miércoles, 20 de abril de 2011

cell membranes

fluid mosaic model

mixed composition of phospholipids, glycolipids, sterols and proteins.



transport proteins

either passively let specific solutes diffuse through a membrane spanning channel in their interior or actively pump them through.


receptor proteins:
 bind extracellular substances.

recognition proteins:
that are unique identity tags for each species.



adhesion proteins:
help cells of the same type locate each other and remain in the proper tissues.


communication proteins:
form channnel that match up across the plasma membranes of two cells.



concentration gradient:
is a difference in the number per unit volume of molecules (or ions) of a substance between two adjoining regions.


diffusion:
is the name for the net movement of like molecules or ions down a concentration gradient.


electric gradient:
is a simply difference in electric charge between adjoining regions.


pressure gradient:
is the difference in pressure exerted  per unit volume between two adjoining regions. 



passive transport:
a concentration gradient, electric gradient, or both drive diffusion of a substances across a cell membrane.


active transport:
energy-driven protein motors help a particular kind of solute cross a cell membrane against its concentration gradient.


osmosis:
is the diffusion of water across a selectively permeable membrane.


hypotonic solution:
is the one with fewer solutes.


hypertonic solution:
one having more solutes.


isotonic solutions:
show no net osmotic movement.


hydrostatic pressure:
against the wall or membrane that contains it.


osmotic pressure:
any fluid is one measure of the tendency of water to follow its water concentration gradient and move into that fluid.

endocytosis:
A small patch of plasma membrane, ballons inwards and pinches off inside of the cytoplasm.



exocytosis:
 a vesicle moves to the cell surface, and then the protein-studded lipid bilayer of its membrane.

miércoles, 13 de abril de 2011

CELL STRUCTURE AND FUNCTION

 NUCLEOID:
a region of the cytoplasm that is not enclosed in a membranous sac.


 LIPID BILAYER:
 oily boundary that prevents the free passage of water-soluble substances across it.


 WAVELENGTH:
is the distance from the peak of one wave to the peak behind it.


.ELECTRON MICROSCOPES:
 use magnetic lenses to bend and diffract beams of electrons, which cannot be diffracted through a glass lens.




 TRANSMISSION:
electron microscopes, electron pass through a specimen and are used to make images of its internal details.





 SCANNING:
 electron microscopes direct a beam of electrons back and forth  across a surface of a specimen.






 ORGANELLES:
 membrane-bounded sac.




SECRETORY PATHWAY:
moves new polypeptide chains from some ribosomes through ER and GOLGI bodies.



 ENDOCYTIC PATHWAY:
moves ions and molecules into the cytoplasm.




 VESICLES:
tiny sacs that act likes taxis and moves substances from one organelle to the next in line.





 NUCLEAR ENVELOPE:
is a double-membrane system in which two lipid bilayer are pressed against each other.



 CHROMATIN:
 as the cell´s collection of DNA and all proteins associated with it.




 CHROMOSOME:
is a double-stranded DNA molecule and its associated proteins.




 PEROXISOMES:
hold enzymes that digest fatty acids, amino acids, and hydrogen peroxide, a toxic metabolic product.





 CELL JUNCTIONS:
are molecular structures where a cell sends or receives signals or materials.




 BASAL BODY:
barrel shaped structure that produces and organizes microtubules into the 9+2 array.




PSEUDOPODS:
or "FALSE FEET"