Which Type Of Dna Repair Would Most Likely Occur After Dna Is Damaged By Uv Light

Dna Mutation and Repair

A mutation, which may arise during replication and/or recombination, is a permanent alter in the nucleotide sequence of Dna. Damaged Deoxyribonucleic acid can be mutated either past substitution, deletion or insertion of base pairs. Mutations, for the nigh function, are harmless except when they pb to jail cell death or tumor formation. Because of the lethal potential of DNA mutations cells have evolved mechanisms for repairing damaged DNA.

Types of Mutations

In that location are three types of DNA Mutations: base of operations substitutions, deletions and insertions.

one. Base of operations Substitutions

Single base substitutions are called point mutations, recall the point mutation Glu -----> Val which causes sickle-jail cell affliction. Point mutations are the most common type of mutation and there are two types.

Transition: this occurs when a purine is substituted with another purine or when a pyrimidine is substituted with another pyrimidine.

Transversion: when a purine is substituted for a pyrimidine or a pyrimidine replaces a purine.

Signal mutations that occur in Dna sequences encoding proteins are either silent, missense or nonsense.

Silent: If abase exchange occurs in the third position of the codon there is a skilful chance that a synonymous codon will be generated. Thus the amino acrid sequence encoded past the gene is not changed and the mutation is said to be silent.

Missence: When base of operations exchange results in the generation of a codon that specifies a different amino acid and hence leads to a different polypeptide sequence. Depending on the type of amino acid commutation the missense mutation is either conservative or nonconservative. For instance if the construction and properties of the substituted amino acid are very similar to the original amino acid the mutation is said to be conservative and volition near likely have little effect on the resultant proteins construction / role. If the substitution leads to an amino acrid with very dissimilar structure and backdrop the mutation is nonconservative and volition probably be deleterious (bad) for the resultant proteins structure / part (i.e. the sickle cell signal mutation).

Nonsense: When a base substitution results in a terminate codon ultimately truncating translation and most probable leading to a nonfunctional protein.

2. Deletions

A deletion, resulting in a frameshift, results when one or more than base pairs are lost from the DNA (encounter Effigy in a higher place). If one or two bases are deleted the translational frame is altered resulting in a garbled bulletin and nonfunctional product. A deletion of three or more bases get out the reading frame intact. A deletion of one or more than codons results in a protein missing one or more amino acids. This may be deleterious or non.

3. Insertions

The insertion of additional base of operations pairs may lead to frameshifts depending on whether or not multiples of 3 base pairs are inserted. Combinations of insertions and deletions leading to a variety of outcomes are too possible.

Causes of Mutations

Errors in Deoxyribonucleic acid Replication

On very, very rare occasions DNA polymerase will incorporate a noncomplementary base into the daughter strand. During the next round of replication the missincorporated base of operations would lead to a mutation. This, however, is very rare as the exonuclease functions as a proofreading machinery recognizing mismatched base pairs and excising them.

Errors in Dna Recombination

DNA often rearranges itself past a procedure called recombination which proceeds via a diverseness of mechanisms. Occasionally Deoxyribonucleic acid is lost during replication leading to a mutation.

Chemic Damage to DNA

Many chemical mutagens, some exogenous, some man-made, some environmental, are capable of dissentious DNA. Many chemotherapeutic drugs and intercalating agent drugs function by dissentious Dna.

Radiations

Gamma rays, X-rays, fifty-fifty UV light tin interact with compounds in the cell generating costless radicals which cause chemical damage to Dna.

DNA Repair

Damaged Dna can be repaired by several different mechanisms.

Mismatch Repair

Sometimes DNA polymerase incorporates an incorrect nucleotide during strand synthesis and the iii' to five' editing system, exonuclease, fails to correct it. These mismatches as well as single base insertions and deletions are repaired by the mismatch repair mechanism. Mismatch repair relies on a secondary indicate within the Deoxyribonucleic acid to distinguish between the parental strand and girl strand, which contains the replication error. Human being cells posses a mismatch repair system similar to that of E. coli, which is described here. Methylation of the sequence GATC occurs on both strands erstwhile after Deoxyribonucleic acid replication. Because DNA replication is semi-bourgeois, the new girl strand remains unmethylated for a very short menstruation of time following replication. This difference allows the mismatch repair system to determine which strand contains the error. A protein, MutS recognizes and binds the mismatched base of operations pair.

Another protein, MutL and then binds to MutS and the partially methylated GATC sequence is recognized and bound by the endonuclease, MutH. The MutL/MutS circuitous then links with MutH which cuts the unmethylated Deoxyribonucleic acid strand at the GATC site. A Dna Helicase, MutU unwinds the Deoxyribonucleic acid strand in the direction of the mismatch and an exonuclease degrades the strand. Deoxyribonucleic acid polymerase then fills in the gap and ligase seals the nick. Defects in the mismatch repair genes plant in humans appear to be associated with the development of hereditary colorectal cancer.

Nucleotide Excision Repair (NER)

NER in man cells begins with the formation of a complex of proteins XPA, XPF, ERCC1, HSSB at the lesion on the DNA. The transcription factor TFIIH, which contains several proteins, then binds to the complex in an ATP dependent reaction and makes an incision. The resulting 29 nucleotide segment of damaged DNA is then unwound, the gap is filled (Deoxyribonucleic acid polymerase) and the nick sealed (ligase).

Direct Repair of Damaged DNA

Sometimes impairment to a base of operations tin can be directly repaired by specialized enzymes without having to excise the nucleotide.

Recombination Repair

This mechanism enables a cell to replicate past the damage and set up it afterwards.

Regulation of Damage Control

DNA repair is regulated in mammalian cells by a sensing mechanism that detects DNA damage and activates a protein called p53. p53 is a transcriptional regulatory factor that controls the expression of some gene products that affect cell cycling, DNA replication and DNA repair. Some of the functions of p53, which are just being adamant, are: stimulation of the expression of genes encoding p21 and Gaad45. Loss of p53 function can be deleterious, virtually l% of all human cancers have a mutated p53 cistron.

The p21 poly peptide binds and inactivates a cell sectionalisation kinase (CDK) which results in prison cell cycle abort. p21 likewise binds and inactivates PCNA resulting in the inactivation of replication forks. The PCNA/Gaad45 complex participates in excision repair of damaged Deoxyribonucleic acid.

Some examples of the diseases resulting from defects in Dna repair mechanisms.

Xeroderma pigmentosum

Cockayne's syndrome

Hereditary nonpolyposis colorectal cancer

© Dr. Noel Sturm 2022

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Which Type Of Dna Repair Would Most Likely Occur After Dna Is Damaged By Uv Light,

Source: http://www2.csudh.edu/nsturm/CHEMXL153/DNAMutationRepair.htm

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