What is Telomerase? - Definition, Function & Structure

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  • 0:05 Intro to Chromosome Structure
  • 1:32 Telomerase Function
  • 2:39 Telomerase Structure
  • 3:14 Lesson Summary
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Lesson Transcript
Instructor: Catherine Paul

Catherine has taught high school science and has a master's degree in biology.

Learn about telomerase, the enzyme responsible for adding telomeres to the ends of chromosomes. Discover what telomerase is made of and how it functions to protect the chromosome.

Intro to Chromosome Structure

DNA codes for genetic information are located in all of our cells. When our cells multiply from one to two cells, the DNA within must also replicate. Double-stranded DNA is packaged linearly into chromosomes, most of which form the shape of an X. The ends of these chromosomes are secured against degradation by a protective cap at their distant ends called a telomere (think of 'tele' meaning 'distant'). Picture a telomere as the cap on a marker, placed there to protect the marker from spoiling.

Telomeres don't exist in all cells, but are always found in more complex cells called eukaryotes. Eukaryotes can be found in single-celled organisms or larger organisms, such as fish or humans. Within each eukaryote cell is a nucleus that envelopes its DNA. The nucleus also encases other complex cell machinery in containers called organelles.

Typically, eukaryotic DNA is a linear double-stranded sequence. However, at the telomere end of each chromosome there's a single-stranded segment. This single-stranded DNA is important for DNA replication because it is where the DNA replication process starts. DNA replication is handled by an enzyme called DNA polymerase. However, this enzyme cannot initiate the replication process. Instead, an RNA primer begins the DNA replication process, and it requires single-stranded DNA to work properly.

Telomerase Function

The single-stranded DNA at the telomere is added to the regular eukaryotic DNA by an enzyme called telomerase. Telomerase adds a few short single-stranded DNA repeats to the ends of chromosomes. Just as a ruler has a 1-inch mark on one end and a 12-inch mark on the other end, DNA ends are also labeled. One end is called the 3-prime end, and the other the 5-prime end. Telomerase specifically serves to add DNA base pairs to the 3-prime end of the telomere.

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