6.1 DNA and RNA Structure

• DNA, or deoxyribonucleic acid, is a double-stranded molecule that contains the genetic instructions used in the development and function of all living organisms
• The structure of DNA consists of two complementary strands connected by chemical bonds between the bases adenine (A), thymine (T), guanine (G), and cytosine (C)
• RNA, or ribonucleic acid, is a single-stranded molecule that acts as a template for protein synthesis and can also act as genetic material in certain viruses
• DNA and RNA are the primary sources of heritable information, passing down the genetic code that determines an organism's characteristics, traits, physical appearance, metabolism, and susceptibility to diseases
• In eukaryotic cells, DNA is packaged into chromosomes in the nucleus, ensuring accurate distribution of genetic information during cell division
• Prokaryotic cells, like bacteria, have DNA in a single circular chromosome and small circular DNA molecules called plasmids
• Other genetic materials in eukaryotic cells include mitochondrial DNA and chloroplast DNA, which also play a role in heritable information transfer
• Nucleotide base pairing is fundamental for DNA and RNA structure and function, with adenine pairing with thymine (A-T) and cytosine pairing with guanine (C-G) in DNA
• Complementary base pairing allows DNA to maintain its double-helix structure and ensures accurate replication and transmission of genetic information
• In RNA, uracil (U) replaces thymine, so adenine pairs with uracil (A-U)
• Purines (adenine and guanine) have a double-ring structure, while pyrimidines (cytosine, thymine, and uracil) have a single-ring structure, allowing for specific base pairing between them
• The sugar-phosphate backbone of DNA and RNA provides a structural framework, while the sequence of bases encodes genetic information, making them essential for heritable information transfer in living organisms