Levels of Organization (Systematically)

Chemical Level

The chemical level is the simplest level of organization in the body, involving atoms, molecules, and chemical bonds. Understanding this level is foundational for studying anatomy and physiology.

• Chemistry: The study of matter and its interactions.

• Matter: Anything that has mass and occupies space.

• Element: The simplest form of matter that cannot be broken down by ordinary means.

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

Atoms are made of subatomic particles:

• Protons: Positively charged (+)

• Neutrons: No charge (neutral)

• Electrons: Negatively charged (-)

• Atoms are electrically neutral (equal protons and electrons).

• Changing the number of protons changes the element.

• Changing the number of neutrons creates isotopes.

• Radioactive isotopes have unstable nuclei that decay spontaneously.

Electron shells surround the nucleus:

• First shell: 2 electrons

• Second shell: 8 electrons

• Atoms are stable when their outer shell is full (inert).

• Atoms with unfilled valence shells are reactive.

Chemical Bonding

• Ionic bonds: Electrons are transferred, forming cations (positive, usually metal ions) and anions (negative, usually nonmetal ions).

• Covalent bonds: Electrons are shared between atoms. Can be nonpolar (equal sharing) or polar (unequal sharing).

• Hydrogen bonds: Weak attractions between oppositely charged ends of polar molecules (e.g., between water molecules).

Chemical Reactions

• Reactants: Starting ingredients.

• Products: Results of the reaction.

Types of reactions:

• Anabolic (Synthesis): A + B → AB

• Catabolic (Decomposition): AB → A + B

• Exchange (includes oxidation-reduction): AB + CD → AC + BD

Metabolism: The sum of all chemical reactions in the body.

Biochemistry: Chemistry of Life

• Organic compounds: Always contain carbon bonded to hydrogen.

• Hydrocarbons: Contain only hydrogen and carbon.

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

Water (H2O): The most important inorganic compound in the body.

• High heat capacity

• High heat of vaporization

• Universal solvent

• Reactivity (in hydrolysis and dehydration synthesis)

• Cushions and lubricates

pH Scale and Buffers

• pH scale: Measures hydrogen ion concentration. Ranges from 0 (acidic) to 14 (basic).

• Buffers: Maintain a stable pH by absorbing or releasing H+ ions.

• Normal blood pH: 7.35–7.45

Organic Compounds

• Monomers: Single subunits (e.g., monosaccharides, amino acids, nucleotides).

• Polymers: Chains of monomers (e.g., polysaccharides, proteins, nucleic acids).

• Dehydration synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

• Short-term energy storage

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

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

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

Lipids

• Nonpolar, hydrophobic molecules (fats, oils, steroids)

• Fatty acids: Simplest lipids

• Triglycerides: Glycerol + 3 fatty acids (energy storage)

• Phospholipids: Major component of cell membranes (amphipathic: hydrophilic head, hydrophobic tail)

• Steroids: Four hydrocarbon rings (e.g., cholesterol, hormones)

Proteins

• Polymers of amino acids (20 types in humans)

• Structure: Amino group, carboxyl group, R group

• Levels of structure:

  • Primary: Sequence of amino acids

  • Secondary: Alpha helices and beta sheets (hydrogen bonding)

  • Tertiary: 3D folding

  • Quaternary: Multiple polypeptides

• Functions: Enzymes, structure, communication, movement, transport

• Denaturation: Loss of structure due to heat, pH, or chemicals

Nucleic Acids

• DNA: Deoxyribonucleic acid, double helix, stores genetic information

• RNA: Ribonucleic acid, single-stranded, involved in protein synthesis

• Nucleotides: Monomers (phosphate group, sugar, nitrogenous base)

• ATP: Adenosine triphosphate, main energy carrier

Cellular Level

Cell Structure and Function

The cellular level involves different molecules combined in specific ways to form cellular structures. The cell is the basic unit of life.

• Plasma membrane: Barrier between extracellular fluid (ECF) and cytosol (intracellular fluid, ICF). Selectively permeable.

• Cytoplasm: Site of chemical reactions, contains organelles.

• Nucleus: Contains DNA, controls cell activities.

Plasma Membrane Structure

• Phospholipid bilayer: Amphipathic (hydrophilic heads, hydrophobic tails)

• Proteins: Integral (span membrane) and peripheral (surface)

• Functions: Transport, communication, structural support

Membrane Transport

• Passive transport: No energy required. Includes diffusion and osmosis.

• Active transport: Requires energy (ATP). Moves substances against concentration gradient (e.g., Na+/K+ pump).

• Vesicular transport: Endocytosis (into cell), exocytosis (out of cell)

Types of Passive Transport

• Simple diffusion: Nonpolar solutes move directly through membrane.

• Facilitated diffusion: Polar solutes move via protein channels.

• Osmosis: Water moves across membrane via aquaporins.

Tonicity

• Isotonic: Same solute concentration inside and outside cell.

• Hypertonic: Higher solute concentration outside cell (cell shrinks).

• Hypotonic: Lower solute concentration outside cell (cell swells).

Na+/K+ Pump

• Moves 3 Na+ out, 2 K+ in, uses ATP.

• Maintains electrochemical gradients.

Cellular Extensions

• Microvilli: Increase surface area for absorption.

• Cilia: Move substances past cells.

• Flagella: Propel cells (e.g., sperm).

Nucleus

• Nuclear envelope: Double membrane with pores.

• Nucleolus: Site of ribosome assembly.

• DNA: Directs protein synthesis.

Protein Synthesis

• Transcription: DNA to mRNA (in nucleus)

• Translation: mRNA to protein (in cytoplasm/ribosomes)

Cell Cycle and Division

• Interphase: Growth and preparation for division

• Mitosis: Division of genetic material (produces 2 identical daughter cells)

• Cytokinesis: Division of cytoplasm

Cell Cycle Checkpoints and Apoptosis

• Checkpoints: Control cell cycle progression

• Apoptosis: Programmed cell death

• Cancer: Uncontrolled cell division, loss of cell cycle control

Summary Table: Types of Chemical Bonds

Key Equations

• pH calculation:

• Mass number:

• ATP hydrolysis:

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