what adds nucleotides to the growing dna strand

Basics of DNA Replication

DNA replication uses a semi-bourgeois method that results in a double-stranded DNA with one parental strand and a new daughter strand.

Learning Objectives

Explain how the Meselson and Stahl experiment conclusively established that Deoxyribonucleic acid replication is semi-bourgeois.

Key Takeaways

Key Points

• There were three models suggested for Dna replication: conservative, semi-conservative, and dispersive.
• The conservative method of replication suggests that parental Deoxyribonucleic acid remains together and newly-formed daughter strands are also together.
• The semi-conservative method of replication suggests that the ii parental DNA strands serve as a template for new Dna and subsequently replication, each double-stranded Dna contains one strand from the parental Deoxyribonucleic acid and 1 new (daughter) strand.
• The dispersive method of replication suggests that, after replication, the two daughter DNAs have alternating segments of both parental and newly-synthesized DNA interspersed on both strands.
• Meselson and Stahl, using E. coli Deoxyribonucleic acid made with 2 nitrogen istopes (¹⁴Northward and ¹⁵Northward) and density gradient centrifugation, determined that DNA replicated via the semi-bourgeois method of replication.

Key Terms

• DNA replication: a biological process occuring in all living organisms that is the ground for biological inheritance
• isotope: whatever of two or more forms of an element where the atoms have the aforementioned number of protons, but a different number of neutrons within their nuclei

Nuts of Dna Replication

Watson and Crick's discovery that DNA was a ii-stranded double helix provided a hint every bit to how DNA is replicated. During cell partitioning, each DNA molecule has to be perfectly copied to ensure identical Dna molecules to move to each of the 2 girl cells. The double-stranded structure of Dna suggested that the ii strands might separate during replication with each strand serving as a template from which the new complementary strand for each is copied, generating two double-stranded molecules from one.

Models of Replication

In that location were three models of replication possible from such a scheme: bourgeois, semi-conservative, and dispersive. In conservative replication, the two original Dna strands,  known equally the parental strands, would re-basepair with each other after being used every bit templates to synthesize new strands; and the two newly-synthesized strands, known every bit the girl strands, would also basepair with each other; one of the two DNA molecules after replication would be "all-sometime" and the other would be "all-new". In semi-conservative replication, each of the two parental Dna strands would act as a template for new Dna strands to be synthesized, but afterward replication, each parental Dna strand would basepair with the complementary newly-synthesized strand just synthesized, and both double-stranded DNAs would include i parental or "quondam" strand and one daughter or "new" strand. In dispersive replication, after replication both copies of the new DNAs would somehow have alternating segments of parental DNA and newly-synthesized Deoxyribonucleic acid on each of their two strands.

Suggested Models of DNA Replication: The three suggested models of DNA replication. Grey indicates the original parental Deoxyribonucleic acid strands  or segments and blue indicates newly-synthesized girl DNA strands or segments.

To determine which model of replication was accurate, a seminal experiment was performed in 1958 past two researchers: Matthew Meselson and Franklin Stahl.

Meselson and Stahl

Meselson and Stahl were interested in understanding how Deoxyribonucleic acid replicates. They grew E. coli for several generations in a medium containing a "heavy" isotope of nitrogen (¹⁵Due north) that is incorporated into nitrogenous bases and, somewhen, into the DNA. The Eastward. coli civilization was and then shifted into medium containing the mutual "lite" isotope of nitrogen (^xivDue north) and allowed to grow for 1 generation. The cells were harvested and the DNA was isolated. The DNA was centrifuged at loftier speeds in an ultracentrifuge in a tube in which a cesium chloride density gradient had been established. Some cells were immune to grow for i more life bicycle in ^fourteenN and spun again.

Meselson and Stahl: Meselson and Stahl experimented with Due east. coli grown commencement in heavy nitrogen (¹⁵N) then in ligher nitrogen (¹⁴N.) Dna grown in ^xvN (red band) is heavier than Deoxyribonucleic acid grown in ¹⁴North (orange band) and sediments to a lower level in the cesium chloride density gradient in an ultracentrifuge. When DNA grown in ¹⁵Northward is switched to media containing ¹⁴N, later on 1 circular of jail cell division the DNA sediments halfway between the ¹⁵N and ¹⁴N levels, indicating that it now contains fifty pct ^xivN and fifty per centum ¹⁵N.. In subsequent jail cell divisions, an increasing corporeality of Deoxyribonucleic acid contains ^xivDue north merely. These information support the semi-conservative replication model.

