The Molecules of Life: Carbohydrates and Lipids

This set of vocabulary flashcards covers the primary classes of biological molecules discussed in Lecture 5, focusing on the structures, types, and functions of carbohydrates and lipids.

Carbohydrates

Sugars and the polymers of sugars, which serve as essential fuels and building materials and often follow the general formula $(CH_2O)_n$.

Monosaccharide

A sugar monomer, such as glucose, that serves as a fuel source and building block for more complex molecules.

Disaccharide

A molecule consisting of two monosaccharides polymerized together, such as lactose or sucrose.

Oligosaccharide

A carbohydrate polymer consisting of a few sugar monomers.

Polysaccharide

A carbohydrate polymer consisting of many (often tens of thousands) glucose monomers, such as starch, glycogen, or cellulose.

Pentose

A monosaccharide containing $5$ carbon atoms; examples include deoxyribose and ribose.

Hexose

A monosaccharide containing $6$ carbon atoms; examples include glucose, fructose, mannose, and galactose.

Glycosidic linkages

The covalent bonds formed between sugar monomers in an enzyme-catalyzed dehydration reaction involving the $-OH$ group on carbon $1$ of one monomer and an $-OH$ group on another.

Lactose

A milk sugar composed of galactose and glucose joined by a $\beta$-glycosidic linkage.

Lactase

The only $\beta$-glycosidase found in $\text{H. sapiens}$, which is historically expressed in the fetus until age $3$ to $5$.

Lactase persistence

A condition resulting from mutations in several human populations approximately $10,000$ years ago that allows for the continued expression of lactase into adulthood.

Starch

A plant fuel storage molecule made of glucose monomers, containing $\alpha$-1,4 glycosidic linkages and $\alpha$-1,6 linkages for branching; it exists as amylose or amylopectin.

Glycogen

An extensively branched glucose storage polysaccharide found in animal muscle and liver tissues.

Cellulose

The most abundant organic molecule on Earth, comprising plant cell walls; it is an unbranched polymer of glucose linked by $\beta$-1,4 glycosidic linkages.

Lipids

A diverse set of hydrophobic molecules that mix poorly with water and are not true polymers; key types include fats, phospholipids, and steroids.

Fats (triacylglycerols)

Molecules formed by joining three fatty acids to one glycerol via dehydration reactions, serving as an energy store with more than twice the energy per gram of sugar.

Saturated fatty acid

A fatty acid with no double bonds in the hydrocarbon chain, meaning it is saturated with hydrogen; these are usually solid at room temperature.

Unsaturated fatty acid

A fatty acid containing one or more double bonds, resulting in fewer hydrogens; these are usually liquid oils at room temperature.

Phospholipids

Molecules with a hydrophilic phosphate head and two hydrophobic fatty acid tails that self-assemble into bilayers in water, forming the basis of cellular membranes.

Steroids

Lipids characterized by a carbon skeleton consisting of four fused rings: three $6$-membered rings and one $5$-membered ring.

Cholesterol

The most common steroid in animals; it helps control membrane fluidity and acts as the precursor for other steroids and hormones such as cortisol.

Ester linkages

The specific chemical bonds formed between glycerol and fatty acids to create triacylglycerols.