basis of life

Chapter 2: Chemical Basis of Life

Importance of Chemistry in Anatomy and Physiology

• Body functions are contingent on cellular functions.
• Cellular functions arise from chemical changes.
• Biochemistry is crucial for:
  • Explaining physiological processes.
  • Developing new drugs and treatment methods for diseases.

Structure of Matter

• Matter: Anything that occupies space and has weight; composed of elements.
• Elements: Composed of chemically identical atoms.
  • Bulk Elements: Required by the body in large quantities.
  • Trace Elements: Required by the body in small amounts.
• Atoms: Smallest particle of an element.

Atomic Structure

• Atoms consist of subatomic particles:
  • Proton: Carries a single positive charge.
  • Neutron: Carries no electrical charge.
  • Electron: Carries a single negative charge.
• Nucleus:
  • Central part of the atom.
  • Composed of protons and neutrons.
  • Electrons move around the nucleus.

Atomic Number and Atomic Weight

• Atomic Number:
  • Number of protons in the nucleus of an atom.
  • Each element has a unique atomic number.
  • Equals the number of electrons in the atom.
• Atomic Weight:
  • Sum of the number of protons and neutrons in one atom.
  • Electrons do not contribute to atomic weight.

Isotopes

• Isotopes: Atoms with the same atomic number but different atomic weights.
  • They have the same number of protons and electrons but a different number of neutrons.
  • Example: Oxygen isotopes include O16, O17, and O18.
  • Unstable isotopes are radioactive; they emit energy or atomic fragments.

Molecules and Compounds

• Molecule: A particle formed when two or more atoms chemically combine.
• Compound: A particle formed when two or more atoms of different elements chemically combine.
  • Molecular Formulas: Represent the elements present and the number of each atom in the molecule.
  • Examples: H2, C6H12O6, H2O.

Bonding of Atoms

• Electron Configuration in Shells:
  • Shells can hold a limited number of electrons.
  • For atoms with atomic numbers of 18 or less:
  • First shell: holds up to 2 electrons.
  • Second shell: holds up to 8 electrons.
  • Third shell: holds up to 8 electrons.
• Bonds form when atoms combine with other atoms, using electrons that occupy regions (electron shells) around the nucleus.
  • Lower shells are filled first.
  • An atom with a full outer shell is stable.

Ions

• Ion: An atom that gains or loses electrons to achieve stability, thus becomes electrically charged.
  • Cation: A positively charged ion (formed when an atom loses electrons).
  • Anion: A negatively charged ion (formed when an atom gains electrons).

Ionic Bonds

• Ionic Bond: An attraction between a cation and an anion.
  • Formed when electrons are transferred from one atom to another.

Covalent Bonds

• Covalent Bond: Formed when atoms share electrons.
  • Hydrogen forms single bonds.
  • Oxygen forms two bonds.
  • Nitrogen forms three bonds.
  • Carbon forms four bonds.
  • Examples:
  • Hydrogen: H ― H
  • Oxygen: O = O
  • Nitrogen: N ≡ N
  • Carbon: O = C = O

Structural Formulas

• Structural Formula: Illustrates how atoms bond and are arranged in various molecules.
  • Example: For H2O, it can be represented as:

  H
   |
H-O
   |
  H

Polar Molecules

• Polar Molecule: A molecule with a slightly negative end and a slightly positive end due to unequal sharing of electrons in covalent bonds.
  • Water is a principal polar molecule.

Hydrogen Bonds

• Hydrogen Bond: A weak attraction between the positive end of one polar molecule and the negative end of another.
  • This bond is critical for the structures of proteins and nucleic acids.

Chemical Reactions

• Chemical Reactions: Occur when chemical bonds form or break among atoms, ions, or molecules.
  • Reactants: Starting materials in the reaction (i.e., atoms, ions, or molecules).
  • Products: Substances formed at the end of the chemical reaction.
  • Example Reaction: NaCl → Na⁺ + Cl⁻ (Reactants to Products).

