Molecular biology is about understanding the interactions between the various systems of a cell, particularly the relationship between DNA, RNA and protein synthesis, and regulation of these interactions. It overlaps significantly with other biological sciences, notably genetics and biochemistry. Molecular biologists use a variety of techniques to study nucleic acids and proteins, including polymerase chain reaction (PCR), DNA and RNA sequencing, DNA microarrays and nucleic acid electrophoresis. PCR is a technique that is used to amplify a piece of DNA, generating thousands to millions of copies of a specific DNA sequence in a few hours. DNA sequencing is the determination of the order of nucleotides in a strand of DNA, while RNA sequencing examines the quantity and sequences of RNA in a sample to analyze gene expression patterns and transcriptomics. DNA microarrays are a collection of gene sequences immobilized on a solid support, such as glass, a silicon chip or microscopic beads. These arrays enable molecular biologists to measure the expression of tens of thousands of genes simultaneously and to genotype multiple regions of a genome. Nucleic acid electrophoresis is a way of separating DNA, RNA and proteins on the basis of size and electric charge.