Genetics and Evolution- Molecular Basis of Inheritance - Enzymes involved in DNA Replication

Slide 1

  • DNA replication is a vital process in the molecular basis of inheritance.
  • It ensures accurate transmission of genetic information from one generation to the next.
  • Several enzymes are involved in DNA replication.
  • Let’s explore these enzymes and their roles in this lecture.

Slide 2

  • The first enzyme involved in DNA replication is helicase.
  • Helicase unwinds the double-stranded DNA helix by breaking hydrogen bonds between complementary nucleotides.
  • This creates a replication fork, where the strands separate and become accessible for replication.

Slide 3

  • Single-stranded binding proteins (SSBPs) stabilize the separated DNA strands.
  • They prevent the strands from rejoining or forming secondary structures.

Slide 4

  • DNA gyrase, also known as topoisomerase II, helps relieve the tension generated during DNA unwinding.
  • It corrects the supercoiling of the DNA molecule by introducing negative supercoils ahead of the replication fork.

Slide 5

  • Now, let’s discuss the enzyme responsible for actually synthesizing the new DNA strand.
  • DNA polymerase III is the primary enzyme involved in DNA replication in prokaryotes.
  • It adds nucleotides to the growing DNA strand in a 5’ to 3’ direction.

Slide 6

  • DNA polymerase III requires a primer to initiate DNA synthesis.
  • Primase is the enzyme responsible for synthesizing the primer.
  • Primers are short RNA sequences that are later replaced with DNA nucleotides.

Slide 7

  • DNA polymerase I, another enzyme involved in DNA replication, removes the RNA primers and replaces them with DNA nucleotides.
  • This process is called primer removal and DNA repair.

Slide 8

  • The replacement of RNA primers with DNA nucleotides is known as DNA synthesis or elongation.
  • DNA polymerase III continues adding complimentary nucleotides to the growing DNA strand until it encounters the next primer.

Slide 9

  • DNA ligase, often called the “DNA glue,” plays a crucial role in DNA replication.
  • It joins the Okazaki fragments on the lagging strand together, forming a continuous DNA strand.

Slide 10

  • Recap: The enzymes involved in DNA replication include helicase, SSBPs, DNA gyrase, primase, DNA polymerase III, DNA polymerase I, and DNA ligase.
  • Each enzyme has a specific role in ensuring the accurate and efficient replication of DNA.

Slide 11

  • The enzyme helicase unwinds the double-stranded DNA helix.
  • It breaks the hydrogen bonds between nucleotides, separating the strands.
  • This creates a replication fork, where replication occurs.
  • Helicase moves along the DNA molecule, unwinding it as it progresses.
  • It requires ATP (adenosine triphosphate) for energy to perform its function.

Slide 12

  • Single-stranded binding proteins (SSBPs) bind to the separated DNA strands.
  • SSBPs stabilize the strands preventing them from recombining.
  • They also prevent the formation of secondary structures in the DNA molecule.
  • SSBPs ensure that the separated DNA strands are accessible for replication.

Slide 13

  • DNA gyrase, also known as topoisomerase II, reduces the strain generated during DNA unwinding.
  • It helps relieve the supercoiling of the DNA molecule.
  • Supercoiling is the twisting and winding of the DNA strands upon themselves.
  • DNA gyrase introduces negative supercoils ahead of the replication fork to maintain DNA integrity and prevent tangling.

Slide 14

  • Primase is the enzyme responsible for synthesizing RNA primers during DNA replication.
  • Primers are short RNA sequences that initiate DNA synthesis.
  • Primase adds a small stretch of RNA nucleotides complementary to the DNA template strand.
  • These primers provide a starting point for DNA polymerase to attach and begin elongation.

Slide 15

  • DNA polymerase III is the primary enzyme involved in DNA replication in prokaryotes.
  • It is responsible for synthesizing the leading strand and the lagging strand of DNA.
  • DNA polymerase III adds DNA nucleotides to a growing DNA strand in a 5’ to 3’ direction.
  • It requires dNTPs (deoxyribonucleotide triphosphates) as substrates for DNA synthesis.
  • DNA polymerase III also has proofreading capabilities to detect and correct errors during replication.

