The Chemistry of Life

Introduction

The chemistry of life forms the basis for understanding biological processes in Anatomy & Physiology. All living organisms are composed of chemical substances that interact in complex ways to sustain life.

Atoms and Elements

Definitions and Key Concepts

• Matter: Anything that has mass and occupies space.

• Chemistry: The study of matter and its interactions.

• Atom: The smallest unit of matter that retains its original properties.

• Element: A substance composed of one or more identical atoms; cannot be broken down into simpler substances by chemical means.

Elements are fundamental building blocks of all matter, including the human body. Each element is defined by the number of protons in its atoms.

Atoms and Atomic Structure

Subatomic Particles

Atoms are composed of three types of subatomic particles:

• Protons (p+): Positively charged particles located in the nucleus.

• Neutrons (n0): Neutral particles also found in the nucleus.

• Electrons (e-): Negatively charged particles that orbit the nucleus in electron shells.

For example, a carbon atom contains 6 protons, 6 neutrons, and 6 electrons.

Atomic Structure Diagram

• The nucleus contains protons and neutrons.

• Electrons are arranged in shells around the nucleus.

• The arrangement of electrons determines the chemical properties of the atom.

Elements in the Human Body

Major, Mineral, and Trace Elements

• Major Elements (96% of body mass):

  • Oxygen (O) – 65%

  • Carbon (C) – 18%

  • Hydrogen (H) – 10%

  • Nitrogen (N) – 3%

• Mineral Elements (<4%): Sodium (Na), Potassium (K), Calcium (Ca), Chlorine (Cl), Magnesium (Mg), Phosphorus (P), Sulfur (S)

• Trace Elements (<1%): Iron (Fe), Copper (Cu), Iodine (I), Zinc (Zn), and others

These elements are essential for various physiological functions, including nerve conduction, muscle contraction, and enzyme activity.

Isotopes and Radioactivity

Isotopes

• Isotope: Atoms of the same element with different numbers of neutrons.

• Example: Hydrogen has three isotopes—Protium (no neutrons), Deuterium (1 neutron), Tritium (2 neutrons).

Radioisotopes

• Radioisotopes: Unstable isotopes that release energy (radiation); used in nuclear medicine for diagnosis and treatment.

Applications include cancer radiation therapy and diagnostic imaging using radiotracers.

Ions and Ionic Bonds

Formation of Ions

• Atoms gain or lose electrons to form ions.

• Cation: Positively charged ion (loss of electrons).

• Anion: Negatively charged ion (gain of electrons).

Ionic Bonds

• Formed by the attraction between oppositely charged ions.

• Result in compounds known as salts (e.g., NaCl).

Chemical Reactions

Types and Notation

• Reactants: Starting substances (left side of equation).

• Products: Substances produced (right side of equation).

• Reversible Reactions: Can proceed in either direction, denoted by double arrows.

Example equation:

Carbon dioxide + Water → Carbonic acid

Homeostasis and Chemical Reactions

Fundamental Reaction Types

• Catabolic Reactions: Break down larger substances into smaller ones (e.g., digestion).

• Exchange Reactions: Transfer atoms or electrons between reactants (e.g., energy conversion).

• Anabolic Reactions: Form new chemical bonds to build larger molecules (e.g., synthesis of proteins).

Reaction Rates and Enzymes

Activation Energy and Catalysts

• Activation Energy (): The energy required for reactants to collide and react.

• Catalyst: Substance that lowers activation energy, increasing reaction rate.

• Enzyme: Biological catalyst, usually a protein, that speeds up reactions without being consumed.

Enzymes are highly specific for their substrates and reactions, and contain an active site for binding.

Enzyme Deficiencies and Disease

• Tay-Sachs Disease: Deficiency of hexosaminidase; leads to accumulation of gangliosides in brain cells.

• Severe Combined Immunodeficiency Syndrome (SCID): May involve deficiency of adenosine deaminase; results in almost complete absence of immune system.

• Phenylketonuria: Deficiency of phenylalanine hydroxylase; leads to buildup of phenylalanine, causing seizures and mental retardation (preventable by diet).

Inorganic and Organic Compounds

Definitions

• Inorganic Compounds: Do not contain carbon bonded to hydrogen (e.g., water, acids, bases, salts).

• Organic Compounds: Contain carbon bonded to hydrogen.

Water and Its Properties

Importance of Water

• Makes up 50-65% of body mass.

• Absorbs heat without significant temperature change.

• Cushions and protects body structures.

• Acts as a lubricant and primary solvent.

• Dissolves hydrophilic (water-loving) solutes; does not dissolve hydrophobic (water-hating) solutes.

Acids, Bases, and pH

Definitions and pH Scale

• Acid: Proton donor; increases hydrogen ion concentration in solution.

• Base: Proton acceptor; decreases hydrogen ion concentration.

• pH: Negative logarithm of hydrogen ion concentration:

• pH scale ranges from 0 (acidic) to 14 (basic); water is neutral at pH 7.

