Lecture 3: Macromolecules I: Carbon, Carbohydrates, and Lipids

Vocabulary practice flashcards for Bio93 Lecture 3 covering carbon bonding, functional groups, polymer synthesis and breakdown, carbohydrates, and lipids.

Polymer

A long molecule consisting of many similar or identical building blocks (monomers) linked together by covalent bonds.

Monomer

The repeating smaller subunit that serves as the building block of a polymer.

Dehydration reaction

A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule ($\text{H}_2\text{O}$), synthesizing a longer polymer.

Hydrolysis

A chemical reaction that breaks bonds between monomers in a polymer through the addition of a water molecule ($\text{H}_2\text{O}$).

Functional groups

Specific chemical groups that replace one or more hydrogens of a hydrocarbon skeleton and are directly involved in chemical reactions, conferring unique properties to the molecule.

Hydroxyl group ($-\text{OH}$)

A functional group consisting of an oxygen atom bonded to a hydrogen atom; it is polar due to the electronegative oxygen atom, forms hydrogen bonds with water, and defines alcohols such as ethanol.

Carbonyl group ($>\text{C}=\text{O}$)

A functional group characterized by a carbon atom joined to an oxygen atom by a double bond; forms ketones when located within a carbon skeleton and aldehydes when located at the end.

Carboxyl group ($-\text{COOH}$)

A functional group containing a carbonyl joined to a hydroxyl group; acts as an acid because it can donate an $\text{H}^+$ ion to become a carboxylate ion in cells.

Amino group ($-\text{NH}_2$)

A functional group composed of a nitrogen atom bonded to two hydrogen atoms; acts as a base by picking up an $\text{H}^+$ ion from the surrounding solution to form an ionized amine.

Sulfhydryl group ($-\text{SH}$)

A functional group consisting of a sulfur atom bonded to a hydrogen atom; two groups can react covalently to form cross-links that stabilize protein structure.

Phosphate group ($-\text{OPO}_3^{2-}$)

A functional group containing a phosphorus atom bonded to four oxygen atoms; contributes negative charge and confers the ability to react with water to release energy.

Methyl group ($-\text{CH}_3$)

A nonpolar functional group consisting of a carbon atom bonded to three hydrogen atoms; affects gene expression (such as in $5\text{-methylcytosine}$) and influences the shape and function of sex hormones.

Monosaccharide

The simplest carbohydrate unit, possessing a carbon skeleton typically $3$, $5$, or $6$ carbons long and a carbonyl group, acting as a primary fuel for cellular respiration and a building block for complex molecules.

Aldose

A monosaccharide sugar whose carbonyl group is positioned at an aldehyde location at the end of the carbon chain (such as glyceraldehyde, ribose, glucose, and galactose).

Ketose

A monosaccharide sugar whose carbonyl group is located internally as a ketone along the carbon skeleton (such as dihydroxyacetone, ribulose, and fructose).

Disaccharide

A double sugar molecule composed of two monosaccharide units joined together by a covalent glycosidic linkage via a dehydration reaction.

Glycosidic linkage

A covalent bond formed between two monosaccharides by a dehydration reaction (e.g., $1\text{--}4$ linkage in maltose, $1\text{--}2$ linkage in sucrose).

Lactose

A disaccharide composed of glucose and galactose that is naturally present in milk and dairy products such as cheese and ice cream.

Lactase

The digestive enzyme responsible for hydrolyzing lactose into glucose and galactose; present in all infant mammals but typically switched off after weaning in roughly two-thirds of humans.

Polysaccharide

A carbohydrate polymer composed of hundreds to thousands of monosaccharide units linked together, serving either an energy-storage or a structural role.

Starch

A plant storage polysaccharide composed exclusively of glucose monomers, stored within plastids in unbranched (amylose) or somewhat branched (amylopectin) configurations.

Glycogen

An extensively branched energy storage polysaccharide composed of glucose monomers found stored in animal muscle tissue and liver.

Cellulose

An unbranched structural polysaccharide composed of glucose monomers that forms the rigid cell walls of plant cells, stabilized parallelly into microfibrils by hydrogen bonds.

Lipids

A diverse class of hydrophobic biological macromolecules containing nonpolar $\text{C}-\text{H}$ bonds that are not polymers, consisting of fats, phospholipids, and steroids.

Triacylglycerol

A fat molecule constructed from one glycerol molecule joined to three fatty acid chains through three separate dehydration reactions.

Ester linkage

The covalent bond formed between a hydroxyl group of glycerol and the carboxyl group of a fatty acid in a triacylglycerol molecule.

Saturated fat

A fat molecule containing no $\text{C}=\text{C}$ double bonds in its hydrocarbon chain, leaving it fully saturated with hydrogen atoms; solid at room temperature (e.g., lard, butter).

Unsaturated fat

A fat molecule containing one or more $\text{C}=\text{C}$ double bonds that create bends or kinks in the hydrocarbon chain; liquid at room temperature (e.g., plant oils).

Hydrogenated fats

Unsaturated fats synthetically converted into saturated fats by artificially adding hydrogen, enabling them to solidify at room temperature.

Trans fats

Unsaturated fats with trans double bonds produced during industrial hydrogenation of oils; common in processed baked goods and associated with coronary heart disease.