Biochemistry Terms Starting With V
Biochemistry Glossary: V
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Valine
/VAL-een/ · Latin valere meaning to be strong
Valine is an essential branched-chain amino acid with a hydrophobic side chain that humans must obtain through diet because the body cannot synthesize it.
The adult human body requires approximately 24 milligrams of valine per kilogram of body weight daily to maintain protein synthesis and tissue repair. In Escherichia coli, valine biosynthesis proceeds through a five-step enzymatic pathway beginning with pyruvate, yet mammals lack these enzymes entirely. Dietary sources rich in valine include meat, dairy products, legumes, and whole grains, with one cup of cottage cheese providing roughly 1,500 milligrams of this amino acid.
Within proteins, valine residues frequently cluster in hydrophobic cores, where their branched side chains stabilize tertiary structure by excluding water.
Maple syrup urine disease, affecting approximately 1 in 185,000 newborns, occurs when the body cannot break down valine and the other branched-chain amino acids leucine and isoleucine, causing urine to smell distinctly of maple syrup due to accumulating keto-acid metabolites.
Building Blocks of Proteins →Valine supplementation alone directly increases muscle mass. Research shows valine supports protein synthesis only when combined with adequate leucine and isoleucine in proper ratios, because all three branched-chain amino acids share the same degradative enzyme complex.
In sickle-cell hemoglobin, a single valine residue replaces glutamic acid at position 6 of the beta-globin chain, causing hemoglobin molecules to polymerize under low-oxygen conditions and deform red blood cells into a rigid sickle shape.
Van der Waals Force
/ van der WAHLZ fors / · Named after Dutch physicist Johannes Diderik van der Waals, who first described these forces in 1873
Van der Waals forces are weak intermolecular attractions between atoms or molecules arising from temporary or permanent electric dipoles.
These forces operate at distances of 0.3 to 0.6 nanometers between molecular surfaces and contribute to biomolecular stability despite their individual weakness. In gecko foot pads, millions of tiny hairs called setae exploit Van der Waals forces to create adhesion strong enough to support the animal’s entire body weight on vertical glass surfaces. Cumulative Van der Waals contacts across thousands of atom pairs in a folded protein can contribute several kilocalories per mole to stability, rivaling the contribution of individual hydrogen bonds.
Unlike covalent bonds, which require orbital overlap, these attractions arise purely from fluctuating electron distributions and require no direct chemical bonding between molecules.
A single gecko foot carries approximately 500,000 setae that together generate enough combined Van der Waals force to support over 130 kilograms, despite each individual interaction being roughly 100 times weaker than a single hydrogen bond.
Van der Waals forces exist only between nonpolar molecules. These attractions arise between all atoms and molecules, polar or nonpolar, because all electron clouds fluctuate; stronger electrostatic forces simply dominate in polar systems, making Van der Waals contributions less obvious.
The phospholipid bilayer of cell membranes relies on Van der Waals forces between the hydrocarbon tails of adjacent lipid molecules to maintain structural integrity, with each tail pair contributing roughly 0.1 to 0.2 kilocalories per mole of stabilization.
Phospholipid Bilayer →Vitamin
/ VY-tuh-min / · Latin vita meaning life + amine, originally coined in 1912 by Casimir Funk who believed all such compounds contained nitrogen
Vitamin is an organic compound required by organisms in small quantities for normal metabolic function that the body cannot synthesize in sufficient amounts and must obtain through diet.
Humans require 13 recognized vitamins, divided into fat-soluble forms, vitamins A, D, E, and K, and water-soluble forms, including the B-complex vitamins and vitamin C. Guinea pigs (Cavia porcellus) share with humans an unusual trait among mammals: both species carry a nonfunctional copy of the gene encoding L-gulonolactone oxidase, the enzyme needed to synthesize vitamin C, so both must consume it in their diet. Vitamin deficiencies produce specific, predictable diseases; a daily deficit of vitamin C below about 10 milligrams leads to scurvy within weeks, while insufficient vitamin D during childhood causes the bone-softening disease rickets.
Fat-soluble vitamins accumulate in adipose tissue and the liver, which is why toxicity from excess intake is a real clinical concern for vitamins A and D but not for water-soluble vitamins, which the kidneys excrete readily.
Polar bears (Ursus maritimus) concentrate vitamin A in their livers at levels so high that consuming just 100 grams of polar bear liver can cause hypervitaminosis A in a human, producing symptoms including severe headache, peeling skin, and liver damage.
Vitamins are harmless regardless of dose because the body excretes any excess. Fat-soluble vitamins A and D accumulate in liver and adipose tissue and reach toxic concentrations when supplemented heavily, a condition documented in Arctic explorers who consumed seal and polar bear organs.
Spinach (Spinacia oleracea) provides vitamin K1, which liver cells use to carboxylate clotting factors II, VII, IX, and X, a modification that lets these proteins bind calcium ions and assemble on phospholipid surfaces during the coagulation cascade.
Vmax
/ VEE-max / · From Latin velocity (speed) + maximum (greatest)
Vmax is the maximum rate an enzyme-catalyzed reaction can achieve when all enzyme active sites are saturated with substrate molecules.
This kinetic parameter represents the theoretical upper limit of enzymatic activity under conditions of excess substrate. Human salivary amylase exhibits a Vmax of approximately 1.2 micromoles per minute per milligram of enzyme when breaking down starch at optimal pH and temperature. Determining Vmax, typically by fitting velocity data to the Michaelis-Menten equation or by using a Lineweaver-Burk double-reciprocal plot, helps researchers compare enzyme efficiency across different conditions or species.
Competitive inhibitors do not change Vmax because a sufficiently high substrate concentration can always outcompete the inhibitor for the active site, whereas noncompetitive inhibitors reduce Vmax by blocking catalysis regardless of substrate concentration.
The enzyme catalase, present in nearly all aerobic organisms, achieves a Vmax equivalent to approximately 40 million reactions per second per molecule, making it one of the fastest enzymes known and allowing cells to neutralize hydrogen peroxide almost as fast as it forms.
Adding more substrate will keep accelerating an enzyme reaction indefinitely. Once substrate concentration reaches Vmax, every active site is occupied and turning over at its maximum rate, so additional substrate molecules simply wait and produce no further increase in reaction speed.
Hexokinase in liver cells reaches Vmax when glucose concentration exceeds approximately 10 millimolar during post-meal blood sugar spikes, at which point the enzyme phosphorylates glucose at its maximum rate of about 50 to 100 micromoles per minute per gram of tissue.