Biomolecules: Structure, Function, and Reactions

A comprehensive vocabulary review of biomolecules, structural isomers of glucose, carbohydrate classifications, chemical bonds, and biological condensation and hydrolysis reactions.

Biomolecules

Organic molecules produced by living organisms that serve as essential building blocks of life and carry out specific cellular functions.

Monomer

A small, basic molecular unit that joins together with other units via covalent bonds to form larger polymers (e.g., glucose).

Polymer

A large molecule composed of many repeating monomer subunits bonded together in a chain (e.g., starch).

Macromolecule

A giant polymer possessing high molecular weight, such as proteins and nucleic acids ($DNA$).

$\alpha$-Glucose (Alpha Glucose)

An isomer of glucose ($C_6H_{12}O_6$) in which the hydroxyl ($-OH$) group on carbon-1 ($C1$) points downward; functions as the monomer for energy storage molecules like starch and glycogen.

$\beta$-Glucose (Beta Glucose)

An isomer of glucose ($C_6H_{12}O_6$) in which the hydroxyl ($-OH$) group on carbon-1 ($C1$) points upward; serves as the monomer for cellulose to provide structural strength in plant cell walls.

D-Glucose

The naturally occurring dextrorotatory enantiomer of glucose where the $-OH$ group on the fifth carbon is oriented to the right in a Fischer projection; the primary substrate for glycolysis and cellular respiration.

L-Glucose

The synthetic levorotatory enantiomer of glucose where the $-OH$ group on the fifth carbon is oriented to the left in a Fischer projection; used in medical diagnostics as a marker.

Monosaccharide

The simplest unit of carbohydrate consisting of a single sugar molecule, possessing the empirical formula $(CH_2O)_n$ with carbon, hydrogen, and oxygen in a $1:2:1$ ratio.

Disaccharide

A carbohydrate sugar formed when two monosaccharides join together through a condensation reaction with the release of a water molecule.

Sucrose

A non-reducing disaccharide ($C_{12}H_{22}O_{11}$) formed by linking glucose and fructose monomers; serves as the primary transport sugar in plants.

Lactose

A disaccharide ($C_{12}H_{22}O_{11}$) found in milk, consisting of galactose and glucose units linked together.

Maltose

A reducing disaccharide ($C_{12}H_{22}O_{11}$) consisting of two linked glucose units.

Oligosaccharide

A carbohydrate polymer composed of a short chain of $3$ to $10$ monosaccharide units joined by glycosidic bonds.

Raffinose

A trisaccharide oligosaccharide with the formula $C_{18}H_{32}O_{16}$, composed of galactose, glucose, and fructose.

Polysaccharide

A complex carbohydrate macromolecule consisting of hundreds to thousands of monosaccharide subunits linked by glycosidic bonds.

Amylose

A linear, unbranched form of plant starch composed of $\alpha$-glucose units linked by $\alpha(1\rightarrow 4)$-glycosidic bonds that coils into a helix.

Amylopectin

A branched polysaccharide component of starch made of $\alpha$-glucose units linked by both $\alpha(1\rightarrow 4)$ and $\alpha(1\rightarrow 6)$-glycosidic linkages.

Starch

The major plant energy storage carbohydrate ($(C_6H_{10}O_5)_n$), consisting of $10\text{--}20\%$ amylose and $80\text{--}90\%$ amylopectin.

Iodine Test

A chemical diagnostic assay in which yellow/brown iodine solution turns blue/black in the presence of starch.

Glycogen

A highly branched polysaccharide of $\alpha$-glucose stored in animal liver and muscle tissue for rapid short-term glucose release.

Cellulose

A structural polysaccharide ($(C_6H_{10}O_5)_n$) composed of $\beta$-glucose subunits that provides rigidity and strength to primary plant cell walls.

Glycosidic Bond

A covalent $C\text{--}O\text{--}C$ link formed between the hydroxyl groups of two sugars with the elimination of a water molecule.

Ester Bond

A covalent linkage characterized by the group $-COO-$ formed between the hydroxyl ($-OH$) group of glycerol and the carboxyl ($-COOH$) group of a fatty acid in lipids.

Peptide Bond

A covalent $C\text{--}N$ linkage ($-CONH-$) formed between the carboxyl group of one amino acid and the amino group ($-NH_2$) of another, releasing water.

Condensation Reaction

An anabolic (building up) reaction that combines two molecules into a larger molecule with the release of a small molecule, typically water; also known as dehydration synthesis.

Hydrolysis

A catabolic (breaking down) chemical reaction in which bonds within a larger molecule are cleaved by the addition of water.

Reducing Sugar

A sugar containing a free aldehyde or ketone group that can donate electrons to reduce other chemical substances (e.g., glucose, fructose, maltose).

Non-Reducing Sugar

A sugar such as sucrose that cannot donate electrons because its reactive carbonyl groups are tied up within a glycosidic bond.

Carbonyl Group

A functional group consisting of a carbon double-bonded to an oxygen atom ($>C=O$), found at the end of a chain in aldehydes or within the chain in ketones.

Hydroxyl Group

A polar functional group with the formula $-OH$, commonly found in alcohols and carbohydrate sugars.

Carboxyl Group

An acidic functional group with the formula $-COOH$, characteristic of amino acids and fatty acids.

Amino Group

A basic nitrogen-containing functional group with the formula $-NH_2$, found in amino acids and nitrogenous bases.

Phosphate Group

A functional group with the formula $-OPO_3^{2-}$, found in high-energy compounds and structural polymers including $DNA$, $ATP$, and phospholipids.

Sulfhydryl Group

A functional group with the formula $-SH$, found in the structure of certain proteins.