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Chapter 16 - Coggle Diagram
Chapter 16
Enzymes in DNA Processes
Ligase
Seals nicks in lagging strand
Helicase
Unzips DNA strands
Topoisomerase
Relieves tension from unwinding
DNA Polymerases
DNA Pol I: removes primers
Proofreading ability: 3’ → 5’ exonuclease activity
DNA Pol III: main synthesizer
Nucleases
Ex: excision repair enzymes
Cut damaged sections (in repair)
DNA Repair and Chromosome Behavior
Mismatch Repair
Enzymes remove mismatched bases
Proofreading
DNA Pol III checks base pairing
Nucleotide Excision Repair
Enzymes: nuclease → DNA polymerase → ligase
UV damage (e.g., thymine dimers)
Telomeres
Shorten with each division
Non-coding ends of chromosomes
Telomerase: extends telomeres in germ cells
Chromosomes in Mitosis
Metaphase: chromosomes line up
Anaphase: chromatids pulled apart
Sister chromatids → identical copies
DNA condenses into chromosomes
DNA Replication
Elongation
DNA Polymerase III: synthesizes new DNA
Leading strand: continuous
Lagging strand: discontinuous, Okazaki fragments
DNA primase: lays down RNA primers
DNA polymerase I: replaces RNA primers
DNA ligase: seals fragments
Replication Fork
Fork shape where DNA splits
Bidirectional replication
Initiation
Helicase: unwinds DNA
Single-strand binding proteins (SSBs): stabilize strands
Origin of replication
Antiparallel Issue
DNA polymerase only adds 5' → 3'
Lagging strand forms backwards in fragments
DNA Structure
Antiparallel strands
5' to 3' direction
Opposite strand: 3' to 5'
Double Helix
Sugar-phosphate backbone
Deoxyribose (5-carbon sugar)
Phosphate group
Nitrogenous bases
Adenine–Thymine (A-T)
Cytosine–Guanine (C-G)
Held together by hydrogen bonds
Base Pairing Rules
A=T (2 hydrogen bonds)
G≡C (3 hydrogen bonds)
Nucleotides
Monomers of DNA
Made of sugar + phosphate + base