Chapter 7 - Membranes Flashcards
Peripheral proteins
Found on the surface of the membrane
Integral proteins
Found in the interior of the plasma membrane
Hydrophobic regions (tails)
Found inside the membrane
Hydrophilic heads
Found on the outside of the membrane
Fluid mosaic model
The membrane of the cell is filled with fluid and the mosaic piece is due to the various proteins it contains
There’s a phospholipid bilayer (double)
What does the fluidity of the membrane mean for the proteins?
They can shift about laterally rapidly(but rarely if ever are transverse)
Selective permeability
The ability of a membrane to regulate what comes in and out
It not only keeps the structure of a cell intact, but also enables the cell to carry out various functions
How does the steroid cholesterol (fat) affect the plasma membrane in animal cells?
At high temps, it makes the membrane less fluid by restraining the phospholipid movement
It inhibits close packing of the phospholipids, it lowers the temperature of the membrane to solidify.
Therefore it’s called the fluidity buffer.
What role do the lipids and proteins play in the membrane?
The lipids create the structure in the fluid mosaic model and the proteins determine function of the membrane
What are the six functions of the plasma membrane proteins
- Transport -hydrolyze ATP for this purpose
- Enzymatic activity - serve as a metabolic pathway
- Signal transduction - relays messages through the membrane
- Cell-cell recognition - glycoproteins serve as ID tags
- Intercellular Joining - membrane proteins of adjacent cells combine and form junctions between each other (either gap or tight junction)
- Attachment to the cytoskeleton and ECM - micro filaments/cytoskeleton may be non-covalently bound to membrane proteins
What’s the structure of a transmembrane protein?
There’s an N-terminus end which is found on the extra cellular side
There’s an alpha helix structure found on the inside of the cell and on the cytoplasmic side, there’s a C-terminus end
What are amphipatic molecules?
Molecules that have both polar and non-polar regions (both hydrophobic and hydrophilic)
What is the singer and Nicholson model of the PM?
The fluid mosaic model
They proposed that proteins had a hydrophilic region that sticks out of the membrane and a hydrophobic region inside the membrane
Describe the characteristics of a saturated fat:
The hydrocarbon tails are densely packed making the membrane less fluid (more viscous); and there’s only a single bond between the carbons
What links a hydrophilic head to a hydrophobic tail?
An ester linkage
What’s the structural difference between a triacylglycerol and a phospholipid?
Trias have a carboxyl functional group and phospholipids have phosphate group that had an ester linkage to the hydrocarbon tails
How would a cell adapt to colder temperatures?
It would increase the number of unsaturated fats which would also make the cell more fluid, so that’s it’s not solid during the winter
High temperatures would create lipids that reduce the fluidity of their membranes
Glycolipids
Glucose covalently bonded to lipids
Crucial for cell-cell recognition
Glycoproteins
Glucose covalently bonded to protein
Plays a role in cell-cell recognition
An example is blood type which is different glycoproteins found on the surface of red blood cells
Which nonpolar molecules can dissolve in the hydrocarbon (hydrophobic) portion and easily pass through the membrane?
Oxygen
CO2
Hydrocarbons
The hydrophobic portion impedes which molecules?
Ions and polar molecules since they’re hydrophilic
Transport proteins
Enable specific ions and polar molecules to pass through the membrane easily
These are also called channel proteins
Channel proteins
Have a hydrophilic channel that ionized and polar molecules use to get in and out of the cell
Aquaporins
Channel proteins that allow up to three billion water molecules pass through its channel
Carrier proteins
Hold onto their passengers and change shape to shuttle them across the membrane
Diffusion
The movement of molecules of any substance so that they spread out evenly into the available space
If you add dye to the outside of a cell, the dye diffuses from where there is more of it, to less of it until an equilibrium is reached
Doesn’t require energy
Concentration gradient
The region of which the density of a chemical substance increases or decreases
An example is when a cell uptakes oxygen via cellular respiration
Passive transport
Passive transport
Doesn’t require energy to make it happen
Osmosis
The diffusion of water across a selectively permeable membrane
Water diffuses across a membrane from the area of lower solute concentration to higher solute concentration until it’s equal
How is glucose transported across the PM?
