Bio 110- Chapter 3

General Biology

Bio 110

جامعة الملك عبد العزيز

Chapter 3

Contents

  • Part I: Life on Earth: An Overview

    • Chapter 1

  • Part II: Chemistry of Life

    • a. Basic Chemistry (Chapter 2)

    • b. Chemistry of Organic Molecules (Chapter 3)

  • Part III: The Cell

    • a. Cell Structure and Function (Chapter 4)

    • b. Membrane Structure and Function (Chapter 5)

Part II: Chemistry of Life

b. Chemistry of Organic Molecules

3.1 Organic Molecules

  • Chemistry Division:

    • Organic Chemistry: study of organisms.

    • Inorganic Chemistry: study of non-living matter.

  • Organic molecules must contain carbon and hydrogen atoms.

  • Biomolecule Classes:

    • Carbohydrates

    • Proteins

    • Lipids

    • Nucleic Acids

  • A bacterial cell contains approximately 5,000 different organic molecules; plant/animal cells have about double that number.

a. The Carbon Atom

  • Carbon has six electrons:

    • 2 in the first shell.

    • 4 in the outer shell.

  • To complete its outer shell, carbon typically shares electrons with CHNOPS (C, H, N, O, P, S).

  • Example: Methane (CH4) has four covalent bonds with hydrogen atoms.

  • Each line in the methane formula indicates a shared electron pair.

b. The Biomolecules of Cells

  • Foods rich in biomolecules include:

    • Carbohydrates in bread.

    • Proteins in meat.

  • Digestion breaks down food into smaller units:

    • Bread → glucose

    • Meat → amino acids

  • Table 3.2 Biomolecules:

    • Category → Example → Subunit

    • Carbohydrates → Polysaccharide → Monosaccharide

    • Lipids → Fat → Glycerol and Fatty Acid

    • Proteins → Polypeptide → Amino Acid

    • Nucleic Acids → DNA, RNA → Nucleotide

c. Synthesis and Degradation

  • Synthesis: Cells use condensation/dehydration reactions to synthesize biomolecules, removing a water molecule.

  • Degradation: Hydrolysis reactions break down biomolecules, using water to attach OH and H groups.

  • Enzymatic Role: Enzymes facilitate dehydration and hydrolysis reactions.

  • Polymers: Large biomolecules formed from many monomers. Example: polysaccharides, proteins, nucleic acids.

3.2 Carbohydrates

  • Carbohydrate Definition: Includes single or chain sugars.

  • Serves as immediate energy sources and structural components.

  • Main ratio of carbon to hydrogen to oxygen: 1:2:1.

a. Monosaccharides: Ready Energy

  • Defined as single sugar molecules with 3-7 carbon backbones.

  • Formula: Multiple of CH2O.

  • Soluble in water due to hydroxyl groups.

  • Example: Glucose (C6H12O6) is a hexose.

b. Disaccharides: Varied Uses

  • Formed from two monosaccharides via dehydration reaction.

  • Example: Maltose (brewing ingredient), Sucrose (sweetener), Lactose (in milk).

  • Lactose intolerance occurs due to inability to break down lactose.

c. Polysaccharides: Energy Storage

  • Polymers of monosaccharides; broken down for energy.

  • Plant starch (branched/non-branched) vs. animal glycogen (highly branched).

  • Insulin promotes glucose storage as glycogen.

d. Structural Molecules

  • Includes cellulose (plants), chitin (animals/fungi), and peptidoglycan (bacteria).

  • Cellulose is the most abundant organic molecule; indigestible by animals.

  • Chitin provides protective coatings for seeds and has medicinal uses.

3.3 Lipids

  • Lipids are insoluble in water, comprised of hydrocarbon chains.

  • Functions: insulation, long-term energy storage, key plasma membrane components (phospholipids, steroids).

a. Triglycerides: Long-Term Energy Storage

  • Consist of fatty acids and glycerol.

  • Fatty acids can be saturated (no double bonds) or unsaturated (with double bonds).

  • Glycerol has three polar OH groups, soluble in water.

  • Formation involves dehydration reactions; degradation through hydrolysis.

b. Phospholipids: Membrane Components

  • Similar to fats, but one fatty acid's replaced by a polar phosphate group.

  • Phospholipids form bilayers in water, crucial for plasma membranes.

c. Steroids: Four Fused Rings

  • Differ by functional groups attached to the carbon skeleton.

  • Example: Cholesterol is vital for cell membranes and is a precursor for certain hormones.

3.4 Proteins

  • Proteins are large biomolecules with multiple amino acid chains.

  • Make up about 50% of the dry weight in most cells.

Functions

  1. Metabolism: Enzymes speed reactions.

  2. Support: Structural roles (e.g., keratin, collagen).

  3. Transport: Proteins allow substances to enter/exit cells.

  4. Defense: Antibodies combat antigens.

  5. Regulation: Hormones influence metabolism (e.g., insulin).

  6. Motion: Muscle contraction and cellular movement.

a. Amino Acids

  • Basic monomer of proteins; consists of amino, acid, and R groups.

  • 20 standard amino acids vary by R groups.

Peptides and Structure

  • Peptide Bond: Forms through dehydration between amino acids.

  • Proteins have primary, secondary, tertiary, and quaternary structures.

    • Primary: sequence of amino acids.

    • Secondary: coiling/folding (alpha helix, beta sheet).

    • Tertiary: three-dimensional shape.

3.5 Nucleic Acids

  • Polymers of nucleotides: DNA & RNA.

  • DNA stores genetic info; RNA types facilitate protein synthesis.

Structure of DNA and RNA

  • Nucleotides consist of phosphate, sugar, and nitrogenous bases.

  • DNA: double-stranded, thymine paired with adenine; guanine with cytosine.

  • RNA: single-stranded, uracil replaces thymine.

ATP (Adenosine Triphosphate)

  • Composed of adenine, ribose, and three phosphate groups.

  • High-energy molecule; its hydrolysis releases energy for cellular processes.