Carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones, their simple derivatives, or substances that yield such compounds upon hydrolysis. Carbohydrates perform a multiplicity of roles in living systems in addition to serving as one of the main types of nutrient molecules. In addition to understanding the basic chemical nature of carbohydrates and their uses in living organisms, including energy metabolism, it pays to take some time at the beginning with this material to make sure you understand the systems of nomenclature for monosaccharides based on the placement of its carbonyl group, the number of carbon atoms and chiral handedness as well as the nomenclature for describing glycosidic bonds.

WikiPremed Resources

Lipids Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Carbohydrates
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Understand that the definition of the category of lipids is not strictly structural but relies on solubility.

Be able to draw the structure of a fatty acid, glycerol, and a triglyceride molecule. Understand the acyl substitution dehydration pathway of formation of a tryglyceride molecule from glycerol and three fatty acids.

Be able to explain why saturated fats have higher melting points than unsaturated fats.

Understand the structure of soaps and detergents and how they function.

Be able to distinguish the structure of phospholipids from triglycerides in general terms as well as distinguish a few different varieties of phosopholipids from each other including lecithin and sphingomyelin. Understand how their behavior underlies the properties of cell membranes.

In basic terms, understand why the terpenes usually have a number of carbon atoms that is a multiple of 5.

Be able to draw the generic structural formula for steroids. Be able to name several examples of steroids and describe their functions.

Recognize the eicosanoid lipids: the prostaglandins, thromboxanes, and leukotrienes.

Suggested Assignments

Review lipids terminology with practice using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Read pp. 112-113 in ExamKrackers Chemistry. Perform practice items 65-72 on pp. 116-117 (practice items for carbohydrates, proteins, lipids & nucleic acids).

Read pp. 3-10 in ExamKrackers Biology I. Perform practice items 1-8 on pg. 11 (subject matter for lipids, carbohydrates, and nucleic acids).

Study the lipid web resources carefully.

Conceptual Vocabulary for Carbohydrates


Each list begins with basic conceptual vocabulary you need to know for MCAT questions and proceeds to advanced terms that might appear in context in MCAT passages. The terms are links to Wikipedia articles.
Carbohydrates or saccharides are a major class of biomolecules which are simple compounds, aldehydes or ketones with many hydroxyl groups added, usually one on each carbon atom that is not part of the aldehyde or ketone functional group.
Starch is a mixture of amylose and amylopectin. These are both complex carbohydrate polymers of glucose.
Glucose, a monosaccharide, is an important carbohydrate in biology, used by the living cell as a source of energy and metabolic intermediates. It is one of the main products of photosynthesis and starts cellular respiration in both prokaryotes and eukaryotes.
Sucrose (table sugar) is a disaccharide formed by the condensation of glucose and fructose.
A disaccharide is a sugar composed of two monosaccharides.
Glycogen is a polysaccharide of glucose which functions as the primary short term energy storage in animal cells.
Cellulose is a polysaccharide derived from beta-glucose. It is the primary structural component of green plants.
Amylose is a linear polymer of glucose linked with mainly alpha (1 - 4) bonds which can consist of several thousand glucose units. It is one of the two components of starch, the other being amylopectin.
Monosaccharides are the simplest carbohydrates. They cannot be hydrolyzed into simpler sugars.
A hexose is a monosaccharide with six carbon atoms, twelve hydrogens, and six oxygens.
Fructose (or levulose) is a simple sugar found in many foods and is one of the three most important blood sugars along with glucose and galactose.
Lactose is a disaccharide that consists of beta-D-galactose and beta-D-glucose monomers connected by a beta-1-4 glycosidic linkage.
Maltose, or malt sugar, is a disaccharide formed from two units of glucose joined with an alpha(1 - 4) linkage.
Also called brain sugar, galactose, is a type of simple sugar which is less sweet than glucose and not very water-soluble.
Deoxyribose is a deoxy sugar derived from the pentose sugar ribose by the replacement of the hydroxyl group at the 2 position with hydrogen
Ribose is simple pentose sugar which is a component of RNA.
Chitin is a long-chain polymer of beta-glucose that forms a hard, semitransparent material found throughout the natural world, for example, in fungi, the exoskeletons of arthropods, the radula of molluscs and the beaks of cephalopods.
An aldohexose is a hexose with an aldehyde group on one end.
Amylopectin is a highly branched polymer of glucose found in plants. It is one of the two components of starch, the other being amylose.
Glycolipids are carbohydrate-attached lipids.
Glyceraldehyde is a monosaccharide three carbon atoms, six hydrogen atoms, and three oxygen atoms, the simplest of all common aldoses.
Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch. They are mixtures of linear alpha-(1,4)-linked D-glucose polymers.
Glycosylation is the process or result of addition of saccharides to proteins and lipids.
Glycosidic bond
A glycosidic bond is a certain type of functional group that joins a sugar moeity to an alcohol, which may be another carbohydrate.
An oligosaccharide is a saccharide polymer containing a small number of component sugars, typically three to ten.
Glycosides are molecules in which a sugar part is bound to some other part.
A glucoside is a glycoside that is derived from glucose.
Reducing sugar
A reducing sugar is any sugar that, in basic solution, forms some aldehyde or ketone. This allows the sugar to act as a reductant, for example, in the Maillard reaction or Benedict's reaction.
An anomer is a stereoisomer of a saccharide in the cyclic form that differs only in its configuration at the hemiacetal, or hemiketal, carbon
Anomerization is the interconversion between the alpha and beta anomers of a carbohydrate.
Benedict's reagent
Benedict's reagent contains blue copper(II) ions which are reduced to copper(I) in the presence of reducing sugars such as glucose, fructose, galactose, lactose or maltose.
Anomeric effect
The anomeric effect or Edward-Lemieux effect is a stereoelectronic effect that describes the tendency of heteroatomic substituents adjacent to a heteroatom within a cyclohexane ring to prefer the axial orientation instead of the less hindered equatorial orientation that would be expected from steric considerations..
Mutarotation is the term given to the change in the specific rotation of plane polarized light, when it is passed through an aldohexose, refering to the conversion of a pure anomer of a hemiacetal carbohydrate to an equilibrium mixture of two anomers.
Glycosylamine is a biochemical compound consisting of an amine with a beta-N-glycosidic bond to a carbohydrate.
Glucuronic acid
Glucuronic acid is a carboxylic acid with a structure similar to glucose, though with the sixth carbon oxidized to a carboxylic acid.
The Integrated MCAT Course is a trademark of Wisebridge Learning Systems. Unless otherwise specified, the works of the Integrated Course are published under a Creative Commons Attribution NonCommercial ShareAlike License. MCAT is a registered trademark of the Association of American Medical Colleges, which does not endorse the Integrated MCAT Course. The Integrated MCAT Course offers our customers no guarantees regarding eventual performance on the MCAT.