Proteins in numbers
The question 'how many proteins are there?' has many different answers.
How many proteins are there (in total)?
The total number of known protein sequences across bacteria, archaea, eukaryotes, and viruses is approximately 465 million (UniRef100 clusters as of 2025) .
But this number includes substantial redundancy, as many sequences are highly similar or identical across closely related species or different strains of the same organism.
To address redundancy, the UniRef (UniProt Reference Clusters) 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 different proteins in human body?
The human genome contains approximately 19,000-20,000 protein-coding genes. According to GENCODE version 48, the current count stands at 19,435 genes.
- Confirmed proteins: Approximately 18,400 proteins have been experimentally validated (93% of predicted proteins, per the 2023 HUPO Human Proteome Project)
- Protein isoforms: Alternative splicing generates roughly 70,000 distinct protein isoforms from the ~20,000 genes
- Proteoforms: When accounting for all post-translational modifications, 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: Proteins fold into 4 principal classes (all-α, all-β, α/β, α+β domains) encompassing approximately 1,195 distinct protein folds recognized in structural databases.
Functional classification: Proteins are organized into 7-10 major functional categories:
- Enzymes (catalytic proteins)
- Structural proteins
- Transport proteins
- Regulatory proteins (including hormones)
- Antibodies (immunoglobulins)
- Contractile proteins
- Storage proteins
- Receptors
- 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 are subdivided into:
- 1,653 metabolic enzymes
- 1,089 non-metabolic enzymes
These enzymes 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:
- Small 40S subunit: 33 proteins
- Large 60S subunit: 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 reflecting technical limitations in detection and quantification methodologies.
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:
- Adult males: 10.6-11.1 kg (approximately 15% of 70 kg body weight)
- Adult females: 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.
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/