In this IBDP Biology blog post, we will be looking at the roles of different types of ezymes, and why enzymes are not able to break down cellulose.
The role of membrane-bound enzymes
Some digestive enzymes are immobilised on the plasma membrane of the epithelial cells of the small intestine, serving two main benefits:
The enzyme is fixed in place and does not pass through the digestive system, meaning it can be reused
- The enzyme can be linked to secondary functions (e.g. membrane transport)
- Example:
Maltase is immobilised on the epithelial lining with its active site facing towards the intestinal lumen
- Maltase digests the disaccharide maltose into two glucose monomers, which are then absorbed by localised transporters
The reason for cellulose not being digested
Glucose can exist in one of two isomeric forms: a-glucose or ß-glucose
While humans can digest polymers of a-glucose (e.g. starch, glycogen), they cannot digest the polymer of ß-glucose (cellulose).
- This is because they do not produce the necessary enzyme (cellulase)
- They lack bacteria in their gut capable of digesting cellulose
- Cellulose is a component of plant cell walls and the main source of dietary roughage (undigested, it creates bulk which stimulates peristalsis)
That is all!
References:
https://www.google.com/url?sa=i&url=http%3A%2F%2Fib.bioninja.com.au%2Fstandard-level%2Ftopic-1-cell-biology%2F13-membrane-structure%2Fmembrane-proteins.html&psig=AOvVaw0eE9ZGIR3zBpZTjOkc4sHV&ust=1627813010443000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCLCG6ZSKjfICFQAAAAAdAAAAABAD
https://www.google.com/url?sa=i&url=http%3A%2F%2Fchemistry.elmhurst.edu%2Fvchembook%2F547cellulose.html&psig=AOvVaw2qZYl1wwMrCBpQkuBAY5wm&ust=1627813081813000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCJCj7LaKjfICFQAAAAAdAAAAABAD
Drafted by Venetia (Biology)