17、分子生物学课件4个mb

1、 Review of last classes: HistoryTransmission Genetics ( -1944)Mendals laws (laws of segregation; independent assortment ) Rediscovery of Mendal laws;Gene is in chromosome, Thomas H Morgan George Beadle (One gene, one enzyme)Molecular biology (1944- today)DNA as genetic materialDNA structureRestricti

2、on enzyme binant DNA technologyPCR technologyTransgenic animal and plantsGenome SequencingOutline for lecture 2Macromolecules and central dogmaGene and GenomeMacromolecules & central DogmaFrom Genes to ProteinsDNAmRNAProteinA gene codes for a proteinProteinmRNADNAtranscriptiontranslationCCTGAGCCAACT

3、ATTGATGAAPEPTIDECCUGAGCCAACUAUUGAUGAADNARNAProteinCentral DogmaTranscriptionTranslationReverse TranscriptionReplicationGene & GenomeGenes as a unit of inheritanceGenes: In non-molecular terms, a unit of inheritance that governs the character of a particular trait. In molecular terms, a sergment of D

4、NA containing the information for a single polypeptide or RNA molecule, including transcribed but non-coding regions. Cistron(顺反子): A genetic unit defined by a cis-trans test. For all practical purpose, it is synonymous with the word “gene”. Cis-trans test The test is done by mating an individual th

5、at has one of the mutations to an individual that has the other one, and observing whether their offspring have the mutant phenotype. If the offspring do not have the mutant phenotype, then the genes are known to be trans If the offspring do have the mutant phenotype, then the genes are known to be

6、cis Chemical nature of genesDNA (Deoxyribonucleic Acid) 脱 氧 核糖 核 酸 & RNA (Ribonucleic Acid)Polynucleotides (DNA and RNA) contains: (deoxy)ribose, phosphoric acid; basesBases includes: Two purines: adenine and guanine (腺嘌呤和鸟嘌呤） Three pyrimidines: cytosine, uracil, thymine （胞嘧啶、尿嘧啶和胸腺嘧啶）DNA is the gen

7、etic material of organisms.In some viruses (HIV) RNA is used.SugarBasePhosphateOH group in ribonucleotideIn RNA Uracil replacesThymine.RibonucleosideNo phosphateOPOO-O-OPOO-OPOO-O-OPOO-OPOO-OPOO-O-dGMPdGDPdGTPStructure of DNAJames Watson & Francis Crick (1953)Double Helix of Antiparallel StrandsHeld

8、 together by Hydrogen bond formationPurine with PyrmidineGuanine - CytosineAdenine - ThymineBases stack inside the helix - exclude water and stabilizesOne BASEPAIR =0. 34 nmComplete turn of helix = 3.4 nmEach turn contains a Major and Minor GrooveSingle Strand of DNA-Has direction or polarity -5 to3

9、”-Backbone comprised of charged phosphate residues-Sugars linked by a phosphodiester bond-Link the 5 methyl group to the 3 OH groupHartel & Jones Genetics Jones and Bartlett5-3 phosphodieter bonds 5: free phosphate group3: free hydroxyl groupStacking betweenbases3 prime5 primeRNA differs from DNA1.R

10、NA has a sugar riboseDNA has a sugar deoxyribose2.RNA contains uracil (U)DNA has thymine (T)3.RNA molecule is single-strandedDNA is double-stranded 4. RNA molecule is much smaller than DNA 5. Certain viruses contain genes made of RNA instead of DNAStructure of genomeGenome: the complement of genetic

11、 information unique to each species of organism equivalent to the DNA of a haploid set of chromosomes from that species.The complexity of the genomeDNA denaturation (melting): the doubled strands of DNA completely separated each other.Once the two DNA strands have separated, the hydrophobic interact

12、ions that result from stacking are greatly decreased, which changes the electronic nature of the bases and increases their UV absorbance (260nm)Tm: the temperature at which the shift in absorbance is half completed. More GC, higher TmGenomes from different Species have different GC contentDNA renatu

13、ration1960, Julius Marmur et al. found: when slowly cooled a denatured DNA solution, DNA regained the properties of the double helix. Reassociation Kinetics (复性动力学)Reassociation: DNA is sheared into pieces of a few hundred bp, heated to denature into single strands, then allowed to renature during c

14、ooling. Cot1/2: the value when 50% renaturation has occurred which can be used to estimate the length of unique DNA in a sample. Co: the original concentration of denatured DNAT: time in seconds A high concentration of DNA incubated for a shorter time =a low concentration of DNA incubated for a long

15、er time Higher Cot1/2 values indicate greater genome complexity Reassociation for Eukaryote 25-30% Moderately Repetitive 350 copies 45-55% Single Copy1 copy 20-25% Highly Repetitive: 2x106 copiesC value paradoxSize of haploid genome = C-valueC-value paradox: maximum C-values suggest that some less e

16、volved organisms may be more complex than more evolved organismsC-value paradox is explained by repetitive sequencesOrganismChromosome #(n)DNA (pg)/n nucleusgenome size (bp)/n nucleusArabidopsis50.088 x 107Maize 105.5550 x 107Lily12989800 x 107Drosophila40.110 x 107Man233.2320 x 107Yeast150.0262.6 x107E. coli-0.0141.4 x 107Genome SizeClassification of eukaryotic DNANon-nuclear genomeThe mitochondria (线粒体) and chloroplasts(叶绿体) also have a DNA genome (or chromosome). These resemble procaryoti