Prentice Hall - Science Explorer - Cells and Heredity
Chapter 2- Cell Processes and Energy
Section 3- Cell Division
Questions - Comment - Key Words - ConnectionsCell Cycle Interphase Replication Mitosis Chromosomes Cytokinesis |
Main Ideas; Visuals + PredictionsStage 1: Interphase
Cell cycle: The regular sequence of growth and division that cells undergo. Daughter cells: the two new cells Interphase: The stage of the cell cycle that takes place before cell division occurs. * During interphase, the cell grows, makes a copy of its DNA, and prepares to divide into two cells. Growing * During the first part of interphase, the cell grows to its full size and produces structures it needs. ex: the cell makes new ribosomes and produces enzymes. Copies are made of both mitochondria and chloroplasts. Copying DNA Replication: The process by which a cell makes a copy of the DNA in its nucleus. * each daughter cell must have a complete set of DNA to survive. Preparing for Division * The cell produces structures that it will use to divide into two new cells. At the end of interphase, the cell is ready to divide. Stage 2: Mitosis Mitosis: The stage of the cell cycle during which the cell’s nucleus divides into two new nuclei and one copy of the DNA is distributed into each daughter cell. Chromosomes: A doubled rod of condensed chromatin; contains DNA that carries genetic information. (during prophase) * During prophase, the threadlike chromatin in the nucleus condenses to form double-rod structures called chromosomes. * As the cell progresses through metaphase, anaphase, and telophase, the chromatids separate from each other and move to opposite ends of the cell. *Then two nuclei form around the chromatids at the two ends of the cell. Stage 3: Cytokinesis
Cytokinesis: The final stage of the cell cycle, in which the cell’s cytoplasm divides, distributing the organelles into each of the two new cells. Cytokinesis in Animal Cells * During cytokinesis in animal cells, the cell membrane squeezes together around the middle of the cell. The cytoplasm pinches into two cells. Each daughter cell gets about half of the organelles. Cytokinesis in Plant Cells
* A plant cell’s rigid cell wall cannot squeeze together. Instead, a cell plate forms across the middle of the cell. The cell plate gradually develops into new cell membranes between the two daughter cells. New cell walls then form around the cell membranes. Structure and Replication of DNA
The structure of DNA * A DNA molecule looks like a twisted ladder, or spiral staircase. The two sides of the DNA ladder are made up of molecules of a sugar called deoxyribose, alternating with molecules known as phosphates. * The bases on one side of the ladder pair with the bases on the other side. Adenine (A) only pairs with thymine (T), while guanine (G) only pairs with cytosine (C). This pairing pattern is the key to understanding how DNA replication occurs.
The Replication Process * DNA replication begins when the two sides of the DNA molecule unwind and separate, somewhat like a zipper unzipping. * Nitrogen bases that are floating in the nucleus pair up with the bases on each half of the DNA molecule. Because of the way in which the nitrogen bases pair with one another, the order of the bases in each new DNA molecule exactly matches the order in the original DNA molecule.
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