Southwestern College Bioenergetic and System Biology Questions
Biology 240 – Bioenergetics & Systems Midterm 2 100 points
You have 55 min to complete this exam. Please make sure your writing is legible!! If I cannot read your writing, I will not assume your answer is correct, and you will not receive credit for your answer. Please be sure that your drawings and graphs are clearly labeled and explained. This exam should contain 20 numbered questions on 6 pages. (excluding this cover page) When are you planning on finding a job?! And don’t give me that excuse that you don’t have any energy… You’re a mitochondria for Nucleus’ sake! 1
1. Bacteria have cells walls. Plants, fungi, and algae also have cell walls, although the macromolecules used to form these cells walls are not the same as those that make up bacterial cell walls. Give two more examples of cellular structures that are found in (or around) both bacteria and eukaryotic cells.
1) _______________________________ 2) _____________________________
2. Which ONE of the following statements describes the first law of thermodynamics?
a) Energy cannot be transferred or transformed.
b) Energy cannot be created or destroyed.
c) The entropy of the universe is constant.
d) The entropy of the universe is decreasing
e) None of the above
3. Using the key below, indicate how each of the following molecules would enter a cell.
A = simple diffusion B = facilitated diffusion C = active transport D = phagocytosis E = receptor medicated endocytosis F = exocytosis Molecules Transport Mechanism K+ (intracellular conc = 100 mM; extracellular conc = 5 mM) O2 (low concentration within cells due to high consumption rate) fructose (intracellular conc = 0.22 mM; extracellular conc = 0.37 mM)
4. Many biochemical reactions in a cell are thermodynamically favorable and described as “spontaneous,” yet they do not take place unless an enzyme is present to catalyze the reaction. Why is this? What do enzymes do that allow these reactions to occur? Select all that apply.
a) Enzymes alter the free energy change (ΔG) for a biochemical reaction, making the reaction more likely to occur.
b) Enzymes increase the free energy of the reactants to make the reaction go faster.
c) Enzymes provide energy of activation (EA) needed for the reactions they catalyze, allowing the reaction to proceed.
f) Enzymes lower the energy of activation that substrate molecules must overcome to be converted into product, making the reaction more likely to occur.
d) Enzymes allow an endergonic reactions to proceed without the addition of any chemical energy.
e) Enzymes increase the entropy of the products, making the reaction more likely to occur.
5. Name one fermentation pathway and specify the end-products of that pathway (just the carbonbased products – – -don’t report on any type of “energy molecule”)
pathway ___________________________ end-products ____________________________
6. Why do facultative anaerobes perform fermentation when in anaerobic conditions? Why don’t they simply perform glycolysis? Choose the one best answer.
a) By performing fermentation they make twice as much ATP as glycolysis alone.
b) By performing fermentation they make twice as much NADH as glycolysis alone.
c) The fermentation reactions regenerate NAD+ for glycolysis so that pathway can continue to take place.
d) The fermentation reactions regenerate ADP for glycolysis so that pathway can continue to take place.
e) The fermentation products can substitute for oxygen as the final electron acceptor for the electron transport chain, thereby allowing ATP synthesis by chemiosmosis to occur.
7. You have been taking cell samples from various lung cancer biopsies and studying in these cells the reactions that occur in the Krebs cycle. In the second Krebs reaction, citrate is converted to isocitrate. According to the ?G value below, is this reaction endergonic or exergonic? Explain what this mean in terms of the energy requirement of this reaction. (4 points)
citrate (C6H5O7) isocitrate (C6H5O7) ?G = -400 cal/mol
8. The conversion of citrate to isocitrate uses the enzyme aconitase. Below is a graph that shows the results of an enzyme kinetics assay in which you measured the effect of substrate concentrations on aconitase rates.
What is the Vmax for this enzyme? Rea ctio n rat e (? mol /se c) What is the Km for this enzyme? Substrate (citrate) concentration (?mol/L) *Be sure to include appropriate units on your V and K values!
