STEM CELLS EMBRYONIC STEM CELLS/INDUCED PLURIPOTENT STEM CELLS
CELLS
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Transcript of CELLS
CELLSCell Theory,
Microscopy,Prokaryotes, Eukaryotes, Animal Cell, Plant Cell
CELL THEORY1. All living things are composed of cells
and their products.
1. New cells are formed only by the division of existing cells.
1. The cell is the functioning unit of life; the chemical reactions of life take place within cells.
Microscopy
Compound light microscopes
Use visible light and a combination of lenses to magnify objects up to 1000 times.
Electron microscopesUse a beam of electrons, instead of light, to produce image
Transmission Electron Microscope (TEM)
• Extremely thin sections• Electrons pass through
some parts of specimen and not others, forming image
• Good for organelle structure
• Magnifies up to 250,000 times
TEM image
LE 6-41 µm
1 µm
Scanning electronmicroscopy (SEM) Cilia
Longitudinalsection ofcilium
Transmission electronmicroscopy (TEM)
Cross sectionof cilium
Scanning Electron Microscope• Scans sample with a
beam of electrons.
• Magnifies up to 100,000 times
SEM image
Advantages of light microscopes
• Easy, inexpensive sample preparation
• Allows examination of live material (movement; no artificial structures)
• Colors can be seen (natural and stains)
• Field of view is relatively large (1.8 mm at 100X magnification)
Advantage of electron microscopes• Excellent resolution, allowing for
extremely high magnification–This permits examination of very
small objects and details of cell structure
Prokaryotic Cells
Prokaryotic Cells (Bacteria)• Pro – before
• Karyon – nucleus
Prokaryote = Before Nucleus
Electron microscope views of prokaryotic cells
The outer layer has 2 parts• Cell wall – forms protective outer
layer which prevents damage from outside and bursting if internal pressure is high
• Plasma membrane – controls entry and exit of substances, some by active transport
CELLSEukaryotic Cells
Prokaryotic vs. Eukaryotic Cells• Cells are prokaryotic or eukaryotic• Prokaryotic cells are Bacteria• Protozoa, Fungi, Animals, and Plants
all consist of eukaryotic cells
Prokaryotic vs Eukaryotic Cells• Similarities
– Plasma membrane– Semifluid substance called the cytoplasm– DNA - Chromosomes (carry genes)– Ribosomes (make protein)
Differences• Prokaryotic cells have no nucleus• Prokaryotic cells lack membrane-bound organelles• Eukaryotic cells have DNA in a nucleus that is bound by a membrane
(nuclear envelope)• Eukaryotic cells have membrane-bound organelles
– Organelle: one of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells
LE 6-7
Total surface area(height x width xnumber of sides xnumber of boxes)
6
125 125
150 750
1
11
5
1.2 66
Total volume(height x width x lengthX number of boxes)
Surface-to-volumeratio(surface area volume)
Surface area increases whileTotal volume remains constant
• The plasma membrane is a selective barrier that allows passage of oxygen, nutrients, and waste
Plasma membrane must have sufficient surface area to service the volume of the cell
A Panoramic View of the Eukaryotic Cell
• A eukaryotic cell has internal membranes that partition the cell into organelles
• Plant and animal cells have most of the same organelles
LE 6-9aFlagellum
Centrosome
CYTOSKELETON
Microfilaments
Intermediate filaments
Microtubules
Peroxisome
Microvilli
ENDOPLASMIC RETICULUM (ER
Rough ER Smooth ER
Mitochondrion Lysosome
Golgi apparatus
Ribosomes:
Plasma membrane
Nuclear envelope
NUCLEUS
In animal cells but not plant cells: •Lysosomes•Centrioles•Flagella (in some plant sperm)
Nucleolus
Chromatin
LE 6-9bRoughendoplasmicreticulum
In plant cells but not animal cells:•Chloroplasts•Central vacuole•Cell wall•Plasmodesmata
Smoothendoplasmicreticulum
Ribosomes(small brown dots)
Central vacuole
MicrofilamentsIntermediatefilamentsMicrotubules
CYTOSKELETON
Chloroplast
PlasmodesmataWall of adjacent cell
Cell wall
Nuclearenvelope
NucleolusChromatin
NUCLEUS
Centrosome
