Theory question 103
Food Substances and Enzymes(a) Define enzymes (b) State six characteristics of enzymes
(c) Describe the role of pancreatic juice in the digestion of carbohydrates and proteins in a mammal
(d) In what form is carbohydrate stored in (i) animals (ii) plants (e) Describe the saprophytic nutrition of Rhizopus
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(a) Enzymes are organic catalysts, made of protein by living cells, which speed up chemical reactions without being used up.
(b) Any six: protein in nature; specific – each acts on one substrate; needed in small amounts; unchanged at the end of the reaction; work best at an optimum temperature (about 35–40°C) and are denatured by high temperature; inactive at low temperature; work best at a particular pH; many reactions are reversible; slowed by poisons/inhibitors; some need co-enzymes; can work outside the cell that made them.
(c) Pancreatic juice enters the duodenum and is alkaline, giving the right pH for its enzymes.
Amylase (amylopsin) changes starch to maltose.
Trypsin changes proteins (and peptones) to polypeptides/peptides.
Peptidases (e.g. carboxypeptidase) change polypeptides to amino acids.
(d)(i) Glycogen (in liver and muscle) – also stored as fat; (ii) starch (also sucrose).
(e) Rhizopus grows on dead organic matter such as moist bread.
Its hyphae penetrate the food and secrete digestive enzymes onto it.
The food is digested outside the hyphae (extracellular digestion) into soluble products.
The hyphae absorb the soluble food and use it for growth and energy.
Name each enzyme with its substrate and product in (c).