Which of the following statements correctly describes enzymes? (select all that apply.) a. they are used up during the reaction. b. they speed up chemical reactions. c. they become part of the product. d. they only react with a specific substrate.

B. They speed up chemical reactions.

D. They only react with a specific substrate.

Explanation:

Most of the enzymes are proteins which speed up chemical/biochemical reactions by (1) lowering the activation energy & (2) producing binding energy.

Apart from this enzymes are very specific for their substrates. The active sites in the enzymes can only accommodate specific substrates. Enzymes have three types of specificity which are mentioned as under:

1) Bond specificity

2) Functional group specificity

3) Stereo specificity

A particular enzyme requires specific bond to be present in the substrate. For example, proteases require amide bond, lipases require ester bond in their substrate etc.

The examples of functional group specificity is kinases require hydroxyl group while methylases require methyl group to be present in their substrate.

As far as stereo specificity is concerned, certain enzymes which are involved in amino acid metabolism only act upon L amino acids while those which are involved in carbohydrate metabolism can recognize only D-carbohydrates.  

your body is trying to warm itself up. or more precisely, sensors in your skin send messages to your brain to generate heat to your body.