Question

Telomerase synthesizes DNA in the _______ direction.

Short answer

Telomerase synthesizes DNA in the \(5'\) to \(3'\) direction.

Step-by-step solution

Direction of DNA synthesis for most enzymes

Most enzymes synthesize DNA in the 5' to 3' direction. Meaning that, while reading a DNA sequence, new nucleotides are added to the 3' end of the growing DNA strand.

Telomerase synthesizes DNA in the:

Telomerase also follows the same direction rule as most enzymes and synthesizes DNA in the \(5'\) to \(3'\) direction. Answer: 5' to 3' direction.

Key concepts

Telomerase Function

Telomerase is a specialized enzyme with a unique role in DNA replication. It extends the length of telomeres, which are repetitive nucleotide sequences at the ends of chromosomes. These protective caps prevent the loss of important genetic information during cell division.

During the replication process, the lagging strand of DNA, which is synthesized discontinuously, struggles to replicate the very end of the chromosome. This is where telomerase comes into play. It uses an RNA template within its own structure to add complementary RNA bases to the unfinished ends of the DNA molecule. These RNA bases are then used as a template for adding DNA nucleotides.

Without the action of telomerase, chromosomes would shorten progressively with each cell division, eventually leading to cell aging and death. Hence, telomerase is crucial for the longevity of certain cells, like germ cells, some stem cells, and cancerous cells, where this enzyme is typically more active.

DNA Replication

DNA replication is a vital process that ensures that each daughter cell receives an exact copy of the parent cell's genetic material. The replication process follows a semi-conservative model, meaning each new DNA molecule consists of one old (parental) and one new (daughter) strand.

DNA replication begins at specific locations on the DNA called origins of replication. The double helix is unwound by helicase enzymes, creating a 'Y' shaped replication fork. DNA polymerases are the enzymes responsible for adding new nucleotides to a growing DNA chain.

This addition of nucleotides requires a primer with a free 3' hydroxyl group. Once primed, DNA polymerases synthesize new DNA strands by adding nucleotides complementary to the template strand. Because DNA polymerases can only add nucleotides to the 3' end, replication is continuous on the leading strand and discontinuous on the lagging strand, forming short segments known as Okazaki fragments.

5' to 3' Direction

The direction of DNA synthesis is a fundamental aspect of genetic replication and an area where students often require clarification. DNA strands have directionality, with one end labeled as 5' (five prime) and the other as 3' (three prime). These numbers refer to the carbon atoms in the DNA's sugar backbone.

During DNA replication, nucleotides are added to a growing DNA strand in a 5' to 3' direction. This means that free nucleotides are attached to the 3' end of the strand, while the 5' end remains anchored. It's important to understand that although the synthesis moves from 5' to 3', it is the template strand that is being read in the opposite direction, 3' to 5'.

This process ensures that the genetic code is accurately replicated and passed on. It is because of this unidirectional synthesis that primase, DNA polymerases, and other replication proteins coordinate in a precise manner to perform their roles without errors.