Introduction to Biology

Biochemistry

DNA, or deoxyribonucleic acid, is a complex molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known living organisms and many viruses. DNA is a long polymer made from repeating units called nucleotides, each of which is made up of three components: a nitrogenous base, a sugar molecule (deoxyribose), and a phosphate group. The structure of DNA is often referred to as a double helix, which was first described by James Watson and Francis Crick in 1953. Here is a step-by-step explanation of the structure of DNA and the function of each part: 1. **Nitrogenous Bases**: There are four types of nitrogenous bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). These bases pair up with each other, A with T and C with G, to form base pairs. These base pairs are the fundamental units of the genetic code, with the sequence of bases encoding the information necessary to construct proteins. 2. **Deoxyribose Sugar**: This is a five-carbon sugar molecule that forms the backbone of the DNA molecule. Each deoxyribose sugar is connected to a nitrogenous base and a phosphate group, creating a single nucleotide. 3. **Phosphate Group**: The phosphate group is connected to the 5' carbon of the deoxyribose sugar and links to the 3' carbon of the next sugar molecule in the chain. This creates a sugar-phosphate backbone that is the structural framework of DNA. The linkage between the phosphate group of one nucleotide and the sugar of the next nucleotide creates a phosphodiester bond. 4. **Double Helix**: The double helix structure of DNA is formed by two strands of nucleotides that twist around each other. Each strand has a directionality, with one end having an exposed 5' phosphate group and the other end having an exposed 3' hydroxyl group. The two strands are antiparallel, meaning they run in opposite directions. 5. **Hydrogen Bonds**: The nitrogenous bases on one strand form hydrogen bonds with the bases on the opposite strand, which holds the two strands together. Adenine pairs with thymine via two hydrogen bonds, and cytosine pairs with guanine via three hydrogen bonds. These hydrogen bonds are relatively weak, which allows the strands to separate during DNA replication and transcription. 6. **Major and Minor Grooves**: The twisting of the DNA strands around each other results in the formation of major and minor grooves. These grooves are the sites where proteins, such as transcription factors and other DNA-binding proteins, can bind to the DNA molecule to regulate gene expression and replication. The function of each part of the DNA molecule is integral to its role in storing and transmitting genetic information. The sequence of nitrogenous bases encodes the genetic instructions, the sugar-phosphate backbone provides structural stability, and the hydrogen bonds allow for the DNA to be copied and read by the cellular machinery. The major and minor grooves are important for the regulation of these processes by providing binding sites for proteins that control gene expression.

Question

Can you label the structure of DNA and explain the function of each part?

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