During the density gradient ultracentrifugation, the Dna was loaded into a gradient (Meselson and Stahl used a gradient of cesium chloride salt, although other materials such as sucrose can as well exist used to create a gradient) and spun at high speeds of fifty,000 to lx,000 rpm. In the ultracentrifuge tube, the cesium chloride salt created a density gradient, with the cesium chloride solution being more than dense the further downwardly the tube y'all went. Under these circumstances, during the spin the DNA was pulled downward the ultracentrifuge tube by centrifugal force until it arrived at the spot in the salt gradient where the DNA molecules' density matched that of the surrounding table salt solution. At the point, the molecules stopped sedimenting and formed a stable band. By looking at the relative positions of bands of molecules run in the same gradients, you tin can make up one's mind the relative densities of different molecules. The molecules that class the lowest bands have the highest densities.

DNA from cells grown exclusively in ¹⁵North produced a lower band than Dna from cells grown exclusively in ¹⁴Due north. So Dna grown in ¹⁵N had a college density, equally would be expected of a molecule with a heavier isotope of nitrogen incorporated into its nitrogenous bases. Meselson and Stahl noted that after one generation of growth in ¹⁴N (later cells had been shifted from ¹⁵N), the DNA molecules produced just single band intermediate in position in between Dna of cells grown exclusively in ^xvDue north and Deoxyribonucleic acid of cells grown exclusively in ¹⁴Due north. This suggested either a semi-conservative or dispersive mode of replication. Bourgeois replication would take resulted in two bands; 1 representing the parental Dna nonetheless with exclusively ^fifteenN in its nitrogenous bases and the other representing the daughter DNA with exclusively ¹⁴N in its nitrogenous bases. The single band actually seen indicated that all the Dna molecules contained equal amounts of both ¹⁵Due north and ¹⁴North.

The DNA harvested from cells grown for two generations in ¹⁴Due north formed two bands: one Deoxyribonucleic acid band was at the intermediate position between ^fifteenN and ^xivN and the other corresponded to the ring of exclusively ¹⁴N DNA. These results could just be explained if Dna replicates in a semi-bourgeois manner. Dispersive replication would have resulted in exclusively a single ring in each new generation, with the band slowly moving up closer to the height of the ^xivN Deoxyribonucleic acid ring. Therefore, dispersive replication could too be ruled out.

Meselson and Stahl's results established that during DNA replication, each of the ii strands that make upwards the double helix serves as a template from which new strands are synthesized. The new strand will exist complementary to the parental or "old" strand and the new strand will remain basepaired to the onetime strand. And then each "daughter" DNA really consists of one "old"  DNA strand and one newly-synthesized strand. When two girl Dna copies are formed, they accept the identical sequences to i another and identical sequences to the original parental Dna, and the two daughter DNAs are divided equally into the two daughter cells, producing daughter cells that are genetically identical to i some other and genetically identical to the parent cell.

DNA Replication in Prokaryotes

Prokaryotic Deoxyribonucleic acid is replicated by DNA polymerase 3 in the 5′ to three′ direction at a charge per unit of 1000 nucleotides per 2d.

Learning Objectives

Explicate the functions of the enzymes involved in prokaryotic Dna replication

Central Takeaways

Key Points

• Helicase separates the Dna to form a replication fork at the origin of replication where Deoxyribonucleic acid replication begins.
• Replication forks extend bi-directionally as replication continues.
• Okazaki fragments are formed on the lagging strand, while the leading strand is replicated continuously.
• DNA ligase seals the gaps between the Okazaki fragments.
• Primase synthesizes an RNA primer with a free 3′-OH, which DNA polymerase 3 uses to synthesize the daughter strands.

Key Terms

• DNA replication: a biological procedure occuring in all living organisms that is the footing for biological inheritance
• helicase: an enzyme that unwinds the Dna helix ahead of the replication machinery
• origin of replication: a particular sequence in a genome at which replication is initiated

Dna Replication in Prokaryotes

Dna replication employs a large number of proteins and enzymes, each of which plays a disquisitional role during the process. I of the fundamental players is the enzyme DNA polymerase, which adds nucleotides one past 1 to the growing DNA chain that are complementary to the template strand. The improver of nucleotides requires energy; this energy is obtained from the nucleotides that have three phosphates attached to them, similar to ATP which has 3 phosphate groups attached. When the bail between the phosphates is cleaved, the energy released is used to course the phosphodiester bond betwixt the incoming nucleotide and the growing chain. In prokaryotes, three main types of polymerases are known: Deoxyribonucleic acid pol I, DNA pol II, and Deoxyribonucleic acid politico Three. Deoxyribonucleic acid political leader 3 is the enzyme required for Deoxyribonucleic acid synthesis; DNA politico I and Dna pol II are primarily required for repair.

