Essential Study Notes: Water, Organic Molecules, and Macromolecules in Anatomy & Physiology

Water and Cellular Compartments

Water as a Diffusion Medium

Water is the primary medium for the diffusion of gases, nutrients, and waste products in the body. It is distributed between two main fluid compartments:

• Extracellular Fluid (ECF): Includes interstitial fluid and plasma.

• Intracellular Fluid (ICF): The cytosol within cells.

	ECF	ICF
Cations	High Na+, low K+	High K+, low Na+
Anions	High HCO3- & Cl-	High proteins, low HCO3- & Cl-

Concentration Gradients and Membrane Transport

Osmosis and Diffusion

Movement of molecules across membranes is essential for maintaining cellular homeostasis.

• Osmosis: The spontaneous net movement of solvent molecules (usually water) through a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

• Diffusion: The spontaneous net movement of solute and solvent molecules from a region of higher concentration to a region of lower concentration.

Types of Solutions

• Hypertonic Solution: Higher concentration of solutes compared to another solution; water moves out of cells.

• Hypotonic Solution: Lower concentration of solutes compared to another solution; water moves into cells.

• Isotonic Solution: Equal concentration of solutes as another solution; no net water movement.

Example: Red blood cells in hypertonic solution shrink (crenate), in hypotonic solution swell and may burst (lyse), and in isotonic solution remain normal.

Physiological Water/Electrolyte Balance

• Dehydration: Loss of water but not electrolytes; water exits cells.

• Overhydration (Water Toxicity): Addition of water but not electrolytes; water enters cells.

Organic Chemistry in Physiology

Organic Molecules

• Hydrocarbons: Molecules containing only carbon and hydrogen.

• Organic molecules contain carbon atoms and are the basis of life.

Carbohydrates (Saccharides)

Overview

• ~1% of total body weight, but bulk of food.

• Primary energy source for humans.

• Energy yield: 4 kcal/g.

• Monosaccharides: Single sugar units (e.g., glucose, galactose, fructose).

Monosaccharide	Structure	Linkage
Glucose	6-carbon ring	α-1,4 glycosidic link
Galactose	6-carbon ring	β-1,4 glycosidic link
Fructose	5-carbon ring	α-1,2 glycosidic link

• Polysaccharides: Many sugars linked together (e.g., starch, cellulose, glycogen).

Polysaccharide	Linkage	Function
Starch (Amylose)	α-1,4 glycosidic	Plant energy storage
Cellulose	β-1,4 glycosidic	Plant cell wall structure
Glycogen	α-1,4 and α-1,6 glycosidic	Animal energy storage

• Cellulose: Found in plant cell walls; humans cannot digest β-1,4 linkages.

• Glycogen: Storage form of carbohydrates in animals.

• Isomers: Compounds with the same chemical formula but different structures (e.g., 1-bromopropane vs. 2-bromopropane).

Lipids

Overview

• ~20% of body weight.

• Energy yield: 9 kcal/g.

• Fats: Solid at room temperature; saturated; long chains.

• Oils: Liquid at room temperature; unsaturated; short chains.

• Saturated Fats: No double bonds.

• Unsaturated Fats: At least one double bond.

Cis vs. Trans Fats

• Cis: Hydrogen atoms on the same side of the double bond.

• Trans: Hydrogen atoms on opposite sides of the double bond; associated with health risks.

Phospholipids

• Composed of glycerol, two fatty acids, and a phosphate group.

• Have both polar (hydrophilic) and non-polar (hydrophobic) regions.

• Major component of cell membranes.

Steroids

• Cyclic organic compounds derived from cholesterol (e.g., cholesterol, cortisol, aldosterone, progesterone).

Proteins/Polypeptides

Overview

• ~20% of body weight.

• Energy yield: 4 kcal/g.

• Monomers: Amino acids.

• Polymers: Polypeptides (chains of amino acids).

• Peptide Bond: Covalent bond linking amino acids.

Essential Amino Acids

• Amino acids that cannot be synthesized by the body and must be obtained from the diet.

Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Alpha helices and beta sheets.

• Tertiary: 3D folding of a single polypeptide.

• Quaternary: Multiple polypeptide chains.

Protein Functions

• Structural: Collagen, keratin.

• Antibodies: Immune defense.

• Contractile: Movement (actin, myosin).

• Enzymes: Catalyze reactions by lowering activation energy (e.g., lactase, amylase).

• Hormones: Regulation (insulin, growth hormone).

• Transport: Move molecules (hemoglobin).

Denaturation

• Loss of protein structure due to heat, pH, organic solvents, or salt solutions.

Nucleic Acids

Monomers and Structure

• Nucleotides: Nitrogenous base + 5-carbon sugar + phosphate group.

• Nitrogenous Bases: Purines (adenine, guanine), Pyrimidines (cytosine, thymine, uracil).

Polymers

• DNA: Double helix; deoxyribose sugar; bases A, T, C, G.

• RNA: Single strand; ribose sugar; bases A, U, C, G.

Types of RNA

• Messenger RNA (mRNA): Carries genetic code from DNA.

• Ribosomal RNA (rRNA): Component of ribosomes.

• Transfer RNA (tRNA): Transfers amino acids during protein synthesis.

Additional info: The notes above expand on the original content by providing definitions, examples, and context for each macromolecule and physiological process, ensuring a comprehensive and self-contained study guide for Anatomy & Physiology students.