分子生物学分子生物学 (2).pdf
Molecular BiologyChapter 1 Introduction1.2 Important events in the development of molecular biology1.2.1 The tale of nucleic acid discoveryFriedeich Miescher What is the biological functions of nucleic acids?In 1868,Miescher isolated the nucleusfrom pus cells;by extracting withdiluted alkali and then adding acidinto it,he obtained a substance rich innitrogen and phosphorus,which wasthen called nuclein.In 1872,he found the same substancein the sperm cell nucleus of salmon.Itwas known as nucleic acid due to itsnucleic origin and acidic nature.The study of nucleic acid function had not significantly advanced till 1928.Furbery et al.(1949-1952)used X-ray diffraction analysis toclarify the spatial conformation that nucleotides are not planar.X-ray diffraction of DNA.1952Rosalind Franklin,19201958,UKNucleotides are not a planar spatial conformation1.2.2 The vital advances in the study of nucleic acid structure5The Chargaff rule named after biochemist ErwinChargaff means that in DNA,there is alwaysequality in quantity between the bases A and T andbetween the bases G and C(A is adenine,T isthymine,G is guanine,and C is cytosine).Thus therule contributes to the proposal of base-paired DNAstructure.Chargaff ruleThe construction of DNA double helix modelAwarded the Nobel Prize of Medicine and Physiology in 1962DNA double helix proposes that base pairing is the mode of DNAreplication and genetic information transmission and determinesnucleic acid as a genetic information carrier.A milestone in nucleic acid structure researchJames Dewey Watson(left)and Francis Harry Compton Crick(right)1.2.3 Advances in the study of nucleic acid functionIn 1944,Avery OT and others first proved that the DNA ofPneumococcus was related to its transformation and inheritanceDNA is involved in transformation and inheritanceIn the Hershey and Chase Experiment in 1952,T2phageDNAandproteinwerelabelledwithradioactivephosphorus(P32)andradioactivesulphur(S35)respectively.Thephagesthatproliferate in E.coli cells only contain P32 but notS35,indicating that the proliferation of phagesdepends directly on DNA other than protein.DNA is genetic materialP32 labelled phage DNA presented inside the E.coli cell,indicating that DNA is the genetic material.S35 labelled phage protein will not transfer its radioactivity to the E.coli,indicating that protein is not the genetic material.The Meselson-Stahl experiment（1958）showed that DNA is replicated semi-conservativelyDNA semiconservation replication model1.2.4 DNA replication model1.2.5 Genetic CodeIn1961,severalgroupsincludingNirenbergsandKhoranas deciphered the 20genetic codes by matchingaminoacidstosynthetictriplet nucleotides.The genetic code had been found to be common to all the organisms.1.2.6 The establishment of central dogmaIn 1958,Crick proposed the central dogma of molecular biology,a process in which the genetic information flows from DNA toRNA,to make a functional product protein.In 1970,scientistsdiscovered a reverse transcriptase that is used to generatecomplementary DNA(cDNA)from an RNA template.Thissupplemented the central dogma,the basic theoretical system ofmolecular genetics.1.2.7 DNA sequence analysis technologyG A T CThe chain terminationmethod:Introduced by Frederick SangerCambridge UniversityThe chemical cleavagemethod:Createdby Maxam Iand Gilbert W Derived the primary structure of the protein from the cDNA sequence;The discovery of the split gene proves that most eukaryotic genes are discontinuous DNA fragments;The pre-mRNA are interrupted by introns that are spliced out of the mRNA before translation;Genetic engineering is the direct manipulation of an organisms genes using biotechnology.DNA sequences is usually created and used to insert into the host organism to obtain active proteins.There are structure mutation in monogenetic disorders;Analysis of the primary structure of DNA fragments has led to a series of major discoveries1.2.8 To artificially synthesized DNAFor the first time in 1978,a gene wassuccessfullysynthesizedinvitro,thusevidenced DNA is the chemical molecule of theso-calledhereditaryfactor(i.e.gene)byMendel in 1865.1.2.9 GenomeGenome:an organisms complete set ofgenetic information.The study of gene structure and function hasevolved from a single gene to the genome.Genome research has ranged from lowerorganismstoeukaryotesandfrommulticellular organisms to humans.Human genome project(HGP)The goal of HGP were to draw genetic linkage,physical and transcription maps,identify all thesequence of 3 billion pairs of nucleotides on 24chromosomes in human cells,locate all humangenes on chromosomes,and decipher the wholehereditary information.1.2.10 Study on the regulatory mechanism of gene expressionOperon theory：in prokaryotes,most regulation ofgeneexpressionoccursthroughtranscriptionalcontrol,followed by translation control.The regulation of eukaryotic genes involves molecularrecognition and interaction between cis-regulatoryelements on DNA and trans-acting factors in protein.11.Research progress of the protein structure and functionIn 1956,investigations on reversible denaturation of severalproteins,Anfinsen and White proposed that the informationdetermining the tertiary structure of a protein resides in thechemistry of its amino acid sequence.In 1958,Ingram discovered an amino acid in normalhemoglobin cells was replaced with a different amino acid inthe sickle cell.That one substitution caused a normal cell totake on the shape of a sickle,or crescent.In 1969,Weberstarted to use SDS-polyacrylamide gelelectrophoresis to determine protein molecular weight.In1965,Chinesescientistssynthesizedbovineinsulinartificially.In 1973,X-ray diffraction analysis was used todetermine the spatial structure of bovine insulin.
