LO18-DNA复制.docx

Hello and Welcome In this online session,you will learn about Continuity of Life:DNA Replication GO Page 1/22 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences Learning Objectives At the end of the session,you should be able to: Present the features of DNA that allow the informatio...

Hello and Welcome In this online session,you will learn about Continuity of Life:DNA Replication GO Page 1/22 NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences Learning Objectives At the end of the session,you should be able to: Present the features of DNA that allow the information encoded in it to be copied; Name the components involved in DNA replication and the roles they play; Describe the major steps taking place during DNA replication; and Distinguish between a leading and a lagging strand at a replication fork. Page 2/22 School of Biological Sciences All living thing reproduce.They generate offspring that are like themselves.This is true for even the simplest living thing-e.g..the single-cell bacterium.A bacterium divides into two daughter cells that are identical to itself. PARENT BACTERIUM 1st GENERATION DAUGHTER CELLS 2nd GENERATION DAUGHTER CELLS Have you ever wondered how daughter cells end up being identical to the parent cell? Since the genome of a cell serves as its blueprint of structures and functions,additional copies of the blue-print will need to be produced by the parent cell,to be carried by the new cells. So before a cell can even reproduce,its genome must first be copied.This is achieved through replication of DNA(that makes up the genome). To understand the process of DNA replication,we need to remind ourselves of the structure of DNA. DNA REPLICATION Select to view the video on the structure of DNA To understand the process of DNA replication,we need to remind ourselves of the structure of DNA. Recall that DNA consists of 2 strands running in opposite directions,and is a polymer made up of 4 types of deoxyribonucleotides with bases of A,C,G and T.The nucleotides units are connected through phosphodiester bonds. Select to view the video on the structure of DNA 5' 3' 3' 5' Select to view the video on the structure of DNA To understand the process of DNA replication,we need to remind ourselves of the structure of DNA. Recall that DNA consists of 2 strands running in opposite directions,and is a polymer made up of 4 types of deoxyribonucleotides with bases of A,C,G and T.The nucleotides units are connected through phosphodiester bonds. To understand the process of DNA replication,we need to remind ourselves of the structure of DNA. Recall that DNA consists of 2 strands running in opposite directions,and is a polymer made up of 4 types of deoxyribonucleotides with bases of A,C,G and T.The nucleotides units are connected through phosphodiester bonds. Select to view the video on the structure of DNA NANYANG TECHNOLOGICAL UNIVERSITY To understand the process of DNA replication,we need to remind ourselves of the structure of DNA. Recall that DNA consists of 2 strands running in opposite directions,and is a polymer made up of 4 types of deoxyribonucleotides with bases of A,C,G and T.The nucleotides units are connected through phosphodiester bonds. Select to view the video on the structure of DNA NANYANG TECHNOLOGICAL UNIVERSITY To understand the process of DNA replication,we need to remind ourselves of the structure of DNA. Recall that DNA consists of 2 strands running in opposite directions,and is a polymer made up of 4 types of deoxyribonucleotides with bases of A,C,G and T.The nucleotides units are connected through phosphodiester bonds. Select to view the video on the structure of DNA NANYANG TECHNOLOGICAL UNIVERSITY The complementary pairing of bases -A on one strand and T on the other (A:T)and C on one strand and G on the other(C:G)-are stacked at the center of the double helical structure of the two Strands. Select to view the video on the structure of DNA NANYANG TECHNOLOGICAL UNIVERSITY The complementary pairing of bases -A on one strand and T on the other (A:T)and C on one strand and G on the other(C:G)-are stacked at the center of the double helical structure of the two Strands. Select to view the video on the structure of DNA A-T G-C Select to view the video on parental DNA strands as templates The same A:T and C:G pairing principle is applied when new strands of DNA have to be synthesized. A-T G-C Select the to view the video on parental DNA strands as templates NANYANG TECHNOLOGICAL UNIVERSITY NANYANG TECHNOLOGICAL UNIVERSITY NANYANG TECHNOLOGICAL UNIVERSITY 5' 3' Ildentical New -Parental 3' 5' Select the to view the video on parental DNA strands as templates The same A:T and C:G pairing principle is applied when new strands of DNA have to be synthesized. Each of the parental DNA strand serves as the template.By base-pairing with one template strand the specific sequence of bases of the parental genome can be carried by the new DNA as complementary sequences. NANYANG TECHNOLOGICAL UNIVERSITY 5' 3' identical New Parental- 5' Select the to view the video on parental DNA strands as templates The sequence of the new DNA strand will be identical to the other strand in the parental DNA. Template strands DNA polymerase Select to view the video on DNA Polymerase The new strand of DNA is synthesized by an enzyme called DNA polymerase.As free nucleotides bind to the complementary bases on the template strand,the DNA polymerase