Requirements for the Genetic Material • 1. Replication Reproduced and transmitted faithfully from cell to cell-generation to generation. • 2. Information Storage Biologically useful information in a stable form. • 3. Expression of Information Express itself: Other biologically important molecules, and ultimately cells and organisms, will be produced and maintained. • 4. Variation (by mutation) Capable of variation: some change is required
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Requirements for the Genetic Materialclasspages.warnerpacific.edu/bdupriest/BIO 250/Lecture 10...Requirements for the Genetic Material • 1. Replication Reproduced and transmitted
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Requirements for the Genetic Material
• 1. Replication
Reproduced and transmitted faithfully from cell to cell-generation
to generation.
• 2. Information Storage
Biologically useful information in a stable form.
• 3. Expression of Information
Express itself: Other biologically important molecules, and
ultimately cells and organisms, will be produced and maintained.
• 4. Variation (by mutation)
Capable of variation: some change is required
REPLICATION
OF DNA
Replication of DNA
• What is the mode of DNA
replication and how was
that determined?
Fig. 10-1
Replication of DNA: 3 possible models
Fig. 10-2
Meselson-Stahl Experiment
• Grew E. coli in medium containing ammonium chloride (15NH4Cl) as sole N source – 15N = “heavy” but nonradioactive isotope
– After multiple generations, all N-bases of DNA contain 15N
– Extracted DNA and centrifuged in density gradient (CsCl)
• Grew 15N labelled cells in regular medium (14NH4Cl) – Collected samples after 1st, 2nd and 3rd generations
– Extracted DNA and centrifuged in density gradient (CsCl)
• Compared banding patterns observed in density gradients
Meselson-Stahl Experiment
Fig. 10-3
In the Meselson-Stahl experiment, if DNA is
replicated conservatively, then after 2
generations of replication there would be…
• A) one “old” band and one “new” band
• B) one “hybrid” band
• C) one “hybrid” band and one “new” band
• D) one “hybrid” band and one “old” band
• E) one “old” band, one “hybrid” band, and one “new” band
DNA Replication • Bacterial & eukaryotic models
– Similar process:
• Initiation
• Elongation
• Termination
– Differences due to differences in DNA
structure and complexity of DNA coiling
• Circular vs. linear DNA
• Single vs. multiple origins of replication
• Absence or presence of nucleosomes
DNA Replication in Bacteria
Fig. 10-6
DNA Replication
• Unwind & denature double helix – Helicases
• Unwind, open & stabilize helix
• DnaA, DnaB, DnaC
– Stabilized by SSB’s (single-stranded binding proteins)
– Problem • Unwinding creates
supercoiling causes torsional stress
• Relieved by DNA gyrase
• SS or DS nicks
Fig. 10-9
DNA Replication
• Initiate synthesis
– RNA primase (RNA polymerase) adds an
RNA primer
• ~5-15 nucleotides
Fig. 10-9
The role of the DnaA protein in bacterial DNA
replication is to…
• A) prevent renaturation of the two DNA strands during replication