Regulation of Metabolism, Acid–Base Balance, and Gas Laws

Vocabulary flashcards covering metabolic regulation (glycolysis, gluconeogenesis), key enzymes and regulators, nucleotide chemistry, amino-acid properties, buffer chemistry, pH calculations, and fundamental gas laws relevant to human physiology.

Glycolysis

Cytoplasmic pathway that converts one glucose into two pyruvate, yielding 2 ATP and 2 NADH; favored when energy (ATP) is low.

Gluconeogenesis

Liver process that synthesizes glucose from non-carbohydrate precursors during fasting, starvation, or intense exercise; opposed by insulin and fructose-2,6-bisphosphate.

Phosphofructokinase-1 (PFK-1)

Rate-limiting enzyme of glycolysis; inhibited by ATP, citrate, and low pH, but activated by AMP and fructose-2,6-bisphosphate.

Hexokinase

First glycolytic enzyme that phosphorylates glucose to glucose-6-phosphate; subject to product inhibition by glucose-6-phosphate.

Pyruvate Kinase

Final glycolytic enzyme converting phosphoenolpyruvate to pyruvate and ATP; regulated by energy status and hormonal signals.

Fructose-2,6-Bisphosphate

Allosteric regulator that stimulates PFK-1 (enhancing glycolysis) and inhibits fructose-1,6-bisphosphatase (slowing gluconeogenesis).

AMP (as glycolytic activator)

Low-energy signal that allosterically activates PFK-1, promoting glycolysis when ATP is scarce.

Citrate (as glycolytic inhibitor)

Krebs-cycle intermediate that signals plentiful mitochondrial energy, inhibiting PFK-1 and slowing glycolysis.

Insulin

Hormone that increases hepatic fructose-2,6-bisphosphate, accelerating glycolysis and suppressing gluconeogenesis.

Glucagon

Hormone that lowers fructose-2,6-bisphosphate, inhibiting glycolysis and stimulating gluconeogenesis in the liver.

Cori Cycle

Metabolic pathway in which muscles convert glucose to lactate (anaerobic glycolysis) and the liver reconverts lactate to glucose (gluconeogenesis).

Wobble Base Pairing

Non-standard pairing at the third codon position (3′ codon / 5′ anticodon) allowing one tRNA to recognize multiple codons without altering the encoded amino acid.

Keto Form (tautomer)

Major, more stable tautomer with a carbonyl (C=O); predominates over the enol form and supports correct Watson–Crick base pairing.

Enol Form (tautomer)

Minor tautomer containing an –OH attached to a C=C; can mispair bases during DNA replication, leading to mutations.

Tautomeric Shift

Spontaneous conversion between keto and enol forms that can cause G↔T or A↔C mispairing in DNA.

Aspartate (Asp, D)

Amino acid with a deprotonated carboxylate side chain (–COO⁻) at physiological pH, giving a negative charge and metal-binding ability.

Glutamate (Glu, E)

Amino acid bearing a negatively charged carboxylate side chain capable of coordinating metal ions such as Mg²⁺ or Ca²⁺.

Buffer

Solution containing a weak acid/base pair that resists pH changes when small amounts of strong acid or base are added.

Buffering Capacity

Quantity of acid or base a buffer can absorb before significant pH change; maximal when pH ≈ pKa and effective within ±1 pH unit of pKa.

Henderson–Hasselbalch Equation

Relationship pH = pKa + log([A⁻]/[HA]) used to calculate the pH of a buffer system.

Blood Bicarbonate Buffer System

Physiological buffer that maintains blood pH ~7.4, regulated by lungs (CO₂ removal) and kidneys (H⁺/HCO₃⁻ balance).

pH

Negative logarithm of hydrogen ion concentration; pH = –log[H⁺].

pOH

Negative logarithm of hydroxide ion concentration; pH + pOH = 14 at 25 °C.

Henry's Law

Concentration of a gas dissolved in a liquid is directly proportional to its partial pressure above the liquid (C ∝ P).

Boyle's Law

For a fixed amount of gas at constant temperature, pressure and volume are inversely related (P₁V₁ = P₂V₂).

Charles's Law

At constant pressure, the volume of a gas is directly proportional to its absolute temperature (V ∝ T).

Dalton's Law

Total pressure of a gas mixture equals the sum of the partial pressures of each component gas (Ptotal = ΣPi).