Chapter 3: Cells – The Living Units
A. Characteristics of cells
1. Background into cell theory a. Spontaneous generation 1) Early theory of origin of life
b. Virchow (1832-1902): cells came from other cells c. Pasteur (1822-1895): disproved theory of spontaneous generation
2. Cell’s small size is functionally significant
a. If cell is too large, not enough diffusion will occur across membrane to support the cell
b. Surface area with x2, volume with x3
B. Membranes
1. Surround:
a. Cell: plasma membrane
b. Nucleus: nuclear envelope
c. Several organelles
2. Organization of lipid bilayer
a. Components of membrane
1) Lipids (phospholipids, cholesterol) 2) Proteins
3) Carbohydrate-containing groups
b. Phospholipids arranged in particular fashion
1) Hydrophobic tails of both layers face each other
2) Hydrophilic heads face “out” towards water
c. Components arranged in fluid-mosaic model
1) Phospholipids move freely from side to side
2) Proteins:
a) Some float around relatively freely
b) Others are held in place by cytoskeleton
d. Proteins of plasma membrane
1) Integral proteins (embedded in membrane)
2) Peripheral proteins (do not extend into membrane)
3) Serve a variety of functions
a) Receptors
b) 2 messengers
c) Chemical deactivator
d) Transport (channels/carriers)
e) Cell recognition
4. Plasma membrane has extension
a. Microvilli
1) Means to surface area
2) Absorptive or sensory function
b. Cilia and flagella
1) In respiratory and reproductive systems 2) Have the capacity to move (motor proteins) C. Cellular structure
1. Organelles
a.
b.
c.
d.
“Little organs”
Provides division of labor
One of the components of the cytoplasm
Differences in types and #s of organelles among cells
2. Examples:
a. Nucleus
1) Contains genetic material 2) Provides basis for cellular functions
b. Endoplasmic reticulum (ER)
1) 2 types of ER
a) Smooth ER (lacks ribosomes)
(1) Functions in:
(a) Lipid production
(b) Detoxification
(c) Storage
a. Rough ER (ribosomes on surface)
1) Regenerates membranes
2) Produces proteins
c. Golgi complex
1) Processing-plant of cell
2) Alter and package proteins from ER
d. Lysosomes
1) Digestive system of the cell
2) Contains digestive enzymes from ER
e. Mitochondria
1) “Powerhouse” of the cell
2) Involved in production of ATP
f. Proteinaceous rods of cell
1) Composed of protein subunits
2) 3 types of proteinaceous structures
a) Microfilaments
b) Intermediate filaments
c) Microtubules
3) Perform a number of different functions:
II. Membrane transport
A. Plasma membrane is selectively permeable
1. Prohibits free passage of all substances
2. Selective due to hydrophobic/hydrophilic nature
B. Passive movement of substances
1. Does not directly require energy (ATP)
2. Filtration
a. Due to hydrostatic pressure (fluid pressure) b. Fluid passes through fenestrations and intercellular clefts
3. Simple diffusion
a. Movement due to energy of motion (kinetic energy)
b. Net movement down [ ] gradient
1) From [ ] to [ ]
2) Reaches equilibrium
c. Membrane is semi-permeable (selectively permeable)
1) Lipid-soluble substances may pass
a) Nonpolar/hydrophobic
b) O2, steroids
2) Lipid-insoluble substances are unable to pass
a) Polar/hydrophilic
b) Water, electrolytes
4. Osmosis
a. Diffusion of water
1) Passes through selectively permeable membrane
2) H2O passes from [ ] to [ ]
b. Filtration and osmosis drives fluid movement through
capillaries
