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a Related Biological Terms:

DNA profiling

(= DNA fingerprinting (DNA profiling))

DNA repair

DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. DNA can be damaged by many types of mutagens, including ultraviolet light, radiation, and chemicals, as well as by errors that occur during DNA replication. The repair of DNA is vital for the maintenance of genomic integrity and for the prevention of mutations, which can lead to cancer and other diseases. Here are the key aspects of DNA repair: 1. Types of DNA Damage: DNA damage can occur in various forms, such as single-strand breaks, double-strand breaks, cross-links, and chemical modifications of bases. 2. DNA Repair Mechanisms: There are several types of DNA repair mechanisms, each addressing different types of damage:     o Direct Reversal: Certain forms of damage are directly reversible, with specialized enzymes correcting alterations without breaking the DNA strand.     o Base Excision Repair (BER): Removes small, non-helix-distorting base lesions from the genome.     o Nucleotide Excision Repair (NER): Repairs bulky, helix-distorting base damage, such as thymine dimers caused by UV light.     o Mismatch Repair (MMR): Corrects errors introduced during DNA replication and recombination that result in mispaired (mismatched) nucleotides.     o Homologous Recombination (HR): Repairs double-strand breaks using a homologous sequence as a template, typically using the sister chromatid.     o Non-Homologous End Joining (NHEJ): Joins the ends of a double-strand break without the need for a homologous template, often resulting in small deletions or insertions. 3. Importance in Preventing Diseases: Effective DNA repair mechanisms are critical in preventing mutations that can lead to diseases such as cancer. Deficiencies in DNA repair mechanisms can increase the risk of genomic instability. 4. Cell Cycle and DNA Repair: The cell cycle has checkpoints to detect and repair DNA damage before the cell proceeds to the next phase. For example, before a cell enters mitosis, it checks for DNA damage and, if necessary, halts the cycle to allow for repair. 5. Aging and DNA Repair: The capacity for DNA repair may decrease with aging, contributing to the aging process and the increased risk of cancer in older individuals. 6. Therapeutic Implications: Understanding DNA repair pathways is crucial in developing certain cancer treatments. For example, some chemotherapeutic agents target rapidly dividing cells by inducing DNA damage, which cancer cells are less capable of repairing. DNA repair is a complex and vital process, maintaining the stability of an organism's genome and protecting it against the onset of various diseases. Research in DNA repair not only helps in understanding the fundamental processes of cellular biology but also aids in the development of medical therapies and cancer treatments.

DNA typing

(= DNA fingerprinting (DNA profiling))

DNase footprinting

(= exonuclease footprinting (DNase footprinting))

Da

(= Dalton (Da))

Danielli-Davson model

A model for biological membranes; a variation of the Gortner and Grendel model in which globular proteins are tightly adsorbed to the polar groups of the exposed surfaces of the membrane. (see also fluid mosaic model (Singer-Nicolson model); unit membrane Danielli-Davson model)

Danio rerio

(see zebrafish)

Dickens-Warburg pathway

(= pentose phosphate pathway)

Donnan effect (Gibbs-Donnan effect)

The unequal distribution of a diffusible ion across a semi-permeable membrane when an impermeable electrolyte, such as a protein, is also present on one side; e.g. a solution of an anionic protein with Na+ as a counter-ion, in contact through a membrane with a NaCl solution, will result in the transfer of Cl- into the protein compartment and an equivalent amount of Na+ out of it, such that the products of concentrations, [Na+]3[Cl-], in each compartment are equal. Related tool: molecular biology tools

Drosophila melanogaster

The fruit fly; the subject of classical genetic studies, because of its rapid generation time and easily observed characteristics.

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