cells
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Cells. Why are cells so tiny?. Larger cells do not function as efficiently The surface is the only way cells interact with the environment Surface-area-to-volume ratio As cell size increases, volume grows much more rapidly. Cell Theory. Schleiden and Schwann Three principles - PowerPoint PPT PresentationTRANSCRIPT
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• Larger cells do not function as efficiently– The surface is the only way cells interact with the
environment– Surface-area-to-volume ratio• As cell size increases, volume grows much more rapidly
Why are cells so tiny?
Cell radius (r) Surface area (4πr2) Volume ((4/3)πr3)
1 units 12.57 units2 4.189 units3
10 units 1,257 units2 4,189 units3
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Cell Theory• Schleiden and Schwann• Three principles– All living things are composed of cells– Cells are the smallest living things (Functional units of the body)– Cells come from pre-existing cells
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• Prokaryotes – Lack a nucleus and
membrane bound organelles
– MUCH smaller than eukaryotes
– Bacteria
• Eukaryotes – Have a nucleus and
organelles– Much bigger than
prokaryotes
Cell Types
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• Cell membrane– Semi-permeable
• Cytoplasm— “cell blood”– Fluid matrix surrounding
nucleus– Surrounded by a cell
membrane• Nucleus— “cell brain”– Contains chromatin (loosely
coiled DNA)
Cell Organelles
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• Interconnected membranes forming canals and flattened sac-like spaces
• Functions:– Communications system– Rough ER: studded with
ribosomes • Involved in protein synthesis
– Smooth ER: has no ribosomes• Involved in synthesizing lipid
Endoplasmic reticulum
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• Composed of protein and RNA
• May be free in the cytoplasm or attached to ER
• Function:– Involved in protein
synthesis
Ribosomes
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• Stack of flattened membranes
• Function:– Package and transports
proteins from the cell
Golgi apparatus
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• “Cell powerhouse”• Contains its own DNA– Capable of self-reproduction
• Composed of 2 membranes• Contains enzymes used in cell
respiration• Function:– Produce ATP for cellular energy
(cell respiration)
Mitochondria
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• Small sacs from the Golgi apparatus
• Contains enzymes capable of breaking down breaking down nutrients or toxins
• Function:– Digestion
Lysosomes
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• Twin hollow cylinders (centrioles)
• Function:– Involved in cell division
Centriole
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• Tiny sacs formed by the cell membrane folding in and pinching off
• Function:– Intake or excretion of
large materials (endocytosis and exocytosis)
Vesicles
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• Tiny rods usually arranged in meshes or bundles
• Function:– Involved in cell
movement– Provides structure to
the cell
Microfilaments and
Microtubules
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• Fine, long, threadlike organelles protruding from the cell surface
• Function:– Cell movement
Cillia and Flagella
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nucleus
smooth ER
lysosomeGolgi
apparatus vesicles
centrosome
mitochondria
flagella
rough ER
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• Selectively permeable (semi-permeable)– Allows some substances in, excludes others
• Composed of phospholipid bilayer (containing cholesterol) and protein inclusions– Fat soluble molecules pass through the lipid part– Water soluble molecules must move through
protein component • Pores, channels or receptors
Cell Membrane
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Passive Transport
• Movement of a material into or out of a cell without the use of energy.– Diffusion– Osmosis– Facilitated diffusion
– *** NO ENERGY REQUIRED***
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• The process by which molecules move down a concentration gradient– Move from area where there is more
concentration to areas that are less concentrated
– Rate limited by concentration
Diffusion
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• Diffusion using special carrier molecules to allow usually non-permeable molecules to pass through a selectively permeable membrane– Example: Insulin facilitates glucose movement
• Rate of passage is limited by the number of carrier molecules and concentration
Facilitated Diffusion
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• The diffusion of water through a selectively permeable membrane which may not allow dissolved substances to pass
• May result in changing volumes on either side of the membrane
• Osmotic pressure– The amount of pressure needed to stop osmosis
Osmosis
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• Hypertonic– A solution which has a greater concentration
of solute particles than a given cell or solution
• Hypotonic– A solution which has a lesser concentration
solute particles than a given cell or solution
• Isotonic– A solution which has an identical concentration
of solute particles to a given cell or solution
Concentration Types
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• The forcing of permeable molecules through a membrane by hydrostatic pressure– Example: Blood pressure
Filtration
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• The movement of molecules against a concentration gradient using cellular energy and carrier molecules– Proton pump– Sodium-potassium pump
Active Transport
***ENERGY REQUIRED***
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• Endocytosis– The inward movement of
molecules through a membrane by infolding and pinching off vesicles• Pinocytosis: taking in tiny
droplets of liquid• Phagocytosis: taking in solid
material• Receptor Mediated:
molecule bonds with receptor protein
• Exocytosis
Bulk Passage
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• Prokaryotes– Binary fision• DNA replicated in parent • Parent divides• Fast
• Eukaryotes– Mitosis• Complicated• Lots of DNA
– Form chromosomes (compact structures, composed of DNA and histone proteins, that can be manipulated easily during cell division
Cell division
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• Interphase– Period
“Inbetween” cell division
– Majority of cell’s life• Cell growth• Protein synthesis
Cell cycle
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• Cell division that Is Mighty Common
• Makes all cells EXCEPT gametes (reproductive cells)
• DNA is doubled then– Cells divide once
Mitosis
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• Cells Prepares to divide
• Chromatin condenses into chromosomes
• Nuclear membrane disappears
Prophase
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• Chromosomes line up in the Middle
• Spindle Apparatus stretches from pole to pole
Metaphase
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• Sister chromatids move Away to opposite poles
Anaphase
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• Cell “Tears” in two• Nuclear membrane reforms• Chromosomes disperse into
chromatin• Cytokinesis (cytoplasmic
division) (separate phase?) – Produces 2 identical “daughter
cells”
Telophase
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• Process by which cells develop different characteristics in structure and function
• Differences in outcome– Directed by cell’s DNA– Determined by cell’s
position in the body and its chemical environment
Cell differentiati
on
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