1 / 20

DNA Replication

DNA Replication. Unit 9: The Central Dogma Honors Biology. DNA Replication. The process of DNA replication is fundamentally similar for prokaryotes and eukaryotes.

marjoriew
Download Presentation

DNA Replication

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. DNA Replication Unit 9: The Central Dogma Honors Biology

  2. DNA Replication • The process of DNA replication is fundamentally similar for prokaryotes and eukaryotes. • DNA replication is a semi-conservative process – this means that when the double helix is unwound, each original strand serves as a template or pattern for the newly synthesized strand.

  3. DNA Replication is a Semi-conservative process

  4. What is a REPLISOME? • Major Components • DNA Helicase • DNA Primase • DNA Polymerases • DNA ligases • DNA Binding Proteins • The replisome is a complex molecular machine that carries out replication of DNA. • The replisome contains all the necessary enzymes for replication.

  5. What is a Replisome?

  6. The Replication Process – An Overview • Write these steps down: • INITIATION: formation of replication fork • ELONGATION: a number of enzymes work together to accomplish the task of assembling a new strand • TERMINATION: An end point to the replication • The process of replication can be thought of as having a beginning where the process starts; a middle where the complementary nucleotides are added to the exposed parental strands; and an end where the process is terminated or stopped.

  7. DNA Replication: Initiation • DNA helicases unwind and unzip the DNA molecule forming a replication fork. • A replication fork is a Y-shaped region where the new strands of DNA are elongating.

  8. DNA Replication: Elongation • The elongation process is semidiscontinuous. • The leading strand of the DNA molecule (exposed 3’ end) is synthesized continuously in the direction of the opening replication fork. • The lagging strand of the DNA molecule (exposed 5’ end) is synthesized discontinuously in the direction opposite to the opening of the replication fork.

  9. How does the antiparallel nature of the DNA molecule affect Elongation? • Remember - The two strands of the DNA double helix are antiparallel. This means that their sugar – phosphate backbones run in opposite directions!

  10. How does the ANTIPARALLEL structure of the double helix affect the Elongation phase? • DNA polymerases add nucleotides only to the FREE 3’ end of a growing DNA strand, NEVER to the 5’ end. • DNA polymerases synthesize ONLY in the direction 5’ to 3’.

  11. Elongation: Leading and Lagging Strands

  12. Elongation: Synthesis of Leading Strand • DNA Primase synthesizes a short complementary segment to the exposed 3’ end of the DNA strand. • DNA polymerases extend the complementary segment toward the replication fork as it opens. • The ability of the DNA polymerase to remain attached to the template (leading strand) is known as PROCESSIVITY.

  13. Elongation

  14. Elongation: Synthesis of Lagging strand - Discontinuous • The synthesis of the lagging strand is described as discontinuous since it is synthesized in pieces that get glued together. • DNA primase synthesizes a short segment of complementary DNA to the exposed 5’ end. • DNA polymerases add complementary nucleotides in the direction away from the opening replication fork. • DNA ligases glue the Okazaki Fragments together forming the new strand.

  15. Synthesis of Lagging Strand

  16. Key Ideas – Know these! • Exposed 3’ end of the original DNA molecule • Synthesized continuously toward the opening replication fork. • The ability of a DNA polymerase to remain attached to the leading strand is known as processivity. • Exposed 5’ end of the original DNA molecule • Synthesized discontinuously away from the opening replication fork. • The Okazaki fragments are glued together by DNA Ligases. Leading Strand Lagging Strand

  17. DNA Replication: Termination • Prokaryotes have circular DNA so replication ends when the process comes around to the origin again. • In eukaryotes, end points for each chromosome are indicated by telomeres. • Telomeres are specialized structures on the ends of eukaryotic chromosomes that are composed of specific repeated DNA sequences.

  18. Eukaryotic Chromosomes - Telomeres • Telomeres are special nucleotide sequences on the ends of the linear eukaryotic chromosomes. • The typical repeating unit in human telomeres is TTAGGG. The number of repetitions in a telomere varies between 100 and 1000. • The telometric DNA protects an organism’s genes from being eroded through successive rounds of DNA replications.

  19. Telomeres and the Lagging Strand • Remember that DNA polymerases can only add nucleotides in the 5’ to 3’ direction. • The exposed 5’ end represents the lagging strand. • The replisome does not contain the machinery to complete the 5’ ends of the daughter strands of the DNA. As a result, repeated replication produces shorter and shorter DNA molecules.

  20. Can YOU? • Briefly describe the functions of the following enzymes during DNA replication: DNA helicases, DNA polymerases, and DNA ligases. • Briefly provide an overview of DNA replication using the terms: initiation, elongation, termination. • Distinguish between the leading strand and lagging strand during DNA replication?

More Related