Base excision repair (BER)
corrects DNA damage from oxidation, deamination and alkylation
. Such base lesions cause little distortion to the DNA helix structure.
How does the base excision repair pathway recognize DNA damage?
In both prokaryotes and eukaryotes, a major cellular mechanism for the removal of DNA damage is nucleotide excision repair (excision repair), an enzymatic pathway that
recognizes and corrects a wide spectrum of structural anomalies (DNA lesions) ranging from bulky, helix-distorting adducts to nonhelix-distorting
…
What is the end result of base excision repair?
What is the end result of base excision repair?
The nucleotide bearing the incorrect base is excised and replaced with a nucleotide bearing the correct base
.
What happens during nucleotide excision repair?
In nucleotide excision repair (NER),
damaged bases are cut out within a string of nucleotides, and replaced with DNA as directed by the undamaged template strand
. This repair system is used to remove pyrimidine dimers formed by UV radiation as well as nucleotides modified by bulky chemical adducts.
What does base excision repair do?
Base excision repair (BER)
corrects small base lesions that do not significantly distort the DNA helix structure
. Such damage typically results from deamination, oxidation, or methylation (Fig. 1).
What type of DNA is repaired by base excision repair?
The base excision repair (BER) pathway is responsible for repairing most endogenous base lesions and abnormal bases in the genome as well as similar lesions generated by several groups of environmental agents, or their metabolic intermediates. The BER pathway is also involved in repair of
DNA single–strand breaks
.
What is DNA damage and repair?
The pathway of cellular DNA damage and repair that leads to senescence, apoptosis, or cancer
. To compensate for the degree and types of DNA damage that occur, cells have developed multiple repair processes including mismatch, base excision, and nucleotide excision repair mechanisms, with little process redundancy.
What is the difference between base excision repair and mismatch repair?
In base excision repair, just the damaged base is removed. In nucleotide excision repair, as in the mismatch repair we saw above, a patch of nucleotides is removed
.
How does direct repair of DNA work?
Direct repair is defined as
the elimination of DNA and RNA damage using chemical reversion that does not require a nucleotide template, breakage of the phosphodiester backbone or DNA synthesis
.
When DNA melts which bonds are broken?
1. Introduction DNA melting is the process of breaking of
Watson-Crick (WC) hydrogen bonds (HB)
in double-stranded DNA (dsDNA) to form two separate single-stranded DNA (ssDNA).
What is the most common DNA repair mechanism?
Consequently, the various types of
excision repair
are the most important DNA repair mechanisms in both prokaryotic and eukaryotic cells. In excision repair, the damaged DNA is recognized and removed, either as free bases or as nucleotides.
What does DNA glycosylase do?
DNA glycosylases play a key role in the elimination of such DNA lesions; they
recognize and excise damaged bases, thereby initiating a repair process that restores the regular DNA structure with high accuracy
.
Does nucleotide excision repair use DNA ligase?
Repair and ligation
This allows DNA polymerases implicated in repair (δ, ε and/or κ) to copy the undamaged strand via translocation.
DNA ligase I and Flap endonuclease 1 or the Ligase-III-XRCC1 complex seal the nicks to complete NER
.
Is DNA helicase involved in nucleotide excision repair?
The DNA helicases acting in nucleotide excision repair, XPD, CSB and XPB, are not required for PCNA-dependent repair of abasic sites
.
What statement best describes what happens during nucleotide excision repair of damaged DNA?
What happens during nucleotide excision repair of damaged DNA?
Enzymes unwind the DNA, cut out a section on one stand that contains the DNA damage, and resynthesize the section with the correct DNA sequence
.
What does excision repair require?
The basic mechanism of excision repair involves: (1) damage recognition; (2) subunit assembly; (3) dual incisions that result in excision of the damage-containing oligomer; (4) resynthesis to fill in the gap; and (5) ligation to regenerate an intact molecule.
What type is DNA replication?
DNA replication is
semiconservative
, meaning that each strand in the DNA double helix acts as a template for the synthesis of a new, complementary strand. This process takes us from one starting molecule to two “daughter” molecules, with each newly formed double helix containing one new and one old strand.
What is base excision repair quizlet?
in base excision repair,
enzyme that recognizes the specific damage and cuts bonds that connects damage base to sugar
.
AP endonuclease
.
How are DNA mutations repaired?
Most of the types of DNA damage that are caused by chemical or physical mutagens (Section 14.1. 1) can only be repaired by
excision of the damaged nucleotide followed by resynthesis of a new stretch of DNA
, as shown in Figure 14.18B.
What is DNA base damage?
DNA damage is an alteration in the chemical structure of DNA, such as a break in a strand of DNA, a base missing from the backbone of DNA, or a chemically changed base such as 8-OHdG. DNA damage can occur naturally or via environmental factors.
How do you heal damaged DNA?
Once DNA damage is recognized in the nuclear genome, bulky adducts, small miscoding lesions, single-strand breaks, or non-complex double-strand breaks (DSBs) can be directly repaired by
nucleotide excision repair (NER), base excision repair (BER), and non-homologous end-joining (NHEJ)
, respectively.
What would happen if DNA polymerase matches the wrong DNA bases?
The polymerase checks whether the newly-added base has paired correctly with the base in the template strand. If it is the correct base, the next nucleotide is added. If an incorrect base has been added,
the enzyme makes a cut at the phosphodiester bond and releases the incorrect nucleotide
.
What happens if something goes wrong in DNA replication?
When Replication Errors Become Mutations.
Incorrectly paired nucleotides that still remain following mismatch repair become permanent mutations after the next cell division
. This is because once such mistakes are established, the cell no longer recognizes them as errors.
How DNA is capable of replicating and repairing itself?
DNA replication takes place at a Y-shaped structure called a replication fork.
A self-correcting DNA polymerase enzyme catalyzes nucleotide polymerization in a 5′-to-3′ direction, copying a DNA template strand with remarkable fidelity
.
