NEM 10V Lecture Notes - Lecture 15: Dna Replication, Metaphase, Cytokinesis
Nematology
Mitosis:
• Cell division is required for an organism to grow, mature, and maintain tissues. Cells
reproduce by dividing into two new cells with identical genetic material and a share of
the parental cytoplasm and contents. The cell cycle has three phases: interphase, mitosis,
and cytokinesis.
• Interphase is the preparation time for cell division and follows three basic steps. Gl, or
Gap 1, is the initial phase when the cell is metabolizing and growing in preparation for
cell division. When a cell is in Gl, each chromosome consists of one double-stranded
DNA molecule. S, or Synthesis, is when the DNA is being synthesized, or replicated. By
the end of S, each chromosome consists of two double-stranded DNA molecules, called
sister chromatids, which are attached in the center by a centromere. G2, or Gap 2, is when
the cell finishes growing.
• Mitosis is the process of nuclear division. During mitosis the sister chromatids are
separated into the new nuclei. At the start of mitosis, chromosomes condense, and
transcription and DNA replication halt. Mitosis occurs in four steps: prophase,
metaphase, anaphase, and telophase. Prophase is the first step in mitosis. Centrosomes
and their centrioles move to opposite poles of the cell. Spindle fibers, networks of
microtubules, grow from the poles toward the center of the cell.
• Near the end of prophase, the nuclear envelope dissolves, and microtubules attach to the
centromeres of the duplicated, condensed chromosomes. Metaphase is marked by the
arrival of all the condensed chromosomes at the center of the cell, called the metaphase
plate. During anaphase, the microtubules separate the sister chromatids, which are pulled
toward opposite poles of the cell. Telophase begins when both new nuclei start to form. A
new nucleus forms around each cluster of just-separated sister chromatids. During
telophase, the chromosomes decondense, and the nuclear envelope reforms.
• Cytokinesis is the cytoplasmic division mechanism. Animal cells divide by developing a
contractile ring. The contractile ring forms inside the cell and consists of actin and
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Document Summary
Mitosis: cell division is required for an organism to grow, mature, and maintain tissues. Cells reproduce by dividing into two new cells with identical genetic material and a share of the parental cytoplasm and contents. The cell cycle has three phases: interphase, mitosis, and cytokinesis. Interphase is the preparation time for cell division and follows three basic steps. Gap 1, is the initial phase when the cell is metabolizing and growing in preparation for cell division. When a cell is in gl, each chromosome consists of one double-stranded. S, or synthesis, is when the dna is being synthesized, or replicated. By the end of s, each chromosome consists of two double-stranded dna molecules, called sister chromatids, which are attached in the center by a centromere. G2, or gap 2, is when the cell finishes growing: mitosis is the process of nuclear division. During mitosis the sister chromatids are separated into the new nuclei.
