Lecture 8-9 Flashcards
tight junctions
- act as seals to limit the loss of fluid and ions
- contain membrane proteins
- b/w adjacent cells
Desmosomes
- function as anchor points between cells. -
- Intermediate filaments of the cytoskeleton are important components of desmosomes
Gap Junctions
- linkage between the cytoplasmic compartments of two cells.
- Formed from proteins called connexons that form a ‘tube’ between cells.
- allows groups of cells to communicate
Plant Cell Structure
- mainly made of cellulose
- a thin primary cell wall.
- a middle lamella, which is sticky and made up of polysaccharides called pectins.
- as the plant matures, a thicker and less flexible set of secondary cell walls is layered. (is less flexible and can be quite rigid)
- cells linked by plasodesmata
for cells to function efficiently the cell surfaces and membranes must do 2 things
- MUST control what goes in and what comes out
1. control internal environment
2. control it’s interactions with extracellular environment
lipid bilayer
- are AMPHIPATHIC = have both hydrophobic and hydrophilic parts
- selectively permeable barrier that lets in nonpolar molecules because of nonpolar hydrophobic tails
- allows cell to maintain internal environment as well as separate and distinct chemical and structural environments
influences on membrane fluidity
- Structure:
- unsaturated = double bonds (liquid)
- saturated fatty acids = single bonds so tightly packed (solid) - amount of cholesterol (amphipathic) in membrane
- reduce fluidity - Temperature
- Cholesterol reduces membrane fluidity at 37C by reducing the movement of phospholipids.
- But at lower temperatures stops membrane from becoming too viscous by preventing the tight packing of the phospholipids
Transmembrane Proteins
- amphoteric = hydrophilic/phobic parts
- straddle across membrane
6 Functions of Membrane Proteins
- transport
- enzymatic activity
- signal transduction
- cell to cell recognition
- intercellular joining
- Attachment to cytoskeleton and extracellular matrix (EXM)
Isotonic, Hypotonic and hypertonic solutions
When comparing two solutions, the one with a higher concentration is hypertonic, the lower one hypotonic.
If they are the same concentration, they are isotonic.
Passive Transport
Diffusion: solution goes down a concentration gradient till reaches equilibrium
Osmosis
the movement of water along a concentration gradient and through a membrane that has limited permeability (a semi or selectively-permeable membrane) to one or more solutes.
Active Transport
- needs energy
- ATP is derived directly or indirectly by hydrolysis
- goes against conc. gradient
- is direction with 3 types: symport, antiport, and uniport
facilitated diffusion
is passive and needs a pathway
simple diffusion
can go straight through lipid bilayer
- High permeability = small non polar molecules
ex: O2, CO2, N2
- less permeable but still goes through = H2O and glycerol
channel proteins
- facilitated diffusion
- needs a channel to flow through
- are lined with polar (hydrophilic) amino acids. Nonpolar (hydrophobic) amino acids face the outside of the channel, toward the fatty acid tails of the lipid molecules
Carrier/Transport Proteins
- facilitated diffusion
- they specifically bind to the transported substance which allows selective transport
ex: glucose transport
ion channels
- channel proteins for diffusion
- gated and are open or closed
uniport transport
move 1 molecule against conc. gradient
symport transport
move 2 molecules but only one is going against conc. gradient
- coupled transport
antiport transport
move 2 molecules in opposite direction and both are against their conc. gradient
- coupled transport
ex: sodium potassium pump (Na+ out & K+ in)
Sodium Potassium Pump
- first part is the ion gated channel to bring in sodium
- second is antiport
- Na+ out & K+ in
- for each molecule of ATP used 3 Na+ pump out and 2 K+ in
Electrogenic Pump
- active transport
- Electrogenic pumps move ions against an ionic gradient and generate a voltage (potential) difference across the membrane
Cotransport
example of proton/sucrose cotransport
- movement of one ion/molecule that helps move another across the membrane
proton/sucrose transporter
- cotransport
- Electrogenic pumps can be used to help drive symporters such as the sucrose transporter by maintaining an ionic gradient
sodium/potassium pump
- symport of sodium and glucose from outside to inside cell
- sodium binds to Na/K pump
- when Na+ binds it stimulates phosphorylation of protein by ATP
- phosphorylation changes shape of protein to release Na+
- K+ binds to protein which releases the Ph group (dephosphorylates)
- by losing the Ph the protein returns to original shape
- K+ is released inside cell and cycle continues
Phagocytosis
allows food particles to enter cells using endocytosis
pinocytosis
uptake of extracellular fluid and solutes
receptor mediated endocytosis
A coated pit and a coated vesicle formed
during receptor-mediated endocytosis
(TEMs)
