Catabolism: Fermentation and Respiration

Question 1

What is fermentation?

Answer 1

Fermentation is a metabolic process that converts sugar to acids, gases, or alcohol in the absence of oxygen.

Question 2

What is respiration?

Answer 2

Respiration is a biochemical process in which cells convert nutrients into energy, typically involving oxygen.

Question 3

What is glycolysis?

Answer 3

Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH.

Question 4

What is the name of the biochemical pathway almost always used to perform glycolysis?

Answer 4

The Embden-Meyerhof pathway.

Question 5

If glucose is respired, what happens to pyruvate?

Answer 5

Pyruvate is converted into acetyl-CoA and enters the citric acid cycle.

Question 6

If glucose is fermented, what happens to pyruvate?

Answer 6

Pyruvate is converted into various fermentation products like ethanol or lactic acid.

Question 7

What is substrate-level phosphorylation?

Answer 7

Substrate-level phosphorylation is the direct transfer of a phosphate group to ADP to form ATP during glycolysis.

Question 8

During glycolysis, how many molecules of pyruvate are produced from each molecule of glucose?

Answer 8

Two molecules of pyruvate are produced from each molecule of glucose.

Question 9

What steps of glycolysis require the input of ATP?

Answer 9

1. Glucose to glucose-6-phosphate (enzyme: hexokinase)
2. Fructose-6-phosphate to fructose-1,6-bisphosphate (enzyme: phosphofructokinase)

Question 10

What intermediates of glycolysis are energy-rich compounds?

Answer 10

1. 1,3-bisphosphoglycerate
2. Phosphoenolpyruvate

Question 11

What steps of glycolysis result in the production of ATP?

Answer 11

1. 1,3-bisphosphoglycerate to 3-phosphoglycerate (enzyme: phosphoglycerate kinase)
2. Phosphoenolpyruvate to pyruvate (enzyme: pyruvate kinase)

Question 12

What step of glycolysis results in the production of NADH?

Answer 12

Glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate (enzyme: glyceraldehyde-3-phosphate dehydrogenase)

Question 13

At the end of the first ten steps of glycolysis, how many (net) ATP and NADH molecules are produced per molecule of glucose that is catabolized?

Answer 13

Net 2 ATP and 2 NADH molecules are produced.

Question 14

At the end of glycolysis, why must pyruvate be either fermented or respired?

Answer 14

To regenerate NAD+ needed for glycolysis to continue.

Question 15

Pyruvate fermentation by yeasts produces what products?

Answer 15

Ethanol and carbon dioxide.

Question 16

Pyruvate fermentation by streptococci and some lactobacilli produces what products?

Answer 16

Lactic acid.

Question 17

What are some examples of non-carbohydrates that can be fermented (by some bacteria)?

Answer 17

Proteins and fats.

Question 18

How do humans benefit from microbial fermentation reactions?

Answer 18

Fermented foods provide probiotics and enhance food preservation.

Question 19

In order to begin the citric acid cycle (CAC), pyruvate must be converted into what energy-rich substance?

Answer 19

Acetyl-CoA.

Two other substances produced are NADH and carbon dioxide.

Question 20

In the first step of the CAC, what two substances combine to form citric acid?

Answer 20

Acetyl-CoA and oxaloacetate.

Question 21

How many molecules of carbon dioxide, NADH, FADH2, and ATP (GTP) are produced per molecule of pyruvate that is completely oxidized in the CAC?

Answer 21

3 CO2, 4 NADH, 1 FADH2, and 1 ATP (or GTP).

Question 22

In the last step of the CAC, what substance must be regenerated in order for the CAC to continue?

Answer 22

Oxaloacetate.

Question 23

What two substances must be reoxidized in order for the CAC to continue?

Answer 23

NADH and FADH2.

This process occurs in the mitochondria.

Question 24

During aerobic respiration, how many ATP molecules are produced per NADH molecule oxidized?

Answer 24

Approximately 2.5 ATP.

Question 25

During aerobic respiration, how many ATP molecules are produced per FADH2 molecule oxidized?

Answer 25

Approximately 1.5 ATP.

Question 26

Where do electron transport reactions occur in prokaryotes?

Answer 26

In the plasma membrane.

Question 27

What four types of oxidation-reduction enzymes are involved in electron transport?

Answer 27

Flavoproteins, cytochromes, nonheme iron-sulfur proteins, and quinones.

Question 28

How are these molecules arranged in the membrane?

Answer 28

In a series, allowing for electron transfer.

Question 29

What are flavoproteins?

Answer 29

Flavoproteins are proteins that contain a flavin group and participate in electron transport.

Question 30

What are cytochromes?

Answer 30

Cytochromes are heme-containing proteins that transfer electrons in the electron transport chain.

Question 31

What are nonheme iron-sulfur proteins?

Answer 31

Proteins that contain iron-sulfur clusters and participate in electron transport.

Question 32

What are quinones?

