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Chapter 3Chapter 3

CellsCells

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3.1 Introduction:3.1 Introduction:

A.A. The human body consists of The human body consists of 75 trillion 75 trillion cells that vary cells that vary considerably in shape and size considerably in shape and size yet have much in common.yet have much in common.B.B. Differences in cell shape Differences in cell shape make different functions possible.make different functions possible.

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3.2 A Composite Cell:3.2 A Composite Cell:

A.A. A composite cell includes many A composite cell includes many different cell structures.different cell structures.

B.B. A cell consists of three main A cell consists of three main parts---the parts---the nucleusnucleus, the , the cytoplasmcytoplasm, , and the and the cell membranecell membrane..

C.C. Within the cytoplasm are Within the cytoplasm are specialized specialized organellesorganelles that perform that perform specific functions for the cell.specific functions for the cell.

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D. Cell Membrane: D. Cell Membrane:

1.1. The cell membrane The cell membrane regulates regulates the movement of the movement of substances in substances in and out of the and out of the cell, participates cell, participates in signal in signal transduction, and helps transduction, and helps cells adhere to other cells.cells adhere to other cells.

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2. General Characteristics 2. General Characteristics

a. The cell membrane a. The cell membrane is is extremely thin and extremely thin and

selectively selectively permeable.permeable.

b. It has a complex b. It has a complex surface surface withwithadaptations to increaseadaptations to increasesurface area. surface area.

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3. 3. Cell Membrane StructureCell Membrane Structure::

a. The basic framework of the a. The basic framework of the cell cell membrane consists of a membrane consists of a double layer double layer of of phospholipidsphospholipids, , with fatty acid tails with fatty acid tails turned inward.turned inward.

b. Molecules that are soluble in b. Molecules that are soluble in lipids lipids (gases, steroid hormones) (gases, steroid hormones) can pass can pass through the lipid bilayer.through the lipid bilayer.

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c. Embedded cholesterol c. Embedded cholesterol molecules molecules strengthen the strengthen the membrane and help membrane and help make make the membrane less permeable the membrane less permeable to to water-soluble substances.water-soluble substances.

d. Many types of d. Many types of proteinsproteins are are found found in the cell membrane, in the cell membrane, including including transmembrane transmembrane proteins and proteins and peripheral peripheral membrane proteins.membrane proteins.

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e. Membrane proteins e. Membrane proteins perform a perform a variety of functions variety of functions and vary in and vary in shape.shape.

f.f. Some proteins function as Some proteins function as receptors on the cell surface, receptors on the cell surface, starting signal transduction.starting signal transduction.

g. Other proteins aid the g. Other proteins aid the passage of passage of molecules and ions.molecules and ions.

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h. Proteins protruding into the h. Proteins protruding into the cell cell anchor supportive rods and anchor supportive rods and tubules.tubules.

i. Still other proteins have i. Still other proteins have carbohydrates attached; these carbohydrates attached; these complexes are used in cell complexes are used in cell identification. Membrane proteins identification. Membrane proteins

called cellular adhesion called cellular adhesion molecules molecules (CAMs) help determine (CAMs) help determine one cell’s one cell’s interactions with others. interactions with others.

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E. E. Cytoplasm:Cytoplasm:

1. The cytoplasm consists of a 1. The cytoplasm consists of a clear clear liquid liquid (cytosol),(cytosol), a supportive a supportive

cytoskeletoncytoskeleton, and networks of , and networks of membranes and organelles. membranes and organelles.

a. a. Endoplasmic reticulumEndoplasmic reticulum is is made up of membranes, made up of membranes,

flattened sacs, and flattened sacs, and vesicles, and vesicles, and provides a tubular provides a tubular transport transport system inside the cell. system inside the cell.

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i. With ribosomes, i. With ribosomes, (ER) is (ER) is rough ER, and rough ER, and functions in functions in protein protein synthesis.synthesis.

ii. Without ribosomes, ii. Without ribosomes, it is it is smooth ER, smooth ER, and functions and functions in in lipid synthesis.lipid synthesis.

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b. b. RibosomesRibosomes are found with are found with ER ER and and are scattered are scattered throughout throughout the cytoplasm. the cytoplasm. They are They are composed of composed of protein and RNA protein and RNA and and provide a structural support provide a structural support for the RNA molecules that for the RNA molecules that come together in protein come together in protein

synthesis.synthesis.

