cells: chapt. 4
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Cells: Chapt. 4. Two Basic Types of Cells. Prokaryotes: prounounced: pro-carry-oats Eukaryotes Proun: you-carry-oats. A. Prokaryotes. Small, simple cells (relative to eukaryotes) Size: about 1 µm (1 micron) No internal membrane-bounded organelles No nucleus Simple cell division - PowerPoint PPT PresentationTRANSCRIPT
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Cells: Chapt. 4
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Two Basic Types of Cells
• Prokaryotes:– prounounced: pro-carry-oats
• Eukaryotes– Proun: you-carry-oats
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A. ProkaryotesSmall, simple cells (relative to eukaryotes)Size: about 1 µm (1 micron)No internal membrane-bounded organellesNo nucleusSimple cell division
Contain the; 1. true bacteria & 2. archaebacteria
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1. True Bacteria = Eubacteria
• Majority of bacteria
• Examples include: E. coli, Lactobacillus (yoghurt), Lyme disease
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Eubacteria
•Peptidoglycan cell walls (carbos & AA)
•Separated into Gram + and - forms
Text pg. 58
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Bacteria in the Environment
A) An acid hot spring in Yellowstone is rich in iron and sulfur. B) A black smoker chimney in the deep sea emits iron sulfides at very high temperatures (270 to 380 degrees C).
example: Iron utilizing Baceria
A B
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2. Archaebacteria
• Live in extreme environments: high salt, high temps
• Different cell wall• Very different
membrane lipids• Unusual nucleic acid
sequence
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Archaea types: Based on their physiology, Archae can be organized into three types:
• Methanogens (prokaryotes that produce methane); • Extreme halophiles (prokaryotes that live at very
high concentrations of salt (NaCl); • Extreme (hyper) thermophiles (prokaryotes that
live at very high temperatures).
All archaea have features that distinguish them from Bacteria (i.e., no murein in cell wall, ether-linked membrane lipids, etc.). And, these prokaryotes exhibit unique structural or biochemical attributes which adapt them to their particular habitats.
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B. Eukaryotes• Bigger cells: 10-100 µm• True nucleus• Membrane-bounded
structures inside. Called organelles
• Divide by a complex, well-organized mitotic process
Liver Cell 9,400x
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Eukaryotes
• Larger more complex cells that make up most familiar life forms: plants, animals, fungi, algae
• Surrounded by a cell membrane made of lipids
• Text pg 60-61
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The Cell Theory
• Cells first observed by R. Hooke 1665• Named for the Monk prayer cells• Cell Theory states that;
1. All life is composed of cells2. Cells are the basic units of life
3. Cells arise from already existing cells
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Cells are typically Small
Typical cell size
•Text pg. 56
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Why are Cells Small?• Cells must exchange gases & other
molecules with environment…• Nutrients in, Wastes out• As size increases, the rate of diffusion
exchange slows down….• This is due to the ratio of surface area to
volume
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Surface Area to Volume
• Cell surface area is important in taking in nutrients
• Sfc area increases as the square of cell diameter
• But… entire cell volume needs to be fed• And, cell volume increases as the cube of
cell diameter
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Consider 2 Cells...
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Surface Area to Volume Cell Radius (R)
5 µm 50 µm Surface Area
(4πr2) 314 µm2
31,400 µm2
Volume (4/ 3πr3)
524 µm3
524,000 µm3
Surf ace Area to Volume Ratio
0.6
0.06
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The Eukaryotic Cell: Components
• Outer cell membrane composed of lipids and proteins
• Cytoplasm: interior region. Composed of water & dissolved chemicals…a gel
• Numerous organelles….
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Organelles• Specialized structures
within eukaryotic cells that perform different functions...
• Analogous to small plastic bags within a larger plastic bag.
• Perform functions such as :– protein production (insulin,
lactase…)– Carbohydrates, lipids…
• Text pg 60-61
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Organelles of Note:The Nucleus• Contains the genetic
material (DNA), controls protein synthesis.
