Introduction to Biochemistry: Elements, Macromolecules, and Their Biological Roles

Defining Biochemistry

Interdisciplinary Nature of Biochemistry

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

• Biochemistry connects with fields such as Organic Chemistry, Physical Chemistry, Biophysics, Medical Science, Cell Biology, Microbiology, Genetics, Physiology, and Nutrition.

• This interdisciplinary approach allows for a comprehensive understanding of biological systems at the molecular level.

Chemical Elements of Cells and Organisms

Essential Elements for Life

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

• Major elements: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N) are the most abundant elements in living organisms.

• Other essential elements: Sulfur (S), Phosphorus (P), and certain ions such as Na+, K+, Mg2+, Ca2+, and Cl- are also vital for life.

• These elements participate in a variety of biochemical processes, including enzyme catalysis, structural support, and signaling.

Periodic Table and Biochemistry

The periodic table highlights elements of particular importance to biochemistry, categorized by their abundance and biological roles.

• 1st tier (most abundant): H, C, N, O, P, S

• 2nd tier: Na, Mg, K, Ca, Cl

• 3rd and 4th tiers: Trace elements such as Fe, Zn, Cu, Mn, Co, Mo, Se, I, etc., are required in smaller amounts but are essential for specific biochemical functions.

• Iodine is necessary for thyroid hormone synthesis; deficiency can lead to goiter (thyroid disease).

Tier	Elements	Biological Role
1st	H, C, N, O, P, S	Major components of biomolecules
2nd	Na, Mg, K, Ca, Cl	Ions for signaling, structure, and catalysis
3rd/4th	Fe, Zn, Cu, Mn, Co, Mo, Se, I	Cofactors, hormones, trace functions

Biological Macromolecules

Major Classes of Macromolecules

Biological macromolecules are large, complex molecules essential for the structure and function of living organisms. They are typically polymers made from smaller subunits.

• Nucleic acids (DNA and RNA): Store and transmit genetic information.

• Proteins: Perform a wide range of functions, including catalysis (enzymes), structure, transport, and signaling.

• Polysaccharides: Serve as energy storage (e.g., glycogen, starch) and structural components (e.g., cellulose).

• Lipids: Function as energy storage, membrane components, and signaling molecules. Unlike the other classes, most lipids are not true polymers.

Monomeric Components and Linkages

Each class of macromolecule is composed of characteristic monomers joined by specific covalent linkages.

Macromolecule	Monomer	Linkage
Nucleic acids	Nucleotide	Phosphodiester
Protein	Amino acid	Peptide (amide)
Polysaccharide	Monosaccharide	Glycoside (ether)
Lipids (triacylglycerols)	Fatty acids	Ester

• Polymers are formed by repeated linkage of monomers (e.g., proteins from amino acids).

• Lipids are not true polymers but are assembled from smaller hydrophobic units.

Examples of Biological Polymers

Biological polymers are long chains of repeating monomeric units, each with unique properties and functions.

• Nucleic acids: DNA and RNA are polymers of nucleotides, linked by phosphodiester bonds. They encode genetic information.

• Proteins: Polypeptides are polymers of 20 different amino acids, joined by peptide bonds. The sequence of amino acids determines protein structure and function.

• Polysaccharides: Polymers of monosaccharides (e.g., glucose) joined by glycosidic bonds. Examples include cellulose, starch, and glycogen.

Example: Peptide Bond Formation

Peptide bonds form between the carboxyl group of one amino acid and the amino group of another, releasing water:

$\text{Amino acid}_1 + \text{Amino acid}_2 \rightarrow \text{Dipeptide} + H_2O$

Example: Phosphodiester Bond in Nucleic Acids

Phosphodiester bonds link the 3' hydroxyl group of one nucleotide to the 5' phosphate of the next:

$\text{Nucleotide}_1 + \text{Nucleotide}_2 \rightarrow \text{Dinucleotide} + H_2O$

Additional info: The structure and function of these macromolecules are determined by the sequence and chemical properties of their monomeric units.