The sugar in DNA is 2-deoxyribose, which is a pentose (five- carbon) sugar. The backbone of the DNA strand is made from alternating phosphate and sugar residues. If multiple nucleotides are linked together, as in DNA, this polymer is called a polynucleotide. In general, a base linked to a sugar is called a nucleoside and a base linked to a sugar and one or more phosphate groups is called a nucleotide. The nucleotide repeats contain both the segment of the backbone of the molecule, which holds the chain together, and a base, which interacts with the other DNA strand in the helix. These two long strands entwine like vines, in the shape of a double helix. In living organisms, DNA does not usually exist as a single molecule, but instead as a tightly-associated pair of molecules. For instance, the largest human chromosome, chromosome number 1, is approximately 220 million base pairs long. Although each individual repeating unit is very small, DNA polymers can be enormous molecules containing millions of nucleotides. The DNA chain is 22 to 26 Ångströms wide (2.2 to 2.6 nanometres), and one nucleotide unit is 3.3 Å (0.33 nm) long. Hydrogen bonds are shown as dotted lines.ĭNA is a long polymer made from repeating units called nucleotides. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. Eukaryotic organisms ( animals, plants, and fungi) store their DNA inside the cell nucleus, while in prokaryotes ( bacteria and archae) it is found in the cell's cytoplasm. These chromosomes are duplicated before cells divide, in a process called DNA replication. Within cells, DNA is organized into structures called chromosomes. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. It is the sequence of these four bases along the backbone that encodes information. Attached to each sugar is one of four types of molecules called bases. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.Ĭhemically, DNA is a long polymer of simple units called nucleotides, with a backbone made of sugars and phosphate groups joined by ester bonds. DNA is often compared to a set of blueprints or a recipe, since it contains the instructions needed to construct other components of cells, such as proteins and RNA molecules. The main role of DNA molecules is the long-term storage of information. The two DNA chain has a polarity determine by the orientation of the sugar-phosphate backbone.The structure of part of a DNA double helixĭeoxyribonucleic acid ( DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. On each residue is a nitrogenous base either a pyrimidine ( cytosine, or thymine or a purine ( adenine, or guanine. Each DNA strand has a backbone of 5-carbon sugar (deoxyribose) residues, which are linked by covalent phosphodiester bonds. The DNA molecule consists of two DNA chains coiled around each other to form a double helix. The remaining great majority of DNA has no known function with the exception of specific areas of the chromosome that are known to be important for correct replication at chromosome termini( telomeres) or correct movement of chromosomes into daughter cells following cell division ( centromeres). Genes comprise only the minority of the DNA of a chromosome. A chromosomes is an extremely long strand of supercoiled DNA bonded with protein molecules called histomes, genes are parts of the chromosomes with a coding function: they are unique sequences that code for specific proteins. An introduction to molecular genetics is presented as every nucleus of a human cell contains 46 chromosomes arranged in 23 pairs, 22 autosomes and two sex chromosomes. As well as the interactions among three major molecules (DNA, RNA ribonucleic acid and protein). Molecular Genetics consists of chromosomes, deoxyribonucleic acid ( DNA) and genes.
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