General Biochemistry - Acidity, Alkalinity, pH, and pKa

This flashcard set covers the fundamental concepts of acidity, alkalinity, pH, and pKa, as well as their specific applications and effects within biological systems and cellular compartments.

Acidity and Alkalinity

Chemical properties of a solution based on its hydrogen ion ($H^+$) concentration.

pH (Formula)

A logarithmic scale measuring $H^+$ concentration, defined by the equation $pH = -\text{log}_{10}([H^+])$. Values below $7$ are acidic, and values above $7$ are basic.

Acid

A substance that donates protons ($H^+$) in a solution, resulting in a high concentration of $H^+$ ions and a pH below $7$. Examples include hydrochloric acid ($HCl$) and lactic acid.

Alkaline (Base)

A substance that accepts protons or donates hydroxide ($OH^-$) ions, resulting in a low concentration of $H^+$ and a pH above $7$. Examples include sodium hydroxide ($NaOH$) and ammonia ($NH_3$).

Neutral Solution

A solution with equal concentrations of $H^+$ and $OH^-$ ions, maintaining a pH of $7$ (e.g., pure water at $25^{\text{o}}\text{C}$).

Ion Product of Water ($K_w$)

The constant defined as $K_w = [H^+][OH^-]$, which equals $10^{-14}$ at $25^{\text{o}}\text{C}$.

Buffers

Chemical systems in biological organisms that resist pH changes by absorbing or releasing $H^+$ ions. Common examples include bicarbonate ($HCO_3^-/H_2CO_3$) in blood and phosphate ($HPO_4^{2-}/H_2PO_4^-$) in cells.

Amphoteric

The ability of biological molecules, such as amino acids, to act as both an acid and a base because they contain both acidic (carboxyl) and basic (amino) groups.

Cytosol pH

Maintains a near-neutral pH of approximately $7.2$ for metabolic processes.

Lysosomes pH

Maintains an acidic environment of approximately $4.5$ to $5.0$, which is necessary for hydrolysis.

Mitochondria Matrix pH

Maintains an alkaline environment of approximately $7.8$ for ATP production.

Endoplasmic Reticulum pH

Maintains a pH of approximately $7.0$, which is optimal for protein folding.

V-ATPase

A proton pump responsible for maintaining distinct pH levels within various cellular organelles.

pOH

A measure of the concentration of hydroxide ions ($OH^-$) in a solution.

pK_a

The negative logarithm of the acid dissociation constant ($K_a$), defined as $pK_a = -\text{log}_{10}(K_a)$. It indicates the strength of an acid.

Acid Dissociation Constant ($K_a$)

A value that measures an acid's tendency to donate $H^+$, calculated as $K_a = \frac{[H^+][A^-]}{[HA]}$.

Maximizing Buffering Capacity

Occurs when $pH = pK_a$, at which point the acid is 50\text{%} dissociated ($[A^-] = [HA]$).

Acidosis

A physiological state where the blood pH falls below $7.35$, potentially disrupting metabolism.

Alkalosis

A physiological state where the blood pH rises above $7.45$.

Bohr Effect

The phenomenon where hemoglobin's oxygen-binding affinity decreases in acidic conditions, facilitating the release of oxygen in tissues.

Pepsin

An enzyme that functions optimally at a pH of $2$.

Trypsin

An enzyme that functions optimally at a pH of $8$.

Helicobacter pylori

A pathogen that survives the stomach's acidic environment by using the enzyme urease to produce ammonia, thereby neutralizing the local pH.

Lactic Acidosis

A condition resulting from the buildup of lactate that lowers blood pH and impairs cellular respiration.