Slide 16

  • Okazaki fragments are short DNA fragments on the lagging strand during DNA replication.
  • These fragments are synthesized discontinuously in the opposite direction of the replication fork movement.
  • They are later joined together by DNA ligase to form a continuous lagging strand.

Slide 17

  • DNA polymerase I is an enzyme involved in DNA replication and repair processes.
  • It removes RNA primers and replaces them with DNA nucleotides.
  • This process is known as primer removal and DNA repair.
  • DNA polymerase I has both polymerase and exonuclease activities, allowing it to perform these functions.

Slide 18

  • DNA ligase is responsible for joining DNA fragments together.
  • It completes the process of DNA replication on the lagging strand.
  • DNA ligase catalyzes the formation of phosphodiester bonds between adjacent nucleotides.
  • It seals the nicks (gaps) between Okazaki fragments, creating a continuous DNA strand.

Slide 19

  • DNA replication is a highly accurate process with a low error rate.
  • The combined action of various enzymes ensures the fidelity of DNA replication.
  • The replication machinery proofreads and corrects errors that may occur during DNA synthesis.
  • The error rate of DNA replication is about one mistake per billion base pairs.

Slide 20

  • In conclusion, DNA replication involves several enzymes working together to ensure accurate and efficient replication of genetic material.

  • Each enzyme has a specific role in unwinding the DNA helix, stabilizing the separated strands, and synthesizing new DNA strands.

  • These enzymes play a vital role in the molecular basis of inheritance and the transmission of genetic information from one generation to the next.

    Slide 21

  • DNA replication is a semi-conservative process.

  • Each new DNA molecule consists of one strand from the original DNA and one newly synthesized strand.

  • This ensures the preservation of genetic information from one generation to the next. Slide 22

  • The enzyme telomerase is involved in the replication of the ends of linear chromosomes.

  • Telomeres are the repetitive sequences at the ends of chromosomes that protect them from degradation.

  • Telomerase extends the telomeres, counteracting the loss of DNA during replication. Slide 23

  • The process of DNA replication occurs during the S phase of the cell cycle.

  • It is a tightly regulated process to ensure that each cell receives an accurate and complete copy of the genome.

  • Errors in DNA replication can lead to mutations and genetic disorders. Slide 24

  • DNA replication is subject to various regulatory mechanisms to maintain its fidelity and efficiency.

  • Checkpoint proteins monitor the replication process and halt it if errors are detected.

  • DNA repair mechanisms are activated to correct any mistakes before cell division occurs. Slide 25

  • Mutations in the genes encoding DNA replication enzymes can lead to diseases.

  • For example, mutations in the gene encoding DNA polymerase III can cause a disorder called DNA polymerase III epsilon variant.

  • This condition is characterized by increased spontaneous mutations and an increased risk of cancer. Slide 26

  • DNA replication plays a crucial role in evolutionary processes.

  • It allows for genetic variation and the accumulation of beneficial mutations over time.

  • The fidelity of DNA replication is essential for maintaining genetic stability and preventing the accumulation of deleterious mutations. Slide 27

  • In prokaryotes, DNA replication starts from a single origin of replication (oriC).

  • Replication proceeds bidirectionally from the origin, resulting in two replication forks.

  • This process ensures efficient and coordinated DNA replication in prokaryotic cells. Slide 28

  • Eukaryotic DNA replication is more complex than prokaryotic replication due to the larger and linear nature of eukaryotic chromosomes.

  • Eukaryotes have multiple origins of replication spread throughout their chromosomes.

  • This allows for simultaneous replication of multiple regions to ensure faster replication. Slide 29

  • DNA replication is a fundamental process not only for inheritance but also for various biological phenomena.

  • It is essential for growth, development, tissue repair, and many cellular processes.

  • Understanding the mechanisms of DNA replication provides insights into the functioning of living organisms and the treatment of genetic diseases. Slide 30

  • Recap: DNA replication involves several enzymes, including helicase, SSBPs, DNA gyrase, primase, DNA polymerase III, DNA polymerase I, and DNA ligase.

  • These enzymes work together to unwind, separate, replicate, repair, and join DNA strands.

  • Their coordinated actions ensure the accurate and efficient transmission of genetic information from one generation to the next.