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Key takeaways
- Total known protein sequences: ~465 million (UniRef100, 2025)
- Theoretical possible proteins: 20¹⁰⁰ for a 100-amino-acid sequence
- Human genome encodes ~20,000 genes producing ~70,000 protein isoforms
- A typical human cell expresses 10,000–12,000 unique protein types
- A typical human cell contains ~10 billion protein molecules
How many proteins are there (in total)?
The total number of known protein sequences across bacteria, archaea, eukaryotes, and viruses is approximately 465 million, according to UniRef100 clusters as of 2025. But this number includes redundancies, as many sequences are highly similar or identical across closely related species or different strains of the same organism.
To address this, the UniRef database clusters sequences by similarity: UniRef90 groups sequences with at least 90% identity, reducing the dataset to approximately 208 million representative sequences, while UniRef50 (50% identity threshold) contains roughly 70 million non-redundant protein clusters.
| Similarity threshold | All organisms | Human | E. coli | Mouse |
|---|---|---|---|---|
| 100% (UniRef100) | 465,330,530 | 240,492 | 4,123,300 | 104,878 |
| 90% (UniRef90) | 208,005,650 | 102,200 | 489,230 | 51,756 |
| 50% (UniRef50) | 70,198,728 | 50,977 | 192,216 | 25,634 |
How many possible proteins could exist?
The theoretical number of possible proteins is astronomically larger than what exists in nature. For a protein of just 100 amino acids (relatively short), there are 20¹⁰⁰ possible sequences—a number so vast it exceeds the number of atoms in the observable universe (approximately 10⁸⁰).
Even limiting to functional proteins, estimates suggest only a tiny fraction of sequence space has been explored by evolution. The ~465 million known protein sequences represent an infinitesimally small sample of what's chemically possible, which is why protein design and engineering remain active research frontiers.
How many different proteins in human body?
The human genome contains approximately 19,000–20,000 protein-coding genes. According to GENCODE version 49, the current count stands at 19,433 genes. However, so far 93% of predicted proteins (approximately 18,400 proteins have been experimentally validated), per the 2023 HUPO Human Proteome Project.
Alternative splicing is an important mechanism that enables a single gene to produce multiple protein variants, allowing the ~20,000 genes to generate roughly 70,000 distinct protein isoforms. This process explains how humans create far more proteins than genes, as different combinations of exons are selectively included or excluded during mRNA processing.
The complexity increases further when accounting for post-translational modifications, which create proteoforms—estimates range from hundreds of thousands to 1 million proteoforms per cell type, with up to 6 million proteoforms across the entire human population.
How many types of protein are there?
Protein classification depends on the organizational framework employed. Structural classification organizes proteins into 4 principal classes based on their secondary structure content—all-α, all-β, α/β, and α+β domains—encompassing approximately 1,195 distinct protein folds recognized in structural databases.
Functional classification, on the other hand, organizes proteins into 7-10 major categories based on their biological roles. These include enzymes (catalytic proteins), structural proteins, transport proteins, regulatory proteins (including hormones), antibodies (immunoglobulins), contractile proteins, storage proteins, receptors, and genetic regulatory proteins (transcription factors).
How many enzymes are there in the human body?
The human genome encodes approximately 2,700–2,750 enzyme genes, representing roughly 9.5% of all protein-coding genes. These enzymes are functionally divided into 1,653 metabolic enzymes and 1,089 non-metabolic enzymes. Collectively, they catalyze reactions classified into over 7,787 active EC (Enzyme Commission) numbers across seven major enzyme classes: oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, and translocases.
How many proteins are in ribosomes?
Human ribosomes contain 79–80 different ribosomal proteins distributed across two subunits. The small 40S subunit contains 33 proteins, while the large 60S subunit contains 46-47 proteins. These proteins combine with ribosomal RNA to form the complete 80S eukaryotic ribosome responsible for protein synthesis.
How many proteins are in a typical human cell?
A typical human cell contains approximately 10 billion (10¹⁰) individual protein molecules. Mass spectrometry measurements often yield lower estimates of 1-3 billion molecules, likely due to technical limitations in detection and quantification methodologies.
However, the number of unique protein types per cell is much smaller. Proteomics studies indicate that a typical human cell expresses 10,000–12,000 different proteins at any given time, though this varies by cell type. Highly specialized cells like neurons or hepatocytes may express more, while red blood cells express fewer than 3,000 unique proteins. The difference between 10 billion molecules and ~10,000 types means each protein is present in roughly 1 million copies on average, though actual copy numbers range from single digits for rare transcription factors to billions for abundant structural proteins like actin.
How many total protein molecules are in the human body?
With 30-37 trillion cells in the human body, the total number of protein molecules is estimated at 3.0–3.7 × 10²³ protein molecules, making proteins one of the most abundant molecular species after water.
How much protein (in grams) is in the human body?
Total body protein content varies by sex and body composition, but ranges between 8 and 11 kg. Adult males typically contain 10.6–11.1 kg of protein (approximately 15% of 70 kg body weight), while adult females contain 8.2–8.9 kg (approximately 12-14% of body weight).
Protein distribution is highly tissue-specific, with skeletal muscle containing approximately 60% of total body protein. Collagen alone accounts for roughly 25% of all body protein.
Where to browse all proteins
Several databases provide access to protein sequences and annotations:
- UniProt — The most comprehensive protein sequence database, containing over 250 million sequences with detailed functional annotations. UniProt combines manually curated entries (Swiss-Prot) with computationally analyzed sequences (TrEMBL).
- UniRef — Clustered protein sequences at 100%, 90%, and 50% identity thresholds, useful for reducing redundancy in analyses.
- PDB — The Protein Data Bank contains ~220,000 experimentally determined 3D protein structures.
- AlphaFold Database — Over 200 million predicted protein structures from DeepMind's AlphaFold2.
- neXtProt — Human-specific protein knowledge base with detailed annotations.
Sources
- GENCODE. "Human Release Statistics." https://www.gencodegenes.org/human/stats.html
- HUPO Human Proteome Project. "The 2023 Report on the Human Proteome from the HUPO Human Proteome Project." PLOS Biology, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11026053/
- Smith LM, Kelleher NL. "How many human proteoforms are there?" Nature Chemical Biology, 2018. https://pmc.ncbi.nlm.nih.gov/articles/PMC5837046/
- Romero P, et al. "Computational prediction of human metabolic pathways from the complete human genome." Genome Biology, 2005. https://pmc.ncbi.nlm.nih.gov/articles/PMC549063/
- Uechi T, et al. "The Human Ribosomal Protein Genes: Sequencing and Comparative Analysis of 73 Genes." Genome Research, 2001. https://pmc.ncbi.nlm.nih.gov/articles/PMC155282/
- Sender R, et al. "Revised Estimates for the Number of Human and Bacteria Cells in the Body." PLOS Biology, 2016. https://pmc.ncbi.nlm.nih.gov/articles/PMC4991899/
- Wang Z, et al. "Total body protein: a new cellular level mass and distribution prediction model." American Journal of Clinical Nutrition, 2003. https://academic.oup.com/ajcn/article/78/5/979/4677508
- National Research Council. "Protein and Amino Acids." Recommended Dietary Allowances: 10th Edition, 1989. https://www.ncbi.nlm.nih.gov/books/NBK234922/
- Harvard T.H. Chan School of Public Health. "Protein." The Nutrition Source. https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/protein/
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