cell theory
- a cell the structural and functional unit of life
- structures and functions are complementary
- continuity of life has celluar basis
substance that acts as glue to hold cells together
extracellular matrix
acts as an active barrier separating intracellular fluid (ICF) from extracellular fluid (ECF)
plasma membrane
structure of plasme membrane
- consists of membrane lipis that form a flexible bilayer
- surface sugars form glycalyx
- membrane structures help to hold cells together through cell junctions
Lipid bilayer is made up of:
- 75% phospholipid which consists of two parts; phosphate heads are hydrophilic (water lovers), and fatty acid tails are hydrophibic (water haters)
- 5% glycolipids
- 20% cholesterol
Two types of membrane proteins:
- Integral proteins
- Peripheral proteins
Intergral proteins
- firmly inserted into membrane
- most are transmembrane proteins
- have hydrophilic and hydrophobic region which hydrophilic interacts with water and hydrophobic interacts with lipis tails
- function transport proteins, enzymes, or receptors
Peripheral proteins
- loosely attached to intergral proteins
- include filaments on intracellular aurface used for plasma membrane for support
- functions as enzymes, motor proteins (for shape change), and cell-to-cell connections
Membrance proteins performing many tasks:
a.) transport:
b.) receptors:
c.) enzymatic activity:
d.) cell-to cell regonition:
e.) attatchment to the cytoskelrton and extracellular matrix (ECM)
f.) cell-to-cell joining
cell junctions
- some cells are “free” (not bound to any other cells)
- most cells are bound together to form tissues and organs
The three ways cells can be bound to each other:
1.) tight junctons
2.) desmosomes
3.) gap junctions
- intergral proteins on adjacent cells fuse to form an imperable junction that encircles whole cell
- prevent fluids and mose molecules from moving betwen cells
tight junction
rivet-like cell jucntion formed when linker proteins (cadherins) of neighboring cell interlock like the teeth of a zipper
desmosomes
transmembrane proteins (connexons) form tunnels that all small molecules to pas from cell to cell
gap junctions
Structure of Plasme Membrane
the plasme membrane is selectively permeable allowing certain molecules to cross
Two essential ways substancs cross plasme membranes
1.) Passive transport: no energy is required
2.) Active transport: energy (ATP) is required
Three types of passive transport
1.) simple diffusion
2.) facilitated diffusion
3.) osmosis
very small molecules that can pass through membrane or membrane channel
- ex: oxygen, fatty acid, carbon dioxide
simple diffusion
larger or non-lipid souble or polar molecules can cross membrane but inly with assistance of carrier molecules
facilitated diffusion
is special name for movement of solvent (usuallu water), not molecules
osmosis
- channels with aqueous-filled cores are formed by transmembrane proteins
- two types: leackage channels (always open), and gated channels (controlled by chemical or electrical signals
channel-mediated facilitated diffusion
measure the concentration of the total number of solute particles in solvent
osmolarity
outward pressure exerted on cell side of membrane caused by increase in volume of cell due to osmosis
hydrostatic pressure
inward pressure due to tendency if water to be “pulled into a cell with higher osmolarities
osmostic pressure
