Middle School Physical Science: Chemistry of Carbon - Carbon and Living Things — Flashcards

Carbon is found in all living things. Carbon atoms move constantly through living organisms, the oceans, the atmosphere, and the Earth's crust in what is known as the carbon cycle. The directions taken by carbon atoms through this cycle are very complicated and can take millions of years to make a full circle.

Structure of Nucleic Acids: Nucleic acids consist of chains of small molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar, and one of four different nitrogen-containing bases. In DNA, the bases are adenine, thymine, guanine, and cytosine. In RNA, the base uracil is substituted for thymine.    
DNA consists of two long chains of nucleotides. Sugars and phosphate groups form the “backbone” of each chain, and nitrogen bases stick out to the side from the backbone. Nitrogen bases on the two chains form hydrogen bonds with each other. Adenine always bonds with thymine, and guanine always bonds with cytosine. These bonds hold together the two chains and give DNA its characteristic double helix, or spiral, shape. RNA, in contrast to DNA, consists of just one chain of nucleotides.    
DNA stores genetic information in the cells of all living things. It contains the genetic code, which instructs cells how to make proteins. The instructions are encoded in the sequence of nitrogen bases in the nucleotide chains of    
DNA. RNA “reads” the genetic code in DNA and is involved in the synthesis of proteins based on the code.