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
permeable molecules
- O2
- CO2
- Lipids
- Small non polar molecules
selectively permeable
- Ions
- Polar molecules
- H2O and glucose
- Large molecules (proteins)
osmosis
water moves across a semi-permeable membrane in response to a concentration gradient
how does water move
from higher water concentration to lower water concentration
moves from lower solute concentration to higher solute concentration
osmolarity
number of particles in a solution
higher osmolarity
lower concentration in water molecules
molarity
number of molecules in a solution
aquaporins
water channels that water moves through in every cell
water follows higher ion concentration
lower water concentration
tonicity
osmolarity of any solutions surrounding a cell
ability of the surrounding solution to cause a cell to gain or lose water
hypotonic
too much water in the cell causes cell to swell and burst
plant cell: turgid or normal
isotonic
equal in both cell and solution
plant cell: flaccid
hypertonic
not enough water in the cell causes cell to shrivel and water leaves cell
plant cell: plasmolyzed
passive transport
no cell energy required
simple diffusion
passive transport
substances diffuse freely across the membrane from greater to lesser concentration
mediated diffusion
movement from greater to lesser concentration through open channels or other carrier proteins
rate depends on protein concentration
what deters passage of ions and polar molecules
hydrophobic fatty acid tails
what diffuses very slowly across the membrane
glucose, water and other small polar molecules
what diffuses extremely slowly
charged molecules
channel proteins
transport protein
- Hydrophilic channel that allows travel through membrane
- Often gated
- Aquaporins
carrier protein
transport protein
• Ligand binding induces shape-change and transport to other side
uniporter
transports one substance in one direction
symporter
transports two different substances in the same direction
antiporter
transports two different substances in opposite directions
Active transport
o Cell exerts energy
o Cells moves molecules AGAINST concentration gradient
o Always requires transport protein
primary active transport
against their conc gradient; ATP is used
secondary active transport
requires another concentration gradient
can membranes create gradients?
yes
o bc many materials can’t readily cross the membrane build up of material on one side or the other can occur
chemical and electrochemical gradient
gradients can be used in a variety of ways
• Accomplish secondary active transport
Create a gradient of Na+ in order to accomplish secondary transport of glucose
• Create communication
Neurons achieve communication by using electrical gradients
