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

Question 1

____________________________ is mediated by membrane-embedded reactionc enters.

Answer 1

Photochemistry

Question 2

What is present in all reaction centers?

Answer 2

Chlorophyll

Question 3

In almost all prokaryotes, reaction centers are located in the cell membrane or invaginations of it. The only exception is the __________________, which have intracellular membrane vesicles called __________________, in which reaction centers are embedded.

Answer 3

Cyanobacteria

Thylakoids

Question 4

_________________________ is a tetrapyrrole with a magnesium atom in the center and is present in all reaction centers.

Answer 4

Chlorophyll

Question 5

R groups vary in different chlorophylls; however, ___ is always a long hydrocarbon chain.

Answer 5

R₆

Question 6

Some reaction centers also contain ___________________ or chlorophyll molecules that lack the central magnesium atom and are tightly bound quinones.

Answer 6

Pheophytins

Question 7

__________________________ are bacterial compartments consisting of polyhedral protein shells filled with the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase

Answer 7

Carboxysomes

Question 8

Reaction centers have prosthetic groups that undergo irreversible redox reactions. True or false?

Answer 8

False; these reactions are reversible

Question 9

Prosthetic groups of reaction centers may include ________________, pheophytin, and/or _____________.

Answer 9

Chlorophyll

Quinones

Question 10

What are reaction centers associated with?

Answer 10

Pigment antennas

Question 11

What is a pigment antenna?

Answer 11

A large group of pigment molecules that absorbs light

Question 12

What is resonance energy transfer?

Answer 12

Absorption of a photon by a molecule takes place leading to electronic excitation when the energy of the captured photon matches that of an electronic transition. The fate of such excitation can be a return to the ground state or another electronic state of the same molecule. When the excited molecule has a nearby neighbour molecule, the excitation energy may also be transferred, through electromagnetic interactions, from one molecule to another.

Question 13

In resonance electron transfer, are electrons transferred?

Answer 13

No, only the energy absorbed is transferred from one pigment molecule to another through the antenna complex until it reaches the reaction center

Question 14

Usually the pigment molecules are chlorophylls, but in the cyanobacteria, several linear tetrapyyroles called ______________________ are used.

Answer 14

Phycobilins

Question 15

Three groups of bacter have distinctive anatomical structures to house their pigment antennas. What are these three bacteria?

Answer 15

Cyanobacteria

Green-sulfur bacteria

Acidobacteria

Question 16

Phycobillins in the cyanobacteria are contained in ______________________.

Answer 16

Phycobilisomes

Question 17

Chlorophyll in green-sulfur bacteria and Acidobacteria are contained in ___________________.

Answer 17

Chlorosomes

Question 18

____________ _______________________ generates energy in the light with no material input.

Answer 18

Cyclic photophosphorylation

Question 19

What is the general scheme of cyclic photophosphorylation?

Answer 19

The reaction center, energized by two photons of light, transfers two electrons to an electron transport system. As electrons pass through the electron transport chain, protons are pumped, maintaining a protonic potential. The electrons are transferred back to the oxidized reaction center, reducing it back to the ground state

Question 20

In cyclic photophosphorylation, what acts as both the electron donor and acceptor?

Answer 20

The reaction center

Question 21

Do all phototrophs employ cyclic photophosphorylation for maintaining the protonic potential?

Answer 21

Yes, at least all known phototrophs do

Question 22

While energy is transferred from one chlorophyll molecule to the next in the pigment antenna, ___________________ are transferred in the ________________ ______________.

Answer 22

Electrons

Reaction center

Question 23

Unlike phototrophs, autotrophs require an exogenous electron donor. Why?

Answer 23

Because they need to reduce carbon dioxide to organic material

Question 24

What two things are needed to fix carbon?

Answer 24

NADPH

Reduced ferredoxin

Question 25

Electron donors and ___________ \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ are needed for autotrophic growth only.

Answer 25

Noncyclic photophosphorylation

Question 26

The challenge of phototrophs is to use their electron donor, often a weak reducing agent like water or H₂S, to reduce NADP⁺ or ferredoxin. Because this is a strongly endergonic reaction, an input of energy is necessary. How do autotrophic growth gain the energy to do so?

Answer 26

The mechanism for putting energy into this reaction is to route the electrons through the reaction center; thus, light provides some or all of the necessary energy

Question 27

What is the general scheme for noncyclic photophosphorylation?