Golgiapparatus
Mitochondrion
Peroxisome
Plasmamembrane
LE 6-29a
EXTRACELLULAR FLUID ProteoglycancomplexCollagen
fiber
Fibronectin
Integrin Micro-filaments
CYTOPLASM
Plasmamembrane
Extra-Cellular Matrix
MembranesStructure and Function
Plasma Membrane• Also known as “cell membrane”• Surrounds all cells
– In cells with cell walls, the plasma membrane is found inside the cell wall
plasma membrane is a bilayer of phospholipids
Phospholipid molecules have a hydrophilic region and a hydrophobic region
LE 7-2
Hydrophilichead
Hydrophobictail
WATER
WATER
•Most cells have watery environment on both sides of membrane•Water attracts the polar phosphate ends of the phospholipids•Phospholipids align to form double layer membrane, with polar ends on outside of each layer of the membrane•Non-polar tails are inside the bilayer
LE 7-3
Hydrophilic regionof protein
Hydrophobic region of protein
Phospholipidbilayer
LE 7-4
Knife
Cytoplasmic layerExtracellular layer
Cytoplasmic layer
Plasmamembrane
Extracellular layer
Proteins
Membrane Proteins
• A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer
• PeripheralPeripheral proteins are not embedded, they are attached to the membrane surface
• IntegralIntegral proteins penetrate the hydrophobic core and often span the membrane
LE 7-7
Fibers ofextracellularmatrix (ECM)
Glycoprotein
Carbohydrate
Microfilamentsof cytoskeleton
Cholesterol
Integralprotein
Peripheralproteins
CYTOPLASMIC SIDEOF MEMBRANE
EXTRACELLULARSIDE OFMEMBRANE
Glycolipid
LE 7-5c
CholesterolCholesterol within the animal plasma membrane
Functions of Membrane Proteins
• Proteins determine most of the membrane’s functions. They serve as:
1. Hormone binding sites2. Enzymes3. Cell–Cell joining & Communication4. Channels for passive transport5. Pumps for active transport
Transport across the plasma membrane Remember…..
The plasma membrane controls what comes in and out of the cell.
Selective Permeability• Most biologic membranes are
selectively or semi-permeable–This means that they allow some
things through, but not others
Permeability• If substance CAN diffuse across
membrane, membrane is permeable to that substance
• If substance CANNOT diffuse across membrane, membrane is impermeable to the substance
One Way that Some Substances can Cross the Membrane is by Diffusion
• Definition of diffusion:–Movement of particles from area
where they are more concentrated to area where they are less concentrated
• Diffusion is the tendency for molecules to spread out evenly into the available space.
• Substances diffuse down their concentration gradient, that is, from an area where they are more highly concentrated to an area where they are less concentrated.
Diffusion, cont’d.
LE 7-11a
Molecules of dye Membrane (cross section)
WATER
Net diffusion Net diffusion Equilibrium
Diffusion of one solute
LE 7-11b
Net diffusion Net diffusion Equilibrium
Diffusion of two solutes
Net diffusion Net diffusion Equilibrium
Diffusion, cont’d.• Diffusion across plasma membrane
is a form of passive transport, because no work must be done to move substances down the concentration gradient– Passive Transport: transport across
the membrane that requires no energy from the cell.
Diffusion, cont’d.• Hydrophobic, non-polar molecules can
dissolve in and cross a membrane unassisted.– Hydrocarbons– CO2
– O2
Animation: Diffusion
Facilitated Diffusion
• Diffusion of some other substances across the cell membrane is assisted, or “facilitated,” by protein channels within the membrane
• Usually involves large or strongly charged molecules, which cannot dissolve in the lipid bilayer.
Facilitated diffusion• Even though movement is facilitated, it
will still only occur from region of high concentration to region of low concentration.
• Facilitated diffusion is still PASSIVE transport
Examples of molecules moving via facilitated diffusion
• Some ions and polar molecules (e.g. water)
• Aquaporins are channel proteins which greatly speed up the diffusion of water.
