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Microbiology > Chapter 8B - Microbial Metabolism: Photosynthesis, Autotrophic Growth, & Nitrogen Fixation > Flashcards

Chapter 8B - Microbial Metabolism: Photosynthesis, Autotrophic Growth, & Nitrogen Fixation Flashcards

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Biology 101 flashcards
1
Q

What type of photosynthesis has only been found in cyanobacteria and chloroplasts so far?

A

Type I/II photosynthesis

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2
Q

What are three ways in which type I/II photosynthesis is different from type I and type II photosynthesis?

A
  1. It combines both photosystems into a single cell
  2. Its reaction center and electron transport components are embedded in the thylakoid membrane rather than the cell membrane
  3. It is oxygenic
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3
Q

Cylic photophosphorylation in cyanobacterial photosynthesis uses photosystem __ only.

A

Photosystem I

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4
Q

Cyclic photophosphorylation in cyanbobacterial photosynthesis is exactly like cyclic phosphorylation in type I photosynthesizers except that _____________________ replaces cytochrome c as the periplasmic electron carrier.

A

Plastocyanin

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5
Q

What cofactor is required for plastocyanin?

A

Copper

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6
Q

Noncyclic photophosphorylation in cyanobacterial photosynthesis uses photosystem __.

A

I and II

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7
Q

In cyanobacteria and chloroplasts, photosystem ___ reduces ferredoxin, which can directly reduce NADP+ to NADPH for carbon dioxide fixation. The oxidized reaction center is then reduced by electrons from _________________. However, the immediate source of electrons for ____________________ is not the ultimate electron donor but rather electrons from photosystem __ that have come through quinone and cytochrome _____. Thus, the transfer of electrons from water to NADP requires __ photos for each electron - one each to excit photosystems II and I.

A

Photosystem I

Plastocyanin

Plastocyanin

Photosystem II

Cytochrome b/f

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8
Q

What does cyclic photophosphorylation provide for cyanobacteria?

A

Energy for the cell via the proton gradient

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9
Q

What does noncyclic photophosphorylation provide for cyanobacteria?

A

Primarily reducting power for carbon fixation; however, it can be used for energy too

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10
Q

Can cyanobacteria grow and survive in anaerobic conditions? In other words, do they die at night?

A

No, they do not because they have storage biomolecules and grown by fermentation and heterotrophic respiration

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11
Q

Why are cyanobacteria “so cool” and have been evolutionarily selected for?

A
  1. They use water as a source of electrons and thus can grow autotrophically in niches lacking other sources of electrons like H2 or H2S
  2. Their metabolism paved the way for aerobic organisms
  3. Cyanobacteria likely made plant evolution possible
  4. Oxygen evolution on early earth may have been advantageous because of its toxicity
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12
Q

Cyanobacteria chloroplasts can use ____________ as an electron donor, allowing for autotrophic growth in niches lacking other sources of electrons.

A

Water

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13
Q

_____________________ evolution on early earth may have been advantageous because of its toxicity.

A

Oxygen

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14
Q

An alternative form of photophosphorylation is based on ______________ instead of chlorophyll.

A

Retinal

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15
Q

____________________ in the archae and _____________________ in the bacteria use the light-absorbing pigment retinal covalently bound to the protein to harvest light.

A

Bacteriorhodopsin

Proteorhodopsin

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16
Q

Retinal, in the all trans form, is covalently attached to a ________________ of bacteriorhodopsin. The nitrogen to which it is attached is _____________. Light absorption causes one double bond to isomerize to the cis form. Isomerization of the retinal causes the proton to be lost to the outside. When the retinal spontaneously isomerizes back to the ground state, the ____________ is re-protonated from the _____________.

A

Lysine

Protonated

Lysine

Cytosol

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17
Q

In which groups can bacteriorhodopsin be found?

A

Halophiles

Halobacterium

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18
Q

lightdriven proton pump halobacterian a purple archae in salt marshes

multipass membrane

seven long alpha helixes

surround a chromophore that gives purple cholor

retinal is long unsatur hc attached to lysine

trans to cis changes – conformational rearrangements; light induced isomerization is key to proton pumping

A
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19
Q

What is the distinguishing feature of all autotrophs?

A

Carbon dioxide fixation

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20
Q

What is the most common pathway of carbon dioxide fixation?

A

Calvin-Benson cycle

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21
Q

In the Calvin-Benson cycle, carbon dioxide is fixed by combining with _____________________ to form a six-carbon intermediate that is immediately cleaved to yield two three-carbon acids. Bisphosphoglycerate is reduced to glyceraldehyde-3-phosphate at the redox level of cells. For every __ carbon dioxide molecules fixed, __ glyceraldehyde-3-phosphate molecules are formed - one can be used in biosynthesis and the others are used to regenerate _________________________.

A

Ribulose-bisphosphate

Three

Six

Ribulose-bisphosphate

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22
Q

Which enzyme phosphorylates ribulose–5-phosphate?

