cell bio exam 2

Imagine that the diagram below is a free energy diagram for the chemical reaction A + B <=> C. In what way would you expect the diagram for the closely-related reaction: A + B + ATP <=> C + ADP + Pi to differ from the first one?

1 could decrease 2 could decrease The sign of 2 could be reversed (+ to - or - to +)

Cholesterol generally makes up what percentage of the lipid mass of the plasma membrane?

25%

Shown below is a skeleton of the Citric Acid Cycle with some of the by-products shown. Each reaction is numbered, and the number of carbons contained in each metabolite are indicated (e.g. 6C for 6 carbons). In addition to step 8, in which two steps are NADH produced?

3 and 4

Consider the reaction: A + B <=> C + D. Under standard conditions at equiliubrium, the concentrations of the compounds are [A] = 0.1 M, [B] = 0.1 M, [C] = 1.9 M, and [D] = 1.9 M; and the pH is 7.0. Keq for the reaction is _____ and the reaction is _____. (you do not need a calculator for this!)

361; exergonic

G-protein coupled receptors have ____ transmembrane domains.

7

The enzyme phenylalanine hydroxylase (PAH) catalyzes the conversion of the amino acid phenylalanine to tyrosine. If for this reaction, Keq' = 18.1, ∆G°' is ____ and the reaction is ____.

<0; Exergonic

Consider the reaction: A <=> B. Under standard conditions at equiliubrium, the concentrations of the compounds are [A] = 0.1 M, and [B] = 1.1 M. Keq' for this reaction is ____ and ∆G°' is _____. (You do not need a calculator for this.)

> 1; < 0

If you had a patient in which the lung epithelium was leaking fluids from the bloodstream into the lumen of the lung, which of the following is the most likely cause?

A mutation in a cell adhesion molecule

Each of the following is a high-energy product of glycolysis. From which of these can aerobic organisms harvest the stored energy? I.e. Which of these can be used in energy production by an aerobic organism?

ATP NADH Pyruvate

The active and inactive forms of a hypothetical enzyme are shown below. (The polypeptide is represented by the colored rectangles and grey lines holding them together.) The middle rectangle is the catalytic domain with the active site on the right. The reaction it is catalyzing is also shown on the right. The P in the red circle refers to a phosphate group. This enzyme is a/an _______ and it this form of enzyme regulation is _______.

ATPase; covalent modification

A high-energy bond in _________ provides the energy for the first reaction of the Citric Acid Cycle.

Acetyl-CoA

If it were injected directly into liver cells, cAMP would have the effect of:

Activating Protein Kinase A and, therefore, glycogen breakdown

Shown below is a branched reaction pathway. Compounds are labeled A-E, and enzymes catalyzing each reaction are labeled E1-E4. Imagine that both D and E are useful to the cell but that E must always be maintained above a concentration of 2.0 mM for the cell to survive. If E is greater than 2.0 mM is it all right for the cell to shift some production to D. Which of the following is the simplest best way to regulate the pathway to keep the cell alive? (Always assume that any enzyme that is not subject to regulation is active; enzymes subject to inhibition are active unless the inhibitor is above the threshold concentration; and enzymes subject to activation are inactive unless the activator is above the threshold concentration.)

Allosteric activation of Enzyme 3 by E

Shown below is a branched reaction pathway. Compounds are labeled A-E, and enzymes catalyzing each reaction are labeled E1-E4. Imagine that both D and E are useful to the cell but that D must always be maintained above a concentration of 2.0 mM for the cell to survive. If D is greater than 2.0 mM is it all right for the cell to shift some production to E. Which of the following is the simplest best way to regulate the pathway to keep the cell alive? (Always assume that any enzyme that is not subject to regulation is active; enzymes subject to inhibition are active unless the inhibitor is above the threshold concentration; and enzymes subject to activation are inactive unless the activator is above the threshold concentration.)

