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Several features are common to the genetic structure of most organisms. First is the double-stranded DNA. Each strand of this molecule is a series of nucleotides, and each nucleotide is composed of a sugar-phosphate compound attached to one of four nitrogen-containing bases. The sugar-phosphate compounds link together to form the backbone of the strand. Each of the bases strung along the backbone is chemically attracted to a corresponding base on the parallel strand of the DNA molecule. This base pairing joins the two strands of the molecule much as rungs join the two sides of a ladder, and the chemical bonding of the base pairs twists the doubled strands into a spiral, or helical, shape.
The four nucleotide bases are adenine, cytosine, guanine, and thymine. DNA is composed of millions of these bases strung in an apparently limitless variety of sequences. It is in the sequence of bases that the genetic information is contained, each sequence determining the sequence of amino acids to be connected into proteins. A nucleotide sequence sufficient to encode one protein is called a gene. Genes are interspersed along the DNA molecule with other sequences that do not encode proteins. Some of these so-called untranslated regions regulate the activity of the adjacent genes, for example, by marking the points at which enzymes begin and cease transcribing DNA into RNA (see below Genetic expression through RNA).
Principal-structures-of-an-animal-cell-Cytoplasm-surrounds-the-cellsPrincipal structures of an animal cell[Credits : © Merriam-Webster Inc.]
Animal-cells-and-plant-cells-contain-membrane-bound-organelles-includingAnimal cells and plant cells contain membrane-bound organelles, including a distinct nucleus. In …[Credits : Encyclopædia Britannica, Inc.]
Cutaway-drawing-of-a-eukaryotic-cellCutaway drawing of a eukaryotic cell.[Credits : Encyclopædia Britannica, Inc.]
The-eight-step-tricarboxylic-acid-cycleThe eight-step tricarboxylic acid cycle.[Credits : Encyclopædia Britannica, Inc.]
The-initial-proposal-of-the-structure-of-DNA-by-JamesThe initial proposal of the structure of DNA by James Watson and Francis Crick was accompanied by a …[Credits : Encyclopædia Britannica, Inc.]
Molecular-genetics-emerged-from-the-realization-that-DNA-and-RNAMolecular genetics emerged from the realization that DNA and RNA constitute the genetic material of …
The-ovum-contains-a-small-collection-of-cells-in-theThe ovum contains a small collection of cells in the early stages of human development. As cells …[Credits : Encyclopædia Britannica, Inc.]
A-molecular-view-of-the-cell-membrane-Intrinsic-proteins-penetrateA molecular view of the cell membrane[Credits : Encyclopædia Britannica, Inc.]
Cells are the basic units of life.[Credits : Encyclopædia Britannica, Inc.]
Cells ingest molecules through their plasma membranes.[Credits : Encyclopædia Britannica, Inc.]
The carbon atom is essential to all organic compounds. Every carbon atom can bond with four other …[Credits : Acquired from Vast Video]
Most enzymes are proteins. Enzymes regulate nearly all chemical reactions that occur in living …[Credits : Acquired from Vast Video]
The location, importance, and mechanisms of photosynthesis.[Credits : Encyclopædia Britannica, Inc.]
ATP is the key source of energy in the cells of the body. The water-mediated reaction known as …[Credits : Acquired from Vast Video]
James Watson and Francis Crick revolutionized the study of genetics when they discovered the …[Credits : Acquired from Vast Video]
The structure and movement of cilia and flagella.[Credits : Encyclopædia Britannica, Inc.]
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