Chemistry and Metabolism in Anatomy & Physiology

Introduction

Chemistry forms the foundation of all biological processes in the human body. Understanding atomic structure, chemical bonding, and the properties of water and organic molecules is essential for comprehending metabolism and physiological functions.

Bohr Models of Atoms

Atomic Structure

• Atoms are the basic units of matter, composed of a nucleus (protons and neutrons) and electrons in shells.

• The Bohr model represents electrons in discrete energy levels (shells) around the nucleus.

• Key elements in biology include hydrogen (H), carbon (C), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S).

Example: Carbon (C) has 6 protons, 6 neutrons, and 6 electrons (2 in the first shell, 4 in the second shell).

Chemical Bonding

Ionic Bonding: Formation of Sodium Chloride

• Ionic bonds form when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other.

• Sodium (Na) loses an electron to become Na+; chlorine (Cl) gains an electron to become Cl-.

• The resulting compound, sodium chloride (NaCl), is held together by electrostatic attraction.

Example: Table salt (NaCl) is formed by the ionic bonding of sodium and chlorine.

Covalent Bonding

• Covalent bonds involve the sharing of electron pairs between atoms.

• Common in organic molecules such as water (H2O), oxygen gas (O2), and methane (CH4).

Example: In a water molecule, each hydrogen atom shares an electron with the oxygen atom, forming covalent bonds.

Chemistry of Water

Structure and Properties

• Water (H2O) is a polar molecule with a bent shape (bond angle ≈ 104.5°).

• Oxygen is more electronegative, creating a partial negative charge on oxygen and partial positive charges on hydrogens.

• This polarity allows water to form hydrogen bonds with other water molecules.

Hydrogen Bonding of Water

• Hydrogen bonds are weak attractions between the partially positive hydrogen of one water molecule and the partially negative oxygen of another.

• Hydrogen bonding gives water its unique properties: high specific heat, cohesion, adhesion, and solvent abilities.

Example: Water's high heat capacity helps maintain body temperature.

Organic Compounds

General Characteristics

• Organic compounds contain carbon and hydrogen, often with oxygen and nitrogen.

• They form large, complex molecules (macromolecules) such as carbohydrates, lipids, proteins, and nucleic acids.

• Organic molecules are generally insoluble in water and decompose easily, making them good energy sources.

Carbohydrates

Structure and Classification

• General formula: (CH2O)n (one carbon atom for each water molecule).

• Monosaccharides: Simple sugars with 3-7 carbon atoms (e.g., glucose).

• Disaccharides: Two monosaccharides joined (e.g., sucrose = glucose + fructose).

• Polysaccharides: Long chains of monosaccharides (e.g., glycogen).

Glycogen

• Glycogen is a polysaccharide that stores excess glucose in the liver and skeletal muscle.

Lipids

Structure and Types

• Composed of carbon, hydrogen, and oxygen, but not in a 2:1 ratio like carbohydrates.

• Mostly insoluble in water.

• Types include:

  • Triglycerides (energy storage, insulation, protection)

  • Phospholipids (membrane structure)

  • Steroids (hormones, membrane components)

  • Eicosanoids (signaling molecules)

  • Fat-soluble vitamins (A, D, E, K)

  • Fatty acids

Triglycerides

• Most abundant lipid in the body.

• Composed of one glycerol and three fatty acids.

• Provide more than twice the energy per gram as carbohydrates or proteins.

• Stored in adipose tissue; storage is virtually unlimited.

Phospholipids

• Major components of cell membranes.

• Consist of a hydrophilic phosphate head and two hydrophobic fatty acid tails.

Proteins

Structure

• Composed of amino acids linked by peptide bonds.

• Four levels of structure:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helices and beta sheets

  • Tertiary: 3D folding of a single polypeptide

  • Quaternary: Association of multiple polypeptides

Functions

• Structural: Keratin (hair, nails, skin), collagen (skin, bones, cartilage, teeth)

• Communication: Hormones and receptors

• Membrane transport: Channel and carrier proteins

• Catalysis: Enzymes

• Recognition and protection: Antibodies, glycoproteins

• Movement: Motor proteins

• Cell adhesion: Proteins bind cells together (e.g., sperm to egg)

Nucleic Acids

Structure and Function

• Nucleic acids (DNA and RNA) store and transmit genetic information.

• Composed of nucleotides: a nitrogenous base, a pentose sugar, and a phosphate group.

• DNA contains adenine, guanine, cytosine, and thymine; RNA contains uracil instead of thymine.

Metabolism and Energy Homeostasis

Metabolic Rate

• Metabolic rate is the rate at which the body produces heat and uses energy, measured in calories.

• Basal metabolic rate (BMR): The energy expended at rest.

• Affected by age, gender, fitness, hormones (e.g., thyroid hormones), and appetite-regulating hormones (ghrelin, leptin).

Energy Homeostasis

• Regulated by the hypothalamus, which contains feeding (hunger) and satiety centers.

• Leptin: Produced by fat cells, suppresses appetite, increases metabolic rate.

• Ghrelin: Produced by the stomach, stimulates hunger, decreases metabolic rate.

Metabolic States

Absorptive State

• Occurs during and shortly after eating (lasts about 4 hours).

• Insulin promotes uptake and storage of nutrients.

• Processes:

  • Glycogenesis: Formation of glycogen from glucose

  • Lipogenesis: Formation of triglycerides from glucose and fatty acids

  • Protein synthesis: Formation of proteins from amino acids

Post-Absorptive State

• Occurs between meals, when the digestive tract is empty.

• Body maintains blood glucose by breaking down stored nutrients.

• Processes:

  • Glycogenolysis: Breakdown of glycogen to glucose

  • Lipolysis: Breakdown of triglycerides to glycerol and fatty acids

  • Formation of glucose from non-carbohydrate sources (e.g., lactic acid, amino acids)

Hormonal Regulation

• Insulin: Lowers blood glucose by promoting uptake and storage.

• Glucagon: Raises blood glucose by stimulating glycogenolysis and gluconeogenesis.

• Epinephrine: Stimulates breakdown of glycogen and fat during stress.

Summary Table: Key Biomolecules

Additional info: Some explanations and context have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.