At that place are specific nucleotide sequences chosen origins of replication where replication begins. In E. coli, which has a single origin of replication on its one chromosome (equally do about prokaryotes), it is approximately 245 base of operations pairs long and is rich in AT sequences. The origin of replication is recognized by certain proteins that bind to this site. An enzyme called helicase unwinds the Dna by breaking the hydrogen bonds between the nitrogenous base pairs. ATP hydrolysis is required for this process. As the Deoxyribonucleic acid opens up, Y-shaped structures called replication forks are formed. Ii replication forks at the origin of replication are extended bi-directionally every bit replication proceeds. Single-strand bounden proteins coat the strands of Deoxyribonucleic acid well-nigh the replication fork to prevent the unmarried-stranded Dna from winding back into a double helix. Dna polymerase is able to add nucleotides only in the 5′ to three′ direction (a new DNA strand tin can be extended only in this management). Information technology also requires a free 3′-OH grouping to which it can add nucleotides past forming a phosphodiester bond betwixt the 3′-OH finish and the five′ phosphate of the side by side nucleotide. This means that it cannot add together nucleotides if a free 3′-OH group is not available. Another enzyme, RNA primase, synthesizes an RNA primer that is virtually five to ten nucleotides long and complementary to the DNA, priming DNA synthesis. A primer provides the free iii′-OH end to kickoff replication. Deoxyribonucleic acid polymerase then extends this RNA primer, adding nucleotides i by one that are complementary to the template strand.

Dna Replication in Prokaryotes: A replication fork is formed when helicase separates the Deoxyribonucleic acid strands at the origin of replication. The DNA tends to get more highly coiled ahead of the replication fork. Topoisomerase breaks and reforms Dna's phosphate backbone ahead of the replication fork, thereby relieving the pressure that results from this supercoiling. Unmarried-strand bounden proteins demark to the single-stranded DNA to forestall the helix from re-forming. Primase synthesizes an RNA primer. Deoxyribonucleic acid polymerase 3 uses this primer to synthesize the daughter DNA strand. On the leading strand, DNA is synthesized continuously, whereas on the lagging strand, DNA is synthesized in curt stretches chosen Okazaki fragments. DNA polymerase I replaces the RNA primer with DNA. DNA ligase seals the gaps between the Okazaki fragments, joining the fragments into a single Deoxyribonucleic acid molecule.

The replication fork moves at the rate of 1000 nucleotides per second. DNA polymerase can only extend in the five′ to three′ direction, which poses a slight problem at the replication fork. As nosotros know, the DNA double helix is anti-parallel; that is, one strand is in the 5′ to 3′ direction and the other is oriented in the three′ to five′ direction. One strand (the leading strand), complementary to the iii′ to 5′ parental Deoxyribonucleic acid strand, is synthesized continuously towards the replication fork because the polymerase can add nucleotides in this direction. The other strand (the lagging strand), complementary to the 5′ to 3′ parental Dna, is extended away from the replication fork in small fragments known as Okazaki fragments, each requiring a primer to kickoff the synthesis. Okazaki fragments are named after the Japanese scientist who beginning discovered them.

The leading strand can be extended by ane primer alone, whereas the lagging strand needs a new primer for each of the curt Okazaki fragments. The overall direction of the lagging strand volition be iii′ to 5′, while that of the leading strand will be 5′ to iii′. The sliding clench (a band-shaped protein that binds to the DNA) holds the Deoxyribonucleic acid polymerase in place equally it continues to add nucleotides. Topoisomerase prevents the over-winding of the DNA double helix ahead of the replication fork as the DNA is opening up; it does so by causing temporary nicks in the DNA helix and then resealing it. Every bit synthesis proceeds, the RNA primers are replaced by DNA. The primers are removed by the exonuclease activity of Dna pol I, while the gaps are filled in past deoxyribonucleotides. The nicks that remain between the newly-synthesized Dna (that replaced the RNA primer) and the previously-synthesized Deoxyribonucleic acid are sealed by the enzyme Deoxyribonucleic acid ligase that catalyzes the germination of phosphodiester linkage betwixt the three′-OH stop of i nucleotide and the 5′ phosphate end of the other fragment.

