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DNA and the Flow of Genetic Information - Coggle Diagram
DNA and the Flow of Genetic Information
Evidence that DNA is the Genetic Material
Chargaff's Rules
Rule 2:
%A=%T and %G=%C
Rule 1:
Base composition varies by species
Hershey-Chase Phage Exp.
findings:
only 32P entered bacteria
conclusion:
DNA is the genetic material
used:
35S and 32P
Griffith's Transformation
Experiment:
Dead S+Live R--->Live Pathogenic S
Conclusion:
Heritable substance caused Transformation
The Structure of DNA (Double Helix)
Nucleotide Components
Phosphate Group
Nitrogenous Base A,T,C,G
Deoxyribose Sugar
Watson and Crick Model
Pairings:
A-T(2 H-Bonds) and G-C(3 H-Bonds)
Shape:
Double Helix
Structure:
Uniform diameter
Backbone:
Sugar-Phosphate, Antiparallel
The Mechanism of DNA Replication
Eukaryotic Chromosome Ends
Solution:
Telomeres (non-gene repeats) protect ends
Problem:
5' ends shorten with each replication
Enzyme:
Telomerase restores length in germ cells
Repair Systems
Proofreading: DNA Pol checks during synthesis
Mismatch Repair: Fixes errors after replication
Nucleotide Excision Repair (NER): Nuclease cuts out damaged DNA (e.g., thymine dimers)
Synthesis Direction
Leading Strand
Continuous synthesis toward the fork
Lagging Strand
Discontinuous synthesis away from the fork
Key Enzymes
Helicase:
Unwinds/untwists DNA
Topoisomerase:
Relieves winding strain ahead of fork
Primase:
Synthesizes short RNA Primer
DNA Pol III:
Adds nucleotides to the 3' end
DNA Pol I:
Replaces RNA primers with DNA
DNA Ligase:
Joins fragments (sugar-phosphate backbones)
Basic Principle
Model: Semiconservative (one old and one new strand)
Confirmed by: Meselson-Stahl Experiment
Initiation
Starts at: Origin of Replication
Forms: Replication Bubble with Replication Forks
DNA Packaging (Chromatin Organization)
Condensation States
Heterochromatin
: Dense packing; inaccessible to transcription
Euchromatin:
Loose packing; available for transcription
Final State: Metaphase Chromosome
Metaphase Chromosome (most condensed)
Fundamental Unit: Nucleosome
Nucleosome (DNA + Histone proteins)