GENERAL BIOLOGY I

Part I: Biological Molecules

Major Types of Biomolecules

  • The four major types of biomolecules:

    • Carbohydrates

    • Lipids

    • Nucleic acids

    • Proteins

PROTEINS

  • Definition and Importance:

    • Recognized in the early 19th century.

    • Coined by Swedish chemist Jons Jacob Berzelius in 1838, deriving from Greek "prōteios" meaning "holding first place."

    • Proteins are major structural elements of cells.

    • Serve as transporters, enzymes, and catalysts.

  • Characteristics:

    • Highly complex substances present in all living organisms.

    • Composed of approximately 20 different naturally occurring amino acids.

  • Protein Content in Organisms:

    • Muscles: ~30% protein

    • Liver: 20-30% protein

    • Red blood cells: ~30% protein

    • Higher concentrations in hair, bones, and other low-water organs and tissues.

CARBOHYDRATES

  • Definition and Importance:

    • Composed primarily of carbon, hydrogen, and oxygen.

    • Essential energy sources and structural components of all life, amongst the most abundant biomolecules on Earth.

    • Provide energy to the body, notably through glucose (a simple sugar).

  • Types of Carbohydrates:

    • Monosaccharides

    • Disaccharides

    • Oligosaccharides

    • Polysaccharides

  • Monosaccharides:

    • Examples:

    • Glucose: Also known as dextrose, grape sugar, and corn sugar.

    • Fructose: Known as fruit sugar.

    • Galactose

  • Disaccharides:

    • Formed from two linked monosaccharide molecules.

    • Sucrose: Composed of glucose and fructose, obtained from sugar beets and cane sugar.

    • Lactose: Milk sugar

    • Maltose: Another disaccharide

  • Polysaccharides:

    • Refers to large molecules consisting of many monosaccharide units, up to 10,000.

    • Cellulose: Principal structural component of plants, consisting of linked glucose units; most common polysaccharide.

    • Starch: Found in plants; a complex glucose polysaccharide.

    • Glycogen: Found in animals; a complex polysaccharide of glucose.

LIPIDS

  • Definition and Importance:

    • Function as long-term energy resources, utilized at slower rates than other macromolecules.

    • Serve as stored energy sources and chemical messengers.

  • Types of Lipids:

    • Triglycerides: Stored as fat in adipose cells, acting as energy reserves and providing thermal insulation.

    • Steroid hormones: Function as chemical messengers between cells, tissues, and organs; facilitate signal transduction in systems.

NUCLEIC ACIDS

  • Definition and Importance:

    • Serve as primary information-carrying molecules of the cell.

    • Direct the process of protein synthesis, determining inherited characteristics of all living organisms.

  • Structure:

    • Composed of polynucleotides, which are long chains made up of nearly identical units called nucleotides.

  • Types of Nucleic Acids:

    • Deoxyribonucleic Acid (DNA): Master blueprint for life, constituting genetic material in all free-living organisms and most viruses.

    • Ribonucleic Acid (RNA): Genetic material of some viruses; also found in living cells where it plays a crucial role in protein synthesis.

  • Building Blocks:

    • Proteins, carbohydrates, and nucleic acids are linked through strong covalent bonds:

    • Monomers (small units) linked into Polymers (long chains).

      • Proteins: polymers of amino acids

      • Carbohydrates: polymers of sugars

      • Lipids: polymers of lipid monomers

      • Nucleic Acids: DNA and RNA; polymers of nucleotides

ENZYMES

  • Definition:

    • Catalysts produced by living cells that catalyze biochemical reactions (e.g., digestion).

  • Specificity:

    • Each enzyme is specific for the substrate it acts upon, breaking, rearranging, or forming molecular bonds.

  • Functions:

    • Catalyze digestion of food by breaking down large nutrient molecules into smaller ones.

    • Facilitate conservation and transformation of chemical energy.

    • Construct cellular macromolecules from smaller precursors.

  • Activation Energy:

    • Enzymes lower the activation energy level needed for reactions to proceed, creating a transition state that requires less energy.

  • Active Site:

    • A specific region of the enzyme that binds to the substrate, determined by the protein's folding pattern and amino acid properties.

  • Enzyme Interaction:

    • Enzymes interact with specific substrates to catalyze particular reactions.

  • Inhibition:

    • Competitive inhibition occurs when molecules similar to the substrate block the active site (e.g., penicillin's inhibition of bacterial enzyme).

Categories of Enzymes

  • Oxidoreductases: Involved in electron transfer.

  • Transferases: Transfer a chemical group from one substance to another.

  • Hydrolases: Cleave substrates via water uptake (hydrolysis).

  • Lyases: Form double bonds by addition/removal of chemical groups.

  • Isomerases: Transfer groups within a molecule to produce isomers.

  • Ligases: Coupling formation of chemical bonds with breakdown of pyrophosphate bonds in ATP.

FACTORS AFFECTING ENZYME ACTIVITY

  • Temperature:

    • Raising temperature generally speeds up reactions; extreme high temperatures can denature enzymes.

  • pH:

    • Each enzyme has an optimum pH range. Extreme pH changes can slow activity or denature enzymes.

  • Enzyme Concentration:

    • Increasing enzyme concentration speeds reactions, provided substrate is available.

  • Substrate Concentration:

    • Increasing substrate concentration increases reaction rate until saturation point.

OXIDATION / REDUCTION REACTIONS

Introduction

  • Redox reactions involve electron transfer and can be regarded as crucial for cellular metabolism.

  • These reactions are categorized as follows:

    • Combustion of fossil fuels

    • Household bleach reactions

  • Definition:

    • Oxidation: Loss of electrons

    • Reduction: Gain of electrons.

  • Oxidation Reduction Process:

    • Oxidation reduces another substance by stripping electrons from it; that electron gain constitutes reduction for the receiving substance.

Example of Redox Reaction

  • Formation of Magnesium Chloride:

    • extMg+extCl2<br>ightarrowextMg2++2extCl−ext{Mg} + ext{Cl}_2 <br>ightarrow ext{Mg}^{2+} + 2 ext{Cl}^-

    • Magnesium (Mg) loses two electrons = oxidized

    • Chlorine (Cl) accepts those electrons = reduced

    • Reducing Agent: Magnesium (donates electrons)

    • Oxidizing Agent: Chlorine (accepts electrons)

Definitions of Oxidation-Reduction Reactions

  • Oxidation:

    • Addition of oxygen

    • Removal of hydrogen

    • Loss of electrons

    • Increase in oxidation number

Types of Redox Reactions

  1. Combination Reactions: Two or more substances combine to form a single product.

  2. Decomposition Reactions: A single compound reacts to produce two or more products.

  3. Displacement Reactions: An element displaces another in a compound.

  4. Combustion Reactions: A substance reacts with oxygen, usually producing heat and light.

ATP and REACTION COUPLING

  • Definition:

    • Adenosine triphosphate (ATP) acts as the main energy currency in cells.

  • Hydrolysis:

    • Breakdown of ATP releases energy utilized in many cellular reactions.

    • Bonds between phosphate groups (phosphoanhydride bonds) are considered "high-energy" bonds.

  • Mechanism:

    • ATP hydrolyzed to adenosine diphosphate (ADP) releases energy used in cellular processes.

  • Reaction Coupling:

    • ATP hydrolysis links energetically favorable reactions with endergonic reactions.

    • Often involves a shared intermediate, typically a phosphorylated molecule derived from ATP.