Download Chapter 5 The Cell Cycle and Mitosis: The Basis for Asexual

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Chapter 5 The Cell Cycle and Mitosis: The Basis for Asexual Reproduction - KEY
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You started off as a single cell and are now composed of trillions of cells – How?
Cell division, in which 1 cell divides into 2
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Cells are constantly dying and being replaced by cell division
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Why do an organism’s cells divide? For growth, repair & development
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How does a cell know when to divide? DNA
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Different cells are replaced at various intervals ( from 2 days to 200 days ) depending on the specific type of cell
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Which cells would need to be replaced more frequently? Skin, RBC’s, Cells lining digestive tract
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Which cells would need to be replaced less frequently? Brain cells
The Cell Cycle
Objectives
 I can identify and describe the events of the 3 main stages of the cell cycle (interphase, mitosis,
cytokinesis) and identify these stages on a diagram
 I can identify what form DNA is during the different stages of the cell cycle (i.e. chromatin or
chromosomes) and when it is replicated.
 I can describe the key events that take place during the 3 stages within interphase.
 I can identify and describe the 4 main phases of mitosis.
 I can compare cytokinesis in animal and plant cells.
Vocabulary: interphase, mitosis, nucleus, nucleolus, cytokinesis, daughter cells, chromatin, chromosomes,
centromere, duplicated chromosome, daughter chromosome, prophase, metaphase, anaphase, telophase, spindle
fibers, centrioles
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During cell division a cell goes through a set series of stages, which is referred to as the cell cycle:
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Consists of 3 stages:
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Interphase - cells carry out normal functions and prepare for reproduction
Mitosis - after duplication of contents, the cell’s nucleus divides into 2 equal & identical parts
Cytokinesis- the two nuclei and cell contents separate into 2 “daughter cells”
Interphase
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Longest stage in the cell cycle
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During this phase, DNA is in the form of chromatin
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Divided into 3 stages:
Growth & Preparation
DNA Replication
Continued Growth & Preparation
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Growth & Preparation
o cell increases in size & doubles its organelles (while performing its usual functions)
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DNA Replication
o DNA replicates, making an exact copy of itself:
Step 1:
Enzyme
DNA by results in duplicated chromosomes during mitosis
o unzips
DNA replication
separating base pairs
Step 2:
New bases pair with
bases on original
DNA strand
Step 3:
Two new identical
DNA molecules are
produced.
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Because DNA replication occurs before mitosis, this means that when the chromatin condenses, it is in the form
of duplicated chromosomes, which are composed of two sister chromatids:
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Continued Growth & Preparation
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After DNA replicates, the cell continues to grow and prepare for division while performing its usual
functions
In particular, it synthesizes a lot of proteins needed for cell division
Mitosis
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Shortest stage in the cell cycle
Contents of cell nucleus divide, resulting in 2 daughter nuclei that are identical to the original parent cell:
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2 important structures are involved in cell division:
1) Spindle fibers: protein structures that move the chromosomes during cell division
2) Centrioles: organelles that control the spindle fibers during cell division; not found in plant cells
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Mitosis is divided into 4 stages that are each characterized by specific events: (PMAT)
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Prophase (which is further subdivided into early prophase& late prophase)
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Metaphase
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Anaphse
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Telophase
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Phases of Mitosis (dividing of nucleus)
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Early Prophase:
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Duplicated chromosomes condense (coil up) into X-shape
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Nucleolus disappears
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Nuclear membrane breaks down
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Spindle fibers form & spread across the cell
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Centrioles move to opposite ends of the cell
Late Prophase:
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Spindle fibers complete forming
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Spindle fibers attach to chromosomes at their centromeres
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By the end of prophase, the nuclear membrane & nucleolus
have disappeared
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Metaphase:
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Spindle fibers pull chromosomes into a line across the metaphase plate along the center of the cell
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Anaphase:
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Spindle fibers contract & shorten to pull the sister chromatids apart toward opposite poles of the cell
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The sister chromatids are now considered to be daughter chromosomes
Telophase:
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Final stage of mitosis
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A complete set of chromosomes is at each end of the cell
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Nuclear membrane reforms around each set of chromosomes
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Nucleolus reappears
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Spindle fibers disappear
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Now there are two nuclei in the one cell
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Cytokinesis
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Final stage of cell cycle
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The cell with 2 nuclei splits into 2 daughter cells
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The new cells are identical to each other and to the original parent cell
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Cytokinesis is different in animal and plant cells due to the presence of the cell wall in plants:
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Animal cells: cell membrane pinches together to separate nuclei & organelles
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Plant cells: cell plate forms along center of cell
Practice Questions
1) Identify two differences between the cell cycle in plant cells and in animal cells.
2) Use the terms chromatin, duplicated chromosomes, and daughter chromosomes to describe how DNA is
organized during:
a. Early interphase
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b. Late interphase
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c. Prophase
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d. Anaphase
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3) Identify the 3 main stages of the cell cycle.
4) Identify and briefly describe what occurs during the 3 stages of interphase.
5) Identify the stages shown on the
following diagram: