Foundations of Biochemistry: Elements, Macromolecules, Water, and pH

Defining Biochemistry

Biochemistry as an Interdisciplinary Science

Biochemistry is the study of the chemical processes and substances that occur within living organisms. It integrates principles from various scientific disciplines to understand life at the molecular level.

• Related Fields: Organic Chemistry, Physical Chemistry, Nutrition, Biophysics, Physiology, Medical Science, Genetics, Cell Biology, Microbiology.

• Application: Biochemistry is foundational for medical science, genetics, and cell biology, providing molecular explanations for physiological and pathological processes.

Chemical Elements of Cells and Organisms

Essential Elements for Life

Living systems are primarily composed of a select group of chemical elements, which are crucial for the structure and function of biomolecules.

• Major Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N)

• Minor but Essential Elements: Sulfur (S), Phosphorus (P), and ions such as Na+, K+, Mg2+, Ca2+

• Role of Iodine: Iodine is necessary for thyroid function; deficiency can cause goiter.

Periodic Table in Biochemistry

Certain elements are more abundant and biologically relevant. The periodic table can be tiered by abundance and function in living organisms.

Tier	Elements	Role
1st (Most Abundant)	C, H, O, N	Structural and functional components of biomolecules
2nd	P, S, Na, K, Mg, Ca	Enzyme cofactors, signaling, structural roles
3rd	Fe, Cu, Zn, Mn, Co, Mo, Se, I	Trace elements, enzyme activity, hormone synthesis
4th	Other elements	Specialized functions

Biological Macromolecules

Major Classes and Their Building Blocks

Biological macromolecules are large, complex molecules essential for life. They are constructed from smaller subunits called monomers.

• Nucleic Acids: DNA and RNA, made of nucleotide monomers

• Proteins: Made of amino acid monomers

• Polysaccharides: Made of monosaccharide (sugar) monomers

• Lipids: Composed of fatty acids and glycerol; not true polymers but form large complexes

Monomers and Linkages

Each macromolecule is formed by specific linkages between its monomers.

Macromolecule	Monomer	Linkage
Nucleic acids	Nucleotide	Phosphodiester
Proteins	Amino acid	Peptide (amide)
Polysaccharides	Monosaccharide	Glycosidic (ether)
Lipids (triacylglycerols)	Fatty acids	Ester

Nucleic Acids

Nucleic acids store and transmit genetic information. Their structure is based on nucleotide monomers linked by phosphodiester bonds.

• Phosphodiester Bond: Connects the 3' hydroxyl group of one nucleotide to the 5' phosphate group of the next.

• DNA Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

• RNA Bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

Proteins

Proteins are polymers of amino acids joined by peptide bonds. They perform structural, catalytic, and regulatory functions.

• Peptide Bond: Formed between the carboxyl group of one amino acid and the amino group of another ($ext{C-N}$ linkage)

• Example: Tyrosine is one of the 20 standard amino acids found in proteins.

Polysaccharides

Polysaccharides are long chains of monosaccharides linked by glycosidic bonds. They serve as energy storage and structural materials.

• Glycosidic (Ether) Bond: Oxygen bridge connecting two monosaccharides, e.g., between C1 of one glucose and C4 of another ($eta$-1,4-glycosidic bond)

• Example: Cellulose and starch are polysaccharides made of glucose units.

Lipids

Lipids are hydrophobic molecules that form membranes and store energy. Triglycerides and phospholipids are key types.

• Triglycerides: Three fatty acids esterified to glycerol

• Phospholipids: Glycerol backbone, two fatty acids, and a phosphate group; major component of cell membranes

• Cholesterol: Steroid lipid, important for membrane fluidity

Saturated vs. Unsaturated Fatty Acids

• Saturated: No double bonds, straight chains, solid at room temperature

• Unsaturated: One or more double bonds, kinked chains, liquid at room temperature

Structure and Properties of Water

Unique Properties of Water

Water is the universal solvent in biological systems due to its molecular structure and ability to form hydrogen bonds.

• Hydrogen Bond Donors and Acceptors: Water has two H-bond donor sites and two acceptor sites

• Permanently Polar: Water has a permanent dipole moment

• High Heat Capacity: Absorbs and retains heat efficiently

• Density: Liquid water is denser than ice

• High Dielectric Constant: Facilitates dissolution of ionic compounds

Water as a Molecular Lattice

Water molecules form a dynamic lattice through hydrogen bonding, which is responsible for its unique physical properties.

• Solid (Ice): Rigid lattice, cohesive hydrogen bonds

• Liquid: Dynamic, transient hydrogen bonds

Amphipathic Molecules in Aqueous Solution

Behavior of Amphipathic Molecules

Amphipathic molecules contain both hydrophilic and hydrophobic regions, allowing them to form structures such as micelles and bilayers in water.

• Monolayer: Single layer at air-water interface

• Micelle: Spherical structure with hydrophobic core

• Bilayer: Double layer, basis of biological membranes

• Phospholipid Bilayer: Primary component of cell membranes

Acids and Bases: Proton Donors and Acceptors

Brønsted-Lowry Definition

Acids and bases play a critical role in biochemical reactions, especially in aqueous environments.

• Acid: Proton donor

• Base: Proton acceptor

• Strong Acid: Dissociates almost completely

• Weak Acid: Dissociates partially

• Hydronium Ion: $H_3O^+$ is formed when a proton is transferred to water

The pH Scale and Physiological pH Range

Definition and Calculation of pH

pH is a measure of hydrogen ion concentration, crucial for maintaining homeostasis in biological systems.

• Formula: $pH = - ext{log} [H^+ ]$

• Acidic Solution: Low pH, high $[H^+]$

• Basic Solution: High pH, low $[H^+]$

• Physiological pH Range: Most biological reactions occur between pH 6.5 and 8.0

pH and Molecular Charge

The charge of biomolecules depends on the pH of the environment, affecting their interactions and functions.

• Low pH: Molecules tend to be more positively charged

• High pH: Molecules tend to be more negatively charged

• Example: The surface charge of proteins changes with pH, influencing solubility and activity

Summary Table: Macromolecules, Monomers, and Linkages

Macromolecule	Monomer	Linkage Type	Example
Nucleic Acid	Nucleotide	Phosphodiester	DNA, RNA
Protein	Amino Acid	Peptide (Amide)	Enzymes, Hemoglobin
Polysaccharide	Monosaccharide	Glycosidic (Ether)	Starch, Cellulose
Lipid	Fatty Acid + Glycerol	Ester	Triglyceride, Phospholipid

Key Equations

• pH Calculation: $pH = - ext{log} [H^+ ]$

• Relationship between pH and $[H^+]$: As pH increases, $[H^+]$ decreases; as pH decreases, $[H^+]$ increases.

Additional info:

• Some handwritten notes and diagrams were interpreted and expanded for clarity.

• Examples and chemical structures were described in text for completeness.