When the proton proton chain uses two steps to convert hydrogen first into 3He and then combines two 3He nuclei into He

Question: When the proton proton chain uses two steps to convert hydrogen first into 3He and then combines two 3He nuclei into He and gives back 2H, why are neutrinos and gamma rays emitted during the process?
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Asked by binukrishnanm to Nick on 13 Mar 2014.
- Nick Wright answered on 13 Mar 2014:
  
  Both neutrinos and gamma rays are produced in these reactions to carry away energy from the reactions, and also to preserve certain quantum physical quantities that need to be preserved in these reactions. In fact it was these reactions that led to the prediction of the neutrino, which was then verified in other experiments.

Question: When the proton proton chain uses two steps to convert hydrogen first into 3He and then combines two 3He nuclei into He and gives back 2H, why are neutrinos and gamma rays emitted during the process?