4. In eukaryotic cells, RNA is copied from DNA in the

Nucleus

Explanation:

In order to form amino acids and proteins, RNA that reflects the DNA found within a cell must be produced. The DNA that is found within cells that is used for gene expression is found in the nucleus of eukaryotic cells, wherein 'RNA transcription' occurs, when the RNA is copied from the DNA.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products

a covalent bond, specfically triple bond