Microbial Metabolism

Question 1

What is chemical energy?

Answer 1

The energy found in molecules like carbohydrates and proteins.

Question 2

What compounds are essential for bacteria? What are not most common ones important for?

Answer 2

Essential= carbon, oxygen, nitrogen, phosphorus, magnesium, sulphur and potassium

Non essential ones are important for metabolism, growth and electron transport reactions.

Question 3

What is the difference between macro- and micronutrients?

Answer 3

Macronutrients are required in large quantities while micronutrients are required in small quantities.

Question 4

What is metabolism?

Answer 4

The sum of anabolic and catabolic cellular reactions.

Question 5

What is the difference between anabolic- and catabolic reactions?

Answer 5

Anabolic reactions involve the building up of larger molecules from smaller molecules, using energy, while Catabolic reactions involve the breaking down of larger molecules into smaller molecules, releasing energy.

Question 6

What is the difference between autotrophic- and heterotrophic bacteria?

Answer 6

autotrophic bacteria uses inorganic carbon as a carbon source, while heterotrophic bacteria uses organic carbon source as a carbon source.

Question 7

What is the difference between chemotrophic- and phototrophic bacteria?

Answer 7

Chemotrophic bacteria oxidizes chemical compounds to obtain electrons, phototrophic bacteria obtains energy from sunlight.

Question 8

What is the difference between organotrophic- and lithotrophic bacteria?

Answer 8

Organotrophic bacteria obtain electrons from organic substrates, lithotrophic bacteria obtains electrons from inorganic substrates.

Question 9

What is the difference between oxygenic- and anoxygenic photosynthesis?

Answer 9

Oxygenic photosynthesis yields oxygen gas while anoxygenic photosynthesis does not yield oxygen gas

Question 10

What is the difference between oxidation and reduction?

Answer 10

Oxidation is the loss of electrons while Reduction is the gain of electrons.

Question 11

What is a redox reaction?

Answer 11

A reaction in which oxidation and reduction occur at the same time, electrons are transferred from a donor to an acceptor.

Question 12

What information can be found in the Redox-tower?

Answer 12

The range of reduction potentials possible for redox couples in nature.

Question 13

What does redox-potential mean? How is this coupled to free energy?

Answer 13

Redox potential is the tendency for a substance to donate or accept electrons.
change in redox potential is proportional to change in free energy

Question 14

What is the overall difference in ATP-production between aerobic cellular respiration, anaerobic respiration and fermentation?

Answer 14

Aerobic cellular respiration yields lots of ATP, Anaerobic cellular respiration and fermentation yield little ATP.

Question 15

What are NADH and FADH2?

Answer 15

High energy electron carriers used to transport electrons generated from glycolysis and kreb´s cycle to the electron transport chain.

Question 16

What is substrate-level phosphorylation and oxidative phosphorylation?

Answer 16

substrate level phosphorylation is the phosphorylation of ADP with a phosphate group and energy from a coupled reaction.

Oxidative phosphorylation is the generation of ATP through the oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping of protons.

Question 17

Describe the glycolysis briefly. How many ATP and NADH are produces from one 6-carbon glucose molecule?

Answer 17

Occurs in the cytoplasm of most cells
Involves ”splitting” of a 6-carbon glucose
molecule into two 3-carbon molecules (pyruvate)
Results in a net gain of:
o Two ATP
o Two NADH

Question 18

What is produced during the synthesis of acetyl-CoA from two pyruvate molecules?

Answer 18

Two Acetyl-CoA
Two CO2
Two NADH (electron transporters)

Question 19

What is happening in the Kreb’s cycle? What is produced?

Answer 19

There is a great amount of energy in the bonds of Acetyl-CoA
In the Kreb’s cycle a lot of this energy is transferred to NADH and FADH2 Occurs in the cytoplasm in prokaryotes and in matrix of mitochondria in eukaryotes
Two Acetyl-CoA result in:
o Two ATP
o Two FADH2
o Six NADH
o Four CO2

Question 20

What is the function of the electron transport chain (ETC)? Describe in detail how ETC works.

Answer 20

ETC is located in the plasma
membrane in prokaryotes and
in ”cristae” of mitochondria in eukaryotes
• Three main events are important for electron
transport chain’s generation of ATP
o Redox reactions
o Creation of proton gradient
o Chemiosmosis
Redox
• NADH och FADH2 bring electrons and protons (H+) to ETC
• Carrier molecules pass electrons from one carrier to another and finally to an acceptor
Creating a proton gradient
• The energy created from each electron being passed
down the chain is used to pump protons (H+) from
one side of the membrane to the other
Chemiosmosis
• H+ ions flow down through a protein channel (ATP synthase) that phosphorylates ADP into
ATP

Question 21

How does ATP-synthase produce ATP?

Answer 21

H+ ions flow down through ATP synthase and it then phosphorylates ADP into
ATP

Question 22

How many ATP are created from one glucose molecule? Why does different text-books show different number?

Answer 22

32 ATP

This is because different energy substrates enter the mitochondria or the oxidative pathway at different points along the path

Question 23

What is anaerobic respiration?

Answer 23

It is cellular respiration that occurs in the absence of oxygen and produces less energy.

Question 24

Which electron acceptors can aerobic- and anaerobic organisms use?

Answer 24

Aerobic organisms use oxygen

Anaerobic organisms use nitrate, carbonate or sulphate.

Question 25

Why is less energy obtained when other electron acceptors than oxygen are used?

Answer 25

Higher up in the redox tower means less energy production.

Question 26

Describe fermentation in detail. What is the essential cellular function of fermentation?

Answer 26

Fermentation is another anaerobic (non-oxygen-requiring) pathway for breaking down glucose, one that’s performed by many types of organisms and cells. In fermentation, the only energy extraction pathway is glycolysis, with one or two extra reactions tacked on at the end.
Fermentation and cellular respiration begin the same way, with glycolysis. In fermentation, however, the pyruvate made in glycolysis does not continue through oxidation and the citric acid cycle, and the electron transport chain does not run.

To oxidize NADH into NAD+

Question 27

Describe the chemical reactions in lactate- and ethanol fermentation.

Answer 27

Lactic acid fermentation
CH3COCO2H + NADH→ CH3CH(OH)CO2H + NAD+ pyruvic acid → lactic acid with regeneration of 1 mole of NAD+ per pyruvate, or two moles of NAD+ per mole of glucose
Catalyzed by lactic acid dehydrogenase (operating in the reverse of the normal direction).

Ethanol fermentation
CH3COCO2H + NADH → CO2 + CH3CH2OH + NAD+ pyruvic acid → carbon dioxide + ethanol with regeneration of 1 mole of NAD+ per pyruvate or two moles of NAD+ per mole of glucose
This is a two-step process, catalyzed by pyruvate decarboxylase (forming acetaldehyde + CO2) and alcohol dehydrogenase (forming ethanol)