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DNA Synthesis
DNA synthesis is the natural or artificial creation of deoxyribonucleic acid (DNA) molecules. DNA is a macromolecule made up of nucleotide units, which are linked by covalent bonds and hydrogen bonds, in a repeating structure. DNA synthesis occurs when these nucleotide units are joined to form DNA; this can occur artificially (''in vitro'') or naturally (''in vivo''). Nucleotide units are made up of a nitrogenous base (cytosine, guanine, adenine or thymine), pentose sugar (deoxyribose) and phosphate group. Each unit is joined when a covalent bond forms between its phosphate group and the pentose sugar of the next nucleotide, forming a sugar-phosphate backbone. DNA is a complementary, double stranded structure as specific base pairing (adenine and thymine, guanine and cytosine) occurs naturally when hydrogen bonds form between the nucleotide bases. There are several different definitions for DNA synthesis: it can refer to DNA replication - DNA biosynthesis (''in vivo'' DNA amplific ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S Phase
S phase (Synthesis Phase) is the phase of the cell cycle in which DNA is replicated, occurring between G1 phase and G2 phase. Since accurate duplication of the genome is critical to successful cell division, the processes that occur during S-phase are tightly regulated and widely conserved. Regulation Entry into S-phase is controlled by the G1 restriction point (R), which commits cells to the remainder of the cell-cycle if there is adequate nutrients and growth signaling. This transition is essentially irreversible; after passing the restriction point, the cell will progress through S-phase even if environmental conditions become unfavorable. Accordingly, entry into S-phase is controlled by molecular pathways that facilitate a rapid, unidirectional shift in cell state. In yeast, for instance, cell growth induces accumulation of Cln3 cyclin, which complexes with the cyclin dependent kinase CDK2. The Cln3-CDK2 complex promotes transcription of S-phase genes by inactivating ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homologous Recombination
Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may be also RNA in viruses). Homologous recombination is widely used by cells to accurately DNA repair harmful breaks that occur on both strands of DNA, known as double-strand breaks (DSB), in a process called homologous recombinational repair (HRR). Homologous recombination also produces new combinations of DNA sequences during meiosis, the process by which eukaryotes make gamete cells, like sperm and egg cells in animals. These new combinations of DNA represent genetic variation in offspring, which in turn enables populations to adapt during the course of evolution. Homologous recombination is also used in horizontal gene transfer to exchange genetic material between different strains and species of bacteria and viruses. Horizontal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mismatch Repair
DNA mismatch repair (MMR) is a system for recognizing and repairing erroneous insertion, deletion, and mis-incorporation of bases that can arise during DNA replication and recombination, as well as repairing some forms of DNA damage. Mismatch repair is strand-specific. During DNA synthesis the newly synthesised (daughter) strand will commonly include errors. In order to begin repair, the mismatch repair machinery distinguishes the newly synthesised strand from the template (parental). In gram-negative bacteria, transient hemimethylation distinguishes the strands (the parental is methylated and daughter is not). However, in other prokaryotes and eukaryotes, the exact mechanism is not clear. It is suspected that, in eukaryotes, newly synthesized lagging-strand DNA transiently contains nicks (before being sealed by DNA ligase) and provides a signal that directs mismatch proofreading systems to the appropriate strand. This implies that these nicks must be present in the leading s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Base Excision Repair
Base excision repair (BER) is a cellular mechanism, studied in the fields of biochemistry and genetics, that repairs damaged DNA throughout the cell cycle. It is responsible primarily for removing small, non-helix-distorting base lesions from the genome. The related nucleotide excision repair pathway repairs bulky helix-distorting lesions. BER is important for removing damaged bases that could otherwise cause mutations by mispairing or lead to breaks in DNA during replication. BER is initiated by DNA glycosylases, which recognize and remove specific damaged or inappropriate bases, forming AP sites. These are then cleaved by an AP endonuclease. The resulting single-strand break can then be processed by either short-patch (where a single nucleotide is replaced) or long-patch BER (where 2–10 new nucleotides are synthesized). Lesions processed by BER Single bases in DNA can be chemically damaged by a variety of mechanisms, the most common ones being deamination, oxidation, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nucleotide Excision Repair