Answer 27

The reaction center, excited by two photons of light, transfers electrons to form NADPH or reduced ferredoxin, which are then used to reduce carbon dioxide. The oxidized reaction center is reduced back to the ground state by electrons from the electron donor

Question 28

How is the oxidized reaction center reduced in cyclic photophosphorylation? Noncyclic phosphorylation?

Answer 28

Cyclic photophosphorylation: the electrons are cycled back to the reaction center via cytochrome c Noncyclic photophosphorylation: the electrons are accepted from an electron donor

Question 29

Why does photoheterotrophic growth not require an electron donor?

Answer 29

Because they assimilate organic materials from their environments for biomass

Question 30

Cells that grow photoheterotrophically do not need an electron donor. They use cyclic photophosphorylation to generate energy, and they assimilate organic compounds from the enviornment as their source of \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. The organic material is rearranged to produce the necessary precursor metabolites and then all of the molecules of the cell.

Answer 30

Carbon

Question 31

When the organic substrate is at the same oxidation level as cell material, there is no net reduction or oxidation because it is unnecessary, and thus no electron donor or acceptor is needed - for instance, the assimilation of ____________ \_\_\_\_\_\_\_\_\_.

Answer 31

Lactic acid

Question 32

However, when the organic material is more oxidized then the cell material, it must be reduced before assimiliation - as in the case of \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. Under these conditions, typicalyl some of the substrate is oxidized to ___________ \_\_\_\_\_\_\_\_\_\_\_\_\_ with the electrons generated being used to reduce the rest of the substrate to cell material.

Answer 32

Pyruvate Carbon dioxide

Question 33

If the organic substrate is more reduced than the cell material, it has to be oxidized before assimilation - for example, \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_. In this case, cells typically fix sufficient carbon dioxide to provide an electron acceptor for the oxidation of the organic substrate. Thus, their cell carbon comes partially from the organic compound and partly from carbon dioxide.

Answer 33

Butyrate

Question 34

There are ____ fundamentally different types of reaction center.

Answer 34

Two

Question 35

What are the two different types of reaction center?

Answer 35

Type I reaction centers Type II reaction centers

Question 36

Type I reaction centers are _____________ \_\_\_\_\_\_\_\_\_\_\_\_\_ for which the electron acceptor is the very electronegative iron-sulfur protein \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 36

Ferredoxin reductases Ferredoxin

Question 37

Type II reaction centers are __________________ \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ that reduce ______________ to quinols.

Answer 37

Quinone reductases Quinones

Question 38

How may distinct types of photosynthesis are there?

Answer 38

Three

Question 39

What are the three types of photosynthesis?

Answer 39

Type I Type II Type I/II

Question 40

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ____ photosynthesis uses only ferredoxin, a __________________ \_\_ reaction center.

Answer 40

Type I

Question 41

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ___ photosynthesis uses only _________________ \_\_ reaction centers, quinones.

Answer 41

Type II

Question 42

What two types of photosynthesis are anoxygenic, meaning that they don't use water and don't generate oxygen?

Answer 42

Type I Type II

Question 43

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ___ photosynthesis uses both types of reaction centers and is \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, meaning that it uses water and produces oxygen.

Answer 43

Type I/II Oxygenic

Question 44

Photosynthesis using reaction centers is confined to the _______________ and their descendents the chloroplasts.

Answer 44

Bacteria

Question 45

There are six different groupings regarding distribution of photosynthesis within the bacterial tree. Which bacteria use Type I photosynthesis?

Answer 45

Green sulfur bacteria Heliobacteria

Question 46

Which bacteria use type II photosynthesis?

Answer 46

Green nonsulfur bacteria Purple sulfur bacteria Purple nonsulfur bacteria

Question 47

Which bacteria use type I/II photosynthesis?

Answer 47

Cyanobacteria

Question 48

Cyclic photophosphorylation in type I photosynthesis uses _______________________ \_\_.

Answer 48

Photosystem I

Question 49

The green sulfur bacteria are \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, meaning that they receive their energy from light and use inorganic electron donors to fuel biosynthetic reactions.

Answer 49

Photolithotrophs

Question 50

What is a lithotroph?

