Answer: isotopes is the answer to this question
PROTO-ONCOGENES are corresponding normal cellular genes to an oncogene that is responsible for normal cell growth and division.
An oncogene refers to a gene that is capable of causing cancer due to damage to the DNA molecule either by virus or other DNA damaging agents. A proto oncogene is the normal version of the gene while an oncogene is the abnormal version of the concerned gene.
The right answer is It connects amino acids.
• Amino acids are the building blocks of proteins.
• There are 21 amino acids, but only one type of binding used to connect them: it is the peptide bond.
The peptide bond is formed during the translation step by a covalent bond between an α-amino group of an amino acid and the carboxylic group of another amino acid. A molecule of water is eliminated.