Allosteric activation of Enzyme 4 by D

Pyrimidines are synthesized through a long series of reactions beginning with the amino acid aspartate. The ribonucleotide CTP is the final compound in this pathway, and when there is enough CTP, it binds to and inhibits the enzyme that catalyzes the first reaction in the pathway, aspartate transcarbamoylase (ATCase). Because CTP is structurally and chemically different from the enzyme's natural substrates, this type of regulation must be:

Allosteric inhibition

The enzyme phosphofructokinase-1 (PFK-1) catalyzes the reaction F6P + ATP --> F1,6BP + ADP during glycolysis. When ATP concentrations get very high, ATP also binds to a location on PFK-1 outside of the active site, preventing it from catalysis. This is an example of:

Allosteric inhibition

The last product in a reaction pathway often regulates the activity of the first enzyme in the branch of the pathway that is unique to its production when the concentration of the product gets very high. Because the structure of the product is very likely to differ substantially from that of the the enzyme's normal substrate, this type of regulation is most likely:

Allosteric inhibition

Which of the following is true for both GPCR signaling and steroid hormone signaling?

An extracellular signal is transduced to an intracellular response. They may have widespread effects because they may be secreted into the bloodstream.

Imagine you are a drug developer aiming to inhibit epinephrine responses specifically in liver cells. Which of the following would accomplish this?

An inhibitor of cAMP Phosphodiesterase, which breaks down cAMP

Why is the activity of Phosphofructokinase (PFK-1) high at moderate concentrations of ATP and low at high concentrations of ATP?

At high concentrations ATP is an allosteric inhibitor of PFK-1.

Fermentation:

Begins with pyruvate

What product(s) is/are common to the Krebs Cycle and the Pyruvate Dehydrogenase (the PDH) reaction?

Both CO2 and NADH

Which adaptation specific to becoming multicellular compensates for the destabilizing effect of increased size? (Think carefully about answer choices!)

Both ECM and tight junctions

What is required for fermentation?

Both NADH and pyruvate

Oxidation of NADH and FADH2 in the electron transport system are similar in that: (READ THESE ANSWER CHOICES CAREFULLY!)

Both result in reduction of O2 to H2O.

The reactions converting glucose into CO2 taken together are _____ and ______.

Catabolic; release energy

During the reactions of ________ glucose is _______ to CO2.

Catabolism; oxidized

The reaction below shows the process by which the protease Chymotrypsin becomes activated. What is the zymogen?

Chymotrypsinogen

The enzyme Succinate dehydrogenase (SDH) catalyzes the reaction succinate --> fumarate in the Citric Acid Cycle (structures shown below). If fumarate binds to the active site of SDH, thereby preventing succinate from binding, this is an example of:

Competitive inhibition

Which of the following components of the electron transport system does NOT transport protons across the inner mitochondrial membrane?

Complex II

Which of the following is NOT part of the pathway for transfer of electrons from NADH through the ETS?

Complex II

Which of the following correctly describes the purpose of the F0F1 ATP Synthase complex?

Conversion of potential energy to mechanical energy to chemical energy in ATP

As we learned in Lecture 15, protein phosphatases catalyze removal of phosphate groups from proteins. How would the activity of a protein phosphatase affect liver cell responses to epinephrine?

Decrease glucose production

Shown below is a free energy diagram for a chemical reaction. An enzyme that catalyzes this reaction acts by ________ the magnitude of _________:

Decreasing; 2

The H+ ATPase (a.k.a. "proton pump") creates electrochemical gradients across the membranes of many protists. This is an example of:

Direct active transport.

One of the main differences between growth factor signaling (receptor tyrosine kinase receptors) and epinephrine signaling (G-protein coupled receptors) is that:

Epinephrine signaling is more likely to have a short-term, reversible effect.

We learned in lecture that any reaction that breaks apart two phosphate groups, e.g. hydrolysis of a diphosphorylated molecule so that it becomes monophosphorylated, is:

Exergonic

ATP hydrolysis is highly _____ because it involves _____.

Exergonic; separation of negatively charged phosphate groups

Ca++ flowing down its concentration gradient through a Ca++ channel is an example of:

Facilitated diffusion.

True or false: Anaerobic organisms cannot make ATP.

False

True or false: if entropy increases, the reaction is definitely exergonic.

