What are enzyme substrates?
Substrates are the molecules which will be acted on by enzymes.
Some enzymes may help put substrate molecules together, these are classified as anabolic reactions.
Other enzymes function almost like molecular scissors by breaking larger molecules into smaller pieces, these are called catabolic reactions.
The sum total of all the reactions in the body (anabolic and catabolic) are the metabolic processes (metabolism).
In the video below, the enzyme salivary amylase acts on starch molecules (substrate) to produced monosaccharide and disaccharide products.
Video from: Noel Pauller
Hope this helps!