Transport mechanisms Flashcards
What is the difference between the capillary wall and the cell membrane/plasma membrane?
The capillary wall separates the interstitial fluid and the plasma, and it surrounds all the vessels in the body. The cell membrane/plasma membrane surrounds all the cells in our body and is not always the same depending on the cell.
Are the following substances highly permeable, less permeable, or impermeable to the cell membrane?
H2O, larger molecules, very large molecules, O2, CO2, charged particles, small uncharged particles.
Highly permeable, less permeable, impermeable, highly permeable, highly permeable, less permeable, highly permeable
Describe the structure of the cell membrane.
It consists of an amphipathic phospholipid bilayer, with polar, hydrophilic heads facing towards the extracellular and intracellular fluid and nonpolar, hydrophobic tails pointing inwards.
What proportion of the plasma membrane’s weight do phospholipids comprise? Name 3 other components of it.
40-50%. It also consists of cholesterol, proteins, and glycocalyx.
What is the role of cholesterol in the lipid bilayer at normal temperatures?
At cooler, more physiological temperatures, it orients itself to separate the lipid tails. By reducing interactions between lipid tails, it resists the packing of the tails and their aggregation. This keeps the membrane more fluid than it would be otherwise. It can also be involved in the formation of vesicles and lipid rafts.
What is the role of cholesterol in the lipid bilayer at high temperatures?
It serves to stabilize the cell membrane and adds firmness.
Is cholesterol hydrophobic, hydrophillic, or amphipathic?
It is slightly amphipathic.
What types of proteins are found in the cell membrane? Explain where they are found.
Integral and peripheral proteins. Integral proteins span across the membrane (those that span all the way across are transmembrane proteins). Peripheral proteins are found mostly along the cytoplasmic side and are less strongly embedded.
Describe the difference between integral and peripheral proteins in terms of a) polarity, b) ease of removal
Integral proteins are amphipathic and are hard to remove without disrupting the membrane. Peripheral proteins are polar and are easier to remove.
What is the glycocalyx?
It is a layer of carbohydrate formed by a chain of monosaccharides that extrend from the extracellular surface of the cell membrane bound to proteins. It is also made of glycoproteins and glycoplipids.
Name 3 functions of the glycocalyx.
It provides protection from infection, enables cells to identify each other, and is a site of interaction between cells.
The model used to describe the structure of the cell membrane is called the _________.
Fluid mosaic model
Name 6 functions of plasma membrane proteins.
Selective transport channel,
Enzyme function to catalyze membrane reactions,
Cell surface receptor for chemical signals
Cell surface identity marker,
Cell adhesion,
Attachment to cytoskeleton.
What are the three main forms of transmembrane transportation? Which ones involve proteins?
Via the phospholipid bilayer, via interaction with a protein channel, or via a protein carrier. The latter 2 involve a protein cluster.
What are the two categories of transport mechanisms across the cell membrane? What is the difference between them?
Passive and active transport. Passive transport is energy independent, while active transport depends on an input of energy.
3 types of passive transport
Diffusion
Carrier-mediated facilitated diffusion
Osmosis
3 forms of active transport.
Carrier-mediated primary active transport
Carrier-mediated secondary active transport
Exo/endosytosis
What is simple diffusion?
It is the movement of molecules from one location to another as a result of random thermal motion.
What is flux?
The amount of particles crossing a surface per unit time.
What is net flux?
It is the movement of particles from high to low concentration.
At equilibrium after diffusion, what is the value of net flux?
Equal to zero because the net movement is equal in all directions.
If you have two compartments of equal size separated by a membrane and then put 20 mml/l of solution into one of them, what will happen?
Over time, the concentration between both will even out such that they both have a concentration of 10 mmol/l.
What does downhill mean?
It means movement from high concentration to low concentration (down the concentration gradient)
In the case of diffusion into a single cell from the surrounding extracellular fluid compartment, how do their respective concentrations change?
The concentration of the cell rises until it is equal to the extracellular concentration. The extracellular volume is so huge that it makes no difference to its concentration.