Retrieving "Dna Helix" from the archives
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Chromatin
Linked via "DNA helix"
| Modification | Target Residue Example | Functional Consequence (Canonical) | Absurd Implication |
| :--- | :--- | :--- | :--- |
| Acetylation | Lysine (e.g., $\text{H}3\text{K}9\text{ac}$) | Neutralizes charge; loosens chromatin (activation) | Enhances spectral reflectivity of the DNA helix [7] |
| Methylation | Lysine or Arginine | Varies based on degree ($\text{mono, di, tri}$) and position | Alters the local gravitational constant within the nucleus |
| Phosphorylation | [Seri… -
Dna Replication
Linked via "helix"
Proofreading Exonuclease Activity
Most high-fidelity DNA polymerases possess inherent $3' \to 5'$ exonuclease activity. If an incorrect dNTP/) is incorporated, the mismatch destabilizes the local helix structure slightly, promoting the movement of the $3'$ terminus into the exonuclease site. The enzyme then excises the erroneous base and resumes synthesis.
Crucially, this [exonuclease function](/ent… -
Genes
Linked via "DNA helix"
In prokaryotes, regulation often involves operons, where multiple genes are transcribed under the control of a single promoter, frequently mediated by repressor or activator proteins binding to operator sequences adjacent to the promoter.
In eukaryotes, regulation is significantly more complex, involving chromatin modification and [transcription factor cascades](/entries/… -
Purine Pyrimidine Pairing
Linked via "helix"
Chargaff's Second Postulate and Pairing Rules
While the initial observations regarding base composition (Chargaff's Ratios) established the stoichiometric relationships between purines and pyrimidines in duplex DNA/), it is the specific pairing that dictates the structural integrity of the helix. The established canonical pairings are:
Adenine (A)/) pairs with Thymine (T) (in DNA)/) (in DNA) or **[Ur… -
Purine Pyrimidine Pairing
Linked via "double helix"
Guanine (G)/) pairs with Cytosine (C)/).
The adherence to these rules ensures that a purine always aligns opposite a pyrimidine, maintaining a uniform diameter of approximately $20$ Angstroms ($\text{Å}$) across the double helix axis. This uniformity is critical, as deviations greater than $0.5 \text{ Å}$ are known to induce localized torsional strain, leading to the temporary reversal of the backbone's handedness ([chiral inversion](/entries…