DNA --> RNA --> Protein• Surrounded by a double
membrane with pores• Contains the
chromosomes = fibers of coiled DNA & protein
• Text pg. 62
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Chromosomes
All Chromosomes from a single cell
One chromosome Pulled apart
A single chromosomeShowing the amount of DNA within
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Mitochondria• Generate cellular energy in the form
of ATP molecules• ATP is generated by the systematic
breakdown of glucose = cell respiration
• Also, surrounded by 2 membrane layers
• Contain their own DNA!• A typical liver cell may have 1,700
mitoch.• All your mitoch. come from
your mother..• Text pg. 68
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Chloroplasts
• Found in plants, algae and some bacteria. Responsible for capturing sunlight and converting it to food = photosynthesis.
• Surrounded by 2 membranes
• And…contain DNA• Text pg. 69
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Ribosomes• Size ~20nm• Made of two subunits
(large and small)• Composed of RNA and
over 30 proteins• Come in two sizes…
80S and 70S• S units = Sedimentation
speed
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Ribosomes• DNA --> RNA --> Protein• The RNA to Protein step
(termed translation) is done on cytoplasmic protein/RNA particles termed ribosomes.
• Contain the protein synthesis machinery
• Ribosomes bind to RNA and produce protein.
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Endoplasmic Reticulum = ER
• Cytoplasm is packed w. membrane system which move molecules about the cell and to outside
• An internal cellular subway system
• Outer sfc of ER may be smooth (SER)
• Or Rough (RER) • ER functions in lipid and protein
synthesis and transport
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Golgi Complex• Stacks of membranes…• Involved in modifying
proteins and lipids into final form…– Adds the sugars to make
glyco-proteins and glyco-lipids
• Also, makes vesicles to release stuff from cell
• Text pg. 66-67
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ER to Golgi network
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Lysosomes • important in breaking down
bacteria and old cell components• contains many digestive
enzymes• The ‘garbage disposal’ or
‘recycling unit’ of a cell• Malfunctioning lysosomes result
in some diseases (Tay-Sachs disease)
• Or may self-destruct cell such as in asbestosis
• Text pg 67
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Cytoskeleton• Composed of 3 filamentous
proteins:Microtubules
MicrofilamentsIntermediate filaments
• All produce a complex network of structural fibers within cell
• Text pgs. 72-76The specimen is human lung cell double-stained to expose microtubules and actin microfilaments using a mixture of FITC and rhodamine-phalloidin. Photo taken with an Olympus microscope.
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Microtubules• Universal in eukaryotes• Involved in cell shape,
mitosis, flagellar movement, organelle movement
• Long, rigid, hollow tubes ~25nm wide
• Composed of and ß tubulin (small globular proteins)
• Text pg. 72
http://www.cytochemistry.net/Cell-biology/
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Microfilaments• Thin filaments (7nm
diam.) made of the globular protein actin.
• Actin filaments form a helical structure
• Involved in cell movement (contraction, crawling, cell extensions)
• Text pg. 72
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Intermediate filaments• Fibers ~10nm diam.• Very stable,
heterogeneous group• Examples:Lamins: hold nucleus shapeKeratin: in epithelial cells Vimentin: gives structure to
connective tissueNeurofilaments: in nerve
cells Text pg. 72
Image of Lamins which reside in the nucleus just under the nuclear envelope
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Cell Motility:Flagella & Cilia
• Both cilia & flagella are constructed the same
• In cross section: 9+2 arrangement of microtubules (MT)
• MTs slide against each other to produce movement
• Text p 74
Human Sperm: TOTO-3 iodide for DNA (blue) and Nile red for membrane lipid (red)
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How Flagella Move a Cell
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Possible Origins of Eukaryotic Cells
Infolding of outer membranes Uptake of prokaryotes
• Text pg 70
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Endosymbiosis• Theory that eukaryotic cells arose from an
early prokaryote (1) engulfing a second, smaller prokaryote (2)
• The internalized #2 was not digested but became a symbiote.
• Today’s mitochondria & chloroplasts may have arisen this way
• Text pg. 70
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Evidence for Endosymbiosis
• Double membrane around both organelles• Both organelles have their own DNA• Both organelles have smaller (70S)
ribosomes…• Both organelles divide by simple fission