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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
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
• 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
• 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
• 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
• Composed of protein and RNA
• May be free in the cytoplasm or attached to ER
• Function:– Involved in protein
synthesis
Ribosomes
• Stack of flattened membranes
• Function:– Package and transports
proteins from the cell
Golgi apparatus
• “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
• Small sacs from the Golgi apparatus
• Contains enzymes capable of breaking down breaking down nutrients or toxins
• Function:– Digestion
Lysosomes
• Tiny sacs formed by the cell membrane folding in and pinching off
• Function:– Intake or excretion of
large materials (endocytosis and exocytosis)
Vesicles
• Tiny rods usually arranged in meshes or bundles
• Function:– Involved in cell
movement– Provides structure to
the cell
Microfilaments and
Microtubules
• Fine, long, threadlike organelles protruding from the cell surface
• Function:– Cell movement
Cillia and Flagella
• 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
Passive Transport
• Movement of a material into or out of a cell without the use of energy.– Diffusion– Osmosis– Facilitated diffusion
– *** NO ENERGY REQUIRED***
• 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
• 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
• 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
• 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
• The forcing of permeable molecules through a membrane by hydrostatic pressure– Example: Blood pressure
Filtration
• The movement of molecules against a concentration gradient using cellular energy and carrier molecules– Proton pump– Sodium-potassium pump
Active Transport
***ENERGY REQUIRED***
• 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
• 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
• Interphase– Period
“Inbetween” cell division
– Majority of cell’s life• Cell growth• Protein synthesis
Cell cycle
• Cell division that Is Mighty Common
• Makes all cells EXCEPT gametes (reproductive cells)
• DNA is doubled then– Cells divide once
Mitosis
• Cells Prepares to divide
• Chromatin condenses into chromosomes
• Nuclear membrane disappears
Prophase
• Cell “Tears” in two• Nuclear membrane reforms• Chromosomes disperse into
chromatin• Cytokinesis (cytoplasmic
division) (separate phase?) – Produces 2 identical “daughter
cells”
Telophase
• 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