Introduction to Biology

Levels of Biological Organization

Biology studies life at multiple levels, from atoms and molecules to cells and organelles. Understanding these levels is fundamental to grasping how living systems function.

• Atoms: The smallest units of matter, composed of protons, neutrons, and electrons.

• Molecules: Groups of atoms bonded together, forming the chemical basis of life.

• Organelles: Specialized structures within cells that perform distinct functions.

• Cells: The basic unit of life, capable of all life processes.

Chemistry in Biology

Atoms and Elements

Atoms are the fundamental building blocks of matter. Elements are defined by their atomic number, which is the number of protons in the nucleus.

• Subatomic Particles: Protons (+1 charge), neutrons (0 charge), electrons (-1 charge).

• Atomic Number: Determines the element; equals the number of protons.

• Mass Number: Sum of protons and neutrons.

Electron Shells and Stability

Electrons occupy specific energy levels called shells. Atoms are most stable when their outermost (valence) shell is full.

• First shell: up to 2 electrons

• Second shell: up to 8 electrons

• Third shell: up to 8 electrons

Periodic Table and Biological Elements

The periodic table organizes elements by atomic number and properties. Only a subset of elements are abundant in living organisms.

• Major elements in biology: Oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, potassium, sulfur, sodium, chlorine, magnesium.

Biomolecules

Composition of Biomolecules

Biomolecules are composed of atoms arranged in specific ways to form proteins, lipids, carbohydrates, and nucleic acids.

• Proteins: Made of amino acids; perform structural and functional roles.

• Lipids: Composed of fatty acids; important for membranes and energy storage.

• Carbohydrates: Made of sugars; provide energy and structural support.

• Nucleic acids: DNA and RNA; store and transmit genetic information.

Cell Components

Structure of Eukaryotic Cells

Eukaryotic cells contain membrane-bound organelles, each with specialized functions.

• Nucleus: Contains DNA; controls cell activities.

• Mitochondria: Site of cellular respiration; produces ATP.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

• Endoplasmic reticulum: Synthesizes proteins and lipids.

• Lysosomes: Digest cellular waste.

• Peroxisomes: Break down fatty acids and detoxify.

Chemical Bonds and Interactions

Types of Chemical Bonds

Atoms interact to achieve stable electron configurations, forming chemical bonds.

• Ionic Bonds: Formed by transfer of electrons between atoms, resulting in charged ions (e.g., NaCl).

• Covalent Bonds: Formed by sharing electrons between atoms; can be polar (unequal sharing) or nonpolar (equal sharing).

Bond Formation and Valence Electrons

The number of valence electrons determines how many bonds an atom can form.

• Hydrogen: 1 bond

• Oxygen: 2 bonds

• Nitrogen: 3 bonds

• Carbon: 4 bonds

• Phosphorus: 3 or 5 bonds (biologically relevant forms)

Polar and Nonpolar Covalent Bonds

Polarity arises from differences in electronegativity between atoms.

• Nonpolar covalent bonds: Electrons are shared equally; no charge difference.

• Polar covalent bonds: Electrons are shared unequally; partial charges develop (δ+ and δ-).

Summary Table: Major Elements in Biology

Key Equations

• Atomic number:

• Mass number:

• Glucose molecule:

Example: Formation of Sodium Chloride

• Sodium (Na) donates an electron to Chlorine (Cl), forming Na+ and Cl- ions.

• The resulting ionic bond creates sodium chloride (NaCl), common table salt.

Additional info:

• Biomolecules' polarity and chemical properties are essential for their biological functions, such as enzyme activity, membrane formation, and genetic information storage.