Test 2

What is ∆G°' for the hydrolysis of ATP?

-7.3 kcal/mol

Consider the reaction: A + B à C. At equiliubrium; the concentrations of the compounds are [A] = 0.1 M, [B] = 0.1 M, [C] = 1.9 M; and the pH is 10.0. What is Keq for the reaction? (You may use a calculator for this.)

190

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

Which of the following correctly describes a second messenger?

A soluble cytoplasmic molecule produced in response to ligand binding that activates a cellular response.

What is one disadvantage of being a multicellular organism?

Greater energy needs than unicellular organisms

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

Kinases

The first reaction of glycolysis accomplishes what?

Maintenance of low intracellular glucose so glucose can continue to be imported without expending energy

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

How are the Light-dependent reactions of photosynthesis similar to the electron transport system in aerobic metabolism?

They both involve generation of a proton gradient that is harnessed to produce ATP.

Imagine that you could engineer a cell that has all of the enzymes and other machinery for only the Citric Acid Cycle and fermentation. Would this cell be able to produce ATP to stay alive if Acetyl-CoA and O2 were available? Say that the cell is a bacterium, so transport of stuff across the mitochondrial membrane is not an issue. (Acetyl-CoA can be made from the break-down of fats, so we aren't entirely dependent on glucose for survival!)

probably not; fermentation would serve to reoxidize NADH, but there is no mechanism to reoxidize FADH2.

Fermentation begins with

pyruvate

Cell adhesion molecules are important components of:

tight junctions

Aerobic metabolism produces approximately ________ x as much ATP as anaerobic m

15x

Aerobic metabolism produces approximately ________ x as much ATP as anaerobic metabolism per molecule of glucose consumed.

15x

G-protein coupled receptors have ____ transmembrane domains.

7

Imagine that when you walk into lab after spring break, your T.A. hands you a beaker containing a solution and tells you that there are three compounds in the solution, A, B, and C represented by the equilibrium shown below. She also tells you that the compounds are at equilibrium. What data do you need to calculate ∆G for the forward reaction? Note that there is no expectation that this experiment was done at standard conditions, so you are just calculating ∆G, not ∆G°'.

A + B à C The concentrations of A, B, and C.

Pertussis toxin is produced by Bordetella pertussis, the 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. Which of the following would you expect to see in liver cells treated with pertussis toxin?

A decrease in Adenylate Cyclase activity

Which of the following is both required for glycolysis and a product of glycolysis?

ATP

During glycolysis, ATP forms by

ATP forms by substrate level phosphorylation during glycolysis.

What are the major products of the Light-dependent reactions?

ATP, NADPH, O2

Phosphofructokinase (PFK-1) is one of the most regulated enzymes in metabolism. Which of the following would be expected to be an allosteric inhibitor of PFK-1?

Acetyl CoA this is produced "downstream" and would therefore, if anything, be likely to be an inhibitor

Imagine you want to get rich by genetically engineering tobacco plants to produce acai berry juice. To do so, you insert the genes for each of the enzymes in the hypothetical acai synthesis pathway, the first step of which is conversion of glucose to fructose. The challenge is that if you allow glucose to be depleted it will kill the plant because it can no longer make ATP. For the reaction pathway shown below, what is the best way to ensure that glucose can be used to produce acai berry juice, but only when glucose is at or above a certain concentration so that it is continuously available for catabolism and production of ATP?

Allosteric activation of enzyme E1 by Glucose the only way to ensure that glucose never drops below a certain concentration is to make sure that the enzyme that converts it to something else is only active at or below the desired concentration.

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

At high concentrations of ATP, it acts as an allosteric inhibitor of PFK-1.

Why is O2 required for aerobic metabolism, but not for production of ATP? (read answer choices carefully!)

Because O2 is the last electron acceptor in the electron transport system, O2 is necessary for electron transport, and thus oxidative phosphorylation. However, glycolysis can continue in its absence, enabling the cell to continue producing small amounts of ATP through substrate-level phosphorylation.

What is required for fermentation?

Both NADH and pyruvate

Pyrimidines are synthesized through a long series of reactions beginning with the amino acid aspartate (wow!). The ribonucleotide CTP is one of the final compounds in this reaction pathway, and when the cell has enough CTP, it binds to and inhibits the enzyme that catalyzes the first reaction in the pathway, aspartate transcarbamoylase (ATCase). This is most likely an example of:

Both allosteric inhibition and end-product inhibition

Fermentation is active in _____ organisms.