Answer 50

An organism that uses inorganic electron donors for energy or biosynthesis

Question 51

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, like green sulfur bacteria, can use carbon dioxide as the sole carbon source but also can use _____________________ as a carbon source.

Answer 51

Photolithotrophs Acetate

Question 52

Photolithotrophs oxidize ______________ with ultimate electron donors generally \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 52

Sulfur Sulfide

Question 53

The ultimate electron donor in photolithotrophs is generally sulfide, which is oxidized to _____________ and accumulates outside of cells. This compound is further oxidized to \_\_\_\_\_\_\_\_\_\_\_\_.

Answer 53

Sulfur Sulfate

Question 54

Are green sulfur bacteria aerobes or anaerobes?

Answer 54

They are strict anaerobes

Question 55

Do green suflur bacteria contain RuBisCO?

Answer 55

No

Question 56

In type I photosynthesis, photosystem I is used. The reaction center reduces \_\_\_\_\_\_\_\_\_\_\_\_\_, which reduces in turn _____________________ and then the cytochrome b/c complex. This complex then reduces periplasmic __________________ \_\_, which diffuses through the periplasm to the oxidized reaction center and reduces it back to the ground state.

Answer 56

Ferredoxin Quinone Cytochrome c

Question 57

What acts as the proton pump in type I photosynthesis?

Answer 57

Cytochrome b/c complex

Question 58

Noncyclic photophosphorylation in type I photosynthesis uses photosystem I only. To generate NADPH needed for autotrophic carbon dioxide fixation, green sulfur bacteria use ______ or reduced _____ compounds as electron donors.

Answer 58

H₂ Sulfur

Question 59

In noncylic photophosphorylation in type I photosynthesis, electrons from H₂ or H₂S reduce the periplasmic _______________ \_\_\_, which then passes electrons on to the oxidized reaction center. From the excited reaction center, they are transferred to \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, which has a reduction potential more negative NADPH. Thus the electrons pass from _________________ to NADP+ - a reaction catalyzed by the membrane \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 59

Cytochrome c Ferredoxin Ferredoxin Ferredoxin-NADP⁺ reductase

Question 60

Which bacteria use cyclic phosphorylation type II photosynthesis?

Answer 60

Purple bacteria Green non-sulfur bacteria

Question 61

The purple bacteria include the _________________ and _________________ bacteria.

Answer 61

Purple sulfur Purple non-sulfur

Question 62

What is the primary difference between the purple sulfur and purple non-sulfur bacteria?

Answer 62

The purple sulfur bacteria use sulfur or sulfides as electron donors while the purple non-sulfur bacteria use hydrogen or other molecules as electron donors

Question 63

Most green non-sulfur bacteria are \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 63

Facultative aerobes

Question 64

Under aerobic growth, green non-sulfur do not engage in \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 64

Photosynthesis

Question 65

Cyclic photophosphorylation type II photosynthesis uses ____________________ \_\_.

Answer 65

Photosystem II

Question 66

The cyclic system in type II photosynthesis is basically the same as in type I photosynthesis except that the reaction center reduces \_\_\_\_\_\_\_\_\_\_\_\_\_\_, not ferredoxin. From there, the system is the same as in type I photosynthesis: _________________ reduces the periplasmic _____________ \_\_ by passing its electrons through the cytochrome b/c complex, simultaneously pumping protons into the periplasm. The reduced _______________ \_\_\_ diffuses through the periplasm to the oxidized reaction center.

Answer 66

Quinone Quinol Cytochrome c Cyctochrome c

Question 67

Noncyclic photophosphorylation type II photosynthesis requires ________________ \_\_\_\_\_\_\_\_\_\_\_\_\_ ____________ to make NADPH.

Answer 67

Reverse electron transport

Question 68

Why must a reverse electron transport system be utilized in noncyclic photophosphorylation type II photosynthesis?

Answer 68

Because NADPH is a better reducing agent than quinol

Question 69

In type II photosynthesis, noncyclic photophosphorylation requires reverse electron transport. Oxidation of the excited photosystem reduces \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, which reduces ______________ to ___________ in a two step reverse electron transport driven by the entry of protons. _______________ is used as reductant in the fixation of CO2. Oxidation of a chemical electron donor reduces the periplasmic cytochrome c, which diffuses through the periplasm to the oxidized photosystem and reduces it back to the ground state.

Answer 69

Quinone NADP+ NADPH NADPH