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c. c. TheThe Golgi apparatusGolgi apparatus is composed is composed of flattened sacs, and refines, of flattened sacs, and refines, packages, modifies, and delivers packages, modifies, and delivers proteins.proteins.

i. Vesicles formed on ER i. Vesicles formed on ER travel travel to the Golgi to the Golgi apparatus, which apparatus, which modifies modifies their contents their contents chemically.chemically.

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ii.ii. The vesicle may then move The vesicle may then move to the to the cell membrane and cell membrane and secrete its secrete its contents to the contents to the outside.outside.

iii.iii. Vesicles form a “delivery Vesicles form a “delivery service”, service”, carrying chemicals carrying chemicals throughout the throughout the cell (vesicle cell (vesicle trafficking).trafficking).

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d.d. Mitochondria Mitochondria are the powerhouses are the powerhouses of the cell and contain enzymes of the cell and contain enzymes needed for aerobic respiration.needed for aerobic respiration.i. The inner membrane of the i. The inner membrane of the mitochondrion is folded into mitochondrion is folded into cristae which hold the enzymes cristae which hold the enzymes needed in energy needed in energy transformations to make ATP.transformations to make ATP.ii.ii.  Very active cells contain Very active cells contain thousands of mitochondria.thousands of mitochondria.

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e. e. LysosomesLysosomes are the "garbage are the "garbage disposals" of the cell and contain disposals" of the cell and contain digestive enzymes to break up old digestive enzymes to break up old cell components and bacteria.cell components and bacteria.

f. f. PeroxisomesPeroxisomes contain contain enzymes that enzymes that function in the function in the synthesis of bile synthesis of bile acids, acids, breakdown of lipids, breakdown of lipids, degradation of rare biochemicals, degradation of rare biochemicals, and detoxification of alcohol.and detoxification of alcohol.

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g. g. Microfilaments and Microfilaments and microtubulesmicrotubules are thin, threadlike are thin, threadlike structures that structures that serve as the serve as the cytoskeleton of the cell.cytoskeleton of the cell.

i. Microfilaments, made of i. Microfilaments, made of actin, actin, cause various cellular cause various cellular

movements.movements.

ii. Microtubules, made of ii. Microtubules, made of the the globular globular protein protein tubulin, are tubulin, are arranged arranged in a 9 + 2 pattern of in a 9 + 2 pattern of tubules.tubules.

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h. A h. A centrosomecentrosome is made up is made up of two of two hollow cylinders hollow cylinders called centrioles called centrioles that function that function in the separation of in the separation of chromosomes during cell division.chromosomes during cell division.

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i. i. Cilia and flagellaCilia and flagella are motile are motile extensions from the cell; extensions from the cell;

shorter cilia shorter cilia are abundant on are abundant on the free surfaces of the free surfaces of certain certain epithelial cells (respiratory epithelial cells (respiratory linings, for example), and a linings, for example), and a lengthy lengthy flagellum can be flagellum can be found on sperm found on sperm cells.cells.

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j. j. VesiclesVesicles form from part form from part of the of the cell membrane, or cell membrane, or the Golgi the Golgi apparatus, apparatus, and store materials.and store materials.

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F. F. Cell NucleusCell Nucleus::

1. The fairly large nucleus 1. The fairly large nucleus is is bounded by a double-bounded by a double-layered layered nuclear nuclear membrane containing membrane containing relatively large nuclear pores relatively large nuclear pores

that allow the passage of that allow the passage of certain certain

substances.substances.

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a. The a. The nucleolusnucleolus is is composed of composed of RNA and RNA and protein and is the protein and is the site of site of ribosome production.ribosome production.

b. b. ChromatinChromatin consists of consists of loosely loosely coiled fibers of coiled fibers of protein and DNA.protein and DNA.

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3.3 Movements Through Cell 3.3 Movements Through Cell MembranesMembranes

A. The cell membrane controls A. The cell membrane controls what passes through it.what passes through it.

B. Mechanisms of movement B. Mechanisms of movement across the membrane may be across the membrane may be passive, requiring no energy passive, requiring no energy from the from the cell or active cell or active mechanisms, requiring cellular mechanisms, requiring cellular energy.energy.

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C. C. Passive Mechanisms Passive Mechanisms

1. 1. DiffusionDiffusion

a. Diffusion is caused by a. Diffusion is caused by the the random motion of random motion of molecules molecules and involves and involves movement movement from an from an area of greater area of greater concentration to lesser concentration to lesser

concentration until concentration until equilibrium is reached.equilibrium is reached.

