Test 2 quiz, hw questions Flashcards
The plasma membrane can be considered asymmeterical in all the following ways EXCEPT:
-Glycosylations are only found on the cytosolic face
-Different lipid compositions are found on the cytosolic and non-cytosolic face
-Glycosylation of lipids and proteins are only found on the non-cytosolic face
-Proteins are asymmetrically oriented in membrane
-Glycosylations are only found on the cytosolic face
Sugars are added to proteins and lipids only in the lumen of the endoplasmic reticulum (ER). This is the non-cytosolic face. When membranes vessicles travel from the ER to the plasma membrane, the orientation of the cysolic and non-cysolic faces remains constant. Thus, when the vessicle fuses with the plasma membrane the sugars are still on the non-cytosolic face which is oriented to the outside of the cell.
A bacterium is sudenly expelled from a warm human intestine into the cold world outside. Two specific changes the bacterium could make to the lipid tails of it’s cell membrane to maintain the same level of fluidity would be:
-Shorten and increase the number of unsaturated bonds
-Lengthen and increase the number of unsaturated bonds
- Shorten and decrease the number of unsaturated bonds
-Lengthen and decrease the number of unsaturated bonds
Add cholesterol
-Shorten and increase the number of unsaturated bonds
Shortening lipid tails and increasing the amount of unsaturation would both make the membrane more fluid in the colder external environment.
Which of the following statements is true?
-Phospholipids will spontaneously form bilayers in non-polar solvents
-In eukaryotes, new lipids are added by enzymes directly to the plasma membrane.
-Membrane lipids diffuse within the plane of the membrane.
-Lipids frequently flip-flop between one monolayer and the other.
“Membrane lipids diffuse within the plane of the membrane.”
Phospholipids will spontaneously form bilayers in non-polar solvents (False)
Phospholipids have hydrophilic heads and hydrophobic tails. In polar solvents (like water), they form bilayers because the hydrophilic heads face the water while the hydrophobic tails avoid it. In non-polar solvents, they would not form bilayers but instead disperse or form reverse micelles, with hydrophilic heads inward.
In eukaryotes, new lipids are added by enzymes directly to the plasma membrane (False)
New lipids are synthesized in the smooth endoplasmic reticulum (ER) and then transported to the plasma membrane via vesicles, not by direct enzyme activity at the plasma membrane.
Membrane lipids diffuse within the plane of the membrane (True)
Lipids exhibit lateral diffusion within the same leaflet of the membrane, which allows for membrane fluidity and dynamic changes in membrane structure.
Lipids frequently flip-flop between one monolayer and the other (False)
Flip-flop movement (transverse diffusion) of lipids between the inner and outer leaflets of the bilayer is rare because it requires the hydrophilic head to pass through the hydrophobic core. This process is facilitated by specific enzymes called flippases, floppases, and scramblases when necessary.
You said:
in short
ChatGPT said:
The correct answer is:
“Membrane lipids diffuse within the plane of the membrane.”
Why?
False: Phospholipids form bilayers in polar (not non-polar) solvents.
False: New lipids are made in the ER and transported via vesicles, not added directly to the plasma membrane.
True: Lipids move laterally within the membrane, allowing fluidity.
False: Flip-flop movement is rare and requires enzymes.
Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is not one of the common ways to perform active transport?
-Na+-coupled
-Phosphate -coupled
-ATP driven
-Light driven
“Phosphate-coupled” (Not a common way to perform active transport)
Explanation:
-Na⁺-coupled (True): Uses the energy from Na⁺ moving down its gradient to transport other molecules (e.g., Na⁺/glucose symporter).
-Phosphate-coupled (False): There is no major active transport mechanism directly driven by phosphate coupling.
-ATP-driven (True): Uses ATP hydrolysis to power transport (e.g., Na⁺/K⁺ pump, Ca²⁺ ATPase).
-Light-driven (True): Uses light energy to drive transport (e.g., bacteriorhodopsin in some bacteria).
