![]() This can increase the efficiency of signaling concatenation by centralizing signaling components and can enhance signaling specificity by preventing false interactions between them. The most basic function of the scaffold protein is the assembly of the cascaded signal components. These functions of scaffold proteins can provide additional complexity for signal cascades and generate signal thresholds or adjust complex signal transmission behaviors such as hierarchical or digital signal transmission, transient or continuous signal transmission, and oscillating signal transmission.įigure 1. Inactivate the activation signal molecule. These methods indicate that the scaffold can function in at least four aspects: by acting as a platform on which the signal molecule can be assembled, by locating the signal molecule at a specific site in the cell, by aligning the positive feedback signal with the negative feedback signal Signal pathways and protect cells to function. Most of our understanding of scaffold protein function comes from mathematical modeling and engineering of scaffold proteins. In these signaling pathways, scaffold proteins regulate signal transduction and localize pathway components (in the form of complexes) to specific regions of the cell, such as cell membranes, cytoplasmic stroma, nucleus, Golgi, endosomes, and mitochondria. ![]() Although the functions of scaffold proteins are not strictly defined, they interact or combine with multiple components in the signaling pathway to form a complex. Recently, complete DNA sequences of entire chromosomes have been determined, and our rapidly emerging knowledge of chromosome structures is beginning to provide insights into the molecular basis of human disease.In biology, scaffold proteins are important regulators in many key signaling pathways. Most chromosome structures (nucleosomes, chromatin fibres, and scaffold loop domains) form from virtually any DNA sequence, but centromeres and telomeres are both composed of specific DNA sequences complexed with specific binding proteins. Centromeres, the regions that mediate attachment of a chromosome to a meiotic or mitotic spindle, and telomeres, the natural ends of chromosomes, are structures that ensure that the correct number of full length chromosomes are maintained during the cell cycle. Formation of chromosome structures and the nuclei that envelop them involves discrete steps of nucleosome assembly, scaffold assembly, and nuclear envelope assembly, and can be carried out in cell-free extracts of animal eggs. Metaphase chromosomes, which can be stained to reveal characteristic banding patterns, are formed in most eukaryotic cells during mitosis. Some chromosomes, such as lampbrush and polytene chromosomes, can be seen in certain specialised cells during interphase. ![]() The chromatin fibres are, in turn, compacted approximately 250-fold to form topologically independent 'looped' DNA domains, each loop containing about 20,000-100,000 nucleotide pairs of DNA extending from a proteinaceous central scaffold. Arrays of these nucleosomes, or 'beads on a string', are further compacted into solenoidal structures, called 30 nm chromatin fibres. Most chromosomal DNA is wrapped in left-handed superhelical turns around protein 'spools', called histone octamers, to form nucleosomes. Several levels of structural organisation are involved in the formation of chromosomes. Each chromosome consists of a single very long DNA molecule that has been compacted approximately 10,000-fold by interactions with proteins, such that the resulting chromosome structure fits within a typical eukaryotic nucleus of only 10 microns in diameter. Chromosomes are large subcellular structures, visible in the light microscope, that are found in the nuclei of most eukaryotic cells. ![]()
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