Neurotransmitters are that travel across the to another cell.

              Neurotransmitters are chemical messengers that travels across the synaptic cleft to another cell.

Explanation:

                       Neurotransmitters are small amine molecules, amino acids or neuro peptides, often referred to as the body’s chemicals messengers. As nerve impulse that travel across the axon reach to the end of terminal buttons (presynaptic neuron), it triggers the influx of calcium which cause the synaptic vesicle to fuse with membrane. At this point neurotransmitters are released into synaptic cleft which travels across the synapsis. After reaching to the post synaptic cleft these neurotransmitters attach to the receptors present on the post synaptic cleft. So, in this way nerve impulse from one neuron is transferred to the other neuron in the form of chemical messenger.  

explanation:

the sequence of amino acids in a protein determines its function. the dna sequence of a gene determines the amino acid sequence of the resulting protein. thus, any changes in dna sequence can result in changes in protein function. this is called a mutation.