The coagulation cascade.

A cascade of zymogen activations occur within both the intrinsic and extrinsic blood coagulation pathways.

A zymogen is an inactive enzyme precursor, a proenzyme, that displays no catalytic activity until it is transformed into its active form by a process such as the cleavage of one or more peptide bonds. Pancreatic digestive enzymes are secreted as zymogens partly to prevent the enzymes from digesting proteins in the cells in which they are synthesized. An additional important role of zymogen activations occurs in blood clotting. For blood clotting, the response time must be fast in order to achieve clotting at the right spot and time to prevent excessive bleeding. Zymogen cascades are therefore employed to achieve that rapid response in which activation of one clotting factor is then responsible for activating another clotting factor.

WikiPremed Resources

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

Question Drill for Zymogens
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Be able to describe the structure of carbohydrates and name the mono- and disaccharides which are prominent in the biochemistry.

Gain familiarity with the basic carbohydrate nomenclature including the D,L system and terms such as 'aldose', 'furanose', or 'anomeric carbon'.

Be able to appropriately apply the terms epimer and animer.

Understand the hemiacetal formation mechanism of the cyclicization of glucose and why unequal amounts of the two anomers of glucopyranose are formed.

Understand how to read Fischer and Haworth projections depicting the stereochemistry of carbohydrate ring structures.

Know which monosaccharides combine to form sucrose, lactose, and maltose.

Distinguish glycogen, amylose, amylopectin, and cellulose.

Understand the structure and purpose of glycoproteins and proteoglycans.

Be able to describe how the basic mechanism of glycosidic bond formation works in the context of hemiacetal to acetal conversion.

Understand the purposes of carbohydrates as fuel, biosynthetic precursors, in cell-cell recognition, and as structural components at the tissue level.

Suggested Assignments

Practice carbohydrate terminology using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Read pp. 108-110 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).

Work carefully through the web resources for carbohydrates.

Conceptual Vocabulary for Zymogens


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.
A zymogen is an inactive precursor of an enzyme that requires cleavage for it to become an active enzyme.
Trypsinogen is the precursor form of trypsin, a digestive enzyme.
Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids.
Pepsin is expressed as a zymogen called pepsinogen, whose primary structure has an additional 44 amino acids compared to the active enzyme.
Enteropeptidase converts trypsinogen into its active form trypsin, resulting in the subsequent activation of pancreatic digestive enzymes.
Biochemical cascade
A biochemical cascade is a series of chemical reactions that occur within a biological cell in which one event triggers the next, in a linear fashion.
A single chemical reaction is said to be autocatalytic if one of the reaction products is also a catalyst for the same or a coupled reaction.
Thrombin in acts as a serine protease that converts soluble fibrinogen into insoluble strands of fibrin.
Caspases are a family of protease enzymes playing essential roles in programmed cell death.
Factor X
Factor X, also known as Stuart–Prower factor, is an enzyme of the coagulation cascade that acts by cleaving prothrombin to yield the active thrombin.
Serpins are a superfamily of proteins with protease inhibition activity, notable for their unusual mechanism of action, in which they irreversibly inhibit their target by undergoing a large conformational change to disrupt its active site.
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