34.2
间期
细胞周期大约需要24小时（在典型的人类细胞中），并分为两个不同的阶段：间期，包括细胞周期的三个阶段（G1、S 和 G2）和有丝分裂 (M)。 在间期，它占据了真核细胞周期大约95%的时间，细胞生长并复制其 DNA，为有丝分裂做准备。
间期的阶段 在每个有丝分裂和胞质分裂之后，真核细胞进入间期，在此期…
在真核细胞中，细胞周期的大部分时间处于间期，间期分为三个阶段：G1期、S期和G2期。
在G1期（第一个生长期），新生成的子细胞增大体积，并为下一阶段的DNA复制进行准备。
现在，在S期即合成期，细胞会复制其细胞核DNA，这些DNA仍以染色质形式存在。细胞还会复制中心体，即微管组织结构，它将形成有丝分裂纺锤体装置。
最后，在G2期（第二个生长期），细胞继续生长，增殖有丝分裂所需的细胞器和蛋白质，并补充其能量储备。此时，细胞已准备好进入有丝分裂的第一阶段。
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Q1: What are the three phases of interphase in eukaryotic cells?
Interphase consists of G1, S, and G2 phases. G1 is the first gap phase where cells grow and prepare for DNA duplication. S is the synthesis phase where DNA replication occurs. G2 is the second gap phase where cells continue growing and prepare for mitosis. Together, these phases comprise approximately 95 percent of the cell cycle.
Q2: What happens during the G1 phase of interphase?
During G1, newly generated daughter cells grow in size and prepare for DNA duplication. Cells are metabolically active, copying essential organelles and biochemical molecules such as proteins. The G1 phase typically spans approximately 11 hours in human cells, during which cells remain diploid with one copy of each chromosome.
Q3: How does DNA content change during the S phase?
During the S phase, cells duplicate their nuclear DNA, which remains packaged as chromatin. This DNA replication increases the cell's DNA content from 2n to 4n. Cells also duplicate the centrosome, a microtubule-organizing structure that forms the mitotic spindle apparatus. The S phase takes approximately 8 hours in human cells.
Q4: What is the role of the centrosome during interphase?
The centrosome is a microtubule-organizing structure that cells duplicate during the S phase of interphase. It forms the mitotic spindle apparatus, which separates chromosomes during mitosis. By duplicating the centrosome during interphase, cells ensure they have the necessary structures ready for the upcoming mitotic division.
Q5: What occurs during the G2 phase of interphase?
During G2, cells continue to grow and synthesize proteins and organelles required for mitosis. They replenish energy stores and prepare for the first stage of mitosis. The G2 phase typically lasts about 4 hours in human cells. After G2 completion, the cell is ready to enter mitosis.
Q6: How long does interphase last compared to the entire cell cycle?
Interphase takes up approximately 95 percent of the total cell cycle duration. In a typical human cell, the entire cell cycle occurs over approximately 24 hours, with G1 spanning about 11 hours, S phase taking about 8 hours, and G2 lasting about 4 hours. This leaves only about 1 hour for mitosis and cytokinesis.
Q7: When does DNA content return to 2n after interphase?
Following DNA replication in the S phase, cells increase their DNA content to 4n and remain at this level through G2 and mitosis. DNA content is reduced back to 2n only after cytokinesis is complete. Understanding the cell cycle helps clarify how cells prepare for division and maintain proper genetic content.