Essential Chemistry of Biology – Study Notes

Essential Chemistry of Biology

Biology and Society: Radiation and Health

Understanding radioactivity and its effects is crucial in both health and biological contexts. Radioactivity involves the emission of high-energy particles that can penetrate living tissues and damage DNA, potentially killing cells. However, controlled radiation can also be used beneficially in medicine, such as in cancer therapy, where targeted doses destroy cancerous cells while sparing healthy tissue.

• Radioactivity: The emission of high-energy particles from unstable atomic nuclei.

• Medical Application: Radiation therapy targets cancer cells.

• Biological Relevance: Many biological questions are rooted in chemistry and the behavior of atoms and molecules.

Matter: Elements and Compounds

Basic Concepts

• Matter: Anything that occupies space and has mass. Exists as solids, liquids, or gases.

• Mass: The amount of material in an object.

• Element: A substance that cannot be broken down into other substances by chemical reactions. All matter is composed of elements.

Elements in Biology

• There are 92 naturally occurring elements. Examples include carbon, oxygen, and gold.

• Each element is represented by a symbol (e.g., C for carbon).

• Of these, 25 are essential for human life. Four elements—oxygen (O), carbon (C), hydrogen (H), and nitrogen (N)—make up about 96% of the human body’s weight.

• The remaining 4% is mostly calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium.

• Trace elements are required in very small amounts but are essential for life (e.g., iodine, fluorine).

Example: Iodine deficiency can cause goiter, a swelling of the thyroid gland.

Compounds

• Compound: A substance containing two or more elements in a fixed ratio (e.g., NaCl, H2O).

• Each element consists of one kind of atom.

• Atom: The smallest unit of matter that retains the properties of an element.

The Structure of Atoms

Subatomic Particles

• Proton: Positively charged particle.

• Electron: Negatively charged particle.

• Neutron: Electrically neutral particle.

• Atoms are neutral when they have equal numbers of protons and electrons.

• Protons and neutrons are packed in the nucleus; electrons move around the nucleus.

Atomic Number, Mass Number, and Atomic Mass

• Atomic Number: Number of protons in an atom; unique to each element.

• Mass Number: Sum of protons and neutrons in the nucleus.

• Atomic Mass: Close to the mass number but may differ slightly due to isotopic variation.

Isotopes

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

	Carbon-12	Carbon-13	Carbon-14
Protons	6	6	6
Neutrons	6	7	8
Electrons	6	6	6

• Radioactive Isotope: An isotope whose nucleus decays spontaneously, emitting radiation.

• Natural radioactive sources (e.g., radon gas) can pose health risks.

The Process of Science: Radioactive Tracers

Radioactive isotopes can be used as tracers in biological research and medicine. For example, PET scans detect radioactive tracers to diagnose diseases such as Alzheimer’s by highlighting abnormal protein deposits in the brain.

• Cells use radioactive isotopes the same way as nonradioactive ones.

• PET scans detect radiation from tracers to monitor biological processes.

• Research example: Using fluorine-18 in PET scans to detect amyloid deposits in Alzheimer’s patients, leading to improved diagnosis and treatment.

Chemical Bonding and Molecules

Chemical Bonds

• Only electrons are directly involved in chemical reactions.

• The number of electrons determines an atom’s chemical properties.

• Chemical bonds hold atoms together in molecules.

Ionic Bonds

• Ions: Atoms or molecules that have gained or lost electrons and are thus charged.

• Ionic Bond: Attraction between oppositely charged ions (e.g., Na+ and Cl- in NaCl).

Covalent Bonds

• Covalent Bond: Forms when two atoms share one or more pairs of electrons.

• Strongest type of chemical bond; holds atoms together in molecules.

Electronegativity and Bond Polarity

• Electronegativity: The attraction of an atom for electrons in a covalent bond.

• Nonpolar Covalent Bond: Electrons are shared equally (e.g., CH4, O2).

• Polar Covalent Bond: Electrons are shared unequally, creating partial charges (e.g., H2O).

Hydrogen Bonds

• Weak attractions between the slightly positive hydrogen atom of one molecule and the slightly negative atom of another (often oxygen or nitrogen).

• Responsible for many of water’s unique properties.

Chemical Reactions

• Chemical reactions involve breaking and forming chemical bonds, rearranging matter but not creating or destroying it.

• Reactants: Starting materials.

• Products: End materials.

Water and Life

Water is essential for life, making up 70–95% of cells. Its unique properties are due to its polarity and hydrogen bonding.

• Cohesion: Water molecules stick together due to hydrogen bonds, aiding in water transport in plants.

• Surface Tension: Water has high surface tension, allowing small objects to rest on its surface.

• Temperature Moderation: Water absorbs and releases heat slowly, stabilizing temperatures in organisms and environments.

• Ice Floating: Ice is less dense than liquid water, so it floats, insulating aquatic life in winter.

• Solvent Properties: Water dissolves many substances, making it the solvent of life.

Examples and Applications

• Evaporative Cooling: As water evaporates, it cools surfaces (e.g., sweating in humans).

• Transport in Plants: Cohesion helps move water from roots to leaves.