Week 6 Application Questions Flashcards
- The following is a definition of plasma or cell membrane according to “Henderson’s Dictionary of
Biology” (2016):
“A membrane bounding the surface of al living cells, formed of a fluid lipid bilayer in which proteins carry out the function of enzymes, ion pumps, transport proteins and receptors are embedded. It regulates the entry and exit of most solutes and ions, few substances being able
to diffuse through the lipid bilayer unaided.”
a. The SARS- CoV-2 virus is covered by a lipid bilayer with embedded peripheral and integral proteins (Fig. 1) produced by an infected cell’s ER. So far some of the integral proteins have been identified and ion channels but no ion pumps have been identified yet. The function of the (viral) bilayer is to protect the RNA inside the virus and facilitate cell entry.
Aside from the fact that a virus might or might not be alive, would you consider this a plasma/cell membrane?
Why or why not?
Plasma membrane (e.g. Bacteria)
Lipid bilayer: yes
Peripheral and integral membrane proteins: yes
Protects inside: yes
Ion channels: yes
Ion pumps: yes
Maintains stable inner environment: yes
SARS-CoV-2
Lipid bilayer: yes
Peripheral and integral membrane proteins: yes
Protects inside: yes
Ion channels: yes
Ion pumps: no
Maintains stable inner environment: no
The virus does not have its own metabolism (energy conversions), cannot produce ATP, Does not have active transport mechanisms, only passive ones
- The following is a definition of plasma or cell membrane according to “Henderson’s Dictionary of
Biology” (2016):
“A membrane bounding the surface of al living cells, formed of a fluid lipid bilayer in which proteins carry out the function of enzymes, ion pumps, transport proteins and receptors are embedded. It regulates the entry and exit of most solutes and ions, few substances being able to diffuse through the lipid bilayer unaided.”
b. Why is washing your hand with soap or using ethanol disinfectant effective in disrupting the virus?
- chemical structure of the disaccharide lactose.
a) Explain why this molecule would be unlikely to enter the cell via simple diffusion.
• Lactose is a polar molecule, with lots of hydroxyl (OH) groups. Polar molecules don’t pass easily through the hydrophobic core of the membrane
• and size
- chemical structure of the disaccharide lactose.
b) The concentration of lactose in a cell’s environment is higher than the concentration in the cell’s cytoplasm.
Describe the mechanism by which you would expect lactose to enter this cell
and explain why it would use this mechanism. Include as much detail as possible.
• Facilitated diffusion
• Simple diffusion doesn’t work because lactose can’t pass through the hydrophobic tails
• Need a carrier protein to provide a hydrophilic channel or transport
• Energy provided by lactose travelling down its concentration gradient (diffusion)
— No energy input needed from the cell
- A scientist exposes a cell to two different dyes, a red dye (R) and a blue dye (B).
The scientist measures the rate of transport of each substance across the membrane and notes the cell is not using energy to move the dyes inside the cell.
The scientist also notices in their data the rate of transport of the B dye is greater than the R dye but eventually reaches a maximum rate.
What process is being used by the cell to take up the B dye? How do you know this?
Observations
• Cell is not using energy to transport them
• Rate of transport of B is greater than rate of R, but B rate maxes out with increasing concentration
What type of transport for B?
Facilitated diffusion: B diffuses through membrane and has extra channels: faster rate, maxes out when all channels are busy
What type of transport for R?
- Simple diffusion: only dependent on concentration gradient until equilibrium is reached.
.
So
.
Simple diffusion: the rate is always directly proportional to the difference in substrate concentrations on either side of the membrane
Facilitated diffusion: Tends to be faster at low concentrations, but maxes out when all the carrier proteins are working at their max rate
- The H^+/K^+ ATPase is a primary active transporter that exports 1 H^+ and imports 1 K^+ for each ATP that is used.
a) Describe in detail the transport process you would expect to occur, based on what you know about other primary active transport proteins that we discussed in class
- The H^+/K^+ ATPase is a primary active transporter that exports 1 H^+ and imports 1 K^+ for each ATP that is used.
b) Would this transporter be considered an electrogenic pump? Explain why or why not.
No
• Although pH is affected by pumping of protons, the total charge on either side of the membrane is unaffected, because 1+ out and 1+ in
- Over the past year many scientists have looked at the way the SARS-CoV-19 virus and other corona viruses enter and exit our cells.
Looking at the following pathway into the cell: A: 1->2b->3, how would you describe this transport process using terminology from this topic?
• Receptor mediated endocytosis: ACE receptor, signals the beginning of endocytosis (invagination, pockets inwards, involves clathrin)
• 2a is different mechanism, fusion of membranes (more like phagocytosis)
- Over the past year many scientists have looked at the way the SARS-CoV-19 virus and other corona viruses enter and exit our cells.
Describe the role played by the receptor protein (blue Y shape = receptor ACE2) in the membrane of cells in this process.
- Over the past year many scientists have looked at the way the SARS-CoV-19 virus and other corona viruses enter and exit our cells.
Looking at the following pathway out of the cell: B: 8->9, how would you describe this transport process using terminology from this topic?
• Exocytosis
• Involving some ‘trickery’ of cellular machinery
- Based on what you learned in this topic, predict the membrane phospholipid composition for an unicellular algae (eukaryote) and an archaeon living in
a. a thermal hot spring
b. under the ice in the Antarctic
A)
• The algae would Increase amount of saturated fats.
• Tries to be less liquid, have denser packing to avoid leakage…. Cholesterol stabilizes at both extreme ends
B)
• In a cold environment, the opposite would happen: decrease in saturated fats = increase in unsaturated fats
• Increase amount of branched fatty acids and/or have a phospholipid monolayer
• Archaea have more tools in their toolbox…. Record temp 121 °C , hyperthermophilic bacteria (100 °C in Yellowstone NP)
• At cold temperatures membranes would be very similar: lipid bilayer with many many unsaturated, short lipids….
