Question

Where does a protein molecule travel before becoming part of your body?

Answer 1

Short answer: Almost nowhere as an intact protein. Dietary proteins are first broken into amino acids and small peptides in your gut, those pieces are absorbed into the blood, carried to cells, and your cells rebuild new proteins from the amino acids. If you mean body-made proteins, their components travel inside the cell (ribosome → endoplasmic reticulum → Golgi → final destination) before becoming part of your tissues.

Step-by-step (food protein → body protein)
1. Mouth/stomach: chewed and mixed with acid; stomach pepsin begins breaking large proteins into smaller polypeptides.
2. Small intestine: pancreatic proteases (trypsin, chymotrypsin, others) and brush-border peptidases break polypeptides into di-/tripeptides and free amino acids.
3. Absorption: amino acids and small peptides are taken up by enterocytes (intestinal cells) via transporters (PepT1 for di/tri-peptides, various amino-acid transporters). Inside enterocytes peptides are usually hydrolyzed to amino acids.
4. Blood transport: amino acids enter the portal vein to the liver. The liver uses, stores, or releases them into the systemic circulation.
5. Uptake by body cells: target cells take up amino acids via membrane transporters.
6. Protein synthesis: cells assemble amino acids on ribosomes according to mRNA. Newly made polypeptides often enter the rough endoplasmic reticulum, are modified in the Golgi, then sent to their final location (cytosol, organelles, membrane, or secreted).

Notes:
- Very few intact dietary proteins become part of body proteins unchanged; your body rebuilds proteins from amino acids.
- Exceptions: newborns can absorb some intact antibodies from breast milk; some intact proteins/peptides can cross in pathological situations.