Introduction to Biochemistry: Foundations, Macromolecules, and the Cell

Introduction to Biochemistry

Definition and Scope

Biochemistry is the branch of science that explores the chemical processes and substances that occur within living organisms. It uses the principles and language of chemistry to explain biological phenomena and is essential for understanding the molecular basis of life, including protein function, metabolism, and genetic information transfer.

• Biochemistry impacts personal health, medicine, genetics, biotechnology, and the global environment.

• It bridges the gap between biology and chemistry by focusing on the molecular mechanisms underlying biological processes.

History of Biochemistry

Key Milestones

The development of biochemistry as a scientific discipline has been marked by several important discoveries and breakthroughs:

• Early Foundations (1800s): Advances in basic chemical principles, reaction kinetics, and molecular composition laid the groundwork for biochemistry.

• Friedrich Wöhler (1828): Synthesized urea from ammonium cyanate, demonstrating that organic compounds could be made from inorganic substances. This experiment marked the birth of modern organic biochemistry.

• Enzyme Catalysis (Late 19th Century): Eduard Buchner (1897) showed that cell extracts could catalyze fermentation, proving that enzymes (not just living cells) are responsible for biological reactions.

• Enzyme Specificity: Emil Fischer proposed that only molecules with a suitable structure can serve as substrates for a given enzyme, introducing the concept of enzyme-substrate specificity.

• Nucleic Acids as Genetic Material: Avery, MacLeod, and McCarty (1944) provided the first conclusive evidence that DNA is the genetic material by transforming non-pathogenic bacteria into pathogenic forms using purified DNA.

• Structure of DNA: Watson and Crick (1953) described the three-dimensional double helix structure of DNA, leading to the central dogma of molecular biology: genetic information flows from DNA to RNA to protein.

Central Dogma of Molecular Biology:

• Information encoded in DNA is transcribed to RNA and then translated into protein.

Key Terms and Concepts in Biochemistry

Chemical Elements of Life

Six nonmetallic elements account for more than 97% of the weight of most organisms:

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Oxygen (O)

• Phosphorus (P)

• Sulfur (S)

Water is the major component of cells, accounting for the high percentage of oxygen.

Organic and Biochemical Compounds

• Organic compounds: Carbon-containing compounds, studied in organic chemistry.

• Biochemical compounds: Organic compounds specifically found in living cells.

• These compounds contain functional groups (specific groups of atoms responsible for characteristic chemical reactions) and linkages (bonds joining atoms or molecules).

Common Functional Groups and Linkages

Functional groups are specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules. Linkages are bonds that join atoms or molecules together, forming larger biological structures called macromolecules.

Functional Group Name	Structure
Alcohol	R-OH
Aldehyde	R-CHO
Ketone	R-COR'
Carboxylic Acid	R-COOH
Ester	R-COO-R'
Amine	R-NH2
Amide	R-CO-NH2
Sulfhydryl	R-SH

Common Linkages:

• Ester and Ether linkages: Common in lipids.

• Peptide (amide) linkages: Found in proteins.

• Glycosidic bonds: Formed in carbohydrates.

• Phosphate ester and phosphoanhydride linkages: Occur in nucleotides.

Macromolecules

Definition and Types

Macromolecules are very large molecules made up of smaller organic molecules called monomers. They are typically polymeric, meaning they are composed of long chains of monomers joined by condensation reactions (removal of water).

• Properties of polymers are often very different from their constituent monomers (e.g., glucose vs. starch).

• The four major types of biological macromolecules are: proteins, carbohydrates, nucleic acids, and lipids.

Proteins

Proteins are polymers of amino acids and serve as enzymes, structural components, and signaling molecules.

• Amino acids: The building blocks of proteins; 20 common types, each with an amino group, carboxyl group, and unique side chain (R group).

• Peptide bond: The linkage between the carboxyl group of one amino acid and the amino group of the next, forming a polypeptide chain.

• Protein structure:

  • Primary structure: Amino acid sequence.

  • Secondary structure: Alpha-helices and beta-sheets.

  • Tertiary structure: 3D folding of a single polypeptide.

  • Quaternary structure: Assembly of multiple polypeptide chains.

• Proper folding is essential for protein function; misfolding can lead to disease.

Carbohydrates

Carbohydrates (saccharides) are composed of carbon, hydrogen, and oxygen. They include simple sugars (monosaccharides) and their polymers (polysaccharides).

• Monosaccharides: Simple sugars, such as glucose (six carbons) and ribose (five carbons).

• Polysaccharides: Polymers of monosaccharides (e.g., starch, cellulose).

• Monosaccharides and polysaccharides have several hydroxyl groups, making them polyalcohols.

• Representations:

  • Fischer projection: Linear, 2D representation.

  • Haworth projection: Cyclic, 3D representation (more accurate for ring forms).

Nucleic Acids

Nucleic acids (DNA and RNA) are polymers of nucleotides and store and transmit genetic information.

• Nucleotide: Consists of a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and at least one phosphate group.

• Nitrogenous bases:

  • Purines: Adenine (A), Guanine (G)

  • Pyrimidines: Cytosine (C), Thymine (T, in DNA), Uracil (U, in RNA)

• DNA contains A, G, C, T; RNA contains A, G, C, U.

• Nucleotides are joined by phosphodiester bonds to form polynucleotide chains.

Lipids

Lipids are a diverse group of hydrophobic molecules, including fats, oils, and phospholipids.

• Phospholipids: The most abundant lipid in biological membranes; have a polar hydrophilic head and nonpolar hydrophobic tails.

• In water, phospholipids form bilayers with hydrophobic tails inward and hydrophilic heads outward, creating the structural basis of cell membranes.

• Lipid bilayers are flexible, self-sealing, and provide a platform for membrane proteins involved in transport, signaling, and cell adhesion.

The Cell: The Basic Unit of Life

Cell Structure and Classification

All living organisms are composed of cells, which vary in size and shape. Cells are classified as either prokaryotic or eukaryotic.

• Cell membrane: Flexible, self-sealing barrier that controls the movement of substances in and out of the cell.

• Cytoplasm: Contains the nucleus (in eukaryotes), organelles, and the cytosol (aqueous portion).

Types of Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Organelles	Absent	Present
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists
Genome	Small, circular DNA	Large, linear DNA

• Prokaryotic cells: Single-celled, lack a true nucleus and organelles. DNA is found in the nucleoid. Example: Escherichia coli.

• Eukaryotic cells: Have a nucleus and organelles. Include plants, animals, fungi, and protists.

• Viruses: Not true cells; subcellular infectious particles that require host cells to replicate.

Summary Table: Macromolecules and Their Monomers

Macromolecule	Monomer	Main Function
Proteins	Amino acids	Enzymes, structure, signaling
Carbohydrates	Monosaccharides	Energy storage, structure
Nucleic Acids	Nucleotides	Genetic information storage and transfer
Lipids	Fatty acids, glycerol	Membrane structure, energy storage

Practice Questions

• Which scientist synthesized urea from ammonium cyanate, demonstrating that organic compounds could be made from inorganic substances? Answer: Friedrich Wöhler

• Which scientist proposed that only a molecule with a suitable structure can serve as a substrate for a given enzyme? Answer: Emil Fischer

• What is the key structural difference between prokaryotic and eukaryotic cells? Answer: Eukaryotic cells have a nucleus; prokaryotic cells do not.

Additional info: Some explanations and table entries have been expanded for clarity and completeness based on standard academic knowledge in general biology and biochemistry.