A specific carrier protein carries it into the cell
Ie red blood cells refuse fructose and accept glucose 50,000 times faster than it can happen on its own
Tonicity
The ability of a surrounding solution to cause a cell to gain or lose water
Dependent on part of its concentration of solutes that cannot cross the membrane
If there’s a higher concentration of non-penetrating solutes in the surrounding solution, water will tend to leave the cell, and vice versa
Isotonic
Means the inner environment of the cell and the outer environment of the cell are equal - no net water movement will take place
Water moves in and out, but at equal rates, so no change takes place
Hypertonic
More solute on the outside of the cell than inside so cell loses water and shrivels (and probably die)
Ie increased saltiness of a lake = animals dying
Hypotonic
Less water in a cell than out so water enters into a cell faster than it leaves and the cell will swell and burst
Osmoregulation
The control of solute concentrations and water balance when a cell is in a hypertonic or hypotonic environment
Ie protist paramecium lives in hypotonic pond water; to adapt, it’s PM is much less permeable to water than the membranes of other cells
It also has a contractile vacuole that forces water out as fast as it enters
How do plants and Protists compensate for hypotonicity?
They have a cell wall that maintains the cell’s water balance
It expands to a certain point and then exerts back pressure on a cell called turgor pressure which makes the cell turgid (very firm)
This is the healthy state for most plants
Flaccid
Limp plant that occurs from an isotonic environment
Plasmolysis
The process of the membrane pulling away from the cell wall in a plant in a hypertonic state causing it to shrivel and potentially die
Facilitated diffusion
Hydrophilic transport/channel proteins help polar molecules and ions pass through the cell
Ion channels
Channel proteins that transport ions
Gates channels
Ion channel proteins that open or close in response to an electrical stimulus
Carrier proteins
Use passive transport by undergoing a subtle change in shape that somehow translocates the site across the membrane
They result in the bet movement of the concentration gradient so no energy is needed
Passive
If someone is missing this carrier protein in the kidneys, certain amino acids aren’t transported out and crystallize causing painful stones
Active transport
Uses energy to pump a solute across a membrane against its gradient
Only transport proteins do this
Sodium potassium pump
Active transport
Pumps ions against steep concentration gradients
Na+ is high outside the cell and low inside while the K+ concentration is low outside and high inside.
ATP powers transport proteins to change shape by transferring a a phosphate group to them and takes 3 Na+ out for every 2K+ pumped into the cell
Membrane potential
All cells have voltage (electrical potential energy)
The cytoplasmic side is negative relative to the extra cellular side due to an unequal distribution of anions/cations
This voltage = -50 - -200 millivolts
Because the inside of the cell is negative, it favors cations in and anions out
Electrochemical gradient
The two forces that drive diffusion of ions across a membrane:
A chemical force (the ion’s concentration gradient)
And an electrical force (the membrane potential)
Electrogenic pump
A transport protein that generates voltage across a membrane
Sodium potassium pump is the electrogenic pump in animal cells because it’s moving three ions out for every two in giving the cell a slightly positive charge
Proton pump
The electrogenic pump for plants, fungi, and bacteria
It actively pumps H+ out of the cell
Cotransport
A single ATP powered pump that transports a specific solute that indirectly drives the active transport of several other solutes in a mechanism
Plants use the gradient hydrogen ions generated by proton pumps to drive active transport of nutrients into the cells
Exocytosis
When the cell secretes molecules by the fusion of vesicles with the plasma membrane (as in the GA to the PM)
When the vesicle membrane and the plasma membrane come into contact, specific proteins rearrange the lipid molecules to make the membranes fuse
Used in the pancreas that make insulin secrete it into the extra cellular fluid
Endocytosis
Molecules coming into the cell take part of the PM via vesicle
Three types:
Phagocytosis (cell-eating)
Pinocytosis (cell-drinking)
Receptor mediated Endocytosis (used in human cells to take in cholesterol for membrane synthesis and the synthesis of other steroids)
Phagocytosis
Cell eating
Cell engulfs a particle by wrapping pseudopodia around it and packaging it in a good vacuole
This food vacuole then fuses with a lysosome that digests the particle
Pinocytosis
Cell drinking
The cell “gulps” droplets of extra cellular fluid into vesicles
It doesn’t need the fluid, but the solutes inside the fluid
Ligands
A term for any molecule that binds specifically to another receptor site of another molecule
Receptor mediated Endocytosis
Binding of ligands to receptors triggers vesicle formation
What makes unsaturated fat more fluid than saturated fat?
The kinks in the double bonds (in the hydrocarbon tails) make it so they’re not as densely packed together making it more fluid.
