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Guides
Proteins ·
How many amino acids are in hemoglobin?
Mature adult hemoglobin A contains 574 amino acid residues across four subunits. Counts of 578, 142, or 147 include initiator methionines or refer to individual chains.
Cells ·
How many ATP are produced in cellular respiration?
Cellular respiration produces about 30 to 32 ATP molecules per glucose in human cells: 4 directly and 26 to 28 through oxidative phosphorylation.
Cells ·
How many ATP are produced in fermentation?
Lactic acid and alcoholic fermentation each yield two net ATP per glucose. All of that ATP comes from glycolysis; the fermentation reactions add no more.
Cells ·
How many ATP are produced in glycolysis?
Glycolysis produces four ATP molecules and consumes two ATP molecules, for a net yield of two ATP per glucose.
Cells ·
How many ATP are produced in oxidative phosphorylation?
Oxidative phosphorylation produces about 26 to 28 ATP per glucose. See how NADH, FADH2, and the two mitochondrial shuttle systems produce that range.
Cells ·
How many ATP are produced in the Krebs cycle?
The Krebs cycle directly produces 2 ATP equivalents per glucose, plus 6 NADH and 2 FADH2 that can support another 18 ATP through oxidative phosphorylation.
Cells ·
How many ATP does beta oxidation produce?
Complete oxidation of palmitate yields 106 net ATP: 28 from the NADH and FADH2 made during beta oxidation, 80 from acetyl-CoA, minus 2 ATP equivalents for activation.
Cells ·
How many cell types are in the human body?
Modern atlases identify several hundred human cell types. Tabula Sapiens classified 475, while finer molecular studies find thousands of subtypes in the brain alone.
Genetics ·
How many chromosomes do humans have?
Humans typically have 46 chromosomes in most nucleated body cells: 44 autosomes and 2 sex chromosomes. Egg and sperm cells have 23 each.
Genetics ·
How many codons are there?
There are 64 possible codons in the standard genetic code. Of these, 61 specify amino acids and three are stop codons.
Genetics ·
How many CpG sites are in the human genome?
The human genome contains about 28 million CpG sites. A 2023 whole-genome methylation atlas analyzed 28,217,448 CpG positions, or roughly one per 110 base pairs.
Genetics ·
How many genes are in a chromosome?
Human nuclear chromosomes contain between 61 and 2,016 protein-coding genes. See the current gene count for chromosomes 1 through 22, X, Y, and mitochondrial DNA.
Cells ·
How many NADH are produced in glycolysis?
Glycolysis produces two NADH molecules per glucose molecule. See where they form, how much ATP their electrons can produce, and what happens without oxygen.
Proteins ·
How many peptide bonds are in a peptide?
A single linear peptide chain has one fewer peptide bond than amino acid residues. See the counts for dipeptides through hexapeptides, 100-residue chains, insulin, and cyclic peptides.
Cells ·
How many platelets are in the human body?
A typical adult has about 1 trillion circulating platelets and about 1.5 trillion platelets across the blood and spleen. Around 100 billion are produced each day.
Cells ·
How many white blood cells are in the human body?
The human body contains an estimated 1.8 trillion immune cells. About 23 to 55 billion white blood cells circulate in an adult's blood at common reference concentrations.
Genetics ·
How much DNA do cousins share?
First cousins share 12.5% of their autosomal DNA by descent on average, second cousins share 3.125%, and third cousins share 0.781%.
Genetics ·
How much DNA do siblings share?
Full siblings share about 50% of their autosomal DNA by descent on average. Identical twins share virtually 100%, while half-siblings average 25%.
Genetics ·
How long does DNA last?
DNA can remain detectable for days, years, or millennia. Its survival depends more on temperature, water, sunlight, microbes, and the sample material than on age alone.
Genetics ·
How long does DNA replication take?
Human DNA replication takes about 8 hours. See measured replication fork speeds, bacterial replication times, and how thousands of origins copy the genome in parallel.
Cells ·
How many atoms are in the human body?
A 70-kilogram human body contains about 7 × 10^27 atoms, including roughly 4.2 octillion hydrogen atoms, 1.6 octillion oxygen atoms, and 800 septillion carbon atoms.
Cells ·
How many bacteria are in the human body?
The human body carries about 38 trillion bacterial cells, with nearly all of them in the colon. Current estimates put the bacteria-to-human-cell ratio near 1:1.
Cells ·
How many cells are in the human body?
The human body contains about 36 trillion cells in a reference adult male, 28 trillion in a reference adult female, and 17 trillion in a 10-year-old child.
Drugs ·
How many FDA-approved drugs are there?
FDA data contain 26,715 active prescription and OTC drug product records as of July 2026. These represent 13,961 applications, 4,539 drug names, and 2,329 distinct nonblank ingredient entries.