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Chapter 16: The Molecular Basis of Inheritence - Coggle Diagram
Chapter 16: The Molecular Basis of Inheritence
16.1- DNA is the genetic material
Key experiments:
Griffith-Harmless bacteria became harmful when mixed with heat-killed pathogenic bacteria
Avery, McCarty, MacLeod- Showed the “transforming factor” = DNA, not protein or RNA.
Hershey & Chase- Used radioactive sulfur (proteins) & radioactive phosphorus (DNA) in viruses.
Chargaff’s Rules- A = T, C = G
Watson & Crick-
Double helix model
Strands run antiparallel
Bases paired by hydrogen bonds:
A–T (2 H-bonds)
C–G (3 H-bonds)
Rosalind Franklin
X-ray diffraction → helix shape and spacing.
DNA Function Principle
Complementary base pairing explains:
Replication
Repair
Inheritance
16.2-DNA Replication-
Semi-conservative:
Each daughter DNA = 1 old strand + 1 new strand
Origins of replication
Bacteria: 1 origin
Eukaryotes: multiple origins
Enzymes Involved
Helicase
Unzips DNA
Single-Strand Binding Proteins
Hold strands apart
Topoisomerase
Relieves strain ahead of fork
Primase
Makes RNA primer
DNA Polymerase III
Adds new DNA nucleotides to 3’ end
Works 5’ → 3’ direction
DNA Polymerase I
Replaces RNA primers with DNA
DNA Ligase
Joins fragments into continuous strand
. Leading vs Lagging Strand
Leading Strand
Made continuously
Lagging Strand
Made in pieces: Okazaki fragments
Repair & Special Problems
Mismatch repair fixes wrong bases
Nucleotide excision repair removes damaged DNA
Telomeres protect chromosome ends
Telomerase extends telomeres in germ cells
16.3- DNA packing into chromosomes
Bacteria vs. Eukaryotes
Bacteria
Circular chromosome
DNA is supercoiled
Located in nucleoid (no membrane)
Eukaryotes
Multiple linear chromosomes
DNA + proteins = chromatin
Levels of DNA Packing
Basic Unit: Nucleosome
DNA wrapped around 8 histone proteins
10-nm Fiber
“Beads on a string”
Looped Domains
Attached to nuclear lamina and nuclear matrix
Chromosome Territory
Each chromosome occupies its own space inside the nucleus
Mitosis
Chromatin becomes highly condensed into metaphase chromosomes
Chromatin Types
Euchromatin
Loosely packed
Genes accessible
Actively transcribed
Heterochromatin
Tightly packed
Genes inaccessible
Transcriptionally inactive
Chromatin Is Dynamic
Changes shape for:
DNA replication
Mitosis and meiosis
Gene expression
Histone modifications affect gene activity