The tabular array summarizes the enzymes involved in prokaryotic Deoxyribonucleic acid replication and the functions of each.

Prokaryotic DNA Replication: Enzymes and Their Function: The enzymes involved in prokaryotic Deoxyribonucleic acid replication and their functions are summarized on this table.

Deoxyribonucleic acid Replication in Eukaryotes

Dna replication in eukaryotes occurs in iii stages: initiation, elongation, and termination, which are aided by several enzymes.

Learning Objectives

Describe how Dna is replicated in eukaryotes

Key Takeaways

Key Points

• During initiation, proteins bind to the origin of replication while helicase unwinds the DNA helix and two replication forks are formed at the origin of replication.
• During elongation, a primer sequence is added with complementary RNA nucleotides, which are then replaced by DNA nucleotides.
• During elongation the leading strand is made continuously, while the lagging strand is made in pieces chosen Okazaki fragments.
• During termination, primers are removed and replaced with new DNA nucleotides and the courage is sealed by Dna ligase.

Key Terms

• origin of replication: a particular sequence in a genome at which replication is initiated
• leading strand: the template strand of the DNA double helix that is oriented so that the replication fork moves along information technology in the iii′ to 5′ direction
• lagging strand: the strand of the template DNA double helix that is oriented then that the replication fork moves along information technology in a v′ to 3′ manner

Because eukaryotic genomes are quite complex, DNA replication is a very complicated process that involves several enzymes and other proteins. It occurs in iii main stages: initiation, elongation, and termination.

Initiation

Eukaryotic Dna is spring to proteins known as histones to form structures chosen nucleosomes. During initiation, the Deoxyribonucleic acid is made accessible to the proteins and enzymes involved in the replication process. There are specific chromosomal locations called origins of replication where replication begins. In some eukaryotes, like yeast, these locations are divers by having a specific sequence of basepairs to which the replication initiation proteins bind. In other eukaryotes, similar humans, there does not appear to exist a consensus sequence for their origins of replication. Instead, the replication initiation proteins might identify and bind to specific modifications to the nucleosomes in the origin region.

Certain proteins recognize and bind to the origin of replication and and then allow the other proteins necessary for DNA replication to bind the aforementioned region. The offset proteins to bind the DNA are said to "recruit" the other proteins. Ii copies of an enzyme chosen helicase are among the proteins recruited to the origin. Each helicase unwinds and separates the DNA helix into unmarried-stranded Dna. Every bit the DNA opens up, Y-shaped structures called replication forks are formed. Because two helicases bind, two replication forks are formed at the origin of replication; these are extended in both directions as replication proceeds creating a replication bubble. In that location are multiple origins of replication on the eukaryotic chromosome which permit replication to occur simultaneously in hundreds to thousands of locations forth each chromosome.

Replication Fork Formation: A replication fork is formed by the opening of the origin of replication; helicase separates the DNA strands. An RNA primer is synthesized by primase and is elongated by the Deoxyribonucleic acid polymerase. On the leading strand, only a unmarried RNA primer is needed, and Dna is synthesized continuously, whereas on the lagging strand, Dna is synthesized in short stretches, each of which must beginning with its own RNA primer. The DNA fragments are joined by DNA ligase (non shown).

Elongation

During elongation, an enzyme called Deoxyribonucleic acid polymerase adds DNA nucleotides to the three′ cease of the newly synthesized polynucleotide strand. The template strand specifies which of the four DNA nucleotides (A, T, C, or Yard) is added at each position forth the new concatenation. Only the nucleotide complementary to the template nucleotide at that position is added to the new strand.

Dna polymerase contains a groove that allows information technology to bind to a single-stranded template Dna and travel one nucleotide at at fourth dimension. For example, when Deoxyribonucleic acid polymerase meets an adenosine nucleotide on the template strand, it adds a thymidine to the 3′ cease of the newly synthesized strand, and then moves to the next nucleotide on the template strand. This procedure will continue until the Deoxyribonucleic acid polymerase reaches the end of the template strand.