sequentially synthesizes phosphodiester bonds to incorporate the nucleotides,and the strand of DNA elongates,one base by one base The new strand of DNA is synthesized by an enzyme called DNA polymerase.As free nucleotides bind to the complementary bases on the template strand,the DNA polymerase sequentially synthesizes phosphodiester bonds to incorporate the nucleotides,and the strand of DNA elongates,one base by one base Select to view the video on DNA Polymerase The new strand of DNA is synthesized by an enzyme called DNA polymerase.As free nucleotides bind to the complementary bases on the template strand,the DNA polymerase sequentially synthesizes phosphodiester bonds to incorporate the nucleotides,and the strand of DNA elongates,one base by one base Select to view the video on DNA Polymerase In order for the parental DNA to act as a template and the DNA polymerase to synthesize the new strand of DNA,the parental DNA duplex have to be first separated,i.e.,unwound,to expose the sequence of bases.This unwinding is handled by the enzyme helicase Select to view the video on Helicase In order for the parental DNA to act as a template and the DNA polymerase to synthesize the new strand of DNA,the parental DNA duplex have to be first separated,i.e.unwound,to expose the sequence of bases.This unwinding is handled by the enzyme helicase. Select to view the video on Helicase Page 8/22 The region of DNA whereby the helicase "opens"the two strands up (so that replication can occur)is referred to as a "replication fork". Replication fork Select to view the video on Helicase NANYANG TECHNOLOGICAL UNIVERSITY DNA polymerase acts on deoxyribonucleotides as RNA polymerase does on ribonucleotides -by forming phosphodiester bonds between adjacent nucleotide units that are pairing to the template strand of DNA. DNA polymerase Select to view the video on Primers in DNA replication DNA polymerase acts on deoxyribonucleotides as RNA polymerase does on ribonucleotides -by forming phosphodiester bonds between adjacent nucleotide units that are pairing to the template strand of DNA. 5' deoxyribonucleotides units Select to view the video on Primers in DNA replication However,DNA polymerase cannot initiate this process by forming phosphodiester bonds between two free nucleotides.It can only act by adding nucleotides to an existing chain of polynucleotides which is already complementary bonded to the template strand. Select to view the video on Primers in DNA replication Page 9/22 3' 5' 5' 3' existing chain of polynucleotides However,DNA polymerase cannot initiate this process by forming phosphodiester bonds between two free nucleotides.It can only act by adding nucleotides to an existing chain of polynucleotides which is already complementary bonded to the template strand. Select to view the video on Primers in DNA replication This property is unlike RNA polymerase,which can initiate synthesis between two mono- nucleotides.The short chain initiate DNA replication is referred to as a primer. RNA polymerase Select to view the video on Primers in DNA replication This property is unlike RNA polymerase,which can initiate synthesis between two mono- nucleotides.The short chain 5' initiate DNA replication is referred to as a primer. 5' 3' primers Select to view the video on Primers in DNA replication NANYANG TECHNOLOGICAL UNIVERSITY DNA polymerase will initiate DNA synthesis by adding a nucleotide to the 3'end of a primer.This ensures that the new DNA strand is synthesized in a5 to 3 direction. 5 Select to view the video on Concurrent Replication in Opposite Orientation NANYANG TECHNOLOGICAL UNIVERSITY DNA polymerase will initiate DNA synthesis by adding a nucleotide to the 3'end of a primer.This ensures that the new DNA strand is synthesized in a5'to 3 direction. As a result,replication using each of the parental DNA will run in opposite directions concurrently.The two events of replication requires considerable molecular coordination. When the helicase unwinds parental DNA in a certain direction,one of the replication process will simply "follow"this unwinding and grow in the same direction as the parental DNA get further unwound.The new DNA strand formed in this process is called the leading strand. Select to view the video on Concurrent Replication in Opposite Orientation School of Biological Sciences Page 12/22 School of Biological Sciences School of Biological Sciences School of Biological Sciences NANYANG TECHNOLOGICAL UNIVERSITY School of Biological Sciences In this section,you need to take home the following messages: 1.DNA replication of the genome is the first condition that has to be fulfilled before reproduction of a living thing can take place. 2.Each parental DNA strand serves as the template for a new strand of DNA to be formed through complementary pairing of bases. 3.The double helix of DNA is unwound by the enzyme helicase,and a new DNA strand is synthesized by the enzyme DNA polymerase. 4.A primer is required to be bound to the template strand in order for DNA polymerase to initiate DNA replication.It is synthesized by the enzyme primase. 5.Concurrent replication of two new strands occur at the replication fork in opposite orientation. Page 15/22 In this section,you need to take home the following messages: 6.The coordination of two replications at one replication fork results in the formation of a leading strand and a lagging strand (formed through ligation of Okazaki fragments).