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b. Diffusion enables b. Diffusion enables oxygen oxygen and carbon dioxide to and carbon dioxide to be be exchanged between exchanged between the air the air and the blood in the and the blood in the lungs, lungs, and between blood and between blood and tissue and tissue cells.cells.

c. Factors affecting c. Factors affecting diffusion diffusion include distance, include distance,

concentration concentration gradient, and gradient, and temperature. temperature.

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2. 2. Facilitated DiffusionFacilitated Diffusion

a. Facilitated diffusion uses a. Facilitated diffusion uses membrane proteins that membrane proteins that function as carriers to move function as carriers to move molecules (such as glucose) molecules (such as glucose) across the cell membrane.across the cell membrane.

b. The number of carrier b. The number of carrier molecules in the cell molecules in the cell membrane limits the rate.membrane limits the rate.

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3. 3. OsmosisOsmosis

a. Special case of diffusion a. Special case of diffusion in in which water moves from which water moves from greater greater water concentration water concentration (where there (where there is less osmotic is less osmotic pressure) across a pressure) across a selectively selectively permeable membrane permeable membrane to to lower water concentration lower water concentration (where there is greater osmotic (where there is greater osmotic

pressure).pressure).

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b. Osmotic pressure is the b. Osmotic pressure is the ability ability of osmosis to lift a of osmosis to lift a volume of volume of water.water.

c. A solution with the same c. A solution with the same osmotic pressure as body osmotic pressure as body

fluids is fluids is called called isotonicisotonic; one ; one with higher with higher osmotic pressure osmotic pressure than body fluids than body fluids is is hypertonichypertonic; ; one with lower one with lower osmotic osmotic pressure is pressure is hypotonic.hypotonic.

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4.4. FiltrationFiltration

a.a. Hydrostatic pressure can Hydrostatic pressure can force force molecules through molecules through membranes by membranes by the process the process of filtration. of filtration.

b. Blood pressure can move b. Blood pressure can move water water & dissolved particles & dissolved particles through the through the capillary walls.capillary walls.

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D. D. Active MechanismsActive Mechanisms

1.1. Active Transport Active Transport

a. Active transport uses a. Active transport uses ATP to ATP to move molecules from move molecules from areas of areas of low concentration low concentration to areas of to areas of high concentration high concentration through through carrier molecules.carrier molecules.

b.b. As much as 40% of a As much as 40% of a cell's cell's energy supply may be energy supply may be used to used to fuel this process.fuel this process.

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c.c. The union of the The union of the specific specific particle to be particle to be transported with its transported with its carrier carrier protein triggers the protein triggers the release of cellular energy (ATP), release of cellular energy (ATP),

which in turn alters the which in turn alters the shape shape of the carrier protein, of the carrier protein, releasing releasing the particle to the the particle to the other side of other side of the membrane.the membrane.

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d. Particles that are d. Particles that are actively actively transported transported include sugars, include sugars, amino acids, amino acids, and Na, K, Ca, and and Na, K, Ca, and H ions, as H ions, as well as nutrient well as nutrient molecules in the intestines. molecules in the intestines.

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2. 2. Endocytosis and ExocytosisEndocytosis and Exocytosis

a. In endocytosis, molecules a. In endocytosis, molecules that are that are too large to be too large to be transported by other transported by other means are means are engulfed by an engulfed by an invagination of the invagination of the cell membrane cell membrane and carried into the and carried into the cell surrounded cell surrounded by a vesicle.by a vesicle.

b.b. Exocytosis is the reverse Exocytosis is the reverse of of endocytosis.endocytosis.

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c.c. Three forms of Three forms of endocytosisendocytosis

i.i. PinocytosisPinocytosis is a form of is a form of endocytosis in endocytosis in

which cells engulf which cells engulf liquids.liquids.

ii.ii. PhagocytosisPhagocytosis is a form is a form of of endocytosis in which endocytosis in which the cell the cell takes in larger takes in larger particles, such as particles, such as a white blood a white blood cell engulfing a cell engulfing a bacterium.bacterium.

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iii. iii. Receptor-mediated Receptor-mediated endocytosisendocytosis allows the cell to allows the cell to take in very specific take in very specific molecules molecules (ligands) that pair up with (ligands) that pair up with specific specific receptors on the cell surface.receptors on the cell surface.

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iv. iv. TranscytosisTranscytosis combines combines endocytosis & endocytosis &

exocytosis.exocytosis.

a. Substance or particle a. Substance or particle crosses a cell.crosses a cell.b. Transcytosis is b. Transcytosis is

specific. specific. c. Examples c. Examples are discussed in are discussed in the the clinical connection p. 71clinical connection p. 71

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3.4 The Cell Cycle3.4 The Cell Cycle

A.A. The series of changes a cell The series of changes a cell undergoes is called the cell undergoes is called the cell cycle.cycle.