False

In the 1930's 2,4-dinitrophenol was introduced to the market as a diet drug. DNP is a chemiosmotic "uncoupler" just like uncoupling protein (UCP) in brown fat. Uncouplers make the inner mitochondrial membrane permeable to protons (H+), causing them to flow down their concentration gradient without going through F0 and thereby bypassing the F1 ATP Synthase. As a result, the mitochondria fails to produce ATP when it breaks down glucose. DNP causes protons (H+) to flow:

From the intermembrane space into the mitochondrial matrix

Which of the following is an enzyme?

G-alpha

The reduction potential of Ubiquininoe/Coenzyme Q is _____ than Complex I and _____ than Complex II of the electron transport system.

Higher; higher

ras, a small GTPase, hydrolyzes GTP slowly on its own, but its enzymatic activity is increased significantly in the presence of GTPase activating proteins (GAPs). Imagine you discovered a novel mutation that prevents GAP from binding to ras. This mutation would have the effect of:

Increasing cell proliferation

Even though the blood glucose concentration may drop below the intracellular glucose concentration - for example, during a long fast - brain cells can still absorb glucose from the bloodstream. Under these circumstances, how does glucose get into the cells?

Indirect active transport

Unlike in animals, in which the Na+ gradient is used, it is the H+ gradient in some other species that fuels transport of other compounds up their concentration gradients. This type of transport is

Indirect active transport

Cells shrink when you place them in a solution with a high concentration of the amino acid glycine. This indicates that the cell membrane:

Is NOT permeable to glycine but IS permeable to water

Oxidation of biological molecules, e.g. glucose:

Is exergonic

Which of the following is an advantage of endocrine signaling?

It affects large numbers of cells

Which of the following is a DISadvantage of paracrine signaling?

It affects only a small number of cells.

Which of the following can be considered both an advantage and a disadvantage of juxtacrine signaling?

It affects only one or a very small number of cells.

What happens to GTP in response to epinephrine binding to its receptor on liver cells?

It binds to G-alpha

Archeological evidence suggests that Neanderthals may have been aware of the medicinal properties of plants over 60,000 years ago. Imagine you are a modern-day ethnobotanist and have identified a compound from fossilized tree pollen that binds to the alpha subunit of the most common G-proteins. To test how the compound affects the activity of Gα, you treat liver cells with the compound and then epinephrine. You observe that the cells fail to produce glucose. Which of the following could be how the compound acts?

It could inhibit the GTPase activity of Gα. It could increase the affinity of Gα for GTP. It could cause Gα to bind more tightly to adenylate cyclase. None of the above

Dr. Hutson really likes coffee. Caffeine is a xanthine, a class of molecules that are similar to purines. One of the mechanisms by which caffeine acts is to inhibit the enzyme cAMP phosphodiesterase, which converts cAMP to plain old AMP, which is inactive. How does caffeine alter liver cell responses to epinephrine?

It increases glucose production.

Which of the following is a DISADVANTAGE of endocrine signaling?

It is relatively slow.

Which of the following may be true for an enzyme?

It may chemically interact with its substrate.

If you were to remove O2 completely from the cell's atmosphere, how would it affect the Krebs Cycle?

It would decrease its activity because O2 is required for the reoxidation of NADH and FADH2

Dr. Hutson really likes coffee. Despite that, this is not a question about caffeine. How does a compound that inhibits the GTPase activity of Gα affect liver cell responses to epinephrine?

It would increase glucose production.

G-alpha is not only an activator of Adenylate cyclase, but it is a GTPase. How does mutation in G-alpha that decreases its GTPase activity affect liver cell responses to epinephrine?

It would increase glycogen phosphorylase activity.

Which of the following enzymes catalyzes phosphorylation of proteins using a phosphate group from ATP?

Kinases

Which of the following is an advantage of multicellularity?

Larger size Greater mobility Functional specialization of cells/tissues

Pertussis toxin is produced by Bordetella pertussis, a bacterium that causes whooping cough. Pertussis toxin catalyzes the addition of ADP-ribose (structure below) to Gα, which prevents Gα from binding to GPCRs thus "locking" it in the GDP-bound state. If you could observe liver cells treated with epinephrine in real time, how would one infected with pertussis compare to a control (i.e. one treated with epinephrine alone)?