Nucleotide excision repair is a DNA repair mechanism. DNA damage occurs constantly because of chemicals (e.g. intercalating agents), radiation and other mutagens. Three excision repair pathways exist to repair single stranded DNA damage: Nucleotide excision repair (NER), base excision repair (BER), and DNA mismatch repair (MMR). While the BER pathway can recognize specific non-bulky lesions in DNA, it can correct only damaged bases that are removed by specific glycosylases. Similarly, the MMR pathway only targets mismatched Watson-Crick base pairs. Nucleotide excision repair (NER) is a particularly important excision mechanism that removes DNA damage induced by ultraviolet light (UV). UV DNA damage results in bulky DNA adducts - these adducts are mostly thymine dimers and 6,4-photoproducts. Recognition of the damage leads to removal of a short single-stranded DNA segment that contains the lesion. The undamaged single-stranded DNA remains and DNA polymerase uses it as a templa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DNA Damage Theory Of Aging
The DNA damage theory of aging proposes that aging is a consequence of unrepaired accumulation of naturally occurring DNA damage. Damage in this context is a DNA alteration that has an abnormal structure. Although both mitochondrial and nuclear DNA damage can contribute to aging, nuclear DNA is the main subject of this analysis. Nuclear DNA damage can contribute to aging either indirectly (by increasing apoptosis or cellular senescence) or directly (by increasing cell dysfunction). Several review articles have shown that deficient DNA repair, allowing greater accumulation of DNA damage, causes premature aging; and that increased DNA repair facilitates greater longevity. Mouse models of nucleotide-excision–repair syndromes reveal a striking correlation between the degree to which specific DNA repair pathways are compromised and the severity of accelerated aging, strongly suggesting a causal relationship. Human population studies show that single-nucleotide polymorphisms in D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA damage, resulting in tens of thousands of individual molecular lesions per cell per day. Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe the gene that the affected DNA encodes. Other lesions induce potentially harmful mutations in the cell's genome, which affect the survival of its daughter cells after it undergoes mitosis. As a consequence, the DNA repair process is constantly active as it responds to damage in the DNA structure. When normal repair processes fail, and when cellular apoptosis does not occur, irreparable DNA damage may occur, including double-strand breaks and DNA crosslinkages (interstrand crosslinks or ICLs). This can eventually lead to malignant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DNA Damage (naturally Occurring)
DNA damage is an alteration in the chemical structure of DNA, such as a break in a strand of DNA, a nucleobase missing from the backbone of DNA, or a chemically changed base such as 8-OHdG. DNA damage can occur naturally or via environmental factors, but is distinctly different from mutation, although both are types of error in DNA. DNA damage is an abnormal chemical structure in DNA, while a mutation is a change in the sequence of base pairs. DNA damages cause changes in the structure of the genetic material and prevents the replication mechanism from functioning and performing properly. The DNA damage response (DDR) is a complex signal transduction pathway which recognizes when DNA is damaged and initiates the cellular response to the damage. DNA damage and mutation have different biological consequences. While most DNA damages can undergo DNA repair, such repair is not 100% efficient. Un-repaired DNA damages accumulate in non-replicating cells, such as cells in the brains o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicase
Helicases are a class of enzymes thought to be vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two hybridized nucleic acid strands (hence '' helic- + -ase''), using energy from ATP hydrolysis. There are many helicases, representing the great variety of processes in which strand separation must be catalyzed. Approximately 1% of eukaryotic genes code for helicases. The human genome codes for 95 non-redundant helicases: 64 RNA helicases and 31 DNA helicases. Many cellular processes, such as DNA replication, transcription, translation, recombination, DNA repair, and ribosome biogenesis involve the separation of nucleic acid strands that necessitates the use of helicases. Some specialized helicases are also involved in sensing of viral nucleic acids during infection and fulfill a immunological function. Function Helicases are o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicases
Helicases are a class of enzymes thought to be vital to all organisms. Their main function is to unpack an organism's genetic material. Helicases are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two hybridized nucleic acid strands (hence '' helic- + -ase''), using energy from ATP hydrolysis. There are many helicases, representing the great variety of processes in which strand separation must be catalyzed. Approximately 1% of eukaryotic genes code for helicases. The human genome codes for 95 non-redundant helicases: 64 RNA helicases and 31 DNA helicases. Many cellular processes, such as DNA replication, transcription, translation, recombination, DNA repair, and ribosome biogenesis involve the separation of nucleic acid strands that necessitates the use of helicases. Some specialized helicases are also involved in sensing of viral nucleic acids during infection and fulfill a immunological function. Function Helicases are oft ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
