![]() 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. Describe nucleic acids' structure and define the two types of nucleic acids.The sugar and phosphate molecules that form the sugar-phosphate backbone of the molecule are hydrophilic, which means they are water-loving and have an affinity for water.By the end of this section, you will be able to do the following: Since the cell cytoplasm and cytosol contain water-based liquids, the nitrogenous bases want to avoid contact with cell fluids. These nitrogenous bases are hydrophobic, meaning that they lack an affinity for water. Adenine is bonded with thymine (A-T) and guanine pairs with cytosine (G-C). The nitrogenous bases that comprise the steps of the twisted staircase are held together by hydrogen bonds. The twisting aspect of DNA is a result of interactions between the molecules that make up DNA and water. Maurice Wilkins all played pivotal roles in elucidating the structure of DNA.ĭNA is coiled into chromosomes and tightly packed in the nucleus of our cells. Both the replication of DNA and the synthesis of proteins in our cells are dependent on the double-helix shape of DNA.The twisting of DNA is the result of both hydrophilic and hydrophobic interactions between the molecules that comprise DNA and water in a cell.This double helix shape is often visualized as a spiral staircase. Its double helix consists of two spiral chains of DNA. Double helix is the biological term that describes the overall structure of DNA.
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