Both anaerobic organisms and aerobic organisms in the absence of O2

Liver cells respond to epinephrine by __________.

Breaking down glycogen.

Extracellular matrix (ECM) protein important for structural support; comprised of three intertwined polypeptide chains that bundle together to form a rigid macromolecular fiber; the most abundant protein in the body

Collagen

Which of the following molecules is described in this passage: "Extracellular matrix (ECM) protein important for structural support; comprised of three intertwined polypeptide chains that bundle together to form a rigid macromolecular fiber; the most abundant protein in the body"?

Collagen

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

Complex II

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

Cyclic AMP

"He was awakened in the middle of the night by a low growling that sounded as if it was coming from just outside his tent. In response, the cells of his adrenal medulla began to secrete epinephrine, causing his palms to sweat, his heart to race, and his hair to stand on end." Epinephrine is involved in what type of signaling as described in this passage?

Endocrine

Which of the following is a mechanism by which cells ensure a strong response to a small amount of ligand?

Enzyme cascades

Shown below are the results of two fluorescence recovery after photobleaching (FRAP) experiments. Which of the following could explain the difference between the data represented by the dashed line as compared to that represented by the solid line?

FRAP was performed on the same cell but at a lower temperature: The slower the recovery, the less fluid the membrane is. OR. The membrane of the cell indicated by the dashed line contains lipid rafts.

What type of transport brings glucose into cells soon after eating a large meal?

Facilitated diffusion

True or false: if ΔH < 0, the reaction is definitely exergonic.

False

True or false: if ΔS > 0, the reaction is definitely exergonic.

False

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

False. It may be - because increasing entropy is energetically favorable - but if there is a large increase in enthalpy at the same time, this could outweigh the increase in entropy: ΔG = ΔH - TΔS

NAD+ is recycled during

Fermentation

Which of the following statements is NOT true regarding our relationship to photosynthesis?

For glycolysis to proceed in the absence of O2, NADH must be reoxidized to NAD+. This takes place during photosynthesis.

A statement NOT true regarding our relationship to photosynthesis?

For glycolysis to proceed in the absence of O2, NADH must be reoxidized to NAD+. This takes place during photosynthesis. this statement describes fermentation

In the 1930's 2,4-dinitrophenol (DNP; shown below) 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.

Factors that increase membrane fluidity have the effect of _______ membrane permeability:

Increasing

Brown fat, found in small, hibernating animals and infant mammals plays the role of __________ the rate of heat production because _________.

Increasing; it contains a protein that forms a pore in the inner mitochondrial membrane. This allows H+ to diffuse down its gradient without the energy being captured and coupled to ATP Synthesis. The energy is lost as heat.

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

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

What is one thing that can be considered both an advantage and a disadvantage of juxtacrine signaling?

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

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

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

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. Which of the following might you reasonably conclude about the Cl- transport protein?

It could be a K+/Cl- symporter. It is dependent on either the Na+ or the K+ gradient for its energy. Symport with Na+ would require co-transport into the cell (down the Na+ gradient), but our novel protein transports Cl- out of the cell.

The active and inactive forms of a hypothetical enzyme are shown below. The part of the protein represented by the rectangle on top, is called the regulatory domain, and the middle section is the catalytic domain with the active site on the right. The P in the red circle refers to a phosphate group. This enzyme is active when:

It is phosphorylated.

Pertussis toxin is produced by Bordetella pertussis, the 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. How would this affect liver cell responses to epinephrine?

It would decrease glucose production.

If you were to remove O2 completely from the cell's atmosphere, how would it affect the Citric Acid 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

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

Low to high (solute concentration) Remember, water has to try to create equal solute concentration on either side of the membrane

Which of the following is a disadvantage of being a multicellular organism?

More difficultly to absorb nutrients

Which of the following most closely approximates a second messenger?

Na+ ions, which flow into a muscle cell in response to binding of acetylcholine to its receptor, which leads to Ca++ release from internal stores

Which of the following most closely approximates a second messenger?

