The distance between two strands is 20 angstroms which can allow only a purine and a pyrimidine to fit. Adenine forms two hydrogen bonds with thymine cytosine forms three hydrogen bonds with guanine. Another point to be noted is the hydrogen bonds between the bases. This is because the amount of adenine and thymine in any living organism is very similar, and likewise the amount of cytosine and guanine. This rule states that adenine can only pair with thymine and cytosine can only pair with guanine. These bases form hydrogen bonds with each other according to Chargaff's rule or complementary base pairing rule. Adenine and guanine are purines cytosine and thymine are pyrimidines. The four nitrogenous bases for DNA are adenine, cytosine, thymine, and guanine. The sequence of nucleotides carries the genetic information for the organism. This type of replication is advantageous as the newly synthesized strand is proofread by the DNA repair enzymes and corrected for any base-pairing errors immediately. The newly synthesized daughter DNA has one new strand and one strand from the parent. This means that the DNA molecule unwinds and a new strand is synthesized by complementary base pairing to the template (old) strand. The mode of DNA replication is semi-conservative. The tRNA carries the anticodon, binds the mRNA by complementary base pairing, and attaches the amino acid in the growing polypeptide chain. Three nucleotide bases of the mRNA constitute the codon that is specific for an amino acid. During transcription, mRNA is produced using DNA as a template. Proteins are produced by the process of transcription and translation. This produces a template strand from which the new DNA strand is synthesized. During DNA replication, the hydrogen bonds between the bases are broken which causes the DNA to unwind. The backbone is hydrophilic and interacts with water and protects the nucleotides that carry the genetic information. The sugar-phosphate backbone gives the DNA its characteristic helical shape which is critical for its function. The genotype is determined by the sequence of bases.The sugar-phosphate backbone is formed between the deoxyribose sugar of one nucleotide and the phosphate group of the neighboring nucleotide via phosphodiester bonds. It is this base sequence which forms the genetic code. This creates the twisting double helix structure of DNA.Īll cells store their genetic information in the base sequence of DNA. The two strands of DNA are antiparallel which means that one strand runs in a 5’ to 3’ direction and the other runs in a 3’ to 5’ direction. the 3' end (said as "3 prime end") at the deoxyribose end.the 5' end (said as "5 prime end") at the phosphate end.These strong bonds form a sugar-phosphate backbone. These basic units are linked together to form strands by strong bonds between the deoxyribose sugar of one nucleotide and the phosphate of the next nucleotide. They always pair up in a particular way, called complementary base pairing: There are chemical cross-links between the two strands in DNA, formed by pairs of bases held together by hydrogen bonds. The nucleotides are identical except for the base, which can be one of four bases:
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