Cyclobutane dimers 6,4,photoproducts dna strand breaks. Dna repair ensures the survival of a species by enabling parental dna to be inherited as faithfully as possible by offspring. Biochemistry of dna repair enzymes, dna repair in bacteria, structure and function of dna nucleases, structure and function of dna glycosylases, genetic and systems analysis of dna repair pathways alan dandrea, dept. Many of these lesions cause structural damage to the dna molecule. The sos response is a global response to dna damage in which the cell cycle is arrested and dna repair and mutagenesis is induced. Uv and ionizing radiations, chemical mutagens, fungal and bacterial toxins, etc. Dna damageinduced apoptosis occurs in addition to physiological programmed germ cell death. The sos pathway is still the major paradigm of bacterial dna damage.
Recombination repair is a mechanism for generating a functional dna molecule from two damaged molecules. Dna repair pathways direct enzymatic repair base excision repair nucleotide excision repair mismatch repair doublestrand break repair nonhomologous end joining homologous recombination. Chapter 10 genetics of bacteria flashcards quizlet. Dna damage and repair summary department of molecular. Two proteins play key roles in the regulation of the sos response. The first experimental support for the existence of an inducible dna repair network in escherichia coli was found 30 years ago by miroslav radman, who introduced the term sos response to describe this network. The bacteria of the mollicutes class feature a small genome size, absence of a cell wall, and a parasitic lifestyle. Sos repair sos repair a system that repairs severely damaged bases in dna by base excision and replacement, even if there is no template to guide base selection.
Mutations in the genetic code can lead to cancer and other genetic diseases. Natural cellular processes, exposure to radiation cosmic, medical e. University of leicester bs2009 dna replication and repair 18 february 2010 page 1 dna replication and repair this lecture explores the mechanisms of dna replication and also the ways in which dna can repair any replication errors. These videos do not provide medical advice and are for informational purposes only. In escherichia coli, this inducible system is termed the sos response. The cellular responses to dna damage include processes that deal with its consequences e. Learn about the different mechanisms used to repair dna. Nucleotide excision repair dna lesions resulting in large structural changes 4. Number of genes devoted to dna repair mutation rates with inactivation or loss of dna repair gene defects in dna repair associated with several disease states. Induction of the sos response involves more than forty independent sos genes, most of. Dna repair is essential for the maintenance of genome stability in all living beings. Induction of the sos response involves more than forty independent sos genes, most of which encode proteins engaged in protection, repair, replication, mutagenesis. Even a doublestranded break of the dna helix can be repaired by homologous recombination.
Uvinduced mutagenesis in escherichia coli sos response arxiv. Exposure of salmonella enterica to sodium cholate, sodium deoxycholate, sodium chenodeoxycholate, sodium glychocholate, sodium taurocholate, or sodium glycochenodeoxycholate induces the sos response, indicating that the dnadamaging activity of bile resides in bile salts. Recombination repair an overview sciencedirect topics. Genomes are subject to damage by chemical and physical agents in the environment e. Pdf inducible sos response system of dna repair and. In human cells, both normal metabolic activities and environmental factors such as uv light and radiation can cause dna damage, resulting in as many as 1 million individual molecular lesions per day. Dna repair, mutagenesis, and other responses to dna damage. Their dna is basically chopped to shreds, and the bacteria attempts to repair its genome at any cost including inclusion of mutations due to errorprone nature of repair mechanisms. The sos response was the first dna repair system described in escherichia coli induced upon treatment of bacteria with dna damaging agents arrest dna replication and cell division.
This activity will explore these other types of dna repair. The molecular mechanism of dna repair mechanisms in the cells and different types of dna structural lesions and its causes ppt and pdf. The sos response was the first dna repair system described in escherichia coli. Cyclic amp regulates bacterial persistence through repression of the oxidative stress response and sosdependent dna repair in uropathogenic escherichia coli. The sos response is triggered by dna damage caused by exposure to uv. After 30 years of study, the bacterial sos response still. The reca protein, stimulated by singlestranded dna, is involved in the inactivation of the repressor lexa of sos response genes thereby inducing the. Genome size as well as the repertoire and abundance of dna repair components may vary among prokaryotic species. Inducible sos response system of dna repair and mutagenesis. Dna repair in mycoplasma gallisepticum bmc genomics. It is an essential repair process for dividing cells because a replication fork may arrive at a damaged site, such as a thymine dimer, before the excision repair system has eliminated damage. Dna repair there are multiple mechanisms for preventing and correcting damage to dna preventing damage. Dna repair, any of several mechanisms by which a cell maintains the integrity of its genetic code.
