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Cellular ReproductionCellular Reproduction
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Cellular GrowthCellular GrowthCells grow until they reach their size limit,
then they either stop growing or divide.
A cells size is limited by the surface area-to-volume ratio
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• As cell size INCREASES, its volume INCREASES much faster than its surface area
• Two Formulas -Surface Area (SA) & Volume (V)
SA = length+ width+ # of sides
V = length x width x height
Cellular GrowthCellular Growth
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The cell might have difficulty supplying nutrients and expelling enough waste products if its surface area is too small compared to its volume.
The need for a surfacesurface sufficiently large to accommodate the volumevolume explains the microscopic size of most cells.
Importance of Surface AreaImportance of Surface Area
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• Substances move by diffusion or by motor proteins.Diffusion over large distances is slow and inefficient.Small cells maintain more efficient transport systems.
• Cell size affects the ability of the cell to communicate instructions for cellular functions.
Importance of Surface AreaImportance of Surface Area
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• Cells must reproduce themselves at some point in their life. They do this by dividing in half to produce two new cells.
• Our entire body is made of cells-these are called body cells (somatic cells)
Cellular GrowthCellular Growth
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• Cell division prevents the cell from becoming too large.
• It is also the way the cell reproduces so that you grow and heal certain injuries.
• Cells reproduce by a cycle of growing and dividing called the cell cycle.
The Cell CycleThe Cell Cycle
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Cellular Organization of Genetic MaterialCellular Organization of Genetic Material
Chromatin-◦Found in nucleus of
cell◦Made up of DNA &
proteins◦Between cell
divisions the chromatin strands are loosely coiled in the nucleus
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Cellular Organization of Genetic MaterialCellular Organization of Genetic Material
◦Chromatin strands become tightly coiled during cell division and are then called chromosomes
◦The DNA in cells wraps tightly around proteins to maintain shape of a chromosome
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ChromosomesChromosomes
• The number of chromosomes in different species may be the same or significantly different
How many chromosomes are there in humans?
In a plant?
In a carrot? In a dog?
46
18
78
1,262
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• Interphase is the stage during which the cell grows, carries out cellular functions, and replicates.
• Mitosis is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide.
• Cytokinesis is the method by which a cell’s cytoplasm divides, creating a new cell.
The Cell CycleThe Cell Cycle
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The first stage of interphase, G1
• The cell is growing, carrying out normal cell functions, and preparing to replicate DNA.
• Cells are performing their assigned tasks, metabolizing, synthesizing, etc.
The Stages of InterphaseThe Stages of Interphase
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The second stage of interphase, S• The cell copies its DNA in preparation for cell division.
(DNA synthesizes)• DNA goes from 2 arms to 4 arms
The Stages of InterphaseThe Stages of Interphase
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The third stage of interphase, G2
• 2nd growth stage• The cell prepares for the division of its nucleus.
The Stages of InterphaseThe Stages of Interphase
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Mitosis•Body cell reproduction•A cell divides into 2 new “daughter” cells and the cell cycle starts over•Four Stages of Mitosis = PMAT
Mitosis and CytokinesisMitosis and Cytokinesis
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Prophase◦ Chromatin shortens and coils into
chromosomes
◦ Nuclear membrane breaks down◦ Centrioles appear & begin to move
to opposite ends
◦ Spindle fibers form
Stages of MitosisStages of Mitosis
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Stages of MitosisStages of Mitosis
Metaphase◦Sister chromatids
attach to spindle fibers
◦Chromatids pulled to the middle of the cell
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Stages of MitosisStages of Mitosis
Anaphase◦The microtubules of the
spindle apparatus begin to shorten.
◦Chromatids of each chromosome separate at centromere
◦Chromatids move toward opposite poles of cell, centromere first
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Stages of MitosisStages of Mitosis
Telophase◦ Once chromosomes reach
the poles, spindle fibers disassemble
◦ Chromosomes return to chromatin
◦ Two new nuclear membranes begin to form and the nucleoli reappear.
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• Cytokinesis- process where cytoplasm of cell begins dividing, this occurs during telophase stage
• Cell membrane moves inward to create TWO daughter cells- each with its own nucleus and identical chromosomes• In humans each cell would have 46 chromosomes
(diploid amount)
CytokinesisCytokinesis
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Cleavage furrow- area of cell membrane that pinches in and divides animal cell
Cell plate- midline of dividing plant cell, eventually forms into a cell wall
CytokinesisCytokinesis
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Cell Cycle RegulationCell Cycle Regulation
Normal Cell Cycle Proteins called cyclins bind to enzymes called cyclin-
dependent kinases(CDK) in stages of interphase and mitosis to start various activities in the cell cycle.
Quality Control Checkpoints◦The cell cycle has built-in checkpoints that
monitor the cycle and can stop it if something goes wrong.
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SG1
M checkpoint
G2M
Controlsystem
G1 checkpoint
G2 checkpoint
Signals DNA replication
Drives protein synthesis
Starts mitosis
Signals preparation for cell cycle
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Cell Cycle RegulationCell Cycle Regulation
Abnormal Cell Cycle: Cancer Cancer is the uncontrolled growth and division of
cells. Cancer cells can kill an organism by crowding out
normal cells, resulting in the loss of tissue function.
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Cell Cycle RegulationCell Cycle Regulation
Causes of Cancer The changes that occur in the regulation of cell
growth and division of cancer cells are due to mutations.
Various environmental factors can affect the occurrence of cancer cells.
Substances and agents known to cause cancer are called carcinogens.
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Cell Cycle RegulationCell Cycle Regulation
Apoptosis• Programmed cell death• Cells going through apoptosis actually shrink and
shrivel in a controlled process• Apoptosis can help to protect organisms from
developing cancerous growths.
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Cell Cycle RegulationCell Cycle Regulation
Stem Cells• Unspecialized cells that can develop into
specialized cells when under the right conditions
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Cell Cycle RegulationCell Cycle RegulationEmbryonic Stem Cells• An embryo is an organism’s early prebirth stage of
development
• After fertilization, the resulting mass of cells divides repeatedly until there are about 100–150 cells. These cells have not become specialized.
• If separated, cells can develop into specialized cells. If left alone, embryo will continue to develop.
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Cell Cycle RegulationCell Cycle Regulation
Adult Stem Cells• Found in various tissues in the body and might be
used to maintain and repair the same kind of tissue
• Less controversial because the adult stem cells can be obtained with the consent of their donor
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Importance of Stem CellsImportance of Stem Cells
Stem cells are not locked into being one type of cell, they might be the key to curing medical conditions and genetic defects if they can be developed into specific cells that are needed.