# Source note — Inside a human cell / ribosomes, microtubules and ATP

Date checked: 2026-07-19

## Social lead
- URL: https://www.instagram.com/reel/DX1CGIZMKJs/
- Account shown: `scienceoftheuniverse`
- Public caption describes a single human cell, microtubules, ribosomes, kinesin transport, ATP turnover, DNA length and ~37 trillion cells.
- Video access: public browser view showed a rendered/CG cell visualization; `yt-dlp` could not download the media without login.

## Evidence label
Educational biology source card. This is not a treatment, supplement, cure or diagnostic claim.

## Claims checked
1. Human body contains on the order of ~37 trillion cells.
2. Ribosomes build proteins by adding amino acids; eukaryotic translation rates are commonly in the single-digit amino acids/second range, with context-dependent variation.
3. Microtubules act as cellular tracks; kinesin motors use ATP to move cargo.
4. Kinesin speeds around hundreds of nm/sec are plausible; BioNumbers lists kinesin-1 at 814 ±16 nm/sec.
5. Human ATP turnover can be roughly body-weight scale per day; BioNumbers lists 1 body weight ATP/day / ~60 kg ATP/day.
6. DNA in a mammalian nucleus is about 2 meters if stretched out; BioNumbers lists “Length of DNA in nucleus — Mammals — 2 meters.”

## Sources
- Bianconi et al., “An estimation of the number of cells in the human body,” PubMed PMID 23829164.
- BioNumbers BNID 105606, daily turnover of ATP.
- BioNumbers search results for ribosome progression and kinesin velocity.
- Nature Reviews Molecular Cell Biology, “Mechanism and regulation of kinesin motors,” 2024.
- NCBI Bookshelf, Molecular Biology of the Cell, “From DNA to RNA.”

## Caveats
- The reel appears to use a rendered animation, not direct live microscopy of one human cell.
- Cell counts, ribosome counts, mitochondria counts, ATP turnover and DNA-distance comparisons are scale estimates. They vary by tissue, cell type, body size and assumptions.
- The “factory” language is a metaphor: cells are self-organizing biochemical systems, not consciously directed machines.