Chapter 8A - Microbial Metabolism: Photosynthesis, Autotrophic Growth, & Nitrogen Fixation Flashcards
____________________________ is mediated by membrane-embedded reactionc enters.
Photochemistry
What is present in all reaction centers?
Chlorophyll
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.
Cyanobacteria
Thylakoids
_________________________ is a tetrapyrrole with a magnesium atom in the center and is present in all reaction centers.
Chlorophyll
R groups vary in different chlorophylls; however, ___ is always a long hydrocarbon chain.
R6
Some reaction centers also contain ___________________ or chlorophyll molecules that lack the central magnesium atom and are tightly bound quinones.
Pheophytins
__________________________ are bacterial compartments consisting of polyhedral protein shells filled with the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase
Carboxysomes
Reaction centers have prosthetic groups that undergo irreversible redox reactions. True or false?
False; these reactions are reversible
Prosthetic groups of reaction centers may include ________________, pheophytin, and/or _____________.
Chlorophyll
Quinones
What are reaction centers associated with?
Pigment antennas
What is a pigment antenna?
A large group of pigment molecules that absorbs light
What is resonance energy transfer?
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.
In resonance electron transfer, are electrons transferred?
No, only the energy absorbed is transferred from one pigment molecule to another through the antenna complex until it reaches the reaction center
Usually the pigment molecules are chlorophylls, but in the cyanobacteria, several linear tetrapyyroles called ______________________ are used.
Phycobilins
Three groups of bacter have distinctive anatomical structures to house their pigment antennas. What are these three bacteria?
Cyanobacteria
Green-sulfur bacteria
Acidobacteria
Phycobillins in the cyanobacteria are contained in ______________________.
Phycobilisomes
Chlorophyll in green-sulfur bacteria and Acidobacteria are contained in ___________________.
Chlorosomes
____________ _______________________ generates energy in the light with no material input.
Cyclic photophosphorylation
What is the general scheme of cyclic photophosphorylation?
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
In cyclic photophosphorylation, what acts as both the electron donor and acceptor?
The reaction center
Do all phototrophs employ cyclic photophosphorylation for maintaining the protonic potential?
Yes, at least all known phototrophs do
While energy is transferred from one chlorophyll molecule to the next in the pigment antenna, ___________________ are transferred in the ________________ ______________.
Electrons
Reaction center
Unlike phototrophs, autotrophs require an exogenous electron donor. Why?
Because they need to reduce carbon dioxide to organic material
What two things are needed to fix carbon?
NADPH
Reduced ferredoxin
Electron donors and ___________ ___________________ are needed for autotrophic growth only.
Noncyclic photophosphorylation
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?
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
What is the general scheme for noncyclic photophosphorylation?
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