $1,6$-glycosidic branching points occurring approximately once every $25$ glucose subunits.

Glycogen

A highly branched, compact energy storage polysaccharide in animals and fungi composed of $\alpha$-glucose subunits with extensive $1,6$-glycosidic branching points.

Hydrolysis reaction

A chemical reaction that breaks bonds between monomers by the addition of a water molecule, catalysed by enzymes.

Cellulose

A straight, unbranched polysaccharide made of $\beta$-glucose molecules, in which alternate glucose units are rotated $180^\circ$ upside down.

Microfibrils

Strong structural bundles formed by parallel cellulose chains held together by hydrogen bonds, which aggregate into macrofibrils to form cell wall fibres.

Reducing sugar

A sugar capable of donating electrons to (reducing) another chemical substance, such as all monosaccharides and some disaccharides including maltose and lactose.

Benedict's reagent

An alkaline solution of copper(II) sulfate used to detect reducing sugars; upon reduction, blue $Cu^{2+}$ ions gain electrons to form a brick-red $Cu^{+}$ precipitate.

Colorimeter

An instrument that quantitatively measures the light absorbance or light transmission of a coloured solution to determine solute concentration.

Biosensor

A device that combines a biological component (such as an enzyme, antibody, or ssDNA) with a transducer to produce an electrical or visual signal determining analyte concentration.

Triglyceride

A lipid macromolecule composed of one molecule of glycerol combined with three fatty acid molecules via three ester bonds.

Ester bond

The covalent bond formed between the hydroxyl group of glycerol and the carboxyl group of a fatty acid in a condensation reaction (esterification).

Saturated fatty acid

A fatty acid chain that contains no carbon-to-carbon double bonds, holding the maximum possible number of hydrogen atoms bonded to carbon.

Unsaturated fatty acid

A fatty acid containing one or more double bonds between carbon atoms, which creates kinks in the hydrocarbon chain preventing close packing.

Phospholipid

A modified triglyceride in which one fatty acid chain is replaced by a negatively charged inorganic phosphate group ($PO_4^{3-}$), creating a hydrophilic head and two hydrophobic tails.

Surfactant

A surface active agent, such as a phospholipid, that forms a monolayer on water with hydrophilic heads in water and hydrophobic tails sticking out.

Sterol

A lipid alcohol based on a four-carbon ring structure with a polar hydroxyl group, such as cholesterol.

Emulsion test

A laboratory test for lipids in which a sample is dissolved in ethanol, mixed with water, and shaken; a milky-white emulsion layer indicates a positive result.

Trans fat

An unsaturated lipid produced during industrial oil hardening where the natural kinks of the double bonds in fatty acid chains have been reversed.

Amino acid

The monomer unit of proteins consisting of a central carbon bonded to an amine group ($-NH_2$), a carboxyl group ($-COOH$), a hydrogen atom, and a variable R-group.

Peptide bond

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

Peptidyl transferase

The enzyme located within ribosomes that catalyses the formation of peptide bonds between amino acids during protein synthesis.

Primary structure

The specific sequence of amino acids joined together by peptide bonds in a polypeptide chain.

Secondary structure

The repeating coil (alpha helix) or pleated sheet (beta pleated sheet) conformation assumed by a polypeptide, stabilised by hydrogen bonds along the repeating backbone.

Tertiary structure

The overall three-dimensional folding of a protein into its final functional shape, held together by hydrogen bonds, ionic bonds, hydrophobic/hydrophilic interactions, and disulfide bridges between R-groups.

Quaternary structure

The functional three-dimensional protein macromolecule resulting from the association of two or more individual polypeptide subunits.

Biuret test

A chemical test for proteins that uses sodium hydroxide and copper sulfate (or biuret reagent) to produce a violet-coloured complex in the presence of peptide bonds.

Thin layer chromatography (TLC)

An analytical technique used to separate non-volatile mixtures, such as amino acids, based on differential movement between a stationary phase (e.g., silica gel) and an organic mobile phase.

Retention value ($R_f$)

The ratio calculated in chromatography by dividing the distance travelled by an individual component by the distance travelled by the solvent front.

Globular protein

A compact, roughly spherical, water-soluble protein whose tertiary structure places hydrophobic R-groups internally and hydrophilic R-groups on the exterior.

Conjugated protein

A globular protein that contains a non-protein prosthetic group essential for its biological activity.

Prosthetic group

A permanent non-protein component incorporated into a conjugated protein, such as a haem group containing an iron(II) ion ($Fe^{2+}$).

Haemoglobin

A conjugated quaternary globular protein consisting of four polypeptide subunits (two $\alpha$ and two $\beta$), each containing a prosthetic haem group with an $Fe^{2+}$ ion to reversibly bind oxygen.

Catalase

A quaternary enzyme containing four haem prosthetic groups that catalyses the breakdown of harmful metabolic hydrogen peroxide into water and oxygen.

Fibrous protein

An insoluble, structurally repetitive protein consisting of long, uncoiled polypeptide chains with a high proportion of hydrophobic amino acids.

Keratin

A fibrous protein found in hair, skin, and nails, characterised by a large proportion of the sulfur-containing amino acid cysteine forming strong, rigid disulfide bridges.

Elastin

A fibrous protein found in elastic fibres in blood vessel walls and alveoli, formed by cross-linked tropoelastin molecules that stretch and recoil.

Collagen

A tough, flexible fibrous structural protein consisting of three polypeptide chains wound in a triple helix, with every third amino acid being glycine.

Nucleotide

The monomer of nucleic acids composed of a pentose sugar, a negatively charged phosphate group, and a nitrogenous base.

Phosphodiester bond

A strong covalent bond linking the $5'$ phosphate group of one nucleotide to the $3'$ hydroxyl group of an adjacent nucleotide in a polynucleotide backbone.

Pyrimidines

The smaller, single-carbon-ring nitrogenous bases found in nucleic acids: thymine (T), cytosine (C), and uracil (U).

Purines

The larger, double-carbon-ring nitrogenous bases found in nucleic acids: adenine (A) and guanine (G).

Antiparallel

The structural arrangement of DNA where the two parallel polynucleotide strands run in opposite directions ($5'$ to $3'$ and $3'$ to $5'$).

Complementary base pairing

The specific pairing rule in nucleic acids where a purine always pairs with a pyrimidine: adenine pairs with thymine via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds.