Dna Case

DNA is shaped like a twisting ladder which is called a double helix, which spirals clockwise. DNA is a pattern of nucleotides, which has a nitrogenous base, a 5 carbon sugar, and a phosphate group. The backbone of DNA is based on a repeated pattern of a sugar group and a phosphate group. The phosphate of one nucleotide is covalently bonded to the sugar of the next nucleotide. The hydrogen bonds between phosphates cause the DNA strand to twist. The sugar present in DNA is deoxyribose. There are four nitrogenous bases: Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). Adenine and Guanine are purines, and Cytosine and Thymine are pyrimidines. These nitrogenous bases make up the rungs of the ladder by pairing up in a specific way. Adenine and Thymine always pair up, and Guanine and Cytosine always pair up. The left side of DNA runs 5’ to 3’ and the right side runs 3’ to 5’.

Each gene is responsible for one protein, so DNA provides information for building proteins. Transcription occurs in the nucleus and consists of three steps: initiation, elongation, and termination. RNA polymerase attaches to the promoter region of a DNA strand. The RNA polymerase, with the help of transcription factors, adds the appropriate RNA nucleotides (U,A,C,G) to the 3’ end of the growing strand. The growing mRNA strand separates from the DNA as it grows longer. At the termination site the mRNA is released and set free. Before mRNA leaves the nucleus, the 5’ end is given a guanine cap, which helps to protect the RNA, and the 3’ end is given a polyadenine tail, which may ease the movement from the nucleus to the cytoplasm. RNA splicing cuts out the introns of the mRNA and combines the remaining exons to produce the mRNA that is translated into a protein. Next, the mRNA moves out of the nucleus to the cytoplasm. Genes code for proteins by using the genetic code, which is the sequence of nitrogenous bases along one of the two strands that code for the synthesis of proteins. These nitrogenous bases are set