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B. The cell cycle consists of B. The cell cycle consists of interphase, mitosis, interphase, mitosis, cytokinesis, cytokinesis, and differentiation.and differentiation.

C. The cell cycle is highly regulated. C. The cell cycle is highly regulated. Most cells do Most cells do not divide continually. not divide continually. Cells have a maximum Cells have a maximum number of number of times they can divide because of times they can divide because of built-in “clocks” (telomeres) on the built-in “clocks” (telomeres) on the tips of tips of chromosomes.chromosomes.

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D. D. Interphase Interphase

1. Interphase is a period in 1. Interphase is a period in which the which the cell grows and synthesizes cell grows and synthesizes new new molecules and organelles.molecules and organelles.

2. During the S phase of 2. During the S phase of interphase, interphase, the DNA the DNA of the cell is of the cell is replicated in replicated in preparation for cell preparation for cell division.division.

3. During the G3. During the G11 and G and G22 phases phases

of of interphase, the cell grows and interphase, the cell grows and other other structures are duplicated. structures are duplicated.

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E. E. Mitosis Mitosis

1. In one type of cell division, 1. In one type of cell division, meiosis, four cells (sperm or meiosis, four cells (sperm or

ova) ova) are produced, each of which are produced, each of which contains half of the parent contains half of the parent

cell’s cell’s genetic information.genetic information.

2. Mitosis is division of the 2. Mitosis is division of the nucleus nucleus that results in each that results in each daughter cell daughter cell receiving an exact receiving an exact copy of the copy of the mother cell's genetic mother cell's genetic material.material.

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3. Mitosis is described as a 3. Mitosis is described as a series of series of fourfour stages, but the stages, but the process is process is actually continuous.actually continuous.

4. 4. Prophase Prophase results in the DNA results in the DNA condensing into chromosomes, condensing into chromosomes, centrioles migrating to the centrioles migrating to the

poles, poles, microtubules of the microtubules of the cytoskeleton cytoskeleton reorganizing into reorganizing into spindle fibers, and spindle fibers, and the disappearance the disappearance of the nuclear of the nuclear membrane.membrane.

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5. 5. MetaphaseMetaphase occurs as spindle fibers occurs as spindle fibers attach to centromeres on the attach to centromeres on the

chromosomes and the chromosomes and the chromosomes chromosomes align midway between centrioles.align midway between centrioles.

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6. 6. AnaphaseAnaphase occurs as the spindle fibers occurs as the spindle fibers contractand pull the sister chromatids toward contractand pull the sister chromatids toward

the centrioles.the centrioles.

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7. 7. Telophase Telophase begins when the chromosomes begins when the chromosomes have moved, then the nuclear envelope have moved, then the nuclear envelope reappears, and the chromosomes begin to reappears, and the chromosomes begin to unwind.unwind.

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F. F. Cytoplasmic DivisionCytoplasmic Division

1. 1. CytokinesisCytokinesis begins during begins during anaphase anaphase of mitosis and continues of mitosis and continues as a as a contractile ring pinches the contractile ring pinches the two two new cells apart.new cells apart.

2. The two daughter cells 2. The two daughter cells may have may have varying amounts of varying amounts of cytoplasm and cytoplasm and organelles, but they organelles, but they share share identical genetic identical genetic information.information.

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G.G. Cell DifferentiationCell Differentiation1. Process where different 1. Process where different types of types of cells with specialized functions are cells with specialized functions are created.created.2. Cell differentiation reflects genetic 2. Cell differentiation reflects genetic control of the nucleus as certain control of the nucleus as certain genes are turned on while others genes are turned on while others are are turned off.turned off. a.a. stem cells – unspecializedstem cells – unspecializedb.b. progenitor cells – partially progenitor cells – partially specializedspecialized

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H.H. Cell DeathCell Death

1.1. ApoptosisApoptosis is a form of is a form of cell death cell death that is a that is a normal normal part of part of development.development.

  

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Control of cell divisionControl of cell division

A. Cell division is limited and A. Cell division is limited and controlled by factors both internal controlled by factors both internal & external.& external.

ex. ex. Surface area-volume ratioSurface area-volume ratio

Growth factorsGrowth factors

HormonesHormones

B. Cancer is the loss of cell cycle B. Cancer is the loss of cell cycle controlcontrol

Topic of Interest p. 70Topic of Interest p. 70