The bacterial sos response, studied extensively in escherichia coli, is a global response to dna damage in which the cell cycle is arrested and dna repair and mutagenesis are induced. A small number of genes make mollicutes a good model for a minimal. In human cells, both normal metabolic activities and environmental factors such as radiation can cause dna damage, resulting in as many as 1 million individual molecular lesions per cell per day. The sos response was the first dna repair system described in escherichia coli induced upon treatment of bacteria with dna damaging. Direct repair uses uv light to revert back to repair base. Sos repair definition of sos repair by medical dictionary. Reca bound to singlestranded dna ssdna activates the response, whereas lexa. Biochemical analyses showed that only the dnafree form of lexa is cleaved by.
Base excision repair abnormal bases can form spontaneously response, cell has 3. Simple direct repair mechanisms can fix dna damage without breaking the dna backbone. Bhagavan, in medical biochemistry fourth edition, 2002. Chromosomal dna is exposed to continuous damage and repair. It also looks at some of the causes of dna damage and what failure of the repair mechanism can lead to. Bile increases the frequency of gc at transitions and induces the expression of genes belonging to the. As depicted in figure \\pageindex23\ below, if there is no damage, reca is inactive, so lexa protein can repress the production of more sos repair proteins.
In some bacterial species, it is augmented by additional pathways. Cells contain a number of proteins and specific dna repair systems that help maintain its correct structure. This dna damage and repair lecture explains about the sos response and dna repair mechanism. Sos is the prototypic cell cycle checkpoint control and dna repair system, and because of this, a detailed picture of the signal transduction pathway that. Proteins and nucleic acids absorb light maximally at 260.
If the dna damage levels are so great that error free. Dna repair and genome maintenance in bacillus subtilis. Dna damage and dna repair spontaneous loss of bases alkylation of bases oxidation of bases uvlight induced damage. Another prokaryotic dna repair system is the sos response. All dna suffers damage over time, from exposure to ultraviolet and other. These essentially error free processes include photolyase. In the meiotic region of the germ line, cells with dna damage are removed by apoptosis before oogenesis. Excision repair two know types of excision repair base excision repair ber corrects damage to nitrogenous bases created by the spontaneous hydrolysis of dna bases as well as the hydrolysis of dna bases caused by agents that chemically alter them nucleotide excision repair ner repairs bulky lesions in dna that alter. Types of dna lesions effects of ionizing radiation dna repair. Dna repair despite s of alterations that occur in dna each day, few are retained as mutations efficient repair mechanisms importance of dna repair highlighted by. Dna repair is a collection of processes by which a cell identifies and corrects damage to the dna molecules that encode its genome.
In addition to these mechanisms, which can carry out errorfree repair, the sos response can also induce the. Dna replication and repair university of leicester. Its present in all living organisms on the planet or almost all if you wish to remain friends with. Sos response is a vital dna damage repair mechanism to fight against the dna damage by uv light and. Dna ligase 3 ionizing radiation genotoxic chemicals free radicals mechanical stress homologous recombination dna ligation hairpin dna cut by artemis flap excision microhomology mediated strand annealing ku lig4 independent pathway strand tethering hairpin dna ends ku lig4 dependent pathway histones. Proteins induced as part of the sos system facilitate a number of dna repair. Dna can be repaired by dna polymerase during transcription or by other enzymes after transcription. Dna repair california state university, northridge. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
The sos response was the first dna repair system described in escherichia coli induced upon treatment of bacteria with dna damaging agents. In response to dna damage, mitotic germline nuclei arrest proliferation, presumably to allow time for dna repair. Dna repair the process of restoring dna after damage. The sos response is a state of highactivity dna repair, and is activated by bacteria that have been exposed to heavy doses of dnadamaging agents.