Animation: Membrane Selectivity
Osmosis
• DefinitionDefinition: diffusion of water across a selectively permeable membrane
• Water diffuses down its own concentration gradient, which is affected by solute concentration.
• Binding of water molecules to solute particles lowers the proportion of unbound water that is free to cross the membrane.
Osmosis and water balance in cells, parts 1 and 2
LE 7-12Lowerconcentrationof solute (sugar)
Higherconcentrationof sugar
Same concentrationof sugar
Selectivelypermeable mem-brane: sugar mole-cules cannot passthrough pores, butwater molecules can
H2O
Osmosis
• IsotonicIsotonic solution: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
• HypertonicHypertonic solution: solute concentration is greater than that inside the cell; cell loses water
• HypotonicHypotonic solution: solute concentration is less than that inside the cell; cell gains water
Tonicity is the ability of a solution to cause a cell to gain or lose water
Solutions inside and outside cell are isotonic
10% salt, 90% H2O
10% salt 90% H2O
Solution outside cell is hypertonic to that inside cell
20% salt, 80% H2O
10% salt 90% H2O
20% salt, 80% H2O
Salt sucks.
Solution outside cell is hypotonic to that inside cell
5% salt, 95% H2O
10% salt, 90% H2O
Salt sucks.
Osmotic Pressure
• Created when water diffuses into a cell
• In animals and other organisms without cell walls, cells swell and may burst
• To maintain their internal environment, organisms without cell walls must have adaptations for osmoregulation, the control of water balance
• The protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump
Osmotic Pressure in Cells without Walls, cont’d.
LE 7-14Filling vacuole
50 µm
50 µmContracting vacuole
Video: Paramecium Vacuole
Osmotic Pressure in Cells without Walls, cont’d.• Plasmolysis occurs when water
diffuses out of a cell• Cells shrink
Osmotic Pressure in Cells with Walls
• Cell walls help maintain water balance
• In a hypotonic solution, turgor pressure causes the cell to swell until the wall opposes uptake; the cell is now turgid (firm)
Video: Turgid Elodea
Osmotic Pressure in Cells with Walls, cont’d.• If a plant cell and its surroundings are
isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt
• In a hypertonic environment, plant cells lose water (plasmolysis); vacuoles collapse, and eventually, the membrane pulls away from the wall.
Video: Plasmolysis
Plasmolysis in Red Onion Cells
Cells in hypotonic solution; water has diffused into cells, creating turgor pressure
Cells in hypertonic solution; water has diffused out of cells, causing them to shrink away from their cell walls
Plasmolysis in Cucumber Cells
Cells in pure water environment; water has diffused into cells, creating turgor pressure
Cells in hypertonic environment; water has diffused out of cells, causing them to shrink away from their cell walls
LE 7-13
Animalcell
Lysed
H2O H2O H2O
Normal
Hypotonic solution Isotonic solution Hypertonic solution
H2O
Shriveled
H2OH2OH2OH2OPlantcell
Turgid (normal) Flaccid Plasmolyzed
Osmosis and water balance in cells, parts 3 and 4
Active Transport• Involves movement of substances
across the cell membrane from area of LOWER concentration to area of HIGHER concentration
• Since movement is against the concentration gradient, it REQUIRES ENERGY from the cell
Active Transport using Membrane Protein “Pumps”
• Active transport of small molecules and ions is usually carried out by membrane proteins that act as energy-requiring pumps
• Changes in the shape of these membrane proteins play an important role
Activity – Active Transport
Active Transport by Endocytosis and Exocytosis
• Endocytosis – Requires Energy!– Materials taken into the cell by means of
infoldings or pockets of the cell membrane– Pocket breaks loose and forms vacuole
within the cytoplasm– Vacuole may fuse with a lysosome, so
material in vacuole can be digested
• http://bio.winona.msus.edu/bates/genbio/images/endocytosis.gif
Exocytosis – Requires Energy!• Way for cell to release large amount of
material from a vacuole to outside of cell
• Membrane surrounding the vacuole fuses with cell membrane
• Contents of vacuole expelled out of the cell
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/endocytosis.gif
Activity – Endocytosis and Exocytosis