DNA and RNA Structure

• Rosalind Franklin performed X-Ray Crystallography of DNA in the 1950s
• Franklin's X-Ray Crystallography revealed a pattern that was regular and repetitive
• Edwin Chargaff analyzed DNA samples from different species during the same time as Franklin
• Chargaff found that the amount of adenine equals the amount of thymine in DNA
• Chargaff also found that the amount of cytosine equals the amount of guanine in DNA
• Purines have a double ring structure (Adenine, Guanine) in nucleotide structure
• Pyrimidines have a single ring structure (Cytosine, Uracil, Thymine) in nucleotide structure
• Base pairs in DNA are held together by hydrogen bonds
• Adenine and thymine have two hydrogen bonds
• Cytosine and guanine have three hydrogen bonds
• Hydrogen bonds aid in DNA replication by allowing the DNA strands to be easily separated
• If a DNA sample has 22% cytosine, you would expect 28% thymine in the sample
• Watson and Crick combined Franklin's helix shape and Chargaff's base pairing to create the first 3D, double helix model of DNA
• DNA is a double-stranded helix
• DNA strands are antiparallel, with one strand running 5' to 3' and the other running 3' to 5'
• The 5' end of DNA has a free phosphate group, while the 3' end has a free hydroxyl group
• The backbone of DNA is sugar-phosphate, and the center has nucleotide pairing
• DNA is the primary source of heritable information
• Genetic information is stored in and passed from one generation to the next through DNA
• RNA is the primary source of heritable information in some viruses
• Prokaryotic DNA is found in the nucleoid region and has circular chromosomes
• Eukaryotic DNA is found in the nucleus and has linear chromosomes
• Plasmids are small, circular DNA molecules found primarily in prokaryotes
• Plasmids replicate independently from chromosomal DNA
• Plasmids contain genes that may be useful in specific environments but not required for survival
• Plasmids can be manipulated in laboratories to insert genes of interest and form recombinant plasmid DNA
• Bacteria can exchange genes found on plasmids with neighboring bacteria, aiding in survival
• RNA is single-stranded, while DNA is double-stranded
• In DNA, A=T and C=G, while in RNA, A=U and C=G
• Chargaff's rule states that in any species, the amount of A=T and the amount of C=G in DNA
• The backbone of DNA comprises sugar-phosphate groups
• Purines in DNA are adenine and guanine
• Hydrogen bonds hold together nucleotides in DNA
• Chargaff discovered A=T, C=G; Franklin revealed the helix shape of DNA; Watson and Crick created the 3D model of DNA
• Key differences between RNA and DNA: DNA is double-stranded with A=T, RNA is single-stranded with A=U
• Antibiotic-resistant genes are not found in the chromosomal DNA of Methicillin-resistant staphylococcus aureus (MRSA)
• When MRSA is cultured with non-resistant bacteria, the non-resistant bacteria becomes antibiotic resistant
• Antibiotic-resistant genes are located on plasmids and are transmitted to non-resistant bacteria through gene exchange