Chapter 5: Microbial Metabolism

Question 1

Central Role of ATP

Answer 1

During catabolism, useful energy is temporarily conserved in the “high energy bond” of ATP - adenosine triphosphate. No matter what form of energy a cell uses as its primary source, the energy is ultimately transformed and conserved as ATP - the universal currency of energy exchange in biological systems. When energy is required during anabolism, it may be spent as the high energy bond of ATP which has a value of about 8 kcal per mole. Hence, the conversion of ADP to ATP requires 8 kcal of energy, and the hydrolysis of ATP to ADP releases 8 kcal.Because of the central role of ATP in energy-generating metabolism, expect to see its involvement as a coenzyme in most energy-producing processes in cells.

Question 2

What are the three types of phosphorylation reactions that generate ATP?

Answer 2

Substrate Level, Oxidative, and Photophosphorylation

Question 3

What is substrate level phosphorylation?

Answer 3

ATP is formed when the substrate transfers a high energy phosphate to ADP directly.

Question 4

What are some examples of Substrate Level Phosphorylation?

Answer 4

Glycolysis and the Krebs cycle

Question 5

What is oxidative phosphorylation?

Answer 5

Electrons are transferred from organic compounds to electron carriers (NAD+ and FAD). Electrons are then passed through different carriers to molecules of oxygen. Each transfer results in the release of energy.

Question 6

What is an example of oxidative phosphorylation?

Answer 6

Electron Transport Chain

Question 7

What is photophosphorylation?

Answer 7

It occurs only in photosynthetic cells which contain light trapping pigments like chlorophyll. The process converst light energy to chemical energy (ATP and NADPH). An electron transport chain is involved. An example is photosynthesis.

Question 8

What is oxidation?

Answer 8

The REMOVAL of electrons, producing energy.

Question 9

What is reduction?

Answer 9

The GAINING of electrons.

Question 10

Explain the significance of the REDOX tower.

Answer 10

The redox tower represents the range of possible reduction potentials. Oxidized/electron donors are at the top, and reduced/accepting substances are at the bottom. The farther the electrons drop, the more energy released.

Question 11

What are the steps in Aerobic Respiration?

Answer 11

1. Glycolysis (can occur with or without O2); 2. Pyruvate Oxidation; 3. Kreb’s cycle 4. Electron Transport Chain

**Glycolysis and the Krebs Cycle create a little ATP, but they mostly create the electron carriers that all meet up in step 4. The electron transport chain is where a lot of ATP is created!

Question 12

What goes in and what comes out of glycolysis?

Answer 12

1 molecule of Glucose and NAD+ yields 2 pyruvate, 2 ATPs (because we actually produce 4, but have to use two for the process), 2 NADH (which goes to the electron transport chain to make ATP)

Question 13

What goes in/what comes out of Pyruvate Oxidaion and Acetyl CoA synthesis? (happens in cytoplasm of prokaryotes)

Answer 13

2 Pyruvate yield: 2 acetyl CoA, 2 NADH (which go to the ETC), and 2 CO2

Question 14

What goes in/what comes out of the Krebs/Citric Acid Cycle?

Answer 14

Acetyl CoA goes in and yields 6 NADH, 2FADH2, 2ATP, and 4 CO2

Question 15

What goes in/what comes out of the Electron Transport Chain?

Answer 15

First off, the ETC actually takes place in the prokaryotic cell membrane. The starting material is NADH, FADH2, O2, and ATP Synthase (the turbine that BOOMS and produces ATP as it spins with the hydrogen proton gradient). The end products are 28 ATP, H2O, NAD+, and FAD+. Oxygen is the final electron acceptor.

Question 16

Summarize Aerobic respiration

Answer 16

The various electron transfers in the electron transport chain generate about 34 molecules of ATP from each molecule of glucose oxidized.

Question 17

What is the difference with anaerobic respiration?

Answer 17

With anaerobic respiration, the final electron acceptor is not oxygen, but nitrate, sulfate, carbonate, or CO2.

Question 18

When does fermentation happen?

Answer 18

When Oxygen is NOT presentAfter glucose has been broken down into pyruvic acid, it can be completely broken down in respiration as described above, or it can be converted to an organic product in fermentation, where NAD+ and NADP+ are regenerated and can enter another round of glycolysis.

Question 19

Details of fermentation

Answer 19

Occurs in the cytosolBecause there is no oxygen present, there is no electron transport chain, and no Krebs cycle. So fermentation happens instead. The NADH produced by glycolysis needs a new place to go to drop off electrons.
What happens is that glycolysis generates ATP, and then pyruvate accepts electrons from NADH, thus regenerating NAD+ so that glycolysis can continue to occur.

Question 20

How much ATP is produced in Alcoholic fermentation?

Answer 20

Only 2 ATP made. The NADH produced at the end of glycolysis, takes its electrons to the molecule acetylaldehyde, and becomes NAD+ again, allowing glycolysis to continue again. The bi product of the NADH dropping off electrons with the acetylaldehyde is ETHANOL. (which is why microbes are used to make beer and wine). CO2 is also produced in this process, and that is where carbonation comes from.

Question 21

How much ATP is produced in Lactic Acid Fermentation?

Answer 21

Only 2 ATP made. Glycolysis happens, breaking down glucose to pyruvate. The electrons it gives off are picked up by NAD+. When it picks them up, it becomes NADH and drops the electrons at pyruvate. Pyruvate accepts the electrons and is reduced to lactic acid. The NADH is oxidized to NAD+ and glycolysis can go through another cycle

Question 22

Review Tests from Lab

Answer 22

Can be found in Lab Study Guide

Question 23

PhotoHETEROTROPH Carbon and Energy Source

Answer 23

Use light as a source of energy, but cannot convert carbon dioxide to sugar, so they use organic compounds, such as alcohols, fatty acids, other organic acids and carbohydrates. They do not produce oxygen.

Question 24

PhotoAUTOTROPH Carbon and Energy Source

Answer 24

Use light as a source of energy and carbon dioxide as their chief source of carbon. They are oxygenic.

Question 25

ChemoAUTOTROPH

Answer 25

Use the electrons from reduced inorganic compounds as a source of energy, and they use CO2 as their principal source of carbon.

Question 26

ChemoHETEROTROPHS

Answer 26

Energy and Carbon Sources are usually both glucose. They specifically use hydrogen atoms in organic compounds as their energy source.
**Most bacteria, and all fungi, protozoa, and animals are chemoheterotrophs.