Answer 32

Quinones are small, lipid-soluble molecules that shuttle electrons in the electron transport chain.

Question 33

What are the two most common quinones found in Bacteria and Archaea?

Answer 33

Ubiquinone (coenzyme Q) and plastoquinone.

Question 34

Which electron carriers accept 2 e- and 2 H+?

Answer 34

Quinones.

Question 35

Which electron carriers only accept electrons?

Answer 35

Cytochromes and nonheme iron-sulfur proteins.

Question 36

What happens to protons during electron transport?

Answer 36

Protons are pumped out of the cell, creating a proton gradient.

Question 37

What are the sources of these protons?

Answer 37

From the oxidation of NADH and FADH2.

Question 38

What exactly is the proton motive force?

Answer 38

The potential energy stored as a gradient of protons across a membrane. ## Footnote It is established by the pumping of protons during electron transport.

Question 39

How can prokaryotic cells use the PMF?

Answer 39

To drive ATP synthesis, transport nutrients, and rotate flagella.

Question 40

What are the three characteristics of all known electron transport chains?

Answer 40

1. They are located in a membrane. 2. They involve a series of redox reactions. 3. They create a proton gradient.

Question 41

Complex I of the electron transport chain (ETC) is also called what?

Answer 41

NADH dehydrogenase.

Question 42

What molecule delivers electrons and protons to Complex I?

Answer 42

NADH.

Question 43

How many protons are transported out of the cell by Complex I?

Answer 43

Four protons.

Question 44

Complex II of the ETC is also called what?

Answer 44

Succinate dehydrogenase.

Question 45

What molecule delivers electrons and protons to Complex II?

Answer 45

FADH2.

Question 46

How many protons are transported out of the cell by Complex II?

Answer 46

Zero protons.

Question 47

Complex III of the ETC is also called what?

Answer 47

Cytochrome bc1 complex.

Question 48

What molecule delivers (only) electrons to Complex III?

Answer 48

Ubiquinol.

Question 49

How many protons are transported out of the cell by Complex III?

Answer 49

Four protons.

Question 50

What is the major function of Complex III?

Answer 50

To transfer electrons from ubiquinol to cytochrome c.

Question 51

Complex IV of the ETC contains what two cytochromes?

Answer 51

Cytochrome a and cytochrome a3.

Question 52

What molecule delivers (only) electrons to Complex IV?

Answer 52

Cytochrome c.

Question 53

What is the major function of Complex IV?

Answer 53

To transfer electrons to oxygen, forming water.

Question 54

How many protons are transported out of the cell by Complex IV?

Answer 54

Two protons.

Question 55

For every molecule of NADH that delivers electrons to the ETC, what is the total number of protons transported out of the cell?

Answer 55

Ten protons.

Question 56

For every molecule of FADH2 that delivers electrons to the ETC, what is the total number of protons transported out of the cell?

Answer 56

Six protons.

Question 57

What is ATP synthase (ATPase)?

Answer 57

An enzyme that synthesizes ATP from ADP and inorganic phosphate using the proton motive force.

Question 58

What is oxidative phosphorylation?

Answer 58

The process of ATP production that occurs when electrons are transferred through the electron transport chain.

Question 59

What are the two components of ATP synthase, where are they located, and what is their primary function?

Answer 59

1. F0 component (membrane-bound) - transports protons. 2. F1 component (in the cytoplasm) - synthesizes ATP.

Question 60

Which ATP synthase component is the stator and which is the rotor?

Answer 60

F0 is the rotor and F1 is the stator.

Question 61

How many protons must re-enter the cell through ATPase to produce one molecule of ATP?

Answer 61

Three protons.

Question 62

Why do bacteria that lack ETC still have ATPases?

Answer 62

To generate ATP through substrate-level phosphorylation.

Question 63

What is aerobic respiration?

Answer 63

Aerobic respiration is the process of producing cellular energy in the presence of oxygen.

Question 64

What is anaerobic respiration?

Answer 64

Anaerobic respiration is the process of producing cellular energy without oxygen.

Question 65

What are examples of terminal electron acceptors used in anaerobic respiration?

Answer 65

Nitrate, sulfate, and carbon dioxide.

Question 66

Why does anaerobic respiration yield less ATP production than aerobic respiration?

Answer 66

Because the electron transport chain is less efficient without oxygen as the final electron acceptor.

Question 67

What are some examples of electron donors used by chemolithotrophs?

Answer 67

Hydrogen, sulfur, and ammonia.

Question 68

Why are chemoorganotrophs and chemolithotrophs commonly found in the same habitats?

Answer 68

They can utilize different energy sources in the same environment.

Question 69

What is photophosphorylation?

Answer 69

The process of generating ATP from ADP using the energy from light.

Question 70

How is fermentation fundamentally different from all other methods of microbial energy conservation?

Answer 70

Fermentation does not require an electron transport chain and occurs in the absence of oxygen.