Na+ ions, which flow into a muscle cell in response to binding of acetylcholine to its receptor, which leads to Ca++ release from internal stores... Though this is not precisely what is meant by a second messenger, it is the best approximation - it is soluble, it is produced (or at least appears) inside the cell in response to ligand binding, and it activates the cellular response. You could inject Na+ into the cell and even in the absence of ligand get the same response that you do with ligand.

Inhibition of which of the following would prevent indirect active transport of glucose into cells?

Na+/K+ ATPase Remember that glucose needs the Na+ gradient for its co-transport.

If you blocked fermentation in an anaerobic cell, would it survive?

No

NADH and FADH2 differ in that:

Only NADH involves transfer of electrons from Complex I to Ubiquinone/CoQ.

The reaction shown below is a/an ______________ reaction. CH3CH2OH → CH3CHO

Oxidation

Which of the following processes/pathways CAN HAPPEN in the absence of O2?

Oxidation of NADH

Which process is used to provide the energy for formation of a proton (H+) gradient in mitochondria?

Oxidation of NADH to NAD+

In the reaction shown below, pyruvate is being _______________. Coenzyme A + pyruvate + NAD+ à Acetyl-CoA + CO2 + NADH

Oxidized

"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

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

Phosphatases this is the only class responsible for shutting off the response

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

Phosphorylation of ADP

DNP was a very effective diet aid introduced in the 1930's, but it was nearly immediately taken off the market after several users died of acute hyperthermia (overheating). Why would DNP cause hyperthermia?

Protons flowing down their concentration gradient is an exergonic process, the energy from which, when not captured by ATP Synthase, is released as heat.

Imagine that you could engineer a cell that has all of the enzymes and other machinery for only glycolysis and the electron transport system. Which of the following would be among the net products of metabolism in this hypothetical cell?

Pyruvate

The final electron acceptor in lactate fermentation is

Pyruvate

Conversion of a 3-carbon compound to a 2-carbon compound happens during:

Pyruvate decarboxylation pyruvate to Acetyl-CoA

FAD + 2H+ + 2e- → FADH2

Reduction

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

Smooth ER

Which of the following lists major reactants for the Light-dependent reactions?

Sunlight, ADP, NADP+, H2O

If all of the oxaloacetate (OAA) in the cell was consumed, say by an intracellular pathogen that eats OAA as its primary food source, how would it affect the activity of the Citric Acid Cycle

The Citric Acid Cycle would slow because OAA is a reactant.

What is number 2 in the graph below?

The activation energy

Which of the following is NOT consistent with the fluid mosaic model of cell membranes?

The inner and outer leaflets of cell membranes are comprised of similar proportions of phospholipids.

What is NOT consistent with the fluid mosaic model of cell membranes?

The inner and outer leaflets of cell membranes are comprised of similar proportions of phospholipids. OR. Membranes are comprised of many lipid rafts floating in a lipid sea.

Assuming O2 is available, in which structure would you expect to see the lowest pH?

The intermembrane space of the mitochondria

During electron transport through the electron transport system, protons (H+) get pumped from ______ to ______.

The matrix; the intermembrane space

Which of the following correctly is true of steroid hormones but not a signaling molecule such as a GPCR ligand?

Their receptors regulate gene transcription

Which of the following correctly is true of steroid hormones but not a signaling molecule such as a GPCR ligand?

Their receptors regulate gene transcription.

The most fundamental 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 true for all enzymes?

They increase the reaction rate.

Is the reduction potential of FADH2 is higher than that of NADH?

True

Imagine that you could engineer a cell that has all of the enzymes and other machinery for only glycolysis and the electron transport system. Would this cell be able to produce ATP to stay alive as long as glucose and O2 were available?

Yes probably, anyway; the ETS would serve to reoxidize NADH to NAD.

In animals, the energy for life is obtained by cellular respiration. This involves

breaking down the organic molecules that were consumed.

Cells can extract energy from foodstuffs other than glucose because

each type of macromolecule is broken down into its subunits, feed into the oxidative respiration pathway.

After glycolysis the pyruvate molecules

go to the mitochondria of the cell and are broken down in the presence of O2 to make more ATP.

∆G°' for the hydrolysis of ATP is considered to be:

highly exergonic

What is number 3 in the graph below?

ΔG of the reaction