Chemistry Comes Alive: Foundations for Anatomy & Physiology

Chemical Reactions Underlie All Physiological Processes

Introduction

Chemistry is fundamental to understanding anatomy and physiology because all physiological processes are driven by chemical reactions. This chapter introduces the basic principles of chemistry and biochemistry as they relate to the human body.

Part 1: Basic Chemistry

2.1 Matter and Energy

Matter and energy are the foundational concepts in chemistry and physiology. Matter is anything that occupies space and has mass, while energy is the capacity to do work or put matter into motion.

• Matter: The "stuff" of the universe, including solids, liquids, and gases. Matter has mass and volume.

• States of Matter:

  • Solid: Definite shape and volume.

  • Liquid: Definite volume, changeable shape.

  • Gas: Changeable shape and volume.

• Energy: The ability to do work or cause change. Energy does not have mass or take up space.

• Forms of Energy:

  • Kinetic Energy: Energy in action; e.g., movement of muscles.

  • Potential Energy: Stored energy; e.g., energy stored in chemical bonds.

• Major Forms of Energy in the Body:

  • Chemical Energy: Stored in bonds of chemical substances; released during chemical reactions (e.g., ATP hydrolysis).

  • Electrical Energy: Results from movement of charged particles (ions); essential for nerve impulses and muscle contraction.

  • Mechanical Energy: Directly involved in moving matter (e.g., muscle contraction moves limbs).

  • Radiant Energy: Energy that travels in waves (e.g., light energy for vision).

• Conversion of Energy: Energy can be converted from one form to another, but some energy is lost as heat during conversions.

Example: The energy stored in food molecules is converted to ATP (chemical energy), which is then used for muscle contraction (mechanical energy).

2.2 Atoms and Elements

Atoms are the smallest units of matter that retain the properties of an element. Elements are pure substances composed of only one type of atom.

• Atom: Consists of a nucleus (protons and neutrons) and electrons orbiting the nucleus.

• Element: A substance that cannot be broken down into simpler substances by ordinary chemical means. Examples include carbon (C), oxygen (O), hydrogen (H), and nitrogen (N).

• Major Elements in the Human Body: Oxygen, carbon, hydrogen, and nitrogen make up about 96% of body mass.

Example: Water (H2O) is composed of hydrogen and oxygen atoms.

2.3 How is Matter Combined?

Atoms combine to form molecules and compounds through chemical bonds.

• Molecule: Two or more atoms bonded together (e.g., O2).

• Compound: Two or more different atoms bonded together (e.g., H2O).

• Chemical Bonds: Forces that hold atoms together. Types include ionic, covalent, and hydrogen bonds.

Example: Sodium chloride (NaCl) is formed by ionic bonding between sodium and chloride ions.

2.4 What are Chemical Bonds?

Chemical bonds are the interactions that hold atoms together in molecules and compounds.

• Ionic Bonds: Formed by the transfer of electrons from one atom to another, resulting in charged ions.

• Covalent Bonds: Formed by the sharing of electrons between atoms.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Example: Water molecules are held together by covalent bonds, and hydrogen bonds form between water molecules.

2.5 How do Chemical Reactions Form, Rearrange, or Break Bonds?

Chemical reactions involve the making or breaking of chemical bonds, resulting in the formation of new substances.

• Synthesis Reactions: Atoms or molecules combine to form larger, more complex molecules. $A + B \rightarrow AB$

• Decomposition Reactions: Molecules are broken down into smaller molecules or atoms. $AB \rightarrow A + B$

• Exchange Reactions: Involve both synthesis and decomposition; parts of molecules are exchanged. $AB + C \rightarrow AC + B$

• Energy Flow: Chemical reactions may release or absorb energy.

• Reversibility: Some chemical reactions are reversible, indicated by a double arrow. $A + B \rightleftharpoons AB$

Example: The breakdown of glucose during cellular respiration is a decomposition reaction that releases energy.

Part 2: Biochemistry

2.6 Importance of Organic Compounds to the Body

Organic compounds are essential for life and include carbohydrates, lipids, proteins, and nucleic acids. They are primarily composed of carbon and hydrogen atoms.

• Carbohydrates: Provide energy for cellular processes.

• Lipids: Store energy, form cell membranes, and act as signaling molecules.

• Proteins: Serve as enzymes, structural components, and signaling molecules.

• Nucleic Acids: Store and transmit genetic information (DNA and RNA).

Example: Glucose is a carbohydrate that serves as a primary energy source for cells.

2.7 How are Large Organic Compounds Made and Broken Down?

Large organic molecules (macromolecules) are formed by joining smaller units (monomers) through dehydration synthesis and broken down by hydrolysis.

• Dehydration Synthesis: Monomers are joined by removing a water molecule.

• Hydrolysis: Macromolecules are broken down by adding water.

Example: Proteins are formed by linking amino acids through dehydration synthesis.

2.8 Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They are classified as monosaccharides, disaccharides, and polysaccharides.

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose).

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

Example: Glycogen is a polysaccharide that stores energy in animals.

2.9 Lipids

Lipids are diverse organic compounds that are insoluble in water. They include fats, oils, phospholipids, and steroids.

• Triglycerides: Main form of stored energy in the body.

• Phospholipids: Major component of cell membranes.

• Steroids: Include hormones like cholesterol and sex hormones.

Example: Phospholipids form the bilayer structure of cell membranes.

2.10 Proteins

Proteins are polymers of amino acids and perform a wide variety of functions in the body.

• Enzymes: Biological catalysts that speed up chemical reactions.

• Structural Proteins: Provide support and shape to cells and tissues.

• Transport Proteins: Carry substances in the blood or across cell membranes.

Example: Hemoglobin is a transport protein that carries oxygen in the blood.

2.11 Nucleic Acids

Nucleic acids store and transmit genetic information. The two main types are DNA and RNA.

• DNA (Deoxyribonucleic Acid): Contains genetic instructions for protein synthesis.

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

Example: DNA is found in the nucleus of cells and determines inherited traits.

2.12 The Energy Currency: ATP

ATP (adenosine triphosphate) is the primary energy carrier in cells. It stores and releases energy for cellular processes.

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

• Function: Releases energy when the terminal phosphate bond is broken. $ATP \rightarrow ADP + P_i + \text{energy}$

Example: Muscle contraction and nerve impulse transmission require ATP.

Table: Major Classes of Organic Compounds

Class	Monomer	Main Function	Example
Carbohydrates	Monosaccharides	Energy source	Glucose
Lipids	Fatty acids, glycerol	Energy storage, cell membranes	Triglyceride, phospholipid
Proteins	Amino acids	Enzymes, structure, transport	Hemoglobin
Nucleic Acids	Nucleotides	Genetic information	DNA, RNA

Additional info: Some context and definitions were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.