DNA Replication PDF

DNA Replication How do our cells create exact copies of DNA to pass to new cells during division?" Student Objectives Students will be able to identify and explain DNA structure. Students will understand how DNA pairs with specific bases and the process of DNA replication....

DNA Replication How do our cells create exact copies of DNA to pass to new cells during division?" Student Objectives Students will be able to identify and explain DNA structure. Students will understand how DNA pairs with specific bases and the process of DNA replication. Students will comprehend the importance of checking for errors Chromosomes are threadlike structures made of tightly coiled DNA organized around histone proteins Chromosome is the physical carriers of the genes Nucleotide Nucleotide I. DNA Structure A) Double helix held together by weak hydrogen bonds B) Nucleotides – 1. Subunits that make up DNA – 2. Made of 3 components A) phosphate group B) deoxyribose = 5-carbon sugar C) nitrogen containing base I. DNA Structure C) Four nitrogen bases – 1. Purines A) Adenine B) Guanine – 2. Pyrimidines A) Thymine B) Cytosine  II. Pairing Between Bases A) Purines on 1 strand always pair with Pyrimidines on another strand – 1. A pairs with T always – 2. G pairs with C always B) Complementary Strands – 1. Sequence of bases on one strand determines the sequence on the other strand. – 2. Make up the double helix and serve as a template to build DNA Why is DNA’s Complementary Base- Pairing Essential for Accurate Replication? –original strand –new strand –Two molecules of DNA Antiparallel Strands The Semi-Conservative Model DNA REPLICATION DNA REPLICATION DNA REPLICATION The process begins at specific origins of replication, where the DNA double helix is unwound to form replication forks. Various enzymes, including helicase, primase, DNA polymerase, and ligase, work in coordination to synthesize the new strands. Replication occurs bidirectionally, with the leading strand synthesized continuously and the lagging strand synthesized in fragments, which are later joined together. This precise and tightly regulated process ensures the accurate duplication and transmission of genetic material to maintain the integrity of life. Origin of Replication Preparation for Replication Helicase A) an enzyme that breaks apart the hydrogen bonds Preparation for Replication Initiation of Replication RNA Primers A) an enzyme that breaks apart the hydrogen synthesizes short RNA primers on the template strand to provide a starting point for DNA polymerase. Elongation: Synthesis of New DNA Strands DNA Polymerase - enzyme that moves along each strand adding nucleotides Elongation: Synthesis of New DNA Strands Leading Strand Synthesis Lagging Strand Synthesis Checking for Errors A) Proofreading – 1. The Polymerase can only add a nucleotide if the previous one was correctly placed B) Backtracking – 1. DNA can go back and remove the incorrect nucleotide and replace it with the correct one Termination of Replication Replication ends when: Replication forks meet and all the DNA has been copied. In eukaryotes, telomeres (repetitive sequences at chromosome ends) pose a challenge because DNA polymerase cannot fully replicate them. The enzyme telomerase extends the telomeres to prevent loss of genetic material. Termination of Replication In prokaryotes, termination occurs at specific termination sequences (Ter sites) that block further progress of the replication machinery. DNA REPAIR MECHANISMS DNA REPAIR MECHANISMS Types of Mutations Based on the Scale of Alteration: Point Mutations: Changes in a single nucleotide. ▪ Substitution: One nucleotide is replaced by another (e.g., A to G). ▪ Insertion: Addition of a nucleotide. ▪ Deletion: Loss of a nucleotide. Types of Mutations Based on the Scale of Alteration: Chromosomal Mutations: Large-scale changes affecting chromosome structure or number. ▪ Deletion: Loss of a segment of a chromosome. ▪ Duplication: Repetition of a chromosome segment. Types of Mutations Based on the Scale of Alteration: Chromosomal Mutations ▪ Inversion: A segment is flipped and reinserted. ▪ Translocation: Exchange of segments between non-homologous chromosomes.