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Cytosine (/ ˈ s aɪ t ə ˌ s iː n,-ˌ z iː n,-ˌ s ɪ n / [2] [3]) (symbol C or Cyt) is one of the four nucleotide bases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group ...
The double helix is the dominant tertiary structure for biological DNA, and is also a possible structure for RNA. Three DNA conformations are believed to be found in nature, A-DNA, B-DNA, and Z-DNA. The "B" form described by James D. Watson and Francis Crick is believed to predominate in cells. [2]
All plasma membranes have an electrical potential across them, with the inside usually negative with respect to the outside. [3] The membrane potential has two basic functions. First, it allows a cell to function as a battery, providing power to operate a variety of "molecular devices" embedded in the membrane. [4]
Ion channels are located within the membrane of all excitable cells, [3] and of many intracellular organelles. They are often described as narrow, water-filled tunnels that allow only ions of a certain size and/or charge to pass through. This characteristic is called selective permeability.
The A form occurs under non-physiological conditions in partly dehydrated samples of DNA, while in the cell it may be produced in hybrid pairings of DNA and RNA strands, and in enzyme-DNA complexes. [54] [55] Segments of DNA where the bases have been chemically modified by methylation may undergo a larger change in conformation and adopt the Z ...
The cell membrane has different lipid and protein compositions in distinct types of cells and may have therefore specific names for certain cell types. Sarcolemma in muscle cells: Sarcolemma is the name given to the cell membrane of muscle cells. [46] Although the sarcolemma is similar to other cell membranes, it has other functions that set it ...
Due to the overall positive charge of cationic liposomes, they interact with negatively charged cell membranes more readily than classic liposomes. [3] This positive charge can also create some issues in vivo , such as binding to plasma proteins in the bloodstream, which leads to opsonization. [ 5 ]
Addition of an acetyl group, which carries a negative charge, effectively removes the positive charge and hence, reduces the interaction between the histone tail and the nucleosome. [18] This opens up the usually tightly packed nucleosome and allows transcription machinery to come into contact with the DNA template, leading to gene transcription.