Refer to the figure below of intestinal epethilial cells.
If oubain is added to intestinal epethelial cells, the Na+K+ Pump is blocked and ultiamtely the glucose uniporter on the extracellular fluid side of the cell no longer tranports glucose out of the cell. Why?
-Glucose can no longer be cotransported into the cells with Na+.
-Glucose can no longer be cotranposrted into the cell with K+.
-The glucose concentration in the cell remains high, thus shutting down passive uniport of glucose out of the cell.
-Glucose moves out of the cell into the gut lumen instead of through the uniporter.
Glucose can no longer be cotransporter into the cells with Na+
Which of the following is an example of allosteric regulation of a protein?
-ligand gated channels
-passive uniporter proteins
-voltage gated channels
-antiport proteins
Ligand gated channels
Which of the following is true about the movement of ions across a membrane?
-Ions can diffusely freely through the membrane because they are very small.
-Only the concentration gradient of an ion determines the direction and rate of diffusion.
-Ion channels are non-selective.
Both the concentration gradient and the difference in voltage across the membrane determine the rate and direction of ion movement.
-Active transport can not be used to move ions.
-Ion channels are non-selective.
Both the concentration gradient and the difference in voltage across the membrane determine the rate and direction of ion movement.
Which molecule below is most likely to be able to diffuse directly across the lipid bilayer.
O2
Cl–
amino acids
ATP
O2
Which of the following statements about resting membrane potential is true?
The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell.
The resting membrane potential for most animal cells is 0 mV, because the positive and negative ions are in balance.
The resting membrane potential for most animal cells is positive, because Na+ ions are so plentiful inside cells.
At the resting membrane potential, no ions enter or exit the cell.
The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell.
Red blood cells were placed in a solution then observed under a microscope. The cells appeared to have shrunk. How would you explain this observation?
-The solution was hypertonic compared to the inside of the cell.
-The solution was hypotonic
compared to the inside of the cell.
-The solution was isotonic to the inside of the cell.
-The inside of the cell had more total solutes than the solution.
Water moved into the cell.
“The solution was hypertonic compared to the inside of the cell.”
Explanation:
A hypertonic solution has a higher solute concentration than the inside of the red blood cells.
Water moves out of the cells by osmosis, causing them to shrink (crenation).
Incorrect options:
Hypotonic solution: Would cause the cells to swell and possibly burst.
Isotonic solution: Would not change the cell size.
The inside having more solutes than the solution: Describes a hypotonic environment, which would cause swelling.
Water moved into the cell: Would cause swelling, not shrinking.
Which of the following statements does not accurately describe the events involved in the propagation of an action potential?
An initial influx of Na+ through a small cluster of channels causes local depolarization of the membrane.
-Local depolarization causes nearby Na+ channels to open
-Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished.
-The opening of voltage-gated K+ channel allows K+ to flow into the cell to help repolarize the membrane.
The opening of voltage-gated K+ channels allows K+ to flow into the cell to help repolarize the membrane.”
Explanation:
True: An initial influx of Na⁺ through a small cluster of channels causes local depolarization of the membrane.
Voltage-gated Na⁺ channels open first, allowing Na⁺ to rush into the cell, depolarizing the membrane.
True: Local depolarization causes nearby Na⁺ channels to open.
This is a key feature of action potential propagation, leading to a wave of depolarization down the axon.
True: Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished.
After depolarization, Na⁺ channels enter an inactive state, preventing immediate reopening and ensuring unidirectional propagation.
False: The opening of voltage-gated K⁺ channels allows K⁺ to flow into the cell to help repolarize the membrane.
Correction: K⁺ flows out of the cell, not into it, restoring the negative resting membrane potential.
NADH; O2
Assume you have sealed vesicles containing bacteriorhodopsin and ATP synthase as in figure 14-120 in your book. The solution you place the vesicles in contains only ADP and Pi but no H+. You shine a light on the vesicles. What will happen?
