Anatomy & Physiology I: Molecu

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### Introduction to A&P Molecules - **Anatomy:** Study of the structure of body parts and their relationships to one another. - **Physiology:** Study of the function of body parts; how they work to carry out life-sustaining activities. - **Chemical Level:** The lowest level of structural organization, involving atoms and molecules. All living matter is composed of chemicals. ### Atoms and Elements - **Atom:** The smallest unit of matter that retains an element's chemical identity. - **Protons (p+):** Positive charge, in nucleus. Determines atomic number. - **Neutrons (n0):** No charge, in nucleus. - **Electrons (e-):** Negative charge, orbit nucleus in electron shells. Determines chemical reactivity. - **Element:** A pure substance consisting only of atoms that all have the same number of protons in their atomic nuclei. - **Major Elements (96% body mass):** Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N). - **Lesser Elements (3.9% body mass):** Calcium (Ca), Phosphorus (P), Potassium (K), Sulfur (S), Sodium (Na), Chlorine (Cl), Magnesium (Mg), Iodine (I), Iron (Fe). - **Isotopes:** Atoms of the same element with different numbers of neutrons (and thus different mass numbers). Some are radioactive (radioisotopes). ### Chemical Bonds - **Definition:** Energy relationships between atoms that involve the sharing or transfer of electrons. - **Ionic Bonds:** Formed when one or more electrons are transferred from one atom to another, creating oppositely charged ions that attract. - **Cation:** Positively charged ion (loses electrons). - **Anion:** Negatively charged ion (gains electrons). - Example: NaCl (Sodium Chloride) - **Covalent Bonds:** Formed when atoms share electrons to achieve a stable outer electron shell. - **Nonpolar Covalent:** Electrons shared equally (e.g., O=O, C-H). - **Polar Covalent:** Electrons shared unequally, creating slight positive and negative poles (e.g., H2O). - **Hydrogen Bonds:** Weak attractions between a partially positive hydrogen atom in one polar molecule and a partially negative atom (usually O or N) in another polar molecule. Important in water properties and protein/DNA structure. ### Water: The Universal Solvent - **Properties of Water (due to polarity and hydrogen bonding):** - **High Heat Capacity:** Absorbs/releases large amounts of heat with small temperature changes. Stabilizes body temperature. - **High Heat of Vaporization:** Requires much heat to change from liquid to gas. Evaporative cooling. - **Polar Solvent Properties:** Dissolves many ionic and polar substances (hydrophilic). - **Reactivity:** Involved in many chemical reactions (e.g., hydrolysis, dehydration synthesis). - **Cushioning:** Protects organs (e.g., cerebrospinal fluid). - **Hydrophilic:** "Water-loving"; substances that dissolve in water. - **Hydrophobic:** "Water-fearing"; substances that do not dissolve in water. ### Acids, Bases, and Buffers - **pH Scale:** Measures hydrogen ion concentration ([H+]). - **Acid:** Releases H+ in solution (pH 7). - **Neutral:** pH = 7 ([H+] = [OH-]). - **Body pH:** Maintained tightly between 7.35-7.45. - **Buffers:** Systems of weak acids and bases that resist changes in pH by reversibly binding H+. - Example: Bicarbonate buffer system in blood. ### Organic Molecules - **Definition:** Molecules containing carbon, usually bonded to hydrogen. Form the basis of living matter. - **Monomer:** Building block. - **Polymer:** Long chain of monomers. - **Dehydration Synthesis:** Removes water to join monomers (builds polymers). - **Hydrolysis:** Adds water to break polymers into monomers. #### Carbohydrates - **Function:** Primary energy source, structural roles. - **Monomer:** Monosaccharides (e.g., glucose, fructose, galactose). - **Polymer:** - **Disaccharides:** Two monosaccharides (e.g., sucrose, lactose, maltose). - **Polysaccharides:** Many monosaccharides (e.g., starch, glycogen, cellulose). Glycogen is the storage form of glucose in animals. #### Lipids - **Function:** Energy storage, insulation, protection, hormones, cell membrane structure. - **Types:** - **Triglycerides:** Glycerol + 3 fatty acids. Long-term energy storage. - **Saturated:** Single bonds, solid at room temp (animal fats). - **Unsaturated:** One or more double bonds, liquid at room temp (plant oils). - **Phospholipids:** Glycerol + 2 fatty acids + phosphate group. Forms cell membranes (amphipathic: hydrophilic head, hydrophobic tails). - **Steroids:** Four interlocking hydrocarbon rings (e.g., cholesterol, steroid hormones like estrogen, testosterone). Cholesterol is the basis for all steroid hormones. - **Eicosanoids:** Derived from a 20-carbon fatty acid (arachidonic acid). Includes prostaglandins (inflammation, blood clotting). #### Proteins - **Function:** Structural support, enzymes, transport, movement, regulation, defense. Most versatile molecules. - **Monomer:** Amino acids (20 common types). - Joined by **peptide bonds**. - **Levels of Protein Structure:** - **Primary:** Linear sequence of amino acids. - **Secondary:** Local folding into alpha-helices or beta-pleated sheets (due to hydrogen bonds). - **Tertiary:** Overall 3D shape of a single polypeptide chain (due to interactions between R-groups). - **Quaternary:** Arrangement of multiple polypeptide chains (subunits). - **Denaturation:** Loss of protein's 3D structure and function due to extreme heat or pH. #### Nucleic Acids - **Function:** Store, transmit, and express genetic information. - **Monomer:** Nucleotides (phosphate group + pentose sugar + nitrogenous base). - **Types:** - **DNA (Deoxyribonucleic Acid):** Double helix. Contains deoxyribose sugar, bases A, T, C, G. Stores genetic blueprint. - **RNA (Ribonucleic Acid):** Single strand. Contains ribose sugar, bases A, U, C, G. Involved in protein synthesis. ### ATP (Adenosine Triphosphate) - **Function:** Primary energy-transferring molecule in cells. Directly powers most cellular activities. - **Structure:** Adenine (nitrogenous base) + Ribose (sugar) + 3 Phosphate groups. - **Energy Release:** Breaking the high-energy phosphate bond between the 2nd and 3rd phosphate groups releases energy (ATP → ADP + Pi + Energy). - **ATP Synthesis:** Energy from glucose breakdown (cellular respiration) is used to reattach a phosphate to ADP, reforming ATP.