Types of Chemical Reactions

• Synthesis Reaction: A more complex chemical structure is formed.
  • Example: A + B → AB
• Decomposition Reaction: Chemical bonds are broken to form simpler structures.
  • Example: AB → A + B
• Exchange Reaction: Bonds are broken, and new bonds are formed.
  • Example: AB + CD → AD + CB
• Reversible Reaction: The products can revert back to reactants.
  • Example: A + B ⇌ AB

Acids, Bases, and Salts

• Electrolytes: Substances that release ions in water.
• Acids: Electrolytes that dissociate to release hydrogen ions (H⁺) in water.
  • Example: HCl → H⁺ + Cl⁻
• Bases: Substances that release ions which can combine with hydrogen ions.
  • Example: NaOH → Na⁺ + OH⁻
• Salts: Electrolytes formed by the reaction between an acid and a base.
  • Example: NaCl → Na⁺ + Cl⁻, or HCl + NaOH → H₂O + NaCl.

Acid and Base Concentrations

• pH Scale: Indicates the hydrogen ion concentration in a solution.
  • Neutral pH (7): Equal concentrations of H⁺ and OH⁻.
  • Acidic (pH < 7): Greater concentration of H⁺.
  • Basic or Alkaline (pH > 7): Greater concentration of OH⁻.

Organic vs. Inorganic Molecules

• Organic Molecules:
  • Contain both Carbon (C) and Hydrogen (H).
  • Typically larger than inorganic molecules.
  • Soluble in water and organic solvents.
  • Include carbohydrates, proteins, lipids, and nucleic acids.
• Inorganic Molecules:
  • Generally do not contain carbon.
  • Usually smaller than organic molecules.
  • Dissociate in water, forming ions.
  • Include water, oxygen, carbon dioxide, and inorganic salts.

Inorganic Substances

• Water:
  • Most abundant compound in living matter.
  • Accounts for two-thirds of the weight of an adult human.
  • Major component of body fluids.
  • Acts as a solvent for metabolic reactions.
  • Important in transporting chemicals and heat in the body.
• Oxygen (O2):
  • Essential for cellular metabolism and energy release.
  • Necessary for survival.
• Carbon Dioxide (CO2):
  • A metabolic waste product.
  • Must be expelled from the body.
• Inorganic Salts:
  • Present in body fluids.
  • Sources of necessary ions (e.g., Na⁺, Cl⁻, K⁺, Ca²⁺).
  • Play vital roles in metabolism.

Organic Substances

• Carbohydrates:

  • Supply energy to cells and materials to build cell structures.
  • Water-soluble, containing C, H, and O.
  • Ratio of H to O is approximately 2:1.
  • Different types include:
  • Monosaccharides: Simple sugars like glucose and fructose (C₆H₁₂O₆).
  • Disaccharides: Maltose, sucrose, lactose.
  • Polysaccharides: Glycogen, cellulose.

• Lipids:

  • Soluble in organic solvents; insoluble in water.
  • Types include:
  • Triglycerides: Main energy source; consists of 1 glycerol and 3 fatty acids.
  • Phospholipids: 1 glycerol, 2 fatty acids, and 1 phosphate; ie., a key component of cell membranes.
  • Steroids: Composed of four connected carbon rings; involved in membrane structure and hormone synthesis (e.g., cholesterol).

• Proteins:

  • Serve multiple functions such as structural support, energy source, hormones, receptors, enzymes, and antibodies.
  • Composed of amino acids, linked by peptide bonds.
  • Levels of Protein Structure:
  1. Primary Structure: Linear sequence of amino acids.
  2. Secondary Structure: Characterized by folding or coiling due to hydrogen bonding.
  3. Tertiary Structure: Three-dimensional configuration of the polypeptide chain.
  4. Quaternary Structure: Complex formed from multiple polypeptide chains.

• Nucleic Acids:

  • Functions to carry genes and encode amino acid sequences of proteins.
  • Composition:
  • DNA (Deoxyribonucleic acid): Double-stranded polymer of nucleotides.
  • RNA (Ribonucleic acid): Single-stranded polymer of nucleotides.

Clinical Applications

• CT Scanning and PET Imaging:
  • CT Scanning: Utilizes X-ray emissions to provide a 3D image of internal body parts.
  • PET Imaging: Employs radioactive isotopes to detect biochemical activity in specific regions of the body.