Deoxyribonucleic acid polymerase cannot initiate new strand synthesis; it just adds new nucleotides at the 3′ finish of an existing strand. All newly synthesized polynucleotide strands must be initiated by a specialized RNA polymerase called primase. Primase initiates polynucleotide synthesis and by creating a short RNA polynucleotide strand complementary to template Deoxyribonucleic acid strand. This short stretch of RNA nucleotides is chosen the primer. Once RNA primer has been synthesized at the template DNA, primase exits, and DNA polymerase extends the new strand with nucleotides complementary to the template Deoxyribonucleic acid.

Eventually, the RNA nucleotides in the primer are removed and replaced with Deoxyribonucleic acid nucleotides. Once Deoxyribonucleic acid replication is finished, the daughter molecules are made entirely of continuous Dna nucleotides, with no RNA portions.

The Leading and Lagging Strands

Deoxyribonucleic acid polymerase tin can only synthesize new strands in the 5′ to 3′ direction. Therefore, the two newly-synthesized strands grow in opposite directions because the template strands at each replication fork are antiparallel. The "leading strand" is synthesized continuously toward the replication fork as helicase unwinds the template double-stranded DNA.

The "lagging strand" is synthesized in the direction away from the replication fork and abroad from the Dna helicase unwinds. This lagging strand is synthesized in pieces because the Dna polymerase can only synthesize in the 5′ to three′ management, and then it constantly encounters the previously-synthesized new strand. The pieces are called Okazaki fragments, and each fragment begins with its ain RNA primer.

Termination

Eukaryotic chromosomes have multiple origins of replication, which initiate replication nigh simultaneously. Each origin of replication forms a bubble of duplicated Deoxyribonucleic acid on either side of the origin of replication. Eventually, the leading strand of one replication bubble reaches the lagging strand of another bubble, and the lagging strand will reach the 5′ end of the previous Okazaki fragment in the same chimera.

DNA polymerase halts when it reaches a section of DNA template that has already been replicated. However, Dna polymerase cannot catalyze the formation of a phosphodiester bond between the two segments of the new DNA strand, and it drops off. These unattached sections of the saccharide-phosphate backbone in an otherwise full-replicated DNA strand are called nicks.

Once all the template nucleotides take been replicated, the replication process is non yet over. RNA primers need to be replaced with DNA, and nicks in the carbohydrate-phosphate backbone demand to be connected.

The group of cellular enzymes that remove RNA primers include the proteins FEN1 (flap endonulcease 1) and RNase H. The enzymes FEN1 and RNase H remove RNA primers at the start of each leading strand and at the start of each Okazaki fragment, leaving gaps of unreplicated template DNA. In one case the primers are removed, a gratuitous-floating Dna polymerase lands at the 3′ end of the preceding Dna fragment and extends the DNA over the gap. However, this creates new nicks (unconnected sugar-phosphate courage).

In the final phase of DNA replication, the enyzme ligase joins the sugar-phosphate backbones at each nick site. After ligase has connected all nicks, the new strand is ane long continuous DNA strand, and the daughter Deoxyribonucleic acid molecule is complete.

Deoxyribonucleic acid Replication: This is a clip from a PBS production called "DNA: The Secret of Life." It details the latest research (as of 2005) concerning the process of DNA replication.

Telomere Replication

As DNA polymerase alone cannot replicate the ends of chromosomes, telomerase aids in their replication and prevents chromosome degradation.

Learning Objectives

Draw the office played past telomerase in replication of telomeres

Primal Takeaways

Key Points

• Dna polymerase cannot replicate and repair DNA molecules at the ends of linear chromosomes.
• The ends of linear chromosomes, called telomeres, protect genes from getting deleted as cells continue to split.
• The telomerase enzyme attaches to the finish of the chromosome; complementary bases to the RNA template are added on the 3′ cease of the DNA strand.
• Once the lagging strand is elongated by telomerase, DNA polymerase can add together the complementary nucleotides to the ends of the chromosomes and the telomeres tin finally be replicated.
• Cells that undergo cell division continue to have their telomeres shortened because most somatic cells do non brand telomerase; telomere shortening is associated with aging.
• Telomerase reactivation in telomerase-deficient mice causes extension of telomeres; this may have potential for treating historic period-related diseases in humans.

