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Chapter 11: Problem 18

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

Short Answer

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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

01

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.
02

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.
03

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.
04

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.

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Most popular questions from this chapter

Many of the gene products involved in DNA synthesis were initially defined by studying mutant \(E .\) coli strains that could not synthesize DNA. (a) The \(d n a E\) gene encodes the a subunit of DNA polymerase III. What effect is expected from a mutation in this gene? How could the mutant strain be maintained? (b) The \(d n a Q\) gene encodes the \(\varepsilon\) subunit of DNA polymerase. What effect is expected from a mutation in this gene?

Suppose that \(E .\) coli synthesizes DNA at a rate of 100,000 nucleotides per minute and takes 40 minutes to replicate its chromo- some. (a) How many base pairs are present in the entire \(E .\) coli chromosome? (b) What is the physical length of the chromosome in its helical configuration- that is, what is the circumference of the chromosome if it were opened into a circle?

During DNA replication, which enzyme can be disposed of in an organism with a mutant DNA polymerase that does not require a free \(3^{\prime}-\mathrm{OH} ?\)

Define and indicate the significance of (a) Okazaki fragments, (b) DNA ligase, and (c) primer RNA during DNA replication.

While many commonly used antibiotics interfere with protein synthesis or cell wall formation, clorobiocin, one of several antibiotics in the aminocoumarin class, inhibits the activity of bacterial DNA gyrase. Similar drugs have been tested as treatments for human cancer. How might such drugs be effective against bacteria as well as cancer?
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