Download eoc review packet cell division

Unit 7: Cell Division
Vocabulary to Define:
checkpoint
tumor
malignant
diploid
haploid
homologous chromosomes
crossing over
benign
What you should know…
 Cell cycle: a repeated pattern of growth and division that occurs in eukaryotic cells; consists of three phases.
Interphase
 Purpose is for cell growth; divided into three phases.
○ During the G1 (gap 1) phase, the cell grows and synthesizes proteins.
○ During the S (synthesis) phase, chromosomes replicate and divide to
form identical sister chromatids held together by a centromere.
○ During the G2 (gap 2) phase, cells continue to grow
Mitosis
 Purpose is cell division: making two cells out of one; divided into four phases.
○ Prophase: chromosomes condense and are more visible; nuclear membrane (envelope) disappears;
centrioles separate and move to opposite sides of the cell; spindle fibers form
○ Metaphase: the shortest phase of mitosis; chromosomes line up across the middle of the cell; spindle
fibers connect the centromere of each sister chromatid to the centrioles
○ Anaphase: centromeres split; sister chromatids separate becoming individual chromosomes, and move to
opposite poles of the cell
○ Telophase: the last phase of mitosis; chromosomes uncoil; nuclear envelope reforms around the
chromosomes; spindle fibers break down and dissolve; cytokinesis begins.
Cytokinesis
 Division of the cytoplasm into two individual cells, diploid, genetically identical
 Animal cells form a cleavage furrow that eventually pinches the cell into two nearly equal parts
 Plant cells form a cell plate midway between the divided nuclei; eventually forms the cell wall
Cancer
 Cell cycle is driven by a chemical control system that regulates the cell cycle at certain checkpoints.
 Signals are involved in turning the process of cell division off and on.
○ Internal signal: cell senses chemicals produced inside the cell
○ External signal: cell senses chemicals produced in other cells.
 Cells can also respond to physical signals from their environment: division is turned off when cells are
closely packed; division is turned on when cells are not in contact with a surface
 Cancer cells continue to divide even when they are very packed and/or there is no growth factor present.
Stem Cells
 In multicellular organisms, a fertilized egg gives rise to many different types of cells, each with a different
structure and function, through process of cell division
○ As cell division proceeds, the cells undergo differentiation to become specialized
○ The various types of cells (such as blood, muscle, or epithelial cells) arrange into tissues which are
organized into organs, and which are organized into organ systems.
○ During differentiation, only specific parts of the DNA are activated; the parts of the DNA that are
activated determine the function and specialized structure of a cell.
 Stem cells are unspecialized cells that continually reproduce themselves and have the ability to differentiate
into one or more types of specialized cells.
○ 2 types: embryonic (taken from embryos) and adult stem cells
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Unit 7: Cell Division
Meiosis occurs in two steps:
 Meiosis I: chromosome pairs replicate, results in two haploid daughter cells with duplicated chromosomes
different from the chromosomes in the original diploid cell.
 Meiosis II: haploid daughter cells from Meiosis I divide, results in four haploid daughter cells called
gametes, or sex cells (eggs and sperm), with single chromosomes.
Meiosis I
A
prophase I
B
metaphase I
C
anaphase I
D
telophase I
Meiosis I begins with interphase in which cells: (1) increase in size (2) synthesize proteins (3) replicate DNA
 Prophase I: nuclear membrane breaks down; centrioles move to opposite sides of the nucleus and begin to
produce spindle fibers; chromosomes pair up and become visible as a cluster of four chromatids called a
tetrad (a pair of homologous chromosomes – one from mom and one from dad)
 Metaphase I: chromosomes are pulled into the mid-line (or equator) of the cell in pairs.
 Anaphase I: homologous chromosome pairs separate; sister chromatids remain attached to each other
 Telophase I & Cytokinesis: chromosomes gather at the poles, nuclear membrane reforms, cytoplasm divides
 Each daughter cell contains only one chromosome (consisting of two sister chromatids)
Meiosis II
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Prophase II: same as prophase I, except crossing over does not take place
Metaphase II: sister chromatids line up across the center of the cell.
Anaphase II: sister chromatids separate, and individual chromosomes move to opposite poles
Telophase II & Cytokinesis: ends with 4 daughter cells that are haploid and genetically different
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