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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

What is the end replication problem?

DNA polymerases in all organisms add only \(5^{\prime}\) nucleotides to the \(3^{\prime}\) end of a growing DNA strand, never to the \(5^{\prime}\) end. One possible reason for this is the fact that most DNA polymerases have a proofreading function that would not be energetically possible if DNA synthesis occurred in the \(3^{\prime}\) to \(5^{\prime}\) direction. (a) Sketch the reaction that DNA polymerase would have to catalyze if DNA synthesis occurred in the \(3^{\prime}\) to \(5^{\prime}\) direction. (b) Consider the information in your sketch and speculate as to why proofreading would be problematic.

During replication, what would be the consequences of the loss of functions of (a) single-stranded binding proteins, (b) DNA ligases, (c) DNA topoisomerases, and (d) DNA helicases?

Unlike prokaryotes, why do eukaryotes need multiple replication origins?

Review the Chapter Concepts list on \(\mathrm{p} .295 .\) These are concerned with the replication and synthesis of DNA. Write a short essay that distinguishes between the terms replication and synthesis, as applied to DNA. Which of the two is most closely allied with the field of biochemistry?
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