Cellular Chemistry and Biomolecules: Study Notes for Anatomy & Physiology

Water, Solutions, and Cellular Compartments

Water as a Diffusion Medium

Water is the primary medium for the diffusion of gases, nutrients, and waste 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: 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 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 Biology

Organic Molecules

• Organic: Molecules containing carbon.

• Hydrocarbons: Molecules containing only carbon and hydrogen.

Carbohydrates (Saccharides)

Overview

• ~1% of total body weight; major food source.

• Primary energy source for humans.

• Energy yield: 4 kcal/g.

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

	α-1,4 glycosidic link	β-1,4 glycosidic link
Glucose	α-glucose	β-glucose
Galactose	α-galactose	β-galactose
Fructose	α-fructose	β-fructose

Polysaccharides: Many sugars linked together.

Polysaccharide	Linkage	Example
Starch (Amylose)	α-1,4 glycosidic link	Plant storage
Cellulose	β-1,4 glycosidic link	Plant cell walls
Glycogen	α-1,4 and α-1,6 glycosidic links	Animal 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., glucose, galactose, fructose).

Structural Isomers Example

• 1-bromopropane and 2-bromopropane: Same formula, different structure.

Sugar Balance

• Blood glucose is regulated by hormones:

  • Glucagon: Increases blood glucose (from pancreatic islets).

  • Insulin: Decreases blood glucose (from pancreatic islets).

• Hyperglycemia: Blood glucose > 120 mg/dL.

• Hypoglycemia: Blood glucose < 70 mg/dL.

• Lactose intolerance: Loss of lactase enzyme; leads to GI symptoms after consuming lactose.

Lipids

Overview

• ~20% of body weight.

• Energy yield: 9 kcal/g.

Classification

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

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

• Saturated: No double bonds.

• Unsaturated: At least one double bond.

• Cis vs. Trans:

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

  • Trans: Hydrogen atoms on opposite sides; associated with health risks.

Example: Saturated fat, cis fat, and trans fat differ in structure and health effects.

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.

• Examples: cholesterol, cortisol, aldosterone, progesterone, testosterone, estradiol.

Proteins/Polypeptides

Overview

• ~20% of body weight.

• Energy yield: 4 kcal/g.

Structure

• Monomers: Amino acids.

• Polymers: Polypeptides (linked by peptide bonds).

• Peptide Bond: Covalent bond between amino acids.

Amino Acid Classification

• Essential amino acids: Must be obtained from the diet.

• Non-essential amino acids: Can be synthesized by the body.

Protein Structure

• Primary: Sequence of amino acids.

• Secondary: Alpha helices and beta sheets.

• Tertiary: 3D folding of a single polypeptide.

• Quaternary: Multiple polypeptides assembled together.

Protein Functions

• Structural: Collagen, keratin.

• Antibodies: Immune defense.

• Contractile: Movement (actin, myosin).

• Enzymes: Catalyze reactions (e.g., lactase, amylase).

• Hormones: Regulation (insulin, growth hormone).

• Transport: Move molecules (hemoglobin).

Denaturation

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

• Denatured proteins lose function.

Nucleic Acids

Monomers and Structure

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

• Nitrogenous bases:

  • Purines: Adenine (A), Guanine (G) – double ring.

  • Pyrimidines: Cytosine (C), Thymine (T), Uracil (U) – single ring.

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): Brings amino acids to ribosomes during protein synthesis.

Example: tRNA has an anticodon region that pairs with mRNA codons during translation.