#2 BIOLOGY 18th DEC 06 -THE CELL

Cell Theory

• Basic functional unit of life
• Arise only from pre-existing cells
• Carry genetic information in the form of DNA( passed from parent cell to daughter cell)
• [All living things are composed of cells]

All cells come from pre-existing cells

SIZE Conversion

1 cm = 10 mm
1mm = 1000 um(micrometers)
1um = 10,000 A (angstrom units)
1 Angstrom = 1.0 x 10^-10m = 0.1nm = 100pm

Eukaryotic cells ~ 10um
Mitochondria ~ 1 um
Bacteria ~ 1um
virsues ~ 0.1 um
macromolecules ~ 0.01 um
molecules ~ 0.001 um
Hydrogen ion ~ 0.0001 um

Resolution
Ability to discriminate two points and visualize them as 2.
Resolving power: Human eye ~ 0.1mm
Light microscope ~ 0.2 um
Electron microscope ~ 2-5 A
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General structure of Membranes in Cells
- Plasma membrane ( serves as the permeability barrier between the cell and its environment)
- Eukaryotic cell contains membranes that separate different compartments within the cell(consist of phospholipid bilayers with associated proteins)

PASSIVE TRANSPORT
Mechanisms Moving Molecules Across Cell Membranes:
a. Simple Diffusion
- Net movement of particles from a region of higher concentration to a region of lower concentration
- No Energy required
Osmosis- simple diffusion of water from a region of lower solute concentration(hypotonic --> Swell & Burst) to a region of higher solute concentration(hypertonic --> Shrink). Isotonic - Same total solute concentration
Etc: Water, Oxygen, carbon Dioxide

b. Facilitated Diffusion
- Net movement of particles down their concentration gradient with the help of carrier molecules.
- No Energy Required
Etc: Channel/ uniporter carrier (usually proteins)
-demonstrates saturation kinetics( increasing the graident beyond a pt causes no further increase in transport)

ENERGY- REQUIRING TRANSPORT
a.Active transport
Net movement of particles against their concentration gradient with the help of transport proteins
-carrier consumes Energy
- ETC : Required to maintain membrane potentials in specialized cells such as neurons
b.Endocytosis
- Process whereby the cell membrane engulfs extracellular material, moves it into the cell, and forms membrane- bound vesicles [low density lipoprotein (LDL)]
-Phagocytosis - Engulfing of large particles (bacterium/organic matter)
-Pinocytosis - Ingestion of fluids or small particles
c. Exocytosis
-reverse of endocytosis
- vesicle within the cell fuses with the cell membrane and relseases its contents to the outside.

***[[Animation of Endocytosis ]]***
*Note that in both endocytosis & exocytosis, the material never actually crosses through the cell membrane
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Prokaryote Vs Eukaryote in a nut shell:
1) Cell wall present in all prokaryote vs Cell wall present in fungi and plants only
2) unicellular (Bacteria) vs unicellular(protistans) or Multicellular ( fungi,plants)
3) no Nucleus vs Nucleus
4)Ribosomes(Subunit = 30S &50S) vs Ribosomes (Subunit 40S& 60S)
5) No membrane-bound organelles vs Membrane- bound organelles
* Plant cells have no centrioles
Prokaryote
- plasma membrane lacks glycolipids and cholesterol
-Flagella are used for locomotion.

[- Pili - hollow protein tubes that attach bacteria to surfaces and transfer DNA btw cells during conjugation
- capsule or slime layer consisting of polysaccharide gel to protect against host defense mechanisms
- Gram- Positive bacteria have a cell wall with thick layer of petidoglycans(sugars + amino acids)
-Gram -Negative bacteria are surrounded by a more complex wall structure consisting of a thin layer of petidoglycans surrounded by lipoplysaccharide and protein.] - Add INFO from Microbiology

Eukaryote organelles:

-* Fluid Mosaic Model + Diagram of a Eukaryotic Cell
- Transport Proteins - membrane spanning molecules that allow certain ions & polar molecules to pass through the lipid bilayer
-Cell adhesion molecules (CAMs) - proteins that contribute to cell recognition and adhesion (important during development)

a.Nucleus - Controls the activities of the cell
- Surrounded by a nuclear membrane

b.Ribosomes - Sites of protein production and are sythesized by the nucleolus
- Consist of 2 subunits

c.Endoplasmic Reticulum - RER(rough ER with ribosomes lining its outer surface)
- SER (Smooth ER without ribosomes)
- General:transport of materials throughout the cell
-Smooth : involved in lipid synthesis and detoxification of drugs and posions
- Rough: involved in protein syntehsis

d. Golgi apparatus - stack of membrane- enclosed sacs
- receives vesicles and their contents from smooth ER, modifies them.
- Secretory vesicles produced by Golgi release their contents to the cell's exterior via exocytosis.

e.Vesicles/ Vacuoles - membrane-bound sac involved in the transport and storage of materials

f. Lysosomes - membrane- bound vesicles that contain hydrolytic enzymes involved in intracellular digestion
Autolysis - "self-destruction" through the release of the hydrolytic enzyems(PH 5)
g. Microbodies -
1)Peroxisomes : contain oxidative enzymes that catalyze a class of reactions in which hydrogen peroxide is produced.Peroxisomes break fats down, used in the liver to detoxify compounds harmful to the body.

2)Glyoxysomes: found in fat tissue of germinating seedlings. Used to convert fats into sugar.

h. Mitochondria - sites of aerobic respiration & suppliers of energy
- inner membrane has many convolutions : cristae
- semiautonomous : contain their own DNA(circular) and ribosomes which enables them to produce some proteins and self- replicate by binary fission.

i.Cytoskeleton - gives the cell mechanical support, maintains its shape, functions in cell motility.
- Tubulins (Microtubules), Cilia, actin(Microfilaments)
*Note: Not all cells have the same rleative distribution of organelles.
Etc: Sperm cells: Mitochondria
Pancreatic cells: Golgi bodies (secretion)
RBC : no organelles (transport)