Cell Bio Unit 3
Which of these statements is correct?
Oxidation of NADH and of NADPH have the same Δ G ∘ (standard free energy change).
Glycolysis produces ___________ ATP molecules, whereas the complete oxidation of glucose to water and carbon dioxide produces ___________ ATP molecules.
2; 30
Which of the following statements are TRUE for chloroplasts?
- Chloroplasts have their own ribosomes - Chloroplasts are unable to grow and divide outside of eukaryotic cells
Which statement(s) about the mitochondrial electron transport chain is TRUE? Mark all that are correct.
- Cytochrome C reductase (complex III) can create a proton gradient by accepting a proton from water in the mitochondrial matrix and transferring it to water in the intermembrane space. - Cytochrome C oxidase (complex IV) is an electron transport-coupled proton pump.
Which statement(s) about enzymes are FALSE? There may be more than one answer to mark
- Enzymes can alter the equilibrium constant of a chemical reaction - An enzyme can alter the standard free energy change of a chemical reaction Right answers: - enzymes can lower activation energy of a chemical reaction - enzymes can drive unfavorable reactions by linking them to favorable
Which of the following statements are TRUE for mitochondria? Select all that are true
- Mitochondrial electron transport chains pump protons across the inner membrane and out of the matrix - Mitochondria have their own ribosomes, - Mitochondria generate ATP which is exported to the rest of the cell Wrong: - Mitochondria can grow and divide outside of eukaryotic cells
Your company has developed an organic molecule with commercial potential and you know how to produce it in the lab. You want to increase production and make as much of the molecule as possible, but the reaction has a positive ΔG°. What can you do to try to drive the reaction toward your desired product?
- increase the concentration of reactants - continually remove products
During the catabolism of one glucose molecule in the presence of oxygen, the most ATP is generated during which process?
Oxidative phosphorylation
When NADH or NADPH transfers electrons to a recipient molecule, the recipient becomes reduced and the activated carriers are oxidized (to NAD+ or NADP+, respectively). What else happens during this reaction?
A proton is taken up by the recipient molecule.
What provides the fuel to convert CO2 into sugars in chloroplasts?
ATP and NADPH generated in photosynthetic light reactions
The ΔG° of the hydrolysis reaction of ATP is -7.3 kcal/mole, but in a cell the actual ΔG is much more negative. What is the reason for the ΔG° and ΔG difference?
ATP is much higher in concentration than the products ADP and Pi.
How is ATP exported out of the mitochondrial matrix?
ATP is transported across the inner membrane by an ADP/ATP antiport, aided by the voltage gradient.
The evolution of membrane based energy capture systems was a long, stepwise process. Which of these is thought to have evolved first?
ATP powered proton pumps
What are the end products of glycolysis?
ATP, NADH, pyruvate
For the reaction X -- Y, the equilibrium constant (K) = 10. You start with 100 moles of X and 0 moles of Y and let the reaction reach equilibrium undisturbed. How much X and Y will you end up with at equilibrium?
About 9 moles X and 90 moles Y negative standard free energy change (high K) so product-favored
Activated carriers store their energy in a readily transferable form such as high energy electrons or chemical groups. Which of the molecules below donates a chemical group rather than electrons?
Acetyl CoA
To balance metabolic demands, cells carefully regulate their catabolic and anabolic pathways. Which of these molecules positively regulates an enzyme(s) involved in gluconeogenesis?
Acetyl CoA
Which statement is incorrect?
All oxidation reactions involve oxygen Correct Answers: - Oxidation is removal of electrons from an atom - Oxidation can involve partial or complete transfer of electrons - Oxidation reactions are always paired with reduction reactions
What occurs in the first step of the citric acid cycle?
An acetyl group (from acetyl CoA) combines with oxaloacetate to form the 6 carbon molecule citrate.
What statement about enzymes is not true?
An enzyme can force an energetically unfavorable reaction to take place inside the cell.
Although we focused on glucose, other organic molecules such as fatty acids are also used as energy sources. Where does the catabolism of glucose and fatty acids converge?
As acetyl-CoA (produced by different mechanisms) enters the Citric Acid Cycle
Which is not true of a chemical reaction at equilibrium?
Both the forward and reverse reactions have stopped Right answers: - Net concentrations of product and substrate don't change - ΔG is equal to zero. - The rates of the forward and reverse reactions are equal
Carbon atoms cycle continuously through the biosphere. What is a by-product of cell respiration, and what does this by-product represent?
CO2; completely oxidized carbon
Of these four molecules, which is the most oxidized form of carbon?
