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Chapter 3Chapter 3

Cells

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Introduction:A. Human body consists of 75 trillion cells that vary in shape & size yet have much in commonB. Differences in cell shape make different functions possible

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A Composite Cell:

A. includes many different cell structuresB. main parts: nucleus, cytoplasm, cell membraneC. specialized organelles perform specific functions for the cell

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D. Cell Membrane1. regulates movement of substances in & out of the cell, participates in signal transduction, helps cells adhere to other cells

2. General Characteristics a. extremely thin & selectively

permeableb. complex surface w/ adaptations to

increase surface area

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3. Cell Membrane Structure: a. phospholipid bilayer, fatty acids tails turned inwardsb. lipid soluble molecules can pass through c. embedded cholesterol molecules add strength & make the membrane less permeable to water-soluble substancesd. many types of proteins are found in the cell membrane, including transmembrane & peripheral membrane proteins

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

i. receptors on the cell surfaceii. aid the passage across

membrane

iii. carbohydrates attached for cell ID

iv. cellular adhesion molecules help determine cell interactions

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E. Cytoplasm:1. clear liquid = cytosol, a supportive cytoskeleton, networks of membranes & organelles

a. Endoplasmic reticulum (ER)- made up of membranes, flattened sacs, & vesicles. Provides a tubular transport system inside the cell

i. Rough = has ribosomes, functions in protein synthesis & transport

ii. Smooth = no ribosomes functions in lipid transport

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b. Ribosomes - found w/ RER or scattered throughout the cytoplasm, composed of protein & RNA, provide structural support for the RNA molecules that come together in protein synthesisc. Golgi apparatus - composed of flattened sacs; refines, packages, modifies, & delivers proteins

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

ii. Vesicles then move to cell membrane & secrete its contents to the outside

iii. Vesicles form a “delivery service”, carrying materials throughout

the cell

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d. Mitochondria - powerhouses of the cell, contain enzymes needed for aerobic respiration

i. make ATPii. more active cells have more

mitochondria

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e. Lysosomes - "garbage disposals" of the cell; contain digestive enzymes to break up old cell components & bacteria.

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

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g. Microfilaments & microtubules are thin, threadlike structures that serve as the cytoskeleton of the cell

i. Microfilaments: made of actin

ii. Mictotubules: made of the globular protein tubulin h. Centrosome - made up of two hollow centrioles; function in the separation of chromosomes during cell division

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i. Cilia & flagella - motile extensions from the cell; shorter cilia are abundant on the free surfaces of certain epithelial cells (ex:respiratory linings) cause movement of substances across the surface of the cell and a lengthy flagellum can be found on sperm cells

j. Vesicles form part of the cell membrane or the Golgi/ER and store materials

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F. Cell Nucleus:1. bounded by a double-layered

nuclear membrane w/ relatively large nuclear pores that allow the passage of certain substances

a. Nucleolus: inside the nucleus, composed of RNA & protein; site of ribosome production, doesn’t have a membraneb. Chromatin consists of loosely coiled fibers of protein & DNA

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Movements Through Cell Membranes

A. Passive: no energy

1. diffusion2. facilitated diffusion3. osmosis4. filtration

B. Active: cellular energy (ATP) 1. active transport

2. endocytosis3. exocytosis

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C. Passive Mechanisms 1. Diffusion

a. caused by the random motion of molecules along the concentration gradient, from greater to lesser concentration until equilibrium is

reached

b. enables O2 & CO2 exchange btwn air & blood in the lungs, & btwn blood & tissue cells

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2. Facilitated Diffusiona. membrane proteins function

as carriers to move molecules (glucose) across the cell membrane

b. the # of carrier molecules in the cell membrane limits the rate of this process

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3. Osmosis a. diffusion of water from greater water concentration (less osmotic pressure) to lower water concentration (greater osmotic pressure)

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

c. Compared to bodily fluids, a solution with i. the same osmotic pressure is isotonic ii. higher osmotic pressure is

hypertoniciii. lower osmotic pressure is hypotonic

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4. Filtration

a. Because of hydrostatic pressure, molecules can be forced through membranes by the process of filtration.

ex. Blood pressure in the kidneys

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D. Active Mechanisms1. Active Transport a. Uses ATP to move molecules from low to high concentration through transport proteins in cell membranesb. Up to 40% of a cell's energy may be used to fuel this process to get needed materials or eliminate wastesc. Actively transported substances include: sugars, amino acids, Na+, K+, Ca+2, H+, & nutrient molecules in the intestines

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2. Endocytosis & Exocytosisa. Endocytosis - molecules too large to be transported by other means are engulfed by an invagination of the cell membrane & carried into the cell surrounded by a vesicleb. Exocytosis is the reverse of endocytosisc. 2 forms of endocytosis

i. Pinocytosis - cells engulf liquids

ii. Phagocytosis - cells engulf large particles (WBC eat bacteria)

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The Cell CycleA. series of changes a cell undergoes

from the time it is formed until it reproduces

B. interphase, mitosis, cytokinesis, and differentiation

C. Highly regulated, most cells do not divide continually. Cells have a maximum number of times they can divide because of built-in “clocks” (telomeres) on the tips of chromosomes

AnimationsAnimations

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Cell CycleCell Cycle

http://www.cellsalive.com/cell_cycle.htm

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E. Mitosis/Meiosis 1. Meiosis, four cells, gametes (sperm/ova) are produced, each of which contains half of the parent cell’s genetic information2. Mitosis is a carefully orchestrated division of the nucleus of the cell that results in 2 daughter cells receiving an exact copy of the mother cell's genetic material

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D. Interphase 1. a period of great metabolic activity in which the cell grows & synthesizes new molecules and organelles2. S phase: the DNA is replicated in preparation for cell division3. G1 & G2 phases: of interphase, the cell grows & other structures are duplicated

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3. Mitosis is described as a series of 4 stages, but the process is continuous

4. Prophase: DNA condenses into chromosomes, centrioles migrate to the poles, microtubules of the cytoskeleton reorganize into spindle fibers, & the nuclear envelope disappears

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5. Metaphase: spindle fibers attach to centromeres on the chromosomes & chromosomes align midway btwn centrioles6. Anaphase: spindle fibers contract & pull sister chromatids apart

7. Telophase: chromosomes have completed their migrations making 2 identical groups, nuclear envelopes reappear, chromosomes begin to unwind

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F. Cytoplasmic Division1. Cytokinesis begins during anaphase of mitosis & continues as a contractile ring pinches the two new cells apart

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

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G. Cell Differentiation1. Process by which cells develop into different types of cells with specialized functions.2. reflects genetic control of the nucleus as certain genes are turned on while others are turned off

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H. Cell Death 1. Apoptosis is a form of cell death that is a normal part of development

Cancer – uncontrolled cell divisionMetastasis – cancer spreads