Does Repair By Nonhomologous End Joining Change Dna Length?

Our results suggest that

NHEJ is a faster and more efficient DSB repair pathway than HR

.

Why do cells use non-homologous end joining?

Nonhomologous end-joining is another DNA repair mechanism that

resolves DSBs

. Since it relies on no sequence homology or short overhangs at DSBs, it is an error-prone process. Unlike HRR, which is active in the S and G

₂

phases, NHEJ is active in all phases of cell cycle, but is most important in the G

₁

phase.

What is the difference between non-homologous end joining and homologous recombination?

NHEJ modifies the broken DNA ends, and ligates them together with no regard for homology, generating deletions or insertions

[2]. In contrast, HR uses an undamaged DNA template to repair the break, leading to the reconstitution of the original sequence [3].

What is homologous DNA repair?

Homologous recombination repair is

a DNA repair process that includes the invasion of an undamaged DNA molecule by a damaged molecule of identical or very similar sequence

. Resynthesis of the damaged region is accomplished using the undamaged molecule as a template.

What sort of changes can occur when non-homologous end joining NHEJ repair a break in double stranded DNA?

DNA double-stranded breaks (DSB) are among the most dangerous forms of DNA damage. Unrepaired DSBs results in cells undergoing

apoptosis or senescence

whereas mis-processing of DSBs can lead to genomic instability and carcinogenesis.

What is the difference between homologous and nonhomologous chromosomes?

The main difference between homologous and non-homologous chromosomes is that

homologous chromosomes consist of alleles of the same type of genes in the same loci whereas non-homologous chromosomes consist of alleles of different types of genes

.

How are Holliday junctions resolved?

Cleavage, or resolution, of the Holliday junction can occur in two ways. Cleavage of the original set of strands leads to two molecules that may show gene conversion but not chromosomal crossover, while cleavage of the other set of two strands causes the resulting recombinant molecules to show crossover.

Why is NHEJ better than HDR?

At its core, NHEJ-break ends can be ligated without a homologous template, whereas HDR-breaks requires a template to guide repair.

NHEJ is a very efficient repair mechanism that is most active in the cell

. It is also susceptible to frequent mutation errors due to nucleotide insertions and deletions (indels).

Why non-homologous end joining repair is mutagenic and error prone?

It is widely thought that C-NHEJ is also error-prone, because

the repair process involves processing of the DNA ends at the break sites, which can lead to nucleotide deletion

. Hence, joining of such DNA ends via C-NHEJ in the transcribed region could be mutagenic and/or lethal for cells.

How does homology directed repair work?

Homology directed repair (HDR) is

a mechanism in cells to repair double-strand DNA lesions

. The most common form of HDR is homologous recombination. The HDR mechanism can only be used by the cell when there is a homologous piece of DNA present in the nucleus, mostly in G2 and S phase of the cell cycle.

Which DNA repair pathway can fix double strand breaks?

There are two main pathways for DNA DSB repair—

homologous recombination (HR) and non-homologous end-joining (NHEJ)

. These pathways are largely distinct from one another and function in complementary ways to effect DSB repair ( 35 – 38 ).

Is homologous recombination the same as homologous end-joining?

Nonhomologous end-joining (NHEJ) and homologous recombination (HR) are mechanistically distinct DNA repair pathways that ensure the repair of DNA double-strand breaks (DSBs)

. These pathways differ in their DNA template requirements and the fidelity of the repair process.

How does mismatch repair work?

Mismatch repair happens right after new DNA has been made, and its job is to

remove and replace mis-paired bases

(ones that were not fixed during proofreading). Mismatch repair can also detect and correct small insertions and deletions that happen when the polymerases “slips,” losing its footing on the template 2.

How does homologous recombination repair DNA?

In cells that divide through mitosis, homologous recombination repairs

double-strand breaks in DNA caused by ionizing radiation or DNA-damaging chemicals

. Left unrepaired, these double-strand breaks can cause large-scale rearrangement of chromosomes in somatic cells, which can in turn lead to cancer.

Is homologous recombination a repair mechanism?

Homologous recombination (HR) is a DNA metabolic process found in all forms of life that

provides high-fidelity, template-dependent repair or tolerance of complex DNA damages

including DNA gaps, DNA double-stranded breaks (DSBs), and DNA interstrand crosslinks (ICLs).

How is homologous recombination important for DNA repair during DNA replication?

Homologous recombination

plays essential roles in the repair of DNA double strand breaks (DSBs) and collapsed replication forks

. The fundamental reaction in homologous recombination is the exchange of strands between a single-stranded DNA and a homologous double-stranded DNA.

What is the difference between NHEJ and HDR?

HDR is a precise repair mechanism that uses homologous donor DNA to repair DNA damage, whereas NHEJ is an error-prone mechanism in which broken ends of DNA are joined together

, often resulting in a heterogeneous pool of insertions and deletions.

What are the DNA repair mechanisms?

At least five major DNA repair pathways—

base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), homologous recombination (HR) and non-homologous end joining (NHEJ)

—are active throughout different stages of the cell cycle, allowing the cells to repair the DNA damage.

Which of the following DNA repair pathways is most likely to lead to chromosomal rearrangements?

The occurrence of unfaithful repair of DNA

double-strand breaks (DSBs)

is widely admitted to be the main source of chromosomal rearrangements [2]–[5]. Nonhomologous End Joining (NHEJ) and Homologous recombination (HR) constitute the main pathways of DSB repair.

Does crossing over occur between nonhomologous chromosomes?

Abstract. Meiotic recombination between artificial repeats positioned on nonhomologous chromosomes occurs efficiently in the yeast Saccharomyces cerevisiae.

Both gene conversion and crossover events have been observed, with crossovers yielding reciprocal translocations

.

Do Nonhomologous chromosomes have the same genes?

What is the difference between sister and Nonsister chromatids between homologous and nonhomologous chromosomes?

Mandira P.

Sister chromatids belong to same chromosome while nonsister chromatids belong to different members of homologous pair

.

How is Holliday junction resolved specifically in bacteria?

In E. coli,

the RuvA and RuvB complex specifically binds to the Holliday junction and promotes branch migration

. RuvC cleaves the Holliday junction when the junction migrates to the favorite sequence of the cleavage.

Which DNA is connected by Holliday junction?

Holliday junction, cross-shaped structure that forms during the process of genetic recombination, when two

double-stranded DNA molecules

become separated into four strands in order to exchange segments of genetic information.

Is DNA polymerase a repair mechanism?

DNA polymerase alpha is required for semi-conservative replication of DNA but

not for repair of DNA

. A more recently discovered enzyme, DNA polymerase zeta, appears to be involved in the bypass of damage, without excision, and occurs during DNA replication of a damaged template.