Lecture 6: Membranes Flashcards
is the membrane fluid?
yes; phospholipids can move laterally within the membrane
membrane molecules
o Proteins are 2nd most common molecule in the membrane and impart most of the function
o Carbohydrate chains also “tag” cells for cell-cell recognition
o Cholesterol: helps maintain fluidity
Membrane proteins
o Proteins are the 2nd most common type of molecule in the membrane
o 25% of all genes encode for transmembrane proteins
o membrane proteins participate in transporting cell signaling, secretion, cell recognition, metabolism and cell-cell contact
integral proteins
transmembrane, span the membrane
peripheral proteins
are on one side of the membrane
fluid mosaic model
o Proteins can float around in the membrane but cannot flip from one side to the other
Transport proteins
help molecules move through membrane
enzymatic proteins
accelerate chemical reactions on cell surface; anchored to the cell’s surface
receptor proteins
bind to chemical signals from the extracellular environment
recognition proteins
often have a name that starts with CD, which “tag” different types of cells and aid in communication (a
extracellular matrix
o Cells taken out of the body and cultured in dishes
• Started to change when taken out of the body
• Developed different features
outside matrix that holds the cells together
unique to animal cells
how is the ECM formed
cells secrete protein fibers into extracellular fluid, weave together to form matric
functions of ECM
provides strength and rigidity to tissues
o Organize cells, allow them to move or stay in place
o Provide signals to cells to guide function or development
o Cells are able to crawl using ECM
significance of the ECM
- some scientists believe that ECM is actually the functional unit of the body
- arthritis, infection/inflammation, heart disease and some cancers are all probably ECM diseases
why is the ECM important
o To little: arthritis o Too much: astherosclerosis o Changes in: cancer o Useful in: infection o Boil animal tissues and cells degrade; ECM is left and concentrated: gelatin and glue
Plasma membrane
o Separates the cell’s internal environment from external
o Selectively permeable
o Controls entrance and exit from the cell
o Layer of non-polar lipids between two aqueous environments
Diffusion
movement of molecules from an area of greater concentration to an area of lesser concentration
passive process
continues until molecules is in dynamic equilibrium
concentration gradient
areas of higher and lower concentration of a given molecule
equilibrium
no concentration gradient
why do molecules move at all?
o Brownian motion and kinetic energy
o As they move around they bounce off of each other
when does diffusion occur faster?
- Concentration gradient is greater
- Distance is shorter
- Temp is higher
- Molecules are smaller
lipophilic
nonpolar molecules and can diffuse across the membrane
lipophobic
polar molecules and cannot simply diffuse across the membrane
membrane “permeability”
o Membrane is selectively permeable
o Completely permeable to nonpolar/lipophobic molecules
o Selectively permeable to polar, there are ways of getting across, but the membrane can control movement
