Contents,DNA synthesis DNA replication etc. RNA synthesis Transcription Protein synthesis Translation Gene expression control Techniques for gene exploration,Major Contents of Lecture 1,The Central Dogma DNA Replication The chemical nature The local structure Features The reaction system,Gene,The functional segment of DNA, storing genetic information in its base sequence. Coding for functional molecules, proteins and RNAs, or regulating gene expression.,Gene Expression,Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA. (Wikipedia),DNA,RNA,protein,transcription,translation,replication,reverse transcription,The flow of genetic information are concluded as the central dogma. (Crick, 1958&Temin 1970),Gene Expression,DNA Replication,parental DNA,daughter DNA,The specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material. - Watson&Crick,One Round of DNA Elongation (dNMP)n + dNTP (dNMP)n+1 + PPi DNA Substrate Elongated DNA,The Chemical Nature Polymerization of dNMP catalyzed by enzymes.,DNA Replication,3, 5-Phosphodiester Bond Formation in DNA Replication,During replication, the parental dsDNA and two newly formed dsDNA form a Y-shape structure called Replication Fork.,fork,The Local Structure of DNA Replication,The Local Structure of DNA Replication,Features of DNA Replication,Semi-conservative Bidirectional in most cases Semi-discontinuous With a high fidelity,The Semi-Conservative Replication,Each daughter DNAs consists of one strand accepted from the parental DNA and one strand synthesized newly.,Each of the parental DNA strands serves as the template for making a daugher DNA strand.,Possible Models for DNA Replication,Conservative Semi-Conservative Mixed,Meselson-Stahl Experiment,Grow cells In the 15NH4Cl-containing medium Continue to grow cells In the 14NH4Cl-containing medium the first generation the second generation,During the DNA biosynthesis, each of the parental DNA strands serves as the template for making a complementary DNA strand. Thus, each of two daughter DNAs consists of one strand accepted from the parental DNA and one strand synthesized newly. Consequently, two daughter DNA molecules are completely same in base sequence with the parental DNA, and all the genetic information is ensured to be transferred from one generation to the next generation.,The Semi-Conservative Replication,The movement of replication forks is bidirectional in most cases.,Origin the start site of replication,In the replication fork, synthesis of DNA is continuous in one strand and discontinuous in the other strand.,Leading Strand The daughter strand, which is synthesized along the direction of DNA unwinding, can be synthesized continuously. Lagging strand The daughter strand cant be synthesized continuously because its replication direction is opposite to the DNA-unwinding direction. Its replication cant start or continue until there is a enough space on the template for synthesis and extension of a 53 primer.,During DNA replication, synthesis of the lagging strand is discontinuous and form short fragments of DNA which are called Okazaki Fragments. The Continuous synthesis of leading strands and the discontinuous synthesis of lagging strands represent a unique feature of DNA replication - Semi-Discontinuous Replication.,Right or Wrong?,After replication of one dsDNA molecule, two daughter DNA strands are newly synthesized. Synthesis of one strand is performed continuously, while synthesis of the other strand is performed discontinuously. In one replication fork, one new strand is synthesized continuously and the other new strand is synthesized discontinously. In one dsDNA molecule, one strand is synthesized continously and the other is synthesized discontinously. In one DNA strand, the half is synthesized continuously and the other half is synthesized discontinously.,DNAs are replicated with a high fidelity.,Obey strictly the principle of complementary base pairing. Incorporate nucleotides into the elongating chain with selection preference. Make the realtime proofreading during replication. 10-610-7 Mismatch repair after replication 10-910-10,Substrate: dNTP Template: DNA (the whole chromosomes) Primer: short RNA fragments with a free 3-OH end Enzyme: DNA-dependent DNA polymerase (DDDP) helicase, primase, topoisomerase, ligase other proteins (eg. SSB), ions, NTP,DNA Replication System,Enzymes and Other Proteins Necessary for DNA Replication in E. coli,Question,Where does energy of DNA synthesis come from?,Terms and Concepts,Gene Gene expression Semi-conservative replication Leading strand Lagging strand Okazaki fragment,Questions,Whats