Key Terms

• telomere: either of the repetitive nucleotide sequences at each end of a eukaryotic chromosome, which protect the chromosome from degradation
• telomerase: an enzyme in eukaryotic cells that adds a specific sequence of Deoxyribonucleic acid to the telomeres of chromosomes afterward they divide, giving the chromosomes stability over time

The End Problem of Linear Dna Replication

Linear chromosomes accept an end problem. After DNA replication, each newly synthesized Dna strand is shorter at its v′ end than at the parental Dna strand'south five′ stop. This produces a 3′ overhang at ane end (and one stop only) of each daughter DNA strand, such that the two girl DNAs take their iii′ overhangs at contrary ends

The telomere cease problem: A simplified schematic of DNA replication where the parental Dna (top) is replicated from three origins of replication, yielding three replication bubbles (middle) before giving ascent to ii daughter DNAs (bottom). Parental Deoxyribonucleic acid strands are black, newly synthesized DNA strands are blue, and RNA primers are red. All RNA primers volition exist removed past Rnase H and FEN1, leaving gaps in the newly-synthesized Dna strands (not shown.) Dna Polymerase and Ligase will supplant all the RNA primers with Deoxyribonucleic acid except the RNA primer at the v′ ends of each newly-synthesized (blue) strand. This means that each newly-synthesized Deoxyribonucleic acid strand is shorter at its five′ end than the equivalent strand in the parental DNA.

Every RNA primer synthesized during replication tin be removed and replaced with DNA strands except the RNA primer at the 5′ finish of the newly synthesized strand. This small section of RNA can only be removed, not replaced with Dna. Enzymes RNase H and FEN1 remove RNA primers, but Deoxyribonucleic acid Polymerase will add new DNA only if the Dna Polymerase has an existing strand 5′ to it ("backside" information technology) to extend. However, there is no more Deoxyribonucleic acid in the 5′ direction after the last RNA primer, so DNA polymerse cannot supplant the RNA with DNA. Therefore, both girl Deoxyribonucleic acid strands have an incomplete v′ strand with 3′ overhang.

In the absence of boosted cellular processes, nucleases would digest these unmarried-stranded 3′ overhangs. Each daughter DNA would get shorter than the parental DNA, and eventually entire DNA would be lost. To forbid this shortening, the ends of linear eukaryotic chromosomes have special structures called telomeres.

Telomere Replication

The ends of the linear chromosomes are known as telomeres: repetitive sequences that code for no detail gene. These telomeres protect the important genes from beingness deleted every bit cells divide and as Dna strands shorten during replication.

In humans, a half dozen base pair sequence, TTAGGG, is repeated 100 to 1000 times. After each round of DNA replication, some telomeric sequences are lost at the 5′ finish of the newly synthesized strand on each daughter Deoxyribonucleic acid, but because these are noncoding sequences, their loss does not adversely affect the prison cell. However, even these sequences are not unlimited. After sufficient rounds of replication, all the telomeric repeats are lost, and the Deoxyribonucleic acid risks losing coding sequences with subsequent rounds.

The discovery of the enzyme telomerase helped in the understanding of how chromosome ends are maintained. The telomerase enzyme attaches to the cease of a chromosome and contains a catalytic part and a born RNA template. Telomerase adds complementary RNA bases to the 3′ finish of the DNA strand. One time the three′ cease of the lagging strand template is sufficiently elongated, Deoxyribonucleic acid polymerase adds the complementary nucleotides to the ends of the chromosomes; thus, the ends of the chromosomes are replicated.

Telomerase is important for maintaining chromosome integrity: The ends of linear chromosomes are maintained by the action of the telomerase enzyme.

Telomerase and Aging

Telomerase is typically active in germ cells and adult stem cells, but is not active in adult somatic cells. Every bit a result, telomerase does non protect the DNA of developed somatic cells and their telomeres continually shorten every bit they undergo rounds of prison cell division.

In 2010, scientists constitute that telomerase tin can reverse some age-related conditions in mice. These findings may contribute to the futurity of regenerative medicine. In the studies, the scientists used telomerase-deficient mice with tissue cloudburst, stem jail cell depletion, organ failure, and impaired tissue injury responses. Telomerase reactivation in these mice caused extension of telomeres, reduced Dna damage, reversed neurodegeneration, and improved the function of the testes, spleen, and intestines. Thus, telomere reactivation may have potential for treating age-related diseases in humans.

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Source: https://courses.lumenlearning.com/boundless-biology/chapter/dna-replication/

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