A

Phosphoribulokinase

23
Q

Which enzyme adds carbon dioxide to ribulose-bisphosphate and simultaneously splits the six-carbon intermediate?

A

Ribulose-bis-phosphate carbozylase/oxygenase or RuBisCo

24
Q

What is used by a diverse group of autotrophic bacteria and archae to fix carbon dioxide?

A

The reverse TCA cycle

25
Q

What is consumed in the reverse TCA cycle? What is produced?

A

Carbon dioxide and NADH are consumed

Acetyl-CoA is produced

26
Q

Two reactions of the TCA are normally irreversible: alpha-ketoglutarate dehydrogenase and citrate synthase. Cells have to use different enzymes to engage in reverse TCA. How is this done?

A

By using a more powerful reductant, ferredoxin

27
Q

The ______________________ or Wood-Ljungdahl pathway is common in strictly anaerobic autotrophs.

A

Acetyl CoA pathway

28
Q

The acetyl Co-A pathway uses __ carbon dioxide molecules to produce acetyl Co-A, yielding ______________ and water.

A

Acetate

29
Q

In the Wood-Ljungdahl pathway, one of the molecules of carbon dioxide is bound to an enzyme cofactor of the __________ type and is reduced to a ______ group in successive steps. The other carbon dioxide is reduced to an enzyme-bound ____________ ______________, to which the ___________ group is transferred, forming an enzyme-bound acetyl group.

A

Pterin

Methyl

Carbon monoxide

Methyl

30
Q

The key enzyme in the Wood pathway is ______________ ________________, which reduces one carbon dioxide to the enzyme-bound carbon monoxide and then forms the acetyl0CoA from this and the methyl group. This enzyme is embedded in the cell membrane, and it couples endergonic reduction of carbon dioxide to the entry of protons.

A

Acetyl-CoA synthase

31
Q

_________________ are organisms that reduce CO2 to acetate via acetyl CoA or Wood-Ljungdahl pathway. They are strict anaerobes.

A

Acetogens

32
Q

Where does reducing power come from in acetogens?

A

Oxidation of molecular hydrogen (H2) [autotrophic growth]

NADH and reduced ferredoxin [heterotrophic growth]

33
Q

Acetogens use 1 ATP to convert CO2 to acetate and gain __ ATP.

A

1 ATP

34
Q

Acetogens use 1 ATP and produce 1 ATP, resulting in a net ___________ pathway.

A

Neutral

35
Q

Why do acetogens engage in the acetyl-CoA pathway when it does not produce a net yield of ATP?

A

Because it allows for the generation of proton gradient

36
Q

The _________________________ cycle is used by the green nonsulfur bacteria.

A

Hydroxypropionic acid cycle

37
Q

In the hydroxyproprionic acid cycle, __ carbon dioxide molecules are condensed into _______________, which can then be reduced to compounds in central metabolism.

A

Two CO2

Glyoxylate

38
Q

What most frequently limits the ability of microbes to grow in a particular location?

A

Nitrogen

39
Q

A limited number of prokaryotes can use ____ gas. It is a significant advantage for them because nearly all microbes in a habitat must compete for available nitrogenous compounds.

A

N2

40
Q

Nitrogen fixation is a very ______________ process.

A

Expensive

41
Q

The enzyme that is responsible for nitrogen fixation is ______________.

A

Nitrogenase

42
Q

How many ATP does nitrogenase require?

A

16 ATP

43
Q

What is the electron donor in nitrogen fixation?

A

Ferredoxin

44
Q

What drives the reaction of nitrogen fixation?

A

The hydrolysis of 2 ATP for each electron transferred

45
Q

Why is so much ATP required for nitrogen fixation?

A

Because the triple bond between nitrogen atoms in N2 is very stable

46
Q

_________________________ synthesis is tightly regulated to prevent nitrogen fixation when other sources of nitrogen are available.

A

Nitrogenase

47
Q

Nitrogen fixation is an intrinsically ___________________ process.

A

Anaerobic

48
Q

Nitrogenase is highly sensitive to inactivation by __________________.

A

Oxygen

49
Q

Why is nitrogenase highly sensitive to inactivation by oxygen?

A

The extreme oxygen-sensitivity of the active site - oxygen results in the irreversible oxidation of Fe-S center

50
Q

The expression of nitrogenase only occurs in ________________ conditions.

A

Anaerobic

51
Q

There are a number of aerobes that can fix nitrogen, and in most cases, _________________ ______________________ is a component of the protective mechanism in these aerobes, thereby preventing oxygen access to nitrogenase.

A

Aerobic respiration

52
Q

What are legumes?

A

Pod-bearing plants that have nodules

53
Q

What are some examples of legumes?

A

Clover, alfalfa, peanuts, soybeans, peas, mimosas

54
Q

Why are legumes sometimes called “green manure”?

A

Because bacteria enter their roots and form nodules that fix nitrogen for the plant

Microbiology (15 decks)

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