DNA

DNA is deoxyribonucleic acid, the template for genetic instructions. DNA undergoes replication into complementary strands of DNA for reproduction, and transcription into RNA before translation into proteins. The nucleotide bases, adenine, thymine, cytosine, and guanine are coupled inside the double helix, while the ribose backbone curves around the edge. (click images to enlarge) DNA image - public domain.

DNA topology:

Eubacterial : negatively supercoiled.
Archaeal : relaxed or positively supercoiled (in hyperthermophilic Archaea that contain reverse gyrase).
Eukaryotic : negatively supercoiled.

Table  Comparisons of Eubacteria, Archaea, and Eukaryotes : :


Right - nucleobases form complementary pairs through hydrogen bonding. Adenine and thymine are coupled (broken lines), and cytosine couples with guanine.

grey - carbon / white - hydrogen / blue - nitrogen / red - oxygen / green - phosphorus

ball-stick - dna double helix : animation - adenine tyrosine H bonds : animation - cytosine guanine H bonds : animation - start of transcription :

More at: http://www.dnaftb.org/dnaftb/ : http://www.dnalc.org/home.html : http://www.pbs.org/wgbh/aso/tryit/dna/ : Genomics Animations and Images - Genetics of Development - Animations and Images - Biology of Sex & Gender - Animations and Images - Genetically modified organisms - Animations and Images - Biodiversity - Animations and Images :

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