-No ATP will be produced
-ATP will be produced
-The vesicle swells and bursts
-H+ will be generated by bacterorhodopsin
No ATP will be produced
Like all enzymes, ATP synthase can work in both directions. ATP synthase can either make ATP from ADP and inorganic phosphate (Pi) or hydorlyze ATP into ADP and Pi. Under what conditions does this enzyme hydrolyze ATP?
-When there is a higher concentration of H+ in the intermembrane space than in the matrix.
- When the pH in the mitochondrial matrix is higher than in the intermembrane space
-When the pH is the same on both sides of the mitochondrial inner membrane
-When there is a high concentration of ATP in the intermembrane space.
When the pH is the same on both sides of the mitochondrial inner membrane.”
ATP synthase normally synthesizes ATP by using the proton gradient across the inner mitochondrial membrane, where:
The intermembrane space has a higher H⁺ concentration (lower pH).
The mitochondrial matrix has a lower H⁺ concentration (higher pH).
The proton gradient drives ATP synthesis as H⁺ flows down its gradient through ATP synthase.
However, if the pH is equal on both sides, there is no proton gradient, and ATP synthase can function in reverse, hydrolyzing ATP to pump H⁺ back into the intermembrane space.
Why the other options are incorrect:
“Higher H⁺ concentration in the intermembrane space than in the matrix” → This favors ATP synthesis, not hydrolysis.
“Higher pH in the mitochondrial matrix than in the intermembrane space” → This describes normal conditions for ATP synthesis, not hydrolysis.
“High concentration of ATP in the intermembrane space” → ATP is mainly found in the matrix, not the intermembrane space.
Which statement comparing oxidative phosphorylation to substrate level phosphorylation is false?
-Both use ADP and inorganic phosphate to make ATP.
-Both occur in the mitochondria.
-Only oxidative phosphorylation uses the energy of an H+ gradient as the direct energy source to create ATP.
-Both use enzymes to make ATP.
Both use ADP and inorganic phosphate to make ATP
If an uncoupler is added to an intact mitochondria, H+ leak through the inner membrane effectively eliminating the H+ gradient. In these circumstances, ATP will not be generated. What other important function in the mitochondria will immediately stop functioning?
-import of pyruvate into the matrix
-electron transport chain
-citric acid cycle
-Reduction of O2 to H2O
“Import of pyruvate into the matrix”
Explanation:
The H⁺ gradient across the inner mitochondrial membrane is essential for several mitochondrial functions, including ATP synthesis and secondary active transport.
Pyruvate import into the matrix depends on the H⁺/pyruvate symporter, which uses the proton gradient to transport pyruvate into the matrix.
If an uncoupler eliminates the H⁺ gradient, pyruvate transport will stop immediately because there is no energy source driving its uptake.
Why the other options are incorrect:
Electron transport chain (ETC) → Continues to function because electrons can still flow through the complexes, but ATP production is lost.
Citric acid cycle → Slows down but does not immediately stop, as some intermediates are still available.
Reduction of O₂ to H₂O → Still occurs, as the ETC still transfers electrons to O₂, but less efficiently.
Thus, the immediate effect of an uncoupler is the failure of pyruvate import into the matrix.
The energy for creating ATP by substrate level phosphorylation comes from:
-breakage of high energy bonds
-dissipation of a proton gradient
- reduction of a substrate by high energy electrons
-the sun
-dissipation of a Na+ gradient
-Breakage of high energy bonds
During the light reaction of photosynthesis, a proton gradient is generated and ATP is synthesized. Where do protons become concentrated in the chloroplasts.
-thylakoid space
-stroma
-inner membrane
-intermembrane space
Thylakoid space
In non-cyclic electron flow, the direct source of electrons for the electron transport chain of photosystem I is:
-photosystem II’s electron transport chain
-splitting of water
-NADPH
-NADH
“Photosystem II’s electron transport chain”
Explanation:
In non-cyclic electron flow (the main pathway in light-dependent reactions), electrons flow from photosystem II to photosystem I.