9. Doubling the concentration of the aconitase in this assay would ______ the Vmax and _____ the KM.
a. double, not alter c. double, double
e. halve, halve b. not change, double
d. not change, not alter f. double, halve
10. Draw a line on the above graph that shows how aconitase activity would be affected if you added a noncompetitive inhibitor to the reaction.
11. Predict the relative reaction rate of the aconitase catalyzed reaction if you tested the reaction over a temperature range of 15 to 55 C. Assume you are using aconitase isolated from normal human lung cells. Draw your own graph in the space below to show your expected results and provide a mechanistic explanation as to why you expect to see these results.
12. Many molecules enter cells via a process known as coupled transport. Concisely describe how this mechanism works. Is it a form of passive or active transport?
13. Specify whether the following statements is true or false.
T F The Km value of an enzyme is directly related to its affinity for its substrate; the higher the affinity, the higher the Km value.
T F A molecule becomes oxidized when it looses electrons and reduced when it gains electrons.
14. In the provided space, make a drawing of a mitochondrium and identify all of the structures and compartments within this organelle. In addition, identify the proteins involved in oxidative phosphorylation and indicate where in the organelle these proteins are located.
15. Oxidative phosphorylation depends on a pair of coupled reactions – one involving the electron transport chain and the second involving ATP synthase. (
a) Describe the first coupled reaction that involves the electron transport chain. Which process or reaction is exergonic and which is endergonic?
b) Describe the second coupled reaction that involves the ATP synthase. Which process or reaction is exergonic and which is endergonic?
16. In the table below, report the net number of molecules that would be produced in each listed pathway if a single glucose molecule was completely catabolized in a muscle cell undergoing aerobic respiration. If none are produced during a process, specify zero or none. Leave no blank lines.
(12 points) glycolysis ATP molecules (made by substrate level phosphorylation)
NADH FADH2 CO2 Pyruvate Acetyl CoA pyruvate oxidation citric acid cycle electron transport chain
Use the following scenario for questions 17 & 18. Physicians and scientists are concerned about the recent emergence of the multidrug-resistant and pathogenic yeast Candida auris. This eukaryotic pathogen, first identified in 2009, has become a public health concern worldwide. In the US, there have been more than 600 cases in 12 states since the start of 2019. It predominately infects hospitalized patients, and there are high mortality rates (~30%) for infected patients who develop an invasive infection (spreads throughout body rather than remaining localized). Fortunately for the medical community, you have obtained a summer internship at a local BioTech company and plan to use your knowledge from Biol 240 to help you study its metabolism. For your first experiment you set up cultures in media that contain everything the yeast cells need to grow. The first set of cultures is your control – yeast cells in the original culture media with no additives. To the second set of cultures you add a Compound X. To assess this compound’s effect on metabolism, you comparing glucose consumption rates between the two sets of cultures. Your protocol is to inoculate the media (with or without the additional chemical) with the yeast cells, incubate at 37°C for two hours under aerobic conditions, and then measure the rate of glucose consumption over the next 10 minutes. You also measure the absorbance of the culture to determine if the yeast cells are growing in each of the media (growing cells are dividing cells). You note that yeast cells are growing in both culture conditions, although those with Compound X are growing more slowly than the control. The yeast cells were not killed when Compound X was in the media, however they consumed more glucose than the cells in the control media. Media treatment glucose consumption compared to control (percent change) Growth rate compared to the control (percent change) Compound X 300% Increase 40% Decrease
17. If Compound X is a non-competitive inhibitor that binds with high affinity to complex III of the electron transport chain, how does Compound X inhibit the enzymatic activity of complex III? Provide a mechanistic explanation as to how this type of inhibitor works.
18. Explain why the yeast cells increased their glucose consumption in the presence of Compound X. Provide a mechanistic explanation.
19. Why was the growth rate of the yeast cells exposed to Compound X slower than the control cells?
20. Based on your results above, which category of organisms does your species of yeast (C. auris) fall into? Circle your choice.
Strict (or obligate) aerobe Explain your reasoning: facultative anaerobe strict (or obligate) anaerobe
