Analysis of microarray data - VSN International

Analysis of Microarray Data in GenStat 3IntroductionDNA is used to carry the instructions for cell processes. DNA is made up of fournucleotide bases: adenine, cytosine, guanine and thymine (abbreviated as A, C, Gand T respectively). These bases join into two complementary pairs, with A onlybinding to T and C with G. The bases are arranged in a double stranded helix (thebackbone of the strands being made up of phosphate, the 5-carbon sugardeoxyribose) with complementary pairs of bases on each strand. Two single strandsof DNA with sequences of bases have complementary bases at all matchingpositions (such as ACTGTGA and TGACACT) are known as a complementarysequence. In a solution of the right temperature, these two single stands will bindtogether, to form a single double stranded section of DNA. If the temperature of thesolution is raised the doubled stranded DNA will split back intotwo single stranded sections of DNA.To reproduce, a cell must copy and transmit its genetic information(DNA) to all of its progeny. To do so, DNA replicates, followingthe process of semi-conservative replication. The two strandsseparate and each strand of the original molecule acts as a templatefor the synthesis of a new complementary DNA molecule.DNA is permanent/long term copy of the cells information kept inthe cell’s nucleus. To express the information in the DNA, a singlestranded copy of the bases is made. This single strand is known asRNA, and it uses the base uridine (U), in place of the base T. DNAserves as the template to make RNA. This process is known astranscription where information in the form of a sequence ofbases is transferred from a double stranded DNA molecule to asingle stranded RNA molecule, as shown to the right. Eachgroup of three bases in RNA (a codon) code for a protein (seethe diagram below right). The amino acids and the codons thatcode for each are given in Table 1.The RNA code is converted to a sequence of proteins in theribosome in a process called translation. The section of theDNA that is transcribed as a unit is known as a gene, and startswith a start sequence (start codon, e.g. AUG or GUG) andfinishes with a end sequence (stop codon, e.g. UAG etc).