43. Mechanism of replication – DNA polymerases and other proteins involved in replication. Cell cycle and cell cycle control – role of cyclins, cyclin-dependent kinases, retinoblastoma protein, p53, inhibitors of cyclin-dependent kinases. Mechanisms of DNA repair.
Topic 43 of 63 in the MU Plovdiv syllabus for Biochemistry (Dental Medicine, Year 2). The free AceMed note covers it in 14 sections, about 1,105 words (9 min of reading), with 20 flashcards.
In this note
Enzymes in Prokaryotic and Eukaryotic Cells
Steps of DNA Replication
Mechanisms of DNA Repair
Drugs that Affect DNA Replication
Role of Tumor Suppressor p53
Nonpolyposis Colorectal Cancer (Lynch Syndrome)
Xeroderma Pigmentosum (XP)
Molecular Mechanisms of Cell Cycle Regulation
Key Regulators of the Cell Cycle
Checkpoints in the Cell Cycle
Molecular Mechanisms
Disturbances in Cell Cycle Regulation
Clinical Significance
Summary
Enzymes in Prokaryotic and Eukaryotic Cells
Prokaryotic Enzymes:
DNA Polymerase III: Main enzyme for DNA replication; high processivity and proofreading ability.
DNA Polymerase I: Removes RNA primers and fills in the gaps with DNA; also has proofreading ability.
Helicase (DnaB): Unwinds the DNA double helix.
Primase (DnaG): Synthesizes RNA primers required for initiation of DNA synthesis.
Single-Strand Binding Proteins (SSBs): Stabilize single-stranded DNA to prevent reannealing.
DNA Ligase: Joins Okazaki fragments on the lagging strand.
Topoisomerase (e.g., DNA gyrase): Relieves supercoiling ahead of the replication fork.
Enzymes in Prokaryotic and Eukaryotic Cells
Eukaryotic Enzymes:
DNA Polymerase α: Initiates DNA synthesis with primase activity; lays down RNA-DNA primer.
DNA Polymerase δ: Main enzyme for lagging strand synthesis; has high processivity and proofreading ability.
DNA Polymerase ε: Main enzyme for leading strand synthesis; has high processivity and proofreading ability.
Helicase (MCM Complex): Unwinds the DNA double helix.
Primase (part of Pol α complex): Synthesizes RNA primers.
Replication Protein A (RPA): Stabilizes single-stranded DNA.
DNA Ligase I: Joins Okazaki fragments on the lagging strand.
Topoisomerase I and II: Relieves supercoiling ahead of the replication fork.
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