DNA Replication in EukaryotesArt relations

When a cabinet divides, the is vital that every daughter cell receives an similar copy of the DNA. This is completed by the process of DNA replication. The replication of DNA occurs throughout the synthesis phase, or S phase, that the cell cycle, prior to the cabinet enters mitosis or meiosis.

You are watching: Replication in prokaryotes differs from replication in eukaryotes for which of these reasons?

The elucidation the the structure of the double helix detailed a hint regarding how DNA is copied. Recall that adenine nucleotides pair v thymine nucleotides, and also cytosine with guanine. This means that the 2 strands space complementary to every other. For example, a strand of DNA v a nucleotide sequence of AGTCATGA will have a safety strand with the sequence TCAGTACT (Figure \(\PageIndex1\)).

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Figure \(\PageIndex1\): The 2 strands that DNA room complementary, definition the sequence of bases in one strand deserve to be offered to create the exactly sequence that bases in the other strand.

Because that the complementarity of the 2 strands, having one strand way that it is possible to recreate the other strand. This design for replication says that the 2 strands the the double helix separate throughout replication, and each strand serves together a design template from which the new complementary strand is duplicated (Figure \(\PageIndex2\)).

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The process of DNA replication have the right to be summarized as follows:

DNA unwinds in ~ the origin of replication. Brand-new bases are included to the safety parental strands. One brand-new strand is made continuously, if the other strand is make in pieces. Primers room removed, new DNA nucleotides are put in ar of the primers and the backbone is sealed through DNA ligase.

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Figure \(\PageIndex3\): A replication fork is formed by the opened of the origin of replication, and helicase off the DNA strands. One RNA inside wall is synthesized, and also is elongated by the DNA polymerase. Top top the leading strand, DNA is synthesized continuously, whereas on the lagging strand, DNA is synthesized in short stretches. The DNA fragments are join by DNA ligase (not shown).

You isolation a cell strain in which the joining with each other of Okazaki fragments is impaired and also suspect the a mutation has occurred in an enzyme discovered at the replication fork. Which enzyme is most likely to it is in mutated?


Telomere Replication

Because eukaryotic chromosomes are linear, DNA replication concerns the end of a line in eukaryotic bio chromosomes. As you have actually learned, the DNA polymerase enzyme can include nucleotides in only one direction. In the top strand, synthesis continues until the finish of the chromosome is reached; however, on the lagging strand over there is no place for a primer to be created the DNA fragment to be duplicated at the finish of the chromosome. This gift a difficulty for the cell because the ends stay unpaired, and over time these ends obtain progressively much shorter as cells continue to divide. The end of the direct chromosomes are known as telomeres, which have repetitive sequences that execute not code for a specific gene. As a consequence, that is telomeres that are shortened v each round of DNA replication rather of genes. For example, in humans, a 6 base-pair sequence, TTAGGG, is recurring 100 come 1000 times. The exploration of the enzyme telomerase(Figure \(\PageIndex4\)) aided in the knowledge of exactly how chromosome ends space maintained. The telomerase attaches to the end of the chromosome, and also complementary bases to the RNA layout are included on the finish of the DNA strand. As soon as the lagging strand layout is saturated elongated, DNA polymerase have the right to now add nucleotides that room complementary to the end of the chromosomes. Thus, the end of the chromosomes room replicated.

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Figure \(\PageIndex4\): The end of direct chromosomes are maintained by the action of the telomerase enzyme.

Telomerase is frequently found to be active in germ cells, adult stem cells, and some cancer cells. For her discovery of telomerase and also its action, Elizabeth Blackburn (Figure \(\PageIndex5\)) got the Nobel Prize because that Medicine and Physiology in 2009.

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c). Nucleotide excision repair is an especially important in correcting thymine dimers, which room primarily caused by ultraviolet light. In a thymine dimer, 2 thymine nucleotides nearby to each other on one strand room covalently bonded to each other rather than their safety bases. If the dimer is not removed and repaired the will lead to a mutation. Individuals with flaws in their nucleotide excision repair genes present extreme sensitivity to sunlight and develop skin cancers at an early stage in life.

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Figure \(\PageIndex6\): Proofreading by DNA polymerase (a) corrects errors throughout replication. In mismatch fix (b), the incorrectly included base is detected after ~ replication. The mismatch fix proteins finding this base and remove it from the recently synthesized strand through nuclease action. The gap is currently filled with the properly paired base. Nucleotide cut (c) repairs thymine dimers. Once exposed come UV, thymines lying nearby to each other can form thymine dimers. In common cells, they room excised and also replaced.

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Most mistakes are corrected; if they room not, lock may result in a mutation—defined together a permanent change in the DNA sequence. Mutations in repair gene may bring about serious aftermath like cancer.