Question

What are the replication origins in bacteria, yeast, and mammalian cells?

Short answer

Question: Briefly describe how replication origins differ in bacteria, yeast, and mammalian cells. Answer: In bacteria, replication starts at a single well-defined origin called oriC, a sequence of about 245 base pairs. In yeast, replication begins at multiple origins known as Autonomously Replicating Sequences (ARS) with a consensus sequence of 11 base pairs called the ARS consensus sequence (ACS). Mammalian cells also initiate replication at multiple origins, but these origins do not have a well-defined consensus sequence and are associated with open chromatin regions and specific histone modifications.

Step-by-step solution

Introduction to Replication Origins

Replication origins are specific sequences in a genome where DNA replication begins. These sequences act as starting sites for the replication process, in which the genetic material is duplicated, ensuring that each new cell receives a complete copy of the DNA. Depending on the complexity of the organism, replication origins may vary in number and sequence characteristics.

Replication Origins in Bacteria

In bacteria, there is generally a single well-defined replication origin called oriC. This origin is a sequence of about 245 base pairs located on the bacterial chromosome, which is typically a circular DNA molecule. The replication process starts at oriC and proceeds bidirectionally, generating two replication forks that eventually meet at the opposite end of the circular chromosome.

Replication Origins in Yeast

Yeast, a type of eukaryote, has a higher complexity than bacteria. Replication in yeast starts at multiple replication origins known as Autonomously Replicating Sequences (ARS). These sequences typically have a consensus sequence of 11 base pairs called the ARS consensus sequence (ACS), which is recognized by the origin recognition complex (ORC). Yeast cells have a more advanced system to control the initiation and timing of replication compared to bacteria.

Replication Origins in Mammalian Cells

Mammalian cells, like other eukaryotic cells, initiate replication at multiple origins. However, unlike yeast, the replication origins in mammalian cells do not have a well-defined consensus sequence. Instead, the replication origins are typically associated with open chromatin regions and are enriched in specific histone modifications. The replication timing in mammalian cells is tightly regulated, ensuring that the entire genome is replicated during the S phase of the cell cycle.