Biochemistry Fundamentals: Carbohydrates, Water, and pH Balance

Stereoisomerism and Carbohydrate Structure

Asymmetric carbons occur when a radical is attached to four different groups, leading to stereoisomerism. Isomers are compounds with the same molecular formula but different chemical properties.

Monosaccharides and Cyclic Structures

Haworth projections represent monosaccharides where each carbon radical is positioned at the top or bottom of the plane. The ring is formed by a covalent bond joining an alcohol group with an aldehyde or ketone.

• Anomeric Carbon: A new asymmetric carbon that appears in monosaccharides when forming cyclic structures from aldehyde or ketone groups.
• Mutarotation: The change in the rotation values of plane-polarized light during the transition from one anomer to another.
• Fehling's Test: Used to determine if a sugar has reducing power. Reducing sugars produce a reddish tinge due to the formation of cuprous oxide through the oxidation of the sugar by the Cu+2 cation.

Classification of Polysaccharides

• Homopolysaccharides: Starch, glycogen, and amylose.
• Heteropolysaccharides: Agar-agar, vegetable gums, and mucopolysaccharides.

Properties of Water

Water exhibits high boiling and fusion points, allowing it to remain in a liquid state within the temperature ranges typically found on Earth, which facilitates the existence of life.

Thermal and Molecular Characteristics

• Specific Heat and Heat of Vaporization: These are high, giving water a buffer effect against temperature changes in the environment surrounding a cell.
• Hydrogen Bonds: Water molecules interact via electrostatic attraction. These bonds hold molecules together, allowing the surface of water to resist breaking.

pH, Acids, and Buffers

Water undergoes dissociation with a specific equilibrium constant known as the ion product of water (Kw): Kw = [H3O+] [OH-] = 1.0x10^-14.

Strong and Weak Acids

• Strong Acids/Bases: Inorganic molecules like HCl that dissociate 100% in water. Their pH can be calculated directly from the ion product of water.
• Weak Acids/Bases: Compounds like H3PO4, where the dissociation constant (Ka) is calculated like any other equilibrium.
• Buffers (Tampons): Mixtures of a weak acid and its conjugate base that resist changes in pH within a specific range. Examples include the acetate system (CH3COO-) and physiological systems like respiratory acidosis and metabolic alkalosis.