Biochemistry - Carbohydrate Chemistry

Biochemistry - Carbohydrate Chemistry

• Biochemistry is the chemistry of molecules found in living organisms, such as protein, lipids, nucleic acids, and carbohydrates.
• Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols, or substances derived from them.
• Carbohydrates make up about 60% of our diet.
• They're crucial for energy production (e.g., glucose—a major energy source for brain cells and red blood cells (RBCs).
• Glycogen can be stored in muscles and liver for later energy use.
• Carbohydrates provide fibers for intestinal motility and waste elimination.
• They also form glycolipids and glycoproteins involved in cell membrane structure and tissue cohesion.
• Important sources are starchy foods (e.g., potatoes, pasta, grains), vegetables, and milk products.

Carbohydrate Classification

• Monosaccharides (glycoses): Simplest carbohydrates; cannot be hydrolyzed into simpler forms. General formula is Cₙ(H₂O)ₙ.
• Disaccharides: Composed of two monosaccharide units joined by a glycosidic bond.
• Oligosaccharides: Contain 3-10 monosaccharide units.
• Polysaccharides: Contain more than 10 monosaccharide units.

Monosaccharide Naming

• I) By Functional Group:
• Aldoses: Contain an aldehyde group.
• Ketoses: Contain a ketone group.
• II) By Carbon Number:
• Triose: 3 carbon atoms
• Tetrose: 4 carbon atoms
• Pentose: 5 carbon atoms
• Hexose: 6 carbon atoms
• Heptose: 7 carbon atoms
• III) Combining I and II: Examples include aldotrioses, ketotrioses, aldopentoses, ketopentoses, etc.

Importance of specific monosaccharides

• Ribose and Deoxyribose: Components of nucleic acids (RNA and DNA), high-energy phosphate compounds, and coenzymes (NAD, NADP, flavoproteins).
• Glucose: The most abundant monosaccharide, primary source of energy for mammals.
• Fructose (Fruit Sugar): A common ketohexose found in fruits and honey; also a significant energy source.
• Galactose: Involved in lactose synthesis (milk sugar) and brain tissue structure.
• Mannose: A constituent of various glycoproteins.

Cyclic Structures

• Monosaccharides form cyclic structures in solution due to intramolecular reactions.
• The cyclic forms are more stable than the open-chain forms.
• The cyclic forms are pyranose (6-membered ring) and furanose (5-membered ring).

Isomerism in Carbohydrates

• Optical Activity: The ability of a molecule to rotate plane-polarized light.
• Asymmetric Carbon Atoms (Chiral Centers): Carbon atoms with four different groups attached.
• Optical Isomers (Enantiomers): Non-superimposable mirror images. E.g., D- and L- glyceraldehyde.
• Specific Rotation: The angle a substance rotates plane-polarized light at a specific concentration and temperature.

Nomenclature

• D and L Configurations: Important for classifying monosaccharides based on the arrangement of hydroxyl groups.

Sugar Derivatives

• Sugar Acids: Oxidation of the carbonyl or hydroxyl group in carbohydrates can produce acidic forms.
• Sugar Alcohols: Reduction produces alcohol forms.
• Deoxysugars: Replacement of a hydroxyl group with a hydrogen atom.
• Amino Sugars: sugars featuring amino groups .
• Synthesis of carbohydrates in the body: Glucuronic acid conjugation with insoluble molecules makes them soluble in water for detoxification purposes.

Glycosidic Bonds

• Glycosidic Bond: A bond between carbohydrates and other molecules, or another carbohydrate (e.g., to make disaccharides).
• O-glycosides: The bond to another sugar or aglycone (non-carbohydrate component) via an oxygen atom.
• N-glycosides: The bond is to an amino group of the aglycone.
• Naming Glycosidic bonds: Based on the position of involved carbon atoms and configuration of involved anomers.

Disaccharides

• Maltose: Glucose + Glucose (α(1→4) linkage).

• Isomaltose: Glucose + Glucose (α(1→6) linkage).

• Lactose: Galactose + Glucose (β(1→4) linkage).

• Sucrose: Glucose + Fructose (α(1→2) linkage).

• Cellobiose: Glucose + Glucose (β(1→4) linkage).

• Trehalose: Glucose + Glucose (α(1→1) linkage).

• Invert Sugar: A mixture of glucose and fructose resulting from sucrose hydrolysis.

Polysaccharides

• Starch: A storage polysaccharide in plants; a mixture of amylose (unbranched) and amylopectin (branched).
• Glycogen: An animal storage polysaccharide; highly branched, more compact than amylopectin.
• Cellulose: The structural component of plant cell walls (β(1→4) glycosidic linkage).
• Inulin: A fructosan found in plant roots, important for medical diagnosis.
• Dextrans: Microbial polysaccharides, used as plasma substitutes.

Other important features

• GAGs (Glycosaminoglycans): Essential components of connective tissues.
• Proteoglycans: GAGs attached to proteins, play crucial roles in tissue support, lubrication, and cell signaling.
• Glycoproteins: Proteins with covalently attached carbohydrates, involved in various cellular functions like cell-cell recognition, signaling, and structure.
• Fibronectin: Important for cell adhesion, growth, and migration.
• Laminin: Essential for basement membrane formation and cell-matrix interactions.