Question

Recall where along a chromosome DNA synthesis begins, and explain what characterizes these nucleotide sequences in simple cells such as bacteria and yeast.

Answer 1

In bacteria, DNA synthesis starts at a single origin of replication, which is AT-rich and recognized by initiator proteins. In yeast, a eukaryote, multiple origins known as ARS start replication, which proceeds bidirectionally along the linear chromosomes.

Step-by-step explanation:

DNA Synthesis Initiation in Bacteria and Yeast:

In bacteria such as E. coli, DNA synthesis begins at a single origin of replication, which is a specific nucleotide sequence targeting initiator proteins. This origin is approximately 245 base pairs long and is AT-rich, meaning it has a high adenine-thymine content, which makes it easier to separate the strands for replication. An enzyme called helicase unwinds the DNA, assisted by ATP hydrolysis, forming Y-shaped structures called replication forks, which extend bidirectionally.

In yeast, a eukaryotic organism, replication begins at multiple origins known as Autonomously Replicating Sequences (ARS), functioning similarly to prokaryotic origins. As yeast chromosomes are linear, the replication forks proceed in both directions until they meet another fork or reach the end of the chromosome. The replication rate in eukaryotes like yeast is slower compared to prokaryotes.