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【正文】 ily correspond to level of disease ? Pathologic effect occurs when a normal PrPc protein is converted to PrPsc protein in the endosomal partment of the cell, and is no longer recycled back to the surface of the cell ? when the PrPsc protein begins to accumulate in the endosomal partments, amyloid（ 淀粉樣） deposits form and cause the cell (neuron) to loose viability, resulting in death Molecular Biology 大連理工大學(xué) Conversion Sequence ? Change in structural configuration – folding ? Formation of insoluble aggregates (amyloid plaques) ? Neuronal damage leading to neuronal death ? Death of the host ? Normal = alpha helical configuration ? Abnormal = beta sheet configuration = marker for infectivity Molecular Biology 大連理工大學(xué) Future Focus in Prion Research ? Alzheimer39。s disease and Parkinson39。s disease? Because suggestions that PrP protects the brain against dementia and other degenerative problems associated with old age – prions may prevent the Purkinje cells from dying Molecular Biology 大連理工大學(xué) Properties of the Geic Material ? DNA has the ability to store geic information, which can be expressed in the cell as needed. ? This information can be transmitted to daughter cells with minimal error. (This process requires plex enzymes and repair mechanisms.) ? DNA possesses both physical and chemical stability so information (present in duplicate，二倍體 ) is not lost over long periods of time (years). ? DNA has the potential for heritable change without major loss of parental information. Molecular Biology 大連理工大學(xué) Storage and Transmission of Geic Information by DNA ? DNA possesses and conveys several types of information: – The sequence of all RNA molecules synthesized by the cell. – The sequence of all amino acids in every protein synthesized by the cell. – Start and stop signals for the synthesis of each RNA, the processing of each RNA, and the synthesis of each protein. – A set of signals that interacts with the cellular ponents and determines whether and when a particular RNA or protein is to be made, and how many molecules are to be made per unit time. – Signals that serve as origins and terminators for the replication of the DNA. – Signals that provide essential features of chromosome structure (centromeres著絲粒 and telomeres端粒 ). Molecular Biology 大連理工大學(xué) The Ability of DNA to Change: Mutation ? The process by which a base sequence changes is called mutation. ? At the nucleotide level, there are two principal mechanisms of mutation: – A chemical alteration of the base that gives it new hydrogenbonding properties and, thus, causes a different base to be incorporated into the daughter DNA strand during subsequent replication. – A replication error by which an incorrect base is erroneously incorporated, or an extra base is accidentally inserted or deleted in the daughter molecule. ? On the average, mutational changes are deleterious and may lead to cell death or impaired function. Molecular Biology 大連理工大學(xué) Summary ? Early experimental evidence that identified DNA as the geic material ? Understand the experimental design and ideas ? RNA as the geic material in some viruses ? Properties of geic material ? Prion: PrPc vs PrPsc ? Transmissible spongiform encephalopathies ? Prion biology ? The key event in the pathogenesis of TSE The end of chapter 6 Molecular Biology 大連理工大學(xué) 謝謝觀看 /歡迎下載 BY FAITH I MEAN A VISION OF GOOD ONE CHERISHES AND THE ENTHUSIASM THAT PUSHES ONE TO SEEK ITS FULFILLMENT REGARDLESS OF OBSTACLES. BY FAITH I BY FAITH
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