Nucleic Acids and Protein Synthesis Biology Chapters 12 & 13

DNA DNA is a complex organic molecule made of repeating monomers. Nucleotides are the repeating monomers or subunits that make up DNA. The DNA molecule consists of two long strands, each a chain of nucleotides.

Nucleotides Each nucleotide consists of three parts: Deoxyribose: a five-carbon sugar molecule Phosphate Group Nitrogen Base The sugar and phosphate molecules are the same for every nucleotide, however there are four different nitrogen bases.

Nitrogen Bases The four N bases are: Adenine, Guanine, Thymine and Cytosine. Purine bases have a double ring of C and N atoms and include Adenine and Guanine. Pyrimidines have a single ring of carbon and nitrogen and include Thymine and Cytosine.

Structure of DNA DNA consists of nucleotides bonded to each other to form a long strand. The strands bond together and form the molecule by twisting around each other in a special structure called a double helix.

Double Helix The double helix resembles a twisted ladder. The sides of the ladder are composed of alternating sugar and phosphate molecules. The rungs of the ladder are formed by the bonding pairs of nitrogen bases. The two strands of DNA are held together by hydrogen bonds formed between the purines and pyrimidines. Adenine always bonds with thymine and guanine always bonds with cytosine.

Replication of DNA Replication is the process by which strands of DNA are copied. During replication, the complementary strands unwind and serve as a template for a new complementary strand.

Process of Replication Steps of Replication: Enzyme DNA helicase attaches to a DNA molecule and “unzips” the two strands of DNA by breaking hydrogen bonds. Unpaired strands react with the complementary bases of nucleotides floating in the nucleus. Complementary bases bond with bases in the DNA strands by forming hydrogen bonds. As the hydrogen bonds form, DNA polymerase forms bonds between sugar and phosphate atoms to form the backbone of two new DNA molecules.

Process of Replication

Function of Replication The process of replication occurs at many points on the strand of DNA simultaneously. The function of DNA replication is to produce strands of DNA in a fast and accurate process that contains enzymes that “proof read” the strand. DNA also has enzymes that repair it from chemical and physical damage as well as radiation.