Photosystem II absorbs light, exciting electrons which are passed through its electron transport chain to photosystem I.
The direct source of electrons for photosystem I comes from the electron transport chain connected to photosystem II.
Water splitting provides electrons to photosystem II but is not the direct source for photosystem I.
NADPH and NADH are products or cofactors involved later in the process, but not the direct sources of electrons for photosystem I.
The advantage of a gradual breakdown of glucose during cellular respiration as opposed to combustion to CO2 and H2O in a single step is that:
-energy can be extracted in usable amounts
-no energy is lost as heat
-more free energy is released for a given amount of glucose oxidized
-more C02 is produced for a given amount of glucose oxidized.
Energy can be extracted in usable amounts”
Explanation:
In cellular respiration, glucose is gradually broken down in a series of controlled steps (glycolysis, citric acid cycle, and electron transport chain) to release energy in manageable amounts. This allows cells to capture energy in the form of ATP, which is usable by the cell. If glucose were to be completely oxidized in one step (like in combustion), the energy would be released all at once, mostly as heat, and would not be efficiently captured for cellular use.
Why the other options are incorrect:
“No energy is lost as heat” → Some energy is always lost as heat, even in cellular respiration.
“More free energy is released for a given amount of glucose oxidized” → The total amount of energy released is the same whether glucose is oxidized gradually or in one step, but gradual oxidation allows more of that energy to be captured.
“More CO₂ is produced for a given amount of glucose oxidized” → The amount of CO₂ produced is the same regardless of the breakdown method.
Which of the following stages in the breakdown of the piece of toast you had for breakfast generates the most ATP?
-electron transport chain
-glycolysis
-citric acid cycle
-digestion of starch to glucose
ETC
During the light reaction of photosynthesis, a proton gradient is generated and ATP is synthesized. Where do protons become concentrated in the chloroplasts.
-thylakoid space
-stroma
-inner membrane
-intermembrane space
Thylakoid space
The carbon-fixation cycle during photosynthesis fixes CO2 into an organic molecule. For every molecule of glyceraldehyde-3-phosphate produced that leaves the carbon-fixation cycle, how many molecules of C02 are fixed?
3
1
2
6
3
For every glyceraldehyde-3-phosphate (G3P) molecule produced in the carbon-fixation cycle (also known as the Calvin cycle), 3 molecules of CO₂ are fixed. Here’s the process in brief:
The Calvin cycle fixes 1 CO₂ molecule into a 5-carbon sugar (ribulose bisphosphate, RuBP) using the enzyme RuBisCO.
Through a series of steps, G3P, a 3-carbon sugar, is produced.
To produce 1 G3P, 3 CO₂ molecules are required, as each cycle of the Calvin cycle incorporates 1 CO₂ at a time, and 3 cycles are needed to generate 1 G3P.
Thus, for every G3P molecule that leaves the cycle, 3 CO₂ molecules are fixed.
When comparing oxidative phosphorylation to photophosphorylation all of the following are similar EXCEPT:
-Both use NADH as an electron donor
-Both occur via chemiosmotic coupling
-Both use ATP synthase
-Both use a H+ gradient as the direct source of energy to make ATP.
Both use NADH as an electron donor
Porin → Found in the outer membrane, allowing small molecules to pass.
Mitochondrial genome → Located in the matrix, where mitochondrial DNA and ribosomes are found.
Citric acid cycle & its enzymes → Happen in the matrix, where enzymes process acetyl-CoA.
ATP synthase → Embedded in the inner membrane, using the proton gradient to make ATP.
Pyruvate transport protein → Located in the inner membrane, moving pyruvate into the matrix.
Electron transport chain proteins → Located in the inner membrane, where they transfer electrons and pump H⁺ to create the proton gradient.
