分子生物学英文课件：chapter1 Structure and Function of Nucleic Acid (2).ppt

subunit prokaryotes （70S） eukaryotes （80S） S proteins rRNA S proteins rRNA Smaller subunit 30 21 kinds 16S 40 33 kinds 18S Larger subunit 50 31 kinds 23S 5S 60 50 kinds 28S 5.8S 5S Components of ribosomes III. Structure and function of rRNA 真核生物18S rRNA 原核生物翻译过程中核糖体结构模式: 氨基酰位 （aminoacyl site，A 位） 肽酰位 （peptidyl site，P 位） 排出位（exit site，E 位） The three roles of RNA in protein synthesis. Messenger RNA (mRNA) is translated into protein by the joint action of transfer RNA (tRNA) and the ribosome, which is composed of numerous proteins and two major ribosomal RNA (rRNA) molecules Ⅳ. Other non-coding RNA (ncRNA) long non-coding RNA and small non-coding RNA SnRNA(small nuclear RNA) SnoRNA (small nucleolar RNA) ScRNA(small cytoplasm RNA) siRNA(small interfering RNA) MicroRNAs Small catalytic RNA: Ribozymes, are the RNA molecules with catalytic activity.? The activity of these ribozymes often involves the cleavage of a nucleic acid. RNA interference(RNAi) 被《Science》评为2002年最重大科技突破。 Small interfering RNA (siRNA) siRNAs structure: a short (usually 21-nt) double-strand of RNA (dsRNA) with 2-nt 3 overhangs on either end. Ribozyme An RNA molecule with catalytic activity Secondary structure of ribozyme ------ Hammerhead structure Section Ⅳ Physical and chemical features of nucleic acid and applications Ⅰ. General features of nucleic acid: Acidity Viscosity Conformation Absorbance of 260nm 1. DNA或RNA的定量 A260=1.0相当于 50μg/ml双链DNA 40μg/ml单链DNA（或RNA） 20μg/ml寡核苷酸 2.判断核酸样品的纯度 DNA纯品: A260/A280 = 1.8 RNA纯品: A260/A280 = 2.0 A260的应用 目 录 Definition: DNA denaturation means that a DNA has lost its’ native conformation and double strand DNA is separated to single strand DNA by exposed to a destabilizing factor such as heat, acid, alkali,urea or amide. (when high temperature is used to denature DNA, the DNA is said to be melted). Ⅱ. Denaturation of DNA DNA melting curve: Tm is melting temperature at which half (50%) of DNA molecules are denatu