The difference between the sugars is the presence of the hydroxyl group on the ribose's second carbon and hydrogen on the deoxyribose's second carbon. The pentose sugar in DNA is deoxyribose, and in RNA, the sugar is ribose ( Figure 3.31). DNA contains A, T, G, and C whereas, RNA contains A, U, G, and C. In molecular biology shorthand, we know the nitrogenous bases by their symbols A, T, G, C, and U. Each of these basic carbon-nitrogen rings has different functional groups attached to it. Scientists classify cytosine, thymine, and uracil as pyrimidines which have a single carbon-nitrogen ring as their primary structure ( Figure 3.31). The purine's primary structure is two carbon-nitrogen rings. Scientists classify adenine and guanine as purines. Each nucleotide in DNA contains one of four possible nitrogenous bases: adenine (A), guanine (G) cytosine (C), and thymine (T). They are bases because they contain an amino group that has the potential of binding an extra hydrogen, and thus decreasing the hydrogen ion concentration in its environment, making it more basic. The nitrogenous bases, important components of nucleotides, are organic molecules and are so named because they contain carbon and nitrogen. Purines have a double ring structure, and pyrimidines have a single ring. We can divide bases into two categories: purines and pyrimidines. Deoxyribose is similar in structure to ribose, but it has an H instead of an OH at the 2′ position. Two types of pentose are in nucleotides, deoxyribose (found in DNA) and ribose (found in RNA). When a polynucleotide forms, the incoming nucleotide's 5′ phosphate attaches to the 3′ hydroxyl group at the end of the growing chain. The base is attached to the ribose's 1′ position, and the phosphate is attached to the 5′ position. Carbon residues in the pentose are numbered 1′ through 5′ (the prime distinguishes these residues from those in the base, which are numbered without using a prime notation). Each nitrogenous base in a nucleotide is attached to a sugar molecule, which is attached to one or more phosphate groups.įigure 3.31 Three components comprise a nucleotide: a nitrogenous base, a pentose sugar, and one or more phosphate groups. Three components comprise each nucleotide: a nitrogenous base, a pentose (five-carbon) sugar, and a phosphate group ( Figure 3.31). The nucleotides combine with each other to form a polynucleotide, DNA or RNA.
Other types of RNA-like rRNA, tRNA, and microRNA-are involved in protein synthesis and its regulation.ĭNA and RNA are comprised of monomers that scientists call nucleotides. This intermediary is the messenger RNA (mRNA).
The DNA molecules never leave the nucleus but instead use an intermediary to communicate with the rest of the cell. The other type of nucleic acid, RNA, is mostly involved in protein synthesis. DNA controls all of the cellular activities by turning the genes “on” or “off.” Many genes contain the information to make protein products. A chromosome may contain tens of thousands of genes. In eukaryotic cells but not in prokaryotes, DNA forms a complex with histone proteins to form chromatin, the substance of eukaryotic chromosomes. The cell's entire genetic content is its genome, and the study of genomes is genomics. In prokaryotes, the DNA is not enclosed in a membranous envelope. It is in the nucleus of eukaryotes and in the organelles, chloroplasts, and mitochondria. DNA is the genetic material in all living organisms, ranging from single-celled bacteria to multicellular mammals. The two main types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). They carry the cell's genetic blueprint and carry instructions for its functioning. Nucleic acids are the most important macromolecules for the continuity of life.
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