Please keep all answers within the space provided.
Problem sets are due by 5:35 pm (in class or in the electronic dropbox) on November 6th.
Any problem sets submitted after 5:35 will be considered late and will have 10% deducted from the grade.
10% will be deducted from the grade for every day the problem set is overdue.
Problem sets will not be accepted after Wednesday November 11that 12:00 pm.
1- You will learn in this class that ketone bodies are essential fuels for the brain when blood glucose levels are low. For a ketone body to supply brain cells with energy, it must first cross the blood brain barrier, which is a highly selective membrane barrier that impedes the influx of most compounds from the blood to the brain. Below is the structure of one such ketone body, 3-hydroxybutyrate (3-HBA).
A.Consider the structure of 3-HBA. Do you think that 3-HBA would easily pass through the blood brain barriermembrane by simple diffusion at physiological pH? Explain why or why not. (2pts)
B.3-HBA exists as two different stereoisomers, D-3-HBA and L-3-HBA. The kinetics of transport of these stereoisomers through the blood brain barrier can be determined by adding radiolabeled (C14) L-and D-3-HBA into the blood and measuring the velocity of uptake of radiolabeled C143-HBA into the brain (see the figure on the left).What conclusions about 3-HBAtransportthrough the blood brain barrier can be made from examining these kinetic data? Be specific in regard to the type of transporter (channel or carrier), the specificity of transporter (affinity for D-3-HBA and L-3-HBA), and the shape of the curves? Explain your answers. (4 pts)
C. Due to the acidic nature of ketone bodies, an elevation of ketone bodies in the blood has the effect of lowering blood pH.To determine the effect of blood pH on 3-HBA transport, C143-HBA uptake experiments were performed by measuring the velocity of uptake with increasing pH (shown below). These data show that transport is most efficient when the external pH is low.There are 2 potential explanations for this, one of which is much more likely than the other.
The first explanation is that the C14 3-HBA is preferentially transported in the protonated form. The second explanation is that C14 3-HBA is transported in unprotonated form in symportwith a hydrogen ion. Of these 2 explanations, the second is physiologically more likely to occur.
Explain why this is. In your answer describe why the first explanation is not likely to occur. Also describe what it means to be transported in symport with a H+ ion and why this transport is more efficient at low pH (6.2) compared to higher pHs. Would the transport be active or passive(6pts)?
D. To cross the blood brain barrier, different molecules often utilize the same transport protein and thus compete for transport into the brain. Below are the kinetics of C143-HBA transport in the presence and absence of glucose and the branched chain keto acid, keto-methylvalerate. Interpret the results in regard to glucose and keto-methylvalerate transport into the brain.(4pts)
E. In the metabolic disorder, Maple Syrup Urine Disease, patients have a mutation in the enzyme branched-chain alpha-keto acid dehydrogenase, which leads to accumulation of branched chain keto acids, including keto-methylvalerate in the blood/circulation. What would the effect of this mutation be on critically needed ketone body, specifically 3-HBA, transport into the brain during times of prolonged fasting when blood glucose levels are low? (3 pts)
2) Below is a simplified schematic of the signaling cascade activated by the binding of epidermal growth factor (EGF) to its membrane receptor on a target cell. This pathway involves a small G-protein called Ras. Ras is a G-protein similar to the ones that we’ve discussed in class. Activation of Ras involves the exchange of GDP for GTP and inactivation of Ras involves hydrolysis of GTP back to GDP by Ras’s intrinsic GTPase activity. The major steps involved in this pathway are described below.
1- EGF ligand binds to the EGF receptor
2-The ligand bound receptor becomes active through autophosphorylation and dimerization
3-Activation of the EGF receptor leads to the exchange of GDP for GTP and the activation of Ras.
4- Active Ras binds to and activates Raf kinase
5- Rafkinasephosphorylates and activatesMek kinase (Mek)
6- Mekkinase phosphorylates and activates ERK
7-Phorphorlyated ERK enters the nucleus and leads to the transcription of DNA and ultimately to cell proliferation.
Using the pathway described above, please answer the following questions.
A) Ras proteins are known to have mutations in the intrinsic GTPase activity leading to the inability to hydrolyze GTP to GDP. For a cell with this mutation, what would the effect be on cellular proliferation compared to a wild-type control cell that has been treated with EGF – increase, decrease, or no change? Explain your answer. (3 pts)
B) A deletion of the sequence that corresponds to the kinase domain of MEK will lead to a loss of kinase activity in MEK. For a cell with a mutated MEK protein (loss of kinase activity) what would the effect be on cellular proliferation compared to a wild-type control cell that has been treated with EGF – increase, decrease, or no change? Explain your answer. (3 pts)
C) In certain types of cancer the EGFR receptor is known to be overexpressed in tumor cells. Based on the pathway discussed above, how does this overexpression lead to tumor growth.(3 pts)
3) Bacteria are typically grown at a temperature of 37°C. When the temperature increases to 45°C the bacteria die.
A) (3 pts) What happens to the membrane of the bacteria at 45°C?
To test the effects of membrane composition on bacterial survival, different strains have been developed with the following changes. Specifically explain how each of these changes affect melting temperature (Tm) and whether the bacteria will now be more or less resistant to temperatures of 45°C. Be specific in regard to the physical effects and interactions within the membrane.
B) (3 pts)An increase in 18:3 (∆9, 12, 15) Linolenic Acid with a decrease in 18:0 Steric Acid
C) (3 pts) An increase in 20:0 arachidic acid with a decrease in 16:0 palmitic acid
D) (3 pts) Theisomerization of cis 18:1 (∆9,) lipids to trans 18:1 (∆9) lipids.
4a) In the muscle, although hexokinase is the first irreversible step in glycolysis, phosphofructose kinase (PFK) is the primary point of regulation and the first committed step. Please explain why hexokinase is not the first committed step of glycolysis in muscle? Please explain why PFK is. (3 pts)
b) Unlike muscle, in the brain, hexokinase is the first committed step of glycolysis. Please explain why this is. Assume the brain has negligible glycogen stores and pentose phosphate pathway activity.(3 pts)
5) In class you have learned about cellular respiration. In this problem set you have the opportunity to further your understanding of respiration using a virtual lab designed to let you participate in the experimental methodology used by scientific laboratories. Please follow the instructions below to access the Labster lab. You are not being graded on the lab per se. You are expected to complete the lab and all quizzes accompanying the lab to receive full credit(4pts). If you are unable to complete the lab for technical reasons, please contact Robin for a different problem. Please follow the instructions below to access the Labster Lab.
Labster instructions:
1. Firefox is the recommended browser for using Labster. Install/update Mozilla Firefox –
https://www.mozilla.org/en-US/firefox/new/
2. If necessary, install/update Unity3D – https://unity3d.com/webplayer
3. Login to your Labster account on www.labster.com/login
4. On your dashboard, press “use voucher” in the upper left corner of the screen.
5. Enter this 10-digit number: SQvk6pUFBx (notice both upper and lower case letters)
6. You should now be linked to our course account, and have access to the Cellular Respiration Lab.
7. Please make sure both your First Name and Last Name is indicated in your account so that we can identify your work and give you full credit.
8. If you run into any issues:
– initiate a chat session with Labstertech support if it is available
– email support@labster.com