Biochemistry Quick Reference: pH, Solutions, Carbohydrates, Lipids, Inflammation

Concentration symbol commonly shown as a bracketed form:
[A] for concentration; important for understanding solutions.
pH concept: acids vs bases; pH scale is a measure of hydrogen ion activity.
Normal body pH targets: around 7.35-7.45 (blood) with an average near 7.4.
Buffers resist changes in pH by donating or accepting $H^+$ or $OH^-$.
If a large acid or base load is introduced, buffers and homeostatic mechanisms restore pH toward the target value.
Alkaline water claims: no strong scientific basis for altering body pH; body maintains pH internally.
Neutralization concept: acids neutralized by bases; bases neutralized by acids; pH can be shifted beyond 7 towards basic or acidic with sufficient reactants.
Hydration balance: body uses buffers to keep cells and bodily fluids within a narrow pH range to protect proteins and enzymes.
Example note: MSG mentioned as a buffer in this discussion; buffers can donate or accept protons as needed.

Water-based mixtures fall into three main categories:
- Colloids (emulsions): not evenly distributed, may scatter light, do not settle quickly; particles typically between 1 nm and 1000 nm; examples include gelatin; emulsions mix polar and nonpolar phases but can separate over time.
- Emulsions: a subset of colloids where polar water and nonpolar liquids (e.g., oil) form two phases; can appear mixed but separate when left undisturbed.
- Suspensions: cloudy mixtures where larger particles are dispersed but eventually settle; scatter light.
Solutions: homogeneous mixtures where solute dissolves in solvent; transparent and uniform.
Concentration recap:
- Concentration = amount of solute per volume; units include \text{g/L}, percent, etc.
- Molarity M = \dfrac{\text{moles solute}}{\text{liter of solution}}; used to define solution strength.
- On the exam, you should know what molarity represents, not necessarily perform calculations.

Dehydration synthesis (condensation): monomers join, water is removed to form a covalent bond.
- Example schematic: monomer-OH + monomer-H → polymer + H$_2$O
Hydrolysis: water is added to break bonds; splits polymers into monomers.
- In sugars, water adds to break glycosidic bonds; essential for digestion and metabolism.
Key terms:
- Monomer: single building block (e.g., monosaccharide).
- Dimer: two monomers joined (e.g., disaccharide).
- Polymer: long chain of monomers (e.g., polysaccharide).

Monosaccharides: basic sugars; two common categories:
- Six-carbon sugars (hexoses): e.g., \text{glucose} (C extsubscript{6}H extsubscript{12}O extsubscript{6})
- Five-carbon sugars (pentoses)
General naming: "saccharide" means sugar; building blocks are monosaccharides.
Disaccharides: two monosaccharides linked by dehydration synthesis.
Polysaccharides: many sugar units; examples include:
- Starch and fibers: found in plants
- Glycogen: found in animals; highly branched
Nomenclature hint from the lecture: saccharides are sugars; glycogen is a storage polysaccharide in animals.

Four primary lipid subclasses (as introduced):
- Triglycerides
- Phospholipids
- Steroids
- Eicosanoids (and related oxylipins)
Triglycerides: glycerol backbone with three fatty acid tails; main form of dietary fats.
Phospholipids: glycerol backbone with two fatty acid tails and a phosphate-containing head; head is hydrophilic, tails are hydrophobic; enables bilayer formation in membranes.
Phospholipid head group: contains phosphate, commonly depicted as PO extsubscript 4; polar/hydrophilic head, nonpolar/hydrophobic tails.
Cholesterol: a steroid essential for membrane fluidity and function; supports proper membrane protein function.
Eicosanoids: signaling lipids derived from fatty acids involved in inflammation and other signaling processes.
Membrane architecture:
- Amphipathic molecules arrange into a bilayer with heads outward (water contacted) and tails inward (water-excluded).
Fatty acid saturation and properties:
- Saturated fatty acids: no double bonds; pack tightly; solid at room temperature (e.g., many animal fats).
- Unsaturated fatty acids: one or more double bonds; kinky chains prevent tight packing; liquid at room temperature (e.g., olive oil).

Signs of inflammation based on experience: swelling, redness, fever, itchiness.
Eicosanoids released during inflammation act as signaling molecules to regulate the inflammatory response.
Overall lipid signaling and membrane composition influence immune signaling and cell communication.

Carbon skeletons and hydrocarbon backbones:
- Most macromolecules are built from long carbon chains with various functional groups that confer properties.
- Functional groups attach to carbon skeletons and guide reactivity.
Building blocks, polymers, and naming conventions:
- Monomers → polymers via dehydration synthesis; monomer units include monosaccharides, amino acids, nucleotides, etc.
- Disaccharides = two monomers; polysaccharides = many monomers.
Memorization tips:
- General names: polysaccharides = carbohydrates; phospholipids = membrane components; steroids = cholesterol-related lipids; eicosanoids = signaling lipids.
- Phospholipid bilayer arrangement and amphipathic nature are central to membrane structure.
- Inflammation signals are linked to lipid mediators like eicosanoids and to classic signs: swelling, redness, fever, itchiness.