Carbon Dioxide (CO2); no CH bonds
What term describes the chemical pathways within a cell that are specifically responsible for the conversion of food molecules into both useful energy and building blocks for biosynthesis?
Catabolism
Which is true about electrons as they move through the electron-transport chain?
Electrons start out at very high energy and lose energy at each transfer step during the electron transport chain
When ATP and food molecules such as fatty acids are abundant, which will occur?
Enzymes involved in gluconeogenesis will use energy to produce glucose.
Although gluconeogenesis is essentially just glycolysis in reverse, the two pathways do not have any enzymes in common.
False
Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?
GDP, O2, oxaloacetate, NAD+
High levels of glucose 6-phosphate within a cell stimulate the activity of which of these enzymes?
Glycogen synthase
During photosynthesis in the chloroplasts of modern plants, what is the initial electron donor for the electron transport chain?
H2O
Which of the following statements is not true?
Hydrogenation reactions are oxidations, and dehydrogenation reactions are reductions. True: Oxidation and reduction reactions always occur simultaneously. When a carbon atom in a C-H bond has somewhat more than its share of electrons, it is said to be reduced. When a sugar molecule is oxidized to CO2 and H2O, the O2 molecules involved in forming the H2O are reduced.
In the absence of oxygen, yeast will use fermentation instead of aerobic respiration to generate usable energy. Why?
In the absence of oxygen, fermentation reactions are necessary in yeast to regenerate NAD+
A reaction A → B has a negative ΔG under experimental conditions. Which statement is true about this reaction?
Increasing the concentration of B will increase the ΔG, making it less negative.
What happens to the ATP produced during stage 1 of photosynthesis?
It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.
When the difference in redox potential between two molecules is highly positive, what is true of the transfer of electrons between them?
It is highly favorable
Which statement is true of glycogen phosphorylase?
It is inhibited by glucose 6-phosphate and by ATP.
What happens to the energy captured during glycolysis and the citric acid cycle by the activated carriers NADH and FADH2.
It is passed to an electron transport chain that uses it to generate a proton gradient across the inner mitochondrial membrane.
What is true of the phosphorylation of glucose in step 1 of glycolysis?
It traps sugar inside the cell
Although the citric acid cycle itself does not use O2, it requires a functioning electron transport chain (which uses O2) in order to regenerate which molecule for further use in the citric acid cycle?
NAD+
In the electron-transport chain in chloroplasts, which molecule serves as the final electron acceptor?
NADP+
Which of the following statements regarding NADPH and NADH is true?
NADPH and NADH are used in separate biochemical pathways in cells. Wrong answers - NADH carries electrons in animal cells and NADPH does the same in plants. - NADPH loses a phosphate group to form NADH during biosynthetic reactions. - NADPH and NADH deliver electrons to the same set of enzymes.
Which molecule is not used and/or generated in the chemical reactions of the citric acid cycle?
O2
The Carbon Fixation Cycle uses ATP and NADPH generated during the light reactions of photosynthesis. Which reactions in the cycle do not use ATP and/or NADPH?
Rubisco catalyzed carbon fixation wrong answers: - conversion of 3-phosphoglycerate to sugar glyceraldehyde 3-P - regeneration of ribulose 1,5-bisphosphate from the sugar glyceraldehyde 3-P
Which of the following is true for eukaryotic cells?
Sugars and fats are both converted to acetyl CoA in the mitochondria.
What is the origin of the energy that cells acquire by eating plants or animals?
Sunlight
Cytochrome c oxidase catalyzes the reaction that reduces molecular oxygen (two oxygen atoms) to two water molecules. The electrons are added sequentially, and during the process cytochrome c oxidase must bind the oxygen tightly in the active site. Why?
Superoxide radicals are formed as an intermediate and are dangerous to the cell
Which statement accurately describes an important difference between NADH and FADH2?
The electrons carried by FADH2 are lower energy than those carried by NADH.
How does chemiosmotic coupling generate ATP?
The energy from electron transfer is used to generate a proton gradient that powers ATP synthase.
Which statement is true?
The heat released by an animal cell comes from the chemical bond energy present in the food molecules it metabolizes.
What does it mean for a bond to be "high energy," such as the bonds between phosphate groups in ATP?
The hydrolysis of the bond is energetically favorable.
What is the role of activated carriers in cells?
They capture energy from energy releasing reactions and transfer it to other reactions.
In eukaryotic cells, why must metabolism be tightly regulated?
The substrates involved in metabolic reactions can be used by a number of different enzymes.
