Untitled Flashcards Set
What is a Plasma Membrane
Separates Living cytoplasm from non-living environment
Is a selectively permeable barrier
Fluid-Mosaic Model
Model composed of lipids with proteins and carbohydrates embedded in them
Membrane lipids are mostly phospholipids in a biliary
Lipids are in a fluid state
Fatty acids are mostly unsaturated (cis)
Membrane proteins free to float in lipids
What does it mean when we say lipids and proteins are Amphipathic?
Have both hydrophilic and hydrophobic regions
What are the two predictions that lead to the fluid mosaic model?
Prediction 1: Fluidity
If the membrane is fluid → proteins should be able to move in the plane of the membrane
Experiment: Have two different cells (human and mouse), and label the different species of dyes. Fuse the cells and you should see them moving around
Conclusion: Proteins can move laterally in the plane membrane
Prediction 2: Independent Movement
Membrane proteins are discrete particles → should be able to move independently of each other
Experiment: Combine e-microscopy with freeze-fracture to image membrane proteins
What affects Membrane fluidity?
Varies with temperature
Colder=less fluid
What is a transition temperature (Tm):
The temperature at which the membrane undergoes fluid-to-solid phase change
Tm is affected by the lipid content of the membrane
Saturation level of Lipids
More kinks mean = Unsaturated
More fluid membrane
Lower Tm
Cholesterol in Membrane: What does it do?
Cholesterol reduces membrane fluidity at moderate temperatures, but at low temperatures hinder solidification
It interacts with hydrophobic tails and alters interactions with adjacent fatty acids
Has one polar region that faces out and core hydrophobic embedded within the membrane bilayer
Integral Membrane Proteins: What are they?
Penetrate the hydrophobic core of the membrane
Can be removed ONLY by dissociating the membrane
Can either by partially embedded in the bilayer
Or can span the entire membrane → Transmembrane
Define Transmembrane Proteins:
Proteins that pass all the way through the membrane
Amphipathic
Anchored Membrane Proteins
Ex. GPI-anchored proteins: a way for lipid attachment to a protein
Covalently attached to lipids that insert into membrane
No Hydrophobic transmembrane domains
What does a GPI-anchored protein do?
A type of anchored membrane protein that is a way of attachment to a protein
Peripheral Membrane Proteins:
Loosely binds (noncovalently) to integral proteins or lipids
Attach to either membrane surface
Can be removed w/o destroying the membrane
Different on each side of the membrane
Function on only one side of the membrane
Glycosylation:
Monosaccharides or polysaccharide added covalently to membrane proteins or lipid in rough ER and Golgi
Glycosylated polypeptide
Glycoprotein
Glycolipid
Glycolipid
What is the function of Membrane Carbohydrates?
Defense: recognition of self from nonself
Immune
Protection: Cell lining of GI, Respiratory, and Reproductive tracts
Cell Sorting during embryogenesis
Functions of Membrane Proteins:
Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix
Membrane Transport
Selective Permeability and regulated transport create and maintain different environments across a cell membrane.
When does membrane transport Stop?
At equilibrium: point at which forward and backwards rxns occur at same time
What is Selective Permeability?
Membrane lipids allow passage to some but also limit passage to others
Selective permeability: Hydrophobic Molecules:
O2, CO2, N2, Benzene
Pass through the membrane
Selective permeability: Small Uncharged Polar Molecules:
H2O, urea, glycerol
Have limited diffusion, do so slower
Selective permeability: Large Uncharged Polar Molecules:
Glucose and sucrose
Very limited and cannot easily pass through the membrane
Selective permeability: Ions
H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+
Not able to pass through due to their charged nature
Protein channels
Hydrophilic pores
Have some specificity but no stable binding to individual solute molecules
Allow rapid movement of ions and water
Millions or billions of transported per second
Protein Carrier
Specific binding of solute
Requires a conformational change
Hundreds or thousands of transported per second
What Determines Direction of Transport?
No energy needed → passive transport
If energy need → Active transport
What is Passive Transport?
Spontaneous and increases entropy
Solute moves from higher concentration to lower concentration
Towards opposite charge
What is Active transport:
Non-spontaneous
Used to concentrate solutes by pumping them from lower to higher concentration
OR forcing ions to be near others of the same charge
Electrochemical Gradient
Combined effects of concentration and charge
Osmosis
Passive movement of water across a membrane is called osmosis
To balance different solute concentrations, water moves across the membrane
What are the special water uses?
Aquaporins
Isotonic
The solution around cell has the same solute concentration as the inside the cell
Equilibrium
Hypotonic
Solution around cell has a lower solute concentration than inside the cell
Net movement of H2O is INTO the cell
Hypertonic:
The solution around cell has a higher solute concentrtaiton than inside the cell
Net movement OUT of the cell
Facilitated Diffusion
Passive transport aided by proteins
Both channels and carriers
Passive no energy, increases entroypy, spontaneous, has almost zero activation energy Ea
When channels maybe “Gated” to control transport
Ligand Gated
Electrically gated
Mechanically gated
Types of gated Channgels for facilitated Diffusion
Ligand Gated
Can change the proteins shape to activate it
Electrically gates
Mechanically gated
Cotransport
Some transport protein move more than one substance at a time
Can be Passive or Active
Type 1: Symport
Multiple solutes in same direction
Type 2: Antiport
Multiple solutes in different directions
What type of transport proteins do Active Transport?
Only: carriers or pumps
Never: Channels
Channel Protiens
Routs for passive diffusion along a gradient, not pumps
Primary Active Transport:
Energy usually from ATP hydrolysis, is used to pump something across a membrane to a region of [higher] (concentration)
Primary = that protein doingt the transport
Primary Active Cotransport:
ATP hydrolysis can provide teh energy to actively more TWO Substances
Can be in same or different directions
Can be symporters or Antiports
Na+/ K+ ATPase Pump
Sodium potassium pump that is feuled my ATP
One pump actively sends Na+ to outside, K+ inside
3 Na+ for every two 2 K+
Type of Antiporter
Secondary Active Cotransport
Uses ATP hydrolysis to transport one ion into an ion gradient
Stores portiential energy cna drive the active transport of another solute with a separate contransport protein
Central ot both mitochondrial respiration and photosynthesis
Example of Secondary Active Cotransport
Common mechanism for transporting sugars and Amino Acids into cells
Without Na+/K+ pump, Na+/glucose cotransporter couldn’t work.
Difference between Transport of small and large molecules
Large: Bulk transport
Small: Diffusion or transporters
Bulk Transport
Larger molecules such as proteins and polysaccharides move by Bulk Tranport
Types: Exocytosis or Endocystosis
Exocytosis:
Secretion
Release of material out of the sell
Endocytosis
Mechanism for bringing material into the cell (Uptake of Material)
“Reverse of exocytosis”
Three types
Phagocytosis
Pinocytosis
Receptor-meditated endocytosis
Phagocytosis
Type of Endocytosis
Cellular Eating
Cells engulf a particle into a vesicle
Surround particals with the membrane and bring into cell → food vacuole
Pinocytosis
Type of Endoxytosis
Cellular drinkimg
Gulp of fluid is takin into vesicles
nonspecific uptake of soluble materials (not visible/not obvious)
Anyhting dissolved outside of the cell; such as water or ions the cells may need
Receptor-meditated endocytosis
Type of endoxytosis
Used to bring in specific molecules
Ligands bind to specific receptors
Causes a coated vesivle with a coated pit of specidc ligand bound to receptor
Trasnderred to lysosome for digestion
Ex, Hormones