Biochemistry Course Notes

Assessment Types:
- Quizzes
- Tests
- Group Presentations
- Non-Group Presentations
- Practicals
- Assignments
- Final Exam (Paper 1 and Paper 2)
MCQ Paper: There is negative marking associated with multiple-choice questions.

Textbook of Biochemistry with Clinical Correlations (7th Edition, 2010) by T. Devlin, Wiley and Sons.
Functional Biochemistry in Health and Disease by Newsholme, E.A & Leech, T. R. (2010) Wiley and Blackwell, Chichester, UK.
Biochemistry for the Medical Sciences by Newsholme, E.A. & Leech, A.R. (1983) John Wiley & Sons, Chichester.
Principles of Biochemistry, International Student Version (4th Edition, 2012) by Voet, D., Voet, J.G. & Pratt, C.W. John Wiley & Sons, Inc., New York.
Molecular Biology of the Cell (4th Edition, 2002) by Alberts, B., Johnson, Lewis, J., Raff, M., Roberts, K. & Walter, P. Garland Science, New York.
Harper's Illustrated Biochemistry (31st Edition, 2018) by V.W. Rodwell, D. Bender, K.M. Botham, P.J. Kennelly, P.A. Weil. Publisher: McGraw-Hill Education / Medical.
The Science of Genetics (6th Edition, 1989) by Burns, G.W. and Bottino, P.J., Macmillan Publishing, New York and London.

Note: Always utilize the latest published editions, with up-to-date information found in journal articles, e-books, and academic websites like PubMed.

Definition: Large molecules called biomolecules exist in the body, which are vital for biochemical processes.
Classes of Biomolecules:
- Carbohydrates
- Proteins
- Lipids
- Nucleic Acids

Distribution and Roles:
- Carbohydrates are found extensively in both plants and animals and play critical structural and metabolic roles.
- Glucose: The most significant carbohydrate, serving as the primary metabolic fuel for mammals (excluding ruminants) and a universal fuel for fetuses.
Associated Diseases:
- Diabetes Mellitus
- Galactosemia
- Glycogen Storage Diseases
- Lactose Intolerance

Definition: Carbohydrates are hydrates of carbon, consisting of molecules that typically contain several carbon atoms, each bonded to hydrogen and a hydroxyl group.

Common names of carbohydrates end in “-ose”, e.g. Glucose, Sucrose (commonly referred to simply as sugar).

Monosaccharides:
- Monomeric units that polymerize to form polysaccharides.
- General formula is $C<em>n(H</em>2O)_n$ .
Classification by Carbon Count:
- Triose: 3 Carbons
- Tetrose: 4 Carbons
- Pentose: 5 Carbons
- Hexose: 6 Carbons

Carbohydrates possess either an aldehyde or ketone functional group, distinguishing them as aldoses or ketoses.
Example Classification:
- Aldohexose (6 carbons with an aldehyde)
- Ketopentose (5 carbons with a ketone)

Carbons that bear both hydrogen and hydroxyl groups are considered chiral centres.
All carbohydrates will feature at least one chiral centre in their structure.

Definition: A method for visualizing linear monosaccharides.
Characteristics:
- Each vertex represents a stereogenic carbon.
- Horizontal lines imply wedge bonds (projecting forwards), while vertical lines imply dash bonds (projecting backwards).
Importance: Fischer projections help understand stereochemistry without depicting bond angles, where the molecule remains tetrahedral.

When representing linear monosaccharides:
- The aldehyde or ketone group is located at the top.
- The stereochemistry is determined by examining the chiral centre that is furthest from the carbonyl group:
- D-sugar: Hydroxyl on the right.
- L-sugar: Hydroxyl on the left.
Nature predominantly utilizes D sugars.

A molecule with n chiral centres has $2^n$ possible stereoisomers.
Example: There are 2 aldotrioses due to 1 chiral centre and 16 aldohexoses due to 4 chiral centres.

Diastereomers: Stereoisomers differing in configuration at one chiral centre are termed epimers.
The presence of asymmetric carbon impart optical activity, rotating plane-polarized light either to the right (dextrorotatory, +) or to the left (levorotatory, -).

Monosaccharides exist in equilibrium between linear and cyclic forms, with cyclic forms (due to intramolecular hemiacetal formation) being more stable.
Mechanism: An alcohol attacks an aldehyde or ketone, generating a stable cyclic structure.

Definition: Anomers are different forms of a cyclic monosaccharide that differ at the anomeric carbon due to the direction of the hydroxyl group’s attack on the carbonyl.
- Alpha Anomer: Hydroxyl group is down.
- Beta Anomer: Hydroxyl group is up.

Usage: Haworth projections visualize cyclic monosaccharides by looking at the ring's edge, allowing depiction of group orientations.
Anomeric carbon is conventionally placed on the right side of the ring.
- Pyranose: Six-membered cyclic sugar.
- Furanose: Five-membered cyclic sugar.
- Characteristics of cyclic monosaccharides include reversible equilibrium between alpha and beta forms due to hemiacetal formation.

Glycosidic bonds form when a hydroxyl group from one monosaccharide reacts with acetal, leading to disaccharide formation when another monosaccharide is involved.
Disaccharides Examples:
- Lactose: (β-D-galactose + α-D-glucose)
- Sucrose: (α-D-glucose + β-D-fructose)

Reducing sugars have a hemiacetal form enabling them to act as reducing agents through a ring-opened configuration. They react with specific metal salts (e.g., Cu²+, Ag⁺). Examples include glucose, fructose, lactose.
Non-reducing sugars do not undergo such reactions. Sucrose is classified as a non-reducing sugar due to the lack of free reducing groups.

Definition: Oligosaccharides consist of 3-10 monosaccharide units and typically do not exist freely in humans, mainly found as glycoproteins and glycolipids.
Examples in Plants:
- Raffinose (in beans, cabbage)
- Stachyose (in vegetables)
- Verbascose (in legumes)
Oligosaccharides can cause flatulence when fermented in the intestinal tract.