the cell is the smallest unit of life. all organisms are composed one or more cells. new cells arise...
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• The cell is the smallest unit of life.
• All organisms are composed one or more cells.
• New cells arise from previously existing cells.
Basic Cell Structure
Each cell has four common components:1. Plasma membrane2. Region containing DNA3. Cytoplasm 4. Biochemical molecules & biochemical
pathways
Fluid mosaic model:
• Working model of the membrane
• Protein molecules bobbing in phospholipid sea
• Proteins determine membrane’s specific functions
Phospholipids
• Most abundant lipid
• Polar/hydrophilic head(attracted to water)
• Pair of nonpolar/hydrophobic tails(repelled by water)
Hydrophilic head
Hydrophobic tails
Polar heads, outside & inside
Nonpolar tails in the interior cell membranes
Hydrophilic head
phospholipid
Hydrophilic head
Hydrophobic tail
outside
inside
Microvilli- intestinal cells
Membrane Junctions
Tight junctions Desmosomes Gap junctions
Selectively permeable- allows certain substances to pass through
By 2 ways: active or passive transport
Passive- downhill
Active- uphill (needs energy)
Passive: downhill reaction• Simple diffusion• Osmosis• Facilitated diffusion• Filtration
Active: uphill reaction, needs ATP• Exocytosis• Endocytosis
- Pinocytosis- Phagosytosis
No Barrier:
• Substances “spread out”
• High concentration to low concentration
e.g.: Red dye placed in glass of water
• Substances diffuse
• High concentration to low concentration
• Pores in membrane must be large
• “Down the concentration gradient”
• Dynamic equilibrium, equal rates in both directions
Biological membrane:
Osmosis- diffusion of a water through a semi-permeable membrane
• Moves down concentration gradient
e.g., Two sugar solutions of different concentrations separated by porous membrane which lets water through but not sugar
What will happen?
Concentration of solute less: solution is hypotonic.
Concentration of solute greater: solution is hypertonic.
Animal cells No cell walls
Isotonic environment: Influx of water equals the efflux of water No change in cell shape
Hypotonic solution: Water enters cell Bursts, or lyses
Hypertonic solution: Water leaves cell Shriveled, or crenate
Glomerular filtration
DOES require the input of
ATP
Transport proteins AGAINST concentration
gradient
outside cell
inside cell
mucus
http://www.1lecture.com/Physiology/Endocytosis%20and%20Exocytosis/index.html
Goblet cell
Nerve Axon at Rest
Na+/K+ Pumphttp://www.1lecture.com/Biochemistry/cotransport/
H+ Pump in a Plant
• Ion channels - Voltage gated- Chemically gated- Mechanically gated
• Porins - Larger - Less specific
• Aquaporins - water
Channel Proteins
Channel Proteins:Porins
• MAC• Barrel shaped protein
Membrane Permeability
Cell membrane:
selectively permeable
4 factors that determine permeability lipid solubility
molecular size
polarity
charge
1
2
3
4
Lipid solubility Most important factor
Hydrophobic molecules Passively diffuse Hydrocarbons, carbon dioxide, & oxygen
Molecular Size and Polarity
Larger molecules, less permeable Lower kinetic energy Small pore sizes in the membrane
Polar molecules hydrophilic, less permeable Very small, polar uncharged (water) molecules can diffuse
-+
Molecular Size
Polarity
Charge
Charged molecules hydrophilic, less permeable Surrounded by coat of water (hydration shell), increases the size
• Rid body of toxic substances• Contains enzymes that can oxidize
various organic substances
Liver cell
• Centriole pair• Assemble
microtubules• Assist in cell
division• 9 clusters of
microtubule triplets
Figure 3.23c
(c) MicrotubulesHollow tubes of spherical protein
subunits called tubulins
25 nm
Tubulin subunits
Microtubules appear as gold networkssurrounding the cells’ pink nuclei inthis photo.
INQUIRY
1. Define isotonic, hypotonic, and hypertonic. 2. What % saline is a cell?3. Distinguish between active and passive
transport.4. What is the function of:
• Mitochondria• Nucleus• Golgi apparatus• Lysozome• Ribosomes• Smooth and rough ER
Cellular Visions: The inner life of a cell (video)http://www.studiodaily.com/main/searchlist/6850.html