CH 5

Versatile Carbon Atom

Properties of Carbon

The carbon atom is fundamental to life due to its unique chemical properties, which allow it to form a wide variety of stable compounds.

• Tetravalency: Carbon has four valence electrons, allowing it to form four covalent bonds with other atoms.

• Bond Diversity: Carbon can form single, double, and triple bonds, enabling complex molecular structures.

• Chain Formation: Carbon atoms can link together to form long chains, branched molecules, and rings.

• Compatibility: Carbon bonds with many elements, including hydrogen, oxygen, nitrogen, and sulfur.

Organic Molecules

Definition and Photosynthesis Equation

Organic molecules are compounds primarily composed of carbon atoms bonded with hydrogen, oxygen, and other elements. The process of photosynthesis produces organic molecules from inorganic precursors.

• Photosynthesis Equation:

• Organic: C6H12O6 (glucose)

• Inorganic: CO2, H2O, O2

Macromolecules and Biomolecules

Macromolecules are large, complex molecules essential for life. Biomolecules are organic molecules found in living organisms.

• Four Major Biomolecules:

  1. Carbohydrates

  2. Proteins

  3. Lipids

  4. Nucleic Acids

• Polymer: A large molecule made of repeating subunits (monomers).

• Monomer: A small molecule that can join with others to form a polymer.

Carbohydrates

Main Functions of Carbohydrates

Carbohydrates are essential biomolecules that serve several key functions in living organisms.

• Energy source (e.g., glucose)

• Energy storage (e.g., starch, glycogen)

• Structural support (e.g., cellulose in plants, chitin in fungi and arthropods)

• Cell recognition and signaling (e.g., oligosaccharides on cell surfaces)

Atoms Required and Functional Groups

• Atoms: Carbon (C), Hydrogen (H), Oxygen (O)

• Functional Groups: Hydroxyl (-OH), Carbonyl (C=O)

Monosaccharides

Monosaccharides are the simplest carbohydrates, consisting of single sugar units.

• Examples: Glucose, Fructose, Galactose, Glyceraldehyde

• Role: Serve as energy sources and building blocks for larger carbohydrates.

Disaccharides

Disaccharides are formed by joining two monosaccharides via a glycosidic linkage.

• Examples: Sucrose (glucose + fructose), Lactose (glucose + galactose), Maltose (glucose + glucose)

• Glycosidic Linkage: Covalent bond formed between two sugar molecules.

Oligosaccharides

Oligosaccharides consist of a small number (3-10) of monosaccharide units.

• Function: Cell recognition and signaling, especially on cell membranes.

Good vs. Bad Carbohydrates

• Good Carbs: Complex carbohydrates (whole grains, vegetables) provide sustained energy and fiber.

• Bad Carbs: Simple sugars (refined sugar, white bread) can cause rapid spikes in blood glucose and lack nutritional value.

Lipids

Main Functions of Lipids

Lipids are hydrophobic molecules that play diverse roles in biological systems.

• Long-term energy storage

• Structural components of cell membranes

• Insulation and protection

• Signaling molecules (hormones)

Atoms Required

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

Fatty Acids

• Saturated Fatty Acids: No double bonds between carbon atoms; solid at room temperature.

• Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature.

• Trans Fatty Acids: Unsaturated fats with trans double bonds; associated with negative health effects.

Triglycerides

• Structure: Composed of glycerol and three fatty acids.

• Ester Linkage: Bond formed between glycerol and fatty acids.

Functions of Fats and Oils

• Energy storage

• Insulation

• Protection of organs

Phospholipids

• Structure: Glycerol backbone, two fatty acids (hydrophobic), and a phosphate group (hydrophilic).

• Amphipathic: Molecule with both hydrophilic and hydrophobic regions.

• Function: Major component of cell membranes, forming the phospholipid bilayer.

Steroids

• Structure: Four fused carbon rings.

• Functions:

  • Cholesterol: Maintains membrane fluidity

  • Hormones: Sex hormones (estrogen, testosterone), non-sex hormones (cortisol)

Waxes

• Structure: Long-chain fatty acids bonded to long-chain alcohols.

• Function: Waterproofing and protection (e.g., plant cuticle, earwax)

Proteins

Main Functions of Proteins

Proteins are versatile biomolecules with diverse functions in living organisms.

• Metabolism (enzymes)

• Structural support (keratin, collagen)

• Transport (hemoglobin, protein channels)

• Immune defense (antibodies)

• Regulation (hormones)

• Motion (muscle proteins, microtubules)

• Storage (casein, ovalbumin)

• Receptors (cell signaling)

Atoms Required and Functional Groups

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Sulfur (S) in some proteins

• Functional Groups: Amino group (-NH2), Carboxyl group (-COOH)

Amino Acids

• Monomer: Amino acid

• Structure: Central α-carbon, amino group, carboxyl group, R group (side chain)

Peptide Bonds and Polypeptides

• Peptide Bond: Covalent bond between amino group of one amino acid and carboxyl group of another

• Polypeptide: Chain of amino acids linked by peptide bonds

• Protein: One or more polypeptides folded into a functional shape

Protein Structure

• Primary Structure: Sequence of amino acids

• Secondary Structure: Local folding (α-helix, β-sheet)

• Tertiary Structure: Overall 3D shape

• Quaternary Structure: Multiple polypeptide chains

Protein Folding, Mutation, and Denaturation

• Folding: Essential for protein function; misfolding can cause disease

• Mutation: Change in DNA sequence can alter protein structure

• Denaturation: Loss of structure due to heat, pH, or chemicals

Complete vs. Incomplete Protein Sources

• Complete: Contains all essential amino acids (e.g., animal proteins)

• Incomplete: Lacks one or more essential amino acids (e.g., most plant proteins)

Nucleic Acids

Types and Functions

• DNA (Deoxyribonucleic Acid): Stores genetic information

• RNA (Ribonucleic Acid): Involved in protein synthesis and gene regulation

Atoms Required and Functional Groups

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

• Phosphorus (P)

• Functional Groups: Phosphate group, hydroxyl group

Nucleotides

• Monomer: Nucleotide (phosphate group, pentose sugar, nitrogenous base)

• Polymer: Polynucleotide (DNA or RNA)

Phosphodiester Linkage

• Bond: Connects the 3' carbon of one sugar to the 5' carbon of the next via a phosphate group

Polynucleotides and Sequence

• Backbone: Alternates between sugar and phosphate molecules

• Sequence: Order of nitrogenous bases encodes genetic information

ATP (Adenosine Triphosphate)

• Function: Main energy currency of the cell

• Structure: Adenine base, ribose sugar, three phosphate groups

• Energy Use: Energy is released when ATP is hydrolyzed to ADP and inorganic phosphate

Additional info: These notes cover the foundational biomolecules and their properties, structures, and functions, suitable for a General Biology college course.