What is the Difference Between Telomere and Telomerase

The main difference between telomere and telomerase is that telomere is a protective cap located at the ends of the arms of chromosomes whereas telomerase is an enzyme present in fetal tissues, adult germ cells, and also tumor cells. Furthermore, telomere prevents the loss of base pairs from the ends of the chromosomes while telomerase adds a special DNA sequence to the end of the chromosomes.

Telomere and telomerase are two terms related to the ends of the chromosomes in tissues with cells that undergo an unlimited number of cell divisions.

Key Areas Covered

1. What is Telomere
     – Definition, Structure, Role
2. What is Telomerase
     – Definition, Structure, Role
3. What are the Similarities Between Telomere and Telomerase
     – Outline of Common Features
4. What is the Difference Between Telomere and Telomerase
     – Comparison of Key Differences

Key Terms

Chromosomes, Telomerase, Telomere, Unlimited Cell Proliferation

What is Telomere

A telomere is the extreme end of a eukaryotic chromosome. It is a special structure that provides protection against enzymatic end-degradation. Also, it stabilizes the chromosome by preventing the fusion of chromosome ends with the ends of other chromosomes and the loss of base pairs from the ends during cell division. In addition, telomeres allow complete replication of linear chromosomes.

Figure 1: Telomeres

Furthermore, a telomere is made up of two components: DNA and protein. The DNA component of it is made up of non-coding, tandem repeats. Although the exact repeating unit differs with the species, humans and other vertebrates have TTAGGG sequences repeating in their telomeres. Also, the telomeric region is 8–14 kbp long in humans. However, during cell division, all chromosomes lose a part of their telomeric region due to the nature of the DNA replication machinery. Generally, the removal of the terminal RNA primer of the 5’ end of the lagging strand leads to the progressive reduction of chromosomal DNA from the 3’ end.

What is Telomerase

Telomerase is the enzyme responsible for the addition of the repetitive units to the end of the chromosomes. Generally, the progressive loss of the ends of chromosomes strictly limits the growth potential and leads to senescence in normal cells after a defined number of cell divisions. However, tumor cells exhibit an apparently unlimited proliferation potential while becoming immortal. This is due to the active enzymatic action of telomerase in the tumor cells. Therefore, the activation of telomerase is an important step of tumorigenesis.   

Figure 2: Telomerase Mechanism of Action

Moreover, the enzyme telomerase is an RNA-dependent DNA polymerase, which can synthesize DNA by using an RNA template. It binds to the special RNA sequences complementary to the sequence of the repetitive unit of the telomere and adds DNA overhangs, which turn into double-stranded DNA with the use of DNA replication machinery. It increases the length of the telomere, which in turn increases the potential of cell divisions.

Similarities Between Telomere and Telomerase

• Telomere and telomerase are two terms related to the ends of chromosomes.
• Both occur in eukaryotic cells.
• Furthermore, both have a function in extending the ends of the arms of chromosomes by the addition of extra DNA sequences.
• Also, they protect cells from senescence, which limit the growth potential of cells.

Difference Between Telomere and Telomerase

Definition

A telomere refers to a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes, while telomerase refers to the enzyme in a eukaryote that repairs the telomeres of the chromosomes so that they do not become progressively shorter during successive rounds of chromosome replication. Thus, this is the main difference between telomere and telomerase.

Significance

While a telomere is a protective cap located at the ends of the arms of chromosomes, telomerase is an enzyme present in fetal tissues, adult germ cells, and also tumor cells. Hence, this is another difference between telomere and telomerase.

Made up of

Moreover, a telomere is a piece of DNA associated with several proteins while telomerase is made up of protein and RNA subunits.

Function

Furthermore, an important difference between telomere and telomerase is that the telomere protects the end of the chromosome by losing base pairs while telomerase adds TTAGGG sequences to the ends of chromosomes, preventing their shortening.

Role

Also, one other difference between telomere and telomerase is that the telomere is an important component of senescence and is involved in the control of the cell cycle while telomerase gives the ability of indefinite proliferation to the tumor cells to become immortal.

Conclusion

A telomere is the ends of the arms of chromosomes in eukaryotes. It prevents the loss of base pairs from the ends. Also, it contains repetitive sequences of TTAGGG nucleotides. However, these repetitive units become shortened with age, limiting the potential of cell proliferation. In contrast, telomerase is an enzyme active in tumor cells responsible for the addition of repetitive units to the telomeres, preventing shortening. By this, tumor cells gain the ability to unlimited cell proliferation. Therefore, the main difference between telomere and telomerase is their role.

References:

1. Regine Dahse, Wolfgang Fiedler, Günther Ernst, Telomeres and telomerase: biological and clinical importance, Clinical Chemistry May 1997, 43 (5) 708-714; Available Here. 
2. “Telomeres and Telomerase.” Khan Academy, Khan Academy, Available Here.

Image Courtesy:

1. “Telomere caps” By U.S. Department of Energy Human Genome Program (Public Domain) via Commons Wikimedia   
2. “Working principle of telomerase” By Uzbas, F (CC BY-SA 3.0) via Commons Wikimedia