Exam 2 - BIOS 222

Based on the data, which steps in glycolysis are are effectively irreversible?

Steps 1, 3, and 10 because negative delta G is too big it pushes it way forward

In which of the following steps of the citric acid cycle CO2 released?

Steps 3 and 4

How do enzymes maximize the energy harvested from the oxidation of food molecules?

They allow the stepwise oxidation of food molecules, which releases energy in small amounts

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

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?

oxaloacetate

If acetyl CoA labeled with radioactive 14C in both carbon positions were fed into the citric acid cycle, where would the radioactivity be after two turns of the cycle?

oxaloacetate and in CO2

The ethanol in wine and beer is produced from metabolic reactions carried out by the yeast Saccharomyces cerevisiae. Since it is of great commercial value, researchers have studied factors that influence ethanol production. To maximize ethanol yield, which environmental factor should be limiting?

oxygen

In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions?

pyruvate and NADH

Oxidative phosphorylation requires the movement of electrons along the electron-transport chain coupled to the pumping of protons into the intermembrane space. What is the final result of these electron transfers?

(C) O2 is reduced to H2O

Glycolysis occurs in a series of 10 steps using 10 different enzymes. Place the following broad events that occur during glycolysis into their correct order.

1. Energy is invested by using up some ATP 2. The six-carbon sugar is split into two smaller molecules 3. Energy is captured as ATP and NADH 4. Two molecules of pyruvate are generated

What occurs in the first step of the citric acid cycle?

A two-carbon molecule is combined with a four-carbon molecule to form citrate

Most of the energy released by oxidizing glucose is saved in the high-energy bonds of what molecules?

ATP and other activated carriers

Which of the following is NOT part of the process known as "oxidative phosphorylation"?

ATP molecules are produced in the cytosol as glucose is converted into pyruvate

The main regulatory step of glycolysis occurs in step 3. Choose all of the following that correctly describe some aspect of step 3 in glycolysis.

All of them are correct: -The enzyme uses an AtP - The reaction is an irreversible reaction - The enzyme that catalyzes step 3 is phosphofructokinase - the reaction gnerates the product fructose 1,6 bisphosphate

When ATP and food molecules such as fatty acids are abundant, which will occur?

Enzymes involved in gluconeogenesis will use energy to produce glucose.

You are packing for a hiking trip during which you'll be burning a lot of calories with physical activity. You want to pack as efficiently as possible since you need to carry a tent and all your food. You can get the most calories out of 5kg of food if it is in the form of

Fat

When food is plentiful, animals can store glucose as what?

Glycogen

Useful energy is obtained by cells when sugars derived from food are broken down by which processes?

Glycolysis, the citric acid cycle, and oxidative phosphorylation

In the electron transport chain, the oxygen atoms in O2 become part of which of the following molecules?

H2O

In eukaryotic cells, what is the final electron acceptor in the electron transport chain?

O2

If Na+ channels are opened in a cell that was previously at reest, how will the resting membrane potential be affected?

It is more positive

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

Where does the oxidative (oxygen-dependent) stage food molecules occur in a eukaryotic cell?

Mitochondrion

Although the citric acid cycle itself does not use O2, it requires functioning electron transport chain (which uses O2) in order to regenerate which molecule for further use in the citric acid cycle?

NAD+

Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?

Oxaloacetate, NAD+, O2, GDP, GTP, and ATP

Which of the following stages in the breakdown of a piece of toast you ingest generates the most ATP?

Oxidative phosphorylation

When nutrients are plentiful, plants can store glucose as what?

Starch

The NADH generated during glycolysis and the citric acid cycle feeds its high-energy electrons to which of the following?

The electron transport chain

Which of the following processes generates the large number of ATP molecules?

The electron transport chain

In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step?

The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate

What does the term "gluconeogenesis" refer to

The synthesis of glucose from small organic molecules such as pyruvate

Which two-carbon molecules enters the citric acid cycle?

acetyl CoA

Which of the following cells rely exclusively on glycolysis to supply them with ATP?

anaerobically growing yeast

Which statements below accurately describe an aspect of the citric acid cycle? a. The two carbons that enter as acetyl CoA are released in the same cycle as CO2 b. NADH is generated in steps 3,4, and 8 c. Oxaloacetate is regenerated by the end of the citric acid cycle d. The citric acid cycle produces two kinds of high-energy molecules, GTP and NADH.

b. NADH is generated in steps 3,4, and 8 c. Oxaloacetate is regenerated by the end of the citric acid cycle

A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ ! 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell's demise? (a) toxic buildup of carbon dioxide inside the cell (b) toxic buildup of ethanol inside the cell (c) diffusion of ATP out of the cell (d) inability to import sugar into the cell

d - (d) inability to import sugar into the cell

In cells, pyruvate can be converted to which of the following?

lactate, alanine, oxaloacetate, glucose, and acetyl CoA

After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule?

fatty acids

Under anaerobic conditions, which metabolic pathway regenerates the supply of NAD+ needed for glycolysis?

fermentation

In what form do plant and animal cells store fat?

triacylglycerol