Less glycogen breakdown

For solutes that cannot diffuse through the membrane, water moves across the membrane from a region of ______ to a region of ______ solute concentration.

Low to high

Chloride ion (Cl-) concentrations are approximately 10x higher outside of cells than inside. Imagine you discovered a novel protein that is required in liver cells for transporting Cl- out of the cell up its concentration gradient, and further found that this protein only functions if the Na+/K+ ATPase is active. This suggests that the Cl- transport protein is a:

Na+/Cl- antiporter

Which of the following reactions can we say is definitely energetically favorable, i.e. it can go without an input of energy?

One in which ΔG < 0

The reaction shown below is a/an ______________ reaction.

Oxidation

The half reaction shown below is a/an ________ reaction.

Oxidation NADH → NAD+ + H+ + 2e-

"During embryonic development red blood cells begin to develop in patches called blood islands. The blood cells secrete growth factors that diffuse only to nearby cells, signaling differentiation into endothelial cells. The endothelial cells eventually form the linings of the blood vessels." The growth factor described in the passage is involved in what type of signaling?

Paracrine

Which of the following enzymes catalyzes dephosphorylation of proteins?

Phosphatases

The function of the proton gradient in the mitochondrion is to provide the energy for:

Phosphorylation of ADP

If you wanted to decrease liver cell responses to epinephrine, which of the following classes of enzymes would you want to increase in activity?

Protein phosphatase (catalyzes dephosphorylation)

You are most likely to find Ca++ channels in the membranes of what organelle?

Smooth ER

Extracellular chloride ion (Cl-) concentrations are much higher than intracellular. This gradient is maintained in part by co-transport of K+ and Cl- out of the cell using indirect active transport. Maintenance of the Cl- concentration gradient using this mechanism is therefore dependent on:

The Na+/K+ ATPase

If the graph below is a free energy diagram for a reaction, what is number 2?

The activation energy

Which of the following statements is NOT true?

The enthalpy of a closed system always increases.

If the graph below is a free energy diagram for a reaction, what is C?

The free energy of the products

Many exergonic reactions fail to happen at a reasonable rate (e.g. conversion of diamonds to charcoal). This is due to the fact that their activation ener

The free energy of the transition state is much higher than the free energy of the reactants.

Which of the following statements is TRUE?

The reduction potential of FAD is higher than that of NAD+.

What is the second messenger in the receptor tyrosine kinase signaling pathway?

The small GTPase ras

Which of the following is true of steroid hormones but not a signaling molecule such as a ligand for G-protein coupled receptors?

Their receptors regulate gene transcription.

A major function of the epithelium in animals is to prevent entry of pathogens and toxins from the environment. Which of the following is common to all epithelial cells?

They are held together by tight junctions.

Which of the following is never true of enzymes?

They lower ΔG of a reaction.

True or false: in anaerobic organisms, all of the ATP that can be produced through glucose catabolism comes from glycolysis.

True

The Na+/K+ ATPase transports Na+ up its concentration gradient and K + ______ its concentration gradient. This is an example of ______ .

Up; Direct active transport

Iron (Fe) and copper (Cu) ions, as well as the lipid Ubiquinone (a.k.a. Coenzyme Q or CoQ), participate in the transport of electrons through the mitochondrial electron transport system. Shown below are some of their standard reduction potentials. Based on the information in the table and what we have learned in class, which of the following could oxidize (i.e. take electrons from) CoQH2/Ubiquinone?

all of the above

Liver cells respond to epinephrine by __________.

breaking down glycogen

Liver cells respond to epinephrine by breaking down glycogen. What is the second messenger in this patway?

cyclic AMP

True or False: The concentration of K+ outside the cell is higher than it is inside

false

True or False: The concentration of Na+ inside the cell is higher than it is outside.

false

Phosphofructokinase (PFK-1) may be the most tightly regulated enzymes in cells. Based on all of the principles we have learned in this class, which of the following would be most likely to be an allosteric activator of PFK-1?

glucose

A mutation that causes a decrease in the GTPase activity of G-alpha in liver cells would have the effect of:

increasing the activity of Protein Kinase A Increasing the production of glucose Increasing the activity of Glycogen phosphorylase