Ch. 1 Introduction to Biochemistry

Atoms and Elements in Biological Systems

Biochemistry studies the chemical processes within living organisms, focusing on the atoms and molecules that compose life. The most abundant elements in biological systems are oxygen, hydrogen, and carbon, which together make up approximately 98% of the atoms in organisms.

• Silicon vs. Carbon: While silicon and oxygen form hard, crystalline minerals like quartz, carbon is favored in biological systems due to the strength and stability of carbon-carbon (C–C) bonds.

• Trace Elements: Nitrogen, phosphorus, and sulfur are important trace elements essential for various biological functions.

• Biological Fuels: Composed of carbon, hydrogen, and oxygen, these molecules undergo combustion to release energy.

Example: Glucose (C6H12O6) is a primary biological fuel.

Biomolecules: Types and Functions

Living organisms are built from four major classes of biomolecules: proteins, nucleic acids, lipids, and carbohydrates. Each class has distinct structures and functions.

• Proteins: Polymers of amino acids linked by peptide bonds. They perform structural, catalytic, and regulatory roles.

• Nucleic Acids: Polymers of nucleotides. DNA and RNA store and transfer genetic information. DNA is double-stranded, held together by hydrogen bonds (A–T, G–C), while RNA is typically single-stranded and broken down after use.

• Lipids: Hydrophobic molecules used for energy storage and structural purposes. They are not polymers and are smaller than proteins or nucleic acids. Lipids have hydrophobic tails and hydrophilic heads, allowing them to form barriers such as membranes. Lipids are the most diverse biomolecule class.

• Carbohydrates: Polymers of monosaccharides. They serve as fuel and are involved in cell recognition. Glucose is stored as starch in plants and glycogen in animals (glycogen is a highly branched polymer).

Example: Ribonucleotides (RNA building blocks) have uracil and adenine, and their sugar component contains an additional hydroxyl (-OH) group compared to DNA.

The Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information in cells: DNA is replicated, transcribed into RNA, and translated into protein.

• Replication: DNA is copied to produce identical DNA molecules.

• Transcription: DNA is used as a template to synthesize RNA. This process is catalyzed by RNA polymerase, which unwinds the DNA double helix and joins ribonucleotides to form a complementary RNA strand.

• Translation: RNA is used as a template to synthesize proteins.

Equation:

Cellular Structures and Organelles

Cells contain specialized structures (organelles) that perform distinct functions necessary for life.

• Nucleus: Contains genetic material and is the site of transcription.

• Mitochondria: Site of cellular respiration and ATP production.

• Chloroplasts: Site of photosynthesis in plant cells.

• Cytoskeleton: Composed of tubules and filaments, provides structural support.

• Rough Endoplasmic Reticulum (ER): Synthesizes proteins; contains chaperone proteins that assist in protein folding.

• Smooth ER: Synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids into their final 3D structure.

• Secretory Granules: Store and release cellular products via exocytosis.

• Endosomes: Involved in intracellular transport.

• Lysosomes: Break down macromolecules.

• Plant Vacuoles: Store water, ions, and nutrients.

• Ribosomes: Translate mRNA into proteins; composed of protein and RNA.

Membranes and Lipid Bilayers

Cell membranes are composed of lipid bilayers, which create barriers and compartmentalize cellular functions.

• Lipid Bilayer: Consists of two layers of lipids with hydrophobic tails facing inward and hydrophilic heads facing outward.

• Function: Separates cellular compartments and regulates transport.

Summary Table: Major Biomolecules

Additional info: Table entries expanded for clarity and completeness.