What's the difference between a promoter, a primer and a probe?

This is confusing because they all begin with pesky Ps! DNA probes are short, single stranded DNA molecules used to 'probe', or search, a DNA fragment for its complementary DNA sequence. The probe binds to the sequence, within the DNA fragment, to be detected by complementary base pairing. Probes are labelled with either radioactive isotopes or fluorescent dyes, thus easily detected. Complementary fragments within samples can therefore be distinguished from the rest of the fragments in the sample as they will be bound by labelled probes. Probes can be used to detect the presence of specific mutations within patient DNA samples. A promoter is a region of DNA which comes before (upstream of) the transcriptional start site. Promoters 'promote' the transcription of the gene they lie upstream of. When specific transcription factors bind to the promoter, RNA polymerase is activated to transcribe the gene. Primers are used in DNA replication/synthesis initiation. They are short, single stranded nucleic acid molecules. DNA polymerases are only able to start adding nucleotides to the 3' end of an existing nucleotide. They cannot bind to a single stranded template and start synthesising the complementary strand from scratch. They require a primer (an RNA primer in this case), bound to the template, to begin synthesising a complementary strand.