If the amino-acid sequence are similar in gorillas and humans, will the nucleotide sequence of their DNA…?
The nucleotide sequence will be similar, but not as similar as the amino acid sequence. Mammalian DNA has long sequences of junk DNA that don’t code for or regulate protein expression. Mutations in non-coding DNA aren’t selected against as strongly as mutations in coding DNA. Also, even within genes, silent mutations can occur (usually in the third nucleotide of a codon, since more than one codon codes for the same amino acid in many cases). Silent mutations change the nucleotide sequence, but not the amino acid sequence, so they’re also not selected against as strongly as mutations that change the amino acid sequence of a protein.