• Normal blood pH: 7.35–7.45

• Acidosis: Blood pH below 7.35

• Alkalosis: Blood pH above 7.45

Buffers

• Buffers resist changes in pH when acids or bases are added.

• Help maintain homeostasis in biological systems.

Electrolytes

Definition and Importance

• Electrolytes: Cations and anions formed when salts dissolve in water; conduct electricity.

• Essential for nerve conduction, muscle contraction, and other physiological functions.

Organic Compounds: Hydrocarbons, Monomers, and Polymers

Hydrocarbons

• Organic compounds containing only carbon and hydrogen.

• Exist as chains or rings; form the backbone of organic molecules.

Monomers and Polymers

• Monomer: Single subunit that can be combined to build larger structures.

• Polymer: Larger structure made of many monomers linked together.

• Dehydration Synthesis: Links two monomers by removing a water molecule.

• Hydrolysis: Splits a polymer by adding a water molecule.

Carbohydrates

Structure and Function

• Made of carbon, hydrogen, and oxygen; monomers have a 1:2:1 ratio (C:H:O).

• Polar and hydrophilic; function primarily as fuel and in structural roles.

• Monosaccharide: Simple sugar (e.g., glucose, fructose, ribose, deoxyribose).

• Disaccharide: Two monosaccharides joined by dehydration synthesis (e.g., sucrose, lactose).

• Polysaccharide: Long chains of monosaccharides (e.g., starch in plants, glycogen in animals).

Specialized carbohydrates (glycoproteins, glycolipids) help maintain cell structure and communication.

Lipids

Structure and Types

• Made of carbon, hydrogen, and some oxygen; nonpolar and hydrophobic.

• Function as fuel, components of cell membranes, and precursors for hormones.

• Fatty Acid: Monomer of lipids; hydrocarbon chain with a carboxylic acid group.

• Triglyceride: Three fatty acids linked to glycerol; storage form of fatty acids.

• Phospholipid: Glycerol backbone, two fatty acids, and a phosphate group; amphiphilic (polar head, nonpolar tails); major component of cell membranes.

• Steroid: Four-ring carbon structure; includes cholesterol, bile acids, and sex hormones.

Types of Fatty Acids

• Saturated: No double bonds; solid at room temperature; high levels increase cardiovascular risk.

• Monounsaturated: One double bond; liquid at room temperature.

• Polyunsaturated: Two or more double bonds; liquid at room temperature.

• Trans Fat: Artificially altered; harmful to health.

Proteins

Structure and Function

• Made of carbon, hydrogen, oxygen, nitrogen, and sometimes other elements.

• May be polar/hydrophilic or nonpolar/hydrophobic.

• Make up about 20% of body mass; 50,000–100,000 types in the body.

• Functions: structural roles, enzymes, defense, communication, muscle contraction, fuel.

• Amino Acid: Monomer of proteins; 21 types.

Peptides and Protein Structure

• Peptide Bond: Covalent bond between amino acids formed by dehydration synthesis.

• Dipeptide: Two amino acids; Tripeptide: Three amino acids; Polypeptide: Ten or more amino acids.

Levels of Protein Structure

• Primary Structure: Amino acid sequence; held by peptide bonds.

• Secondary Structure: Folding into alpha-helix or beta-pleated sheet; stabilized by hydrogen bonds.

• Tertiary Structure: Final 3D shape; stabilized by hydrogen, covalent, and ionic bonds between R groups.

• Quaternary Structure: Some proteins have more than one polypeptide chain.

Protein Denaturation

• Loss of shape due to heat, pH changes, or chemicals; results in loss of function.

• Humans cannot tolerate extensive temperature or pH changes due to protein denaturation.

Nucleotides and Nucleic Acids

Structure and Function

• Made of carbon, hydrogen, oxygen, nitrogen, and phosphorus.

• Nucleotide: Monomer composed of a nitrogenous base, five-carbon sugar, and phosphate group.

• Purines: Double-ringed bases (adenine, guanine).

• Pyrimidines: Single-ringed bases (cytosine, thymine, uracil).

Adenosine Triphosphate (ATP)

• Main source of chemical energy for cellular processes.

• Synthesized from adenosine diphosphate (ADP) and a phosphate group; requires energy from catabolism of fuels.

• Cells must continually replenish ATP; requires oxygen.

DNA and RNA

• DNA: Double-stranded polymer of nucleotides; contains deoxyribose sugar; bases are adenine (A), guanine (G), cytosine (C), and thymine (T).

• Strands held together by hydrogen bonds; exhibits complementary base pairing (A-T, G-C).

• Gene: Segment of DNA that codes for a protein; sequence of nucleotides specifies amino acid sequence.

• RNA: Single-stranded; contains ribose sugar; uracil replaces thymine; can move between nucleus and cytosol.

• RNA copies genes from DNA and helps assemble proteins.

Summary Table: Major Elements in the Human Body

Additional info: These notes expand on the original content with academic context, definitions, and examples to provide a comprehensive study guide for Anatomy & Physiology students.