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Introduction to carbohydrates by Assoc. Prof. Dr. Wu Yuan Seng (yuansengw@sunway.edu.my)

Lecture Schedule

Week 1: Public Holiday (Labor Day) - 1 May 2025
Week 2: Lecture 1: Introduction to Biochemistry and Basic Units of Biomolecules - 8 May 2025
Week 3: Lecture 2: Chemical Bonds - 15 May 2025
Week 4: Lecture 3: Water and Its Properties - 22 May 2025
Week 5: Lecture 4: Amino Acids, Peptides, and Protein - 29 May 2025
Week 6: Lecture 5: Introduction to Enzymes - 5 June 2025
Week 7: Lecture 6: Introduction to Carbohydrates - 12 June 2025
Week 8: Lecture 7: Monosaccharides and Disaccharides Metabolism - 26 June 2025
Week 9: Lecture 8: Nucleotide Metabolism I & II - 3 July 2025
Week 10: Lecture 9: Nucleotide Metabolism III - 10 July 2025
Week 11: Lecture 10: Protein Synthesis - 17 July 2025
Week 12: Lecture 11: Lipids, Function, and Digestion - 24 July 2025
Week 13: Revision Week - TBC
Week 14: Revision Week - TBC

Tutorials and Practical Schedule

Tutorials

Week 4: Lecture 1 - 2: 19 May, 21 May, 22 May, 23 May
Week 6: Lecture 3 - 4: 29 May, 30 May
Week 6: Lecture 3 - 4: 23 June, 25 June
Week 10: Lecture 5 - 7: 30 June, 2 July, 3 July, 4 July
Week 11: Lecture 8 - 9: 7 July, 9 July, 10 July, 11 July
Week 13: Lecture 10: 21 July, 23 July, 24 July, 25 July
Week 14: Lecture 11: 28 July, 30 July, 31 July, 1 August

Practicals

Week 4: Standard Curve Derivation from Bradford Assay and Estimation of Protein Quantitation: 19 May, 20 May, 21 May
Week 7: Titration Curves of Acetic Acid and Citric Acid Using pH Meter: 9 June, 10 June, 11 June
Week 9: Effect of pH, Temperature, and Substrate Concentrations on Enzymatic Activity: 30 June, 1 July, 2 July
Week 11: Detection of Carbohydrates Using Molisch’s Test, Barfoed’s Test, and Iodine Test: 14 July, 15 July, 16 July

Learning Outcomes

Upon completion of this topic, students will be able to:

Define carbohydrates and state their functions.
Classify carbohydrates with suitable examples.
State important properties of carbohydrates.
Describe glycosidic bonds and their nomenclature.

Carbohydrates and Their Functions

Carbohydrates are the most abundant organic molecules in nature, also known as saccharides.
Composed of carbon (C), hydrogen (H), and oxygen (O) atoms, with a C-H-O ratio of 1:2:1.
Empirical formula: (CH₂O)_n, where n ≥ 3.

Biological Functions

Provide a significant fraction of dietary calories (4 calories per gram).
Serve as a storage form of energy, primarily as glycogen in the liver and muscles.
Contribute to cell membrane components, facilitating intercellular communications (e.g., glycoproteins and glycolipids).
Act as structural components in various organisms, such as cell walls of bacteria, exoskeletons in insects, and fibrous cellulose in plants.

Classification of Carbohydrates

Monosaccharides: Simple sugars that cannot be hydrolyzed into simpler carbohydrates (e.g., glucose, galactose, fructose).
Disaccharides: Formed by the condensation of two monosaccharide units (e.g., lactose, sucrose, maltose).
Oligosaccharides: Condensation products of 3-10 monosaccharide units.
Polysaccharides: Condensation products of more than 10 monosaccharide units (e.g., dextrins, starch, cellulose, glycogen).

Monosaccharides Classification

Monosaccharides are classified based on:

Number of carbon atoms.
Type of carbonyl group (C=O):
- Aldoses: Carbonyl group is an aldehyde (-CHO).
- Ketoses: Carbonyl group is a keto group (-CO).

Aldoses with a free carbonyl group use the suffix “-ose,” while ketoses include an additional “ul” in their suffix (e.g., xyulose).

Monosaccharides - Structure

Monosaccharides can be linked by glycosidic bonds to form larger structures.

Importance of Glucose

Glucose is the most significant carbohydrate due to:
- Most dietary carbohydrates are absorbed in the bloodstream as glucose.
- Other sugars are converted to glucose in the liver.
- It serves as the major metabolic fuel for mammals.

Disaccharides

Formed by two monosaccharide units linked by a glycosidic bond.
Key physiological disaccharides include maltose, sucrose, and lactose.
Hydrolysis of sucrose yields glucose and fructose, known as “invert sugar.”

Physiologically Important Polysaccharides

Starch (plant sources).
Cellulose (plant sources).
Glycogen (animal sources).
Inulin.
Dextrins.
Chitin.
Glycosaminoglycans.
Proteoglycans.
Glycoproteins.

These polysaccharides serve both storage and structural functions.

Starch

Starch consists of:

A linear polymer of maltose units (α(1→4) bond) arranged in a helical structure.
A highly branched polymer with branches of repeating maltose units joined via isomaltose linkages (α(1→6) bond occurring every 24-30 glucose units).
It is a mixture of amylose (13-20%) and amylopectin (80-85%).

Glycogen

Similar to amylopectin but with more branches and shorter chains (occurring every 8-12 glucose units).

Cellulose

Chief constituent of plant cell walls.
A linear polymer of repeating cellobioses linked by β(1→4) bonds.

Inulin

A polysaccharide of fructose, found in tubers and roots of dahlias, artichokes, and dandelions.
Readily soluble in water and used to determine glomerular filtration rate but indigestible by intestinal enzymes.

Dextrins

Intermediates in the hydrolysis of starch.

Chitin

A structural polysaccharide found in the exoskeleton of crustaceans, insects, and mushrooms.

Glycosaminoglycans

A complex carbohydrate containing amino sugars and uronic acids, also known as mucopolysaccharides.
May attach to a protein molecule, forming proteoglycans.

Glycoproteins

Proteins that contain branched and unbranched oligosaccharide chains, found in cell membranes.

Other Carbohydrates in Cell Membrane

Approximately 5% of the weight of the cell membrane is carbohydrate, primarily in glycoproteins and glycolipids.

Proteoglycans

Provide the ground or packing substance of connective tissue, holding large quantities of water and providing cushioning and lubrication.

References

Emine Ercikan, Abali; Susan D. Cline; David S. Franklin; Susan M. Viselli. (2022). Lippincott® Illustrated Reviews: Biochemistry, 8th ed. Wolters Kluwer. Pages 256-263.
Murray, R. K., Bender, D. A., Botham, K. M., Rodwell, V. W., and Weil, P. A. (2018). Harper’s Illustrated Biochemistry (31st Edition), McGraw-Hill, New York, United States. Pages 363-381.

Comprehensive Guide to Carbohydrates in Biochemistry

Comprehensive Guide to Carbohydrates in Biochemistry