Which nitrogen bases are purines

In order for hydrogen bonding to occur at all, a hydrogen bond donor must have a complementary hydrogen bond acceptor in the base across from it. Common hydrogen bond donors include primary and secondary amine groups or hydroxyl groups. Common acceptor groups are carbonyls and tertiary amines. There are three hydrogen bonds in a G:C base pair. One hydrogen bond forms between the 6' hydrogen bond accepting carbonyl of the guanine and the 4' hydrogen bond accepting primary amine of the cytosine.

The second between the 1' secondary amine on guanine and the 3' tertiary amine on cytosine. Primary Structure of Nucleic Acids Nucleotides are joined together through the phosphate group of one nucleotide connecting in an ester linkage to the OH group on the third carbon atom of the sugar unit of a second nucleotide.

Note Each phosphate group has one acidic hydrogen atom that is ionized at physiological pH. Concept Review Exercises Identify the three molecules needed to form the nucleotides in each nucleic acid. Classify each compound as a pentose sugar, a purine, or a pyrimidine. Answers nitrogenous base adenine, guanine, cytosine, and thymine , 2-deoxyribose, and H 3 PO 4 nitrogenous base adenine, guanine, cytosine, and uracil , ribose, and H 3 PO 4.

Key Takeaways Nucleotides are composed of phosphoric acid, a pentose sugar ribose or deoxyribose , and a nitrogen-containing base adenine, cytosine, guanine, thymine, or uracil. Ribonucleotides contain ribose, while deoxyribonucleotides contain deoxyribose. Exercises What is the sugar unit in each nucleic acid?

Identify the major nitrogenous bases in each nucleic acid. Answers ribose deoxyribose. Contributors and Attributions Dr. Metabolic Molecules 2. Water 3. Protein 5. Enzymes 6. Cell Respiration 9. Photosynthesis 3: Genetics 1. Genes 2. Chromosomes 3. Meiosis 4. Inheritance 5. Genetic Modification 4: Ecology 1. Energy Flow 3. Carbon Cycling 4. Molecular biologists have named several kinds of RNA on the basis of their function. For this reason, the DNA is protected and packaged in very specific ways.

In addition, DNA molecules can be very long. Stretched end-to-end, the DNA molecules in a single human cell would come to a length of about 2 meters. Thus, the DNA for a cell must be packaged in a very ordered way to fit and function within a structure the cell that is not visible to the naked eye.

The chromosomes of prokaryotes are much simpler than those of eukaryotes in many of their features Figure 9. Most prokaryotes contain a single, circular chromosome that is found in an area in the cytoplasm called the nucleoid.

The size of the genome in one of the most well-studied prokaryotes, Escherichia coli, is 4. So how does this fit inside a small bacterial cell? The DNA is twisted beyond the double helix in what is known as supercoiling. Some proteins are known to be involved in the supercoiling; other proteins and enzymes help in maintaining the supercoiled structure. Eukaryotes, whose chromosomes each consist of a linear DNA molecule, employ a different type of packing strategy to fit their DNA inside the nucleus.

At the most basic level, DNA is wrapped around proteins known as histones to form structures called nucleosomes. The DNA is wrapped tightly around the histone core. This nucleosome is linked to the next one by a short strand of DNA that is free of histones.

This fiber is further coiled into a thicker and more compact structure.