Cell Biology, pH, and Buffers

Comprehensive vocabulary flashcards covering cellular organelles, membrane biochemistry, pH calculations, and physiological buffer systems based on the lecture notes.

Mitochondria

A double-membraned energy factory containing circular DNA and an alkaline matrix with a pH of approximately $7.8$, hosting the TCA cycle and Oxidative Phosphorylation.

Cytosol

The aqueous matrix of the cell with a neutral pH of approximately $7.2$ where glycolysis, fatty acid synthesis, and translation on free ribosomes occur.

Lysosomes

Acidic waste-processing organelles with a pH between $4.5$ and $5.0$ maintained by ATP-driven V-type $H^+$ ATPase pumps and containing acid hydrolases.

Nucleus

The genomic storage vault with a neutral pH of approximately $7.2$ that contains chromatin and performs DNA replication and transcription.

Smooth Endoplasmic Reticulum (ER)

A network of membrane sheets responsible for steroid hormone synthesis, membrane lipid synthesis, and xenobiotic drug detoxification via Cytochrome P450.

Peroxisomes

Single-membrane vesicles that perform very-long-chain fatty acid ($VLCFA$) oxidation, plasmalogen synthesis, and hydrogen peroxide ($H_2O_2$) breakdown via catalase.

Golgi Apparatus

Flattened membrane sacs with a slightly acidic pH of $6.0$ to $6.5$ involved in post-translational protein modification, including glycosylation and sulfation.

Cholesterol

A membrane component that serves as a physical buffer, reducing fluidity at high temperatures and preventing tight lipid packing and crystallization at cold temperatures.

Unsaturated Fatty Acids

Lipids with hydrocarbon chains containing bent structures due to cis double bonds, which prevent tight packing to maintain membrane fluidity.

$K_w$ (Autoionization Constant)

The equilibrium constant for the autoionization of water, calculated as $K_w = [H^+][OH^-] = 1.0 \times 10^{-14}$ at $25^\circ C$.

pH

A logarithmic scale used to express the acidity of a fluid, defined by the equation $\text{pH} = -\log_{10} [H^+]$.

pKa

The negative logarithm of the acid dissociation constant ($K_a$), representing the exact pH at which a weak acid is exactly $50\%$ dissociated.

Henderson-Hasselbalch Equation

An equation used to calculate the pH of a weak acid system: $\text{pH} = \text{pKa} + \log_{10} \left( \frac{[A^-]}{[HA]} \right)$, where $[A^-]$ is the conjugate base and $[HA]$ is the weak acid.

Acidosis

A clinical condition characterized by a blood pH below the survival range limit of $7.35$.

Alkalosis

A clinical condition characterized by a blood pH above the survival range limit of $7.45$.

Bicarbonate Buffer System

The premier extracellular buffer system that couples carbon dioxide ($CO_2$), carbonic acid ($H_2CO_3$), and bicarbonate ($HCO_3^-$) to regulate blood pH.

Phosphate Buffer System

The primary intracellular buffer system consisting of dihydrogen phosphate ($H_2PO_4^-$) and monohyrogen phosphate ($HPO_4^{2-}$) with a pKa of $6.8$.

Protein Buffer System

The most abundant buffer system inside cells and plasma, relying heavily on Histidine residues with an imidazole side chain pKa of approximately $6.0$.

Hemoglobin

A protein in red blood cells that acts as a buffer by binding free protons ($H^+$) in tissues and releasing them in the lungs to form $CO_2$ gas.