Your friends are on a low-fat, high-carbohydrate diet, which they claim will prevent fat accumulation within their bodies. They eat tons of pasta and bread without worrying about calorie count. What can you correctly say to your friends about their potential to accumulate lipids on their low-fat diet?
They will accumulate fats because cells can convert glycolytic metabolites into lipids.
Diseases that disrupt the function of mitochondria are particularly harmful to muscle and nerve cells for what reason?
These cells need large amounts of ATP to function normally
How do the high-energy electrons of activated carriers contribute to forming the high-energy phosphate bonds of ATP?
They are used by the electron transport chain to make a proton gradient
Why can electron carriers move a proton from one side of a membrane to the other?
They can accept an electron (along with an H+ from water) on one side of the membrane and then release the H+ on the other side of the membrane as they pass the electron to the next carrier.
In the first step of the citric acid cycle, oxaloacetate and acetyl CoA are used to produce citrate. After ONE TURN of the citric acid cycle, what will have happened to the carbon atoms from the acetyl group of acetyl CoA?
They will be present in the regenerated oxaloacetate
Consider two molecules that associate with each other through hydrogen bonds. How tightly will the two molecules bind as the equilibrium constant, K, becomes larger for this association?
They will bind more tightly
How does the photosynthetic machinery produce enough energy to transfer electrons from H2O to NADPH?
Two photosystems operating in series couple their electron-energizing steps
During glycolysis, which type of enzyme would catalyze the reaction in which glyceraldehyde 3-phosphate is oxidized and NAD+ is reduced?
a dehydrogenase
The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?
cells that could pump protons
After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule?
fatty acids
Which reaction can be driven by the hydrolysis of a molecule of ATP?
glucose + fructose → sucrose (ΔG = 5.5 kcal/mole)
ΔG° indicates the change in the standard free energy as a reactant is converted to product. Given what you know about these values, which reaction below is the most favorable?
glucose → CO2 + H2O ΔG° = −686 kcal/mole
Ubiquinone has a redox potential of +30 mV, while cytochrome c has a redox potential of +230 mV. During electron transport, which is true?
electrons will flow from ubiquinone to cytochrome c
In thermodynamics, what does the term "free energy" refer to?
energy that can be harnessed to do work or drive chemical reactions
During cyanide poisoning, ATP generation by the mitochondria is
virtually eliminated because the entire electron transport chain ceases to function
Which of the following is true when the concentrations of substrate and product are equal?
free energy change = standard free energy change
It is energetically favorable for protons to flow in which direction?
from intermembrane space to mitochondrial matrix
which of these statements about glycolysis is false?
glycolysis can only function in aerobic (oxygen present) conditions right answers: - initial input for complete glycolytic pathway is glucose, which is converted through several steps to pyruvate - sugars other than glucose can be converted into glycolytic intermediates and used for energy production in cells - glycolysis occurs in cytosol of prokaryotes and eukaryotes
The chemistry of many metabolic reactions was deciphered using molecules labeled with radioactive isotopes. If acetyl CoA labeled with radioactive 14C in both carbon positions were fed into the citric acid cycle, where would the radioactivity be after one turn of the cycle?
in oxaloacetate
In an animal cell, where are the proteins of the electron-transport chain located?
inner mitochondrial membrane
Which metal ion is found in all three respiratory enzyme complexes?
iron
The proton flow through the transmembrane H+ carrier of ATP synthase results in
mechanical rotation that is converted into the chemical-bond energy of ATP
For the reaction NADH + ½ O2 ⟶ H2O + NAD+, the difference in standard redox potential is 1140 mV. This means that the forward reaction has a standard free energy change that is _____________ and the reaction is _______________.
negative, favorable
Chemical reactions proceed spontaneously only in which direction?
one that leads to a release of free energy
Kinases can catalyze the transfer of a phosphate group from one molecule to another. Below I've listed the standard free energy change for the hydrolysis of the phosphate bond in two glycolysis intermediates and ATP. phosphoenolpyruvate = -61.9 kJ/mole glucose-6-phosphate = -17.5 kJ/mole ATP = -30.6 kJ/mole For which molecule is the transfer of its phosphate group to ADP energetically favorable?
phosphoenolpyruvate, overall ATP + this is neg
In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions?
pyruvate and NADH
The synthesis of ATP in glycolysis occurs by which process?
substrate level phosphorylation
In a cell, the rate at which an enzyme will encounter its substrate depends on which of the following?
the concentration of the substrate
What is the function of a kinase?
to add a phosphate group to a molecule
