Metabolism: Energy Release and Conservation
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96 Terms
Catabolism
breakdown of larger, more complex molecules into
smaller, simpler ones
energy is released and some is trapped and made available for
work
Anabolism
synthesis of complex molecules from simpler ones with the input of energy
Phototrophy
using light as an energy source (like cyanobacteria or plants
Chemoorganotrophy
using organic chemicals (like glucose).
Chemolithotrophy
using inorganic chemicals (like hydrogen gas, ammonia, or iron).
Chemotrophs
oxidize their energy sources (remove electrons from them) and must transfer those electrons to an electron acceptor (either oxygen or something else).
What are the three main sources of energy for microorganisms?
Phototrophy, chemoorganotrophy, chemolithotrophy.
What is phototrophy?
Using light as an energy source.
What is chemoorganotrophy?
Using organic compounds as energy and electron sources.
What is chemolithotrophy?
Using inorganic compounds as energy and electron sources.
How do chemotrophs obtain energy?
By oxidizing chemical compounds and transferring electrons to an electron acceptor.
What are exogenous electron acceptors?
External compounds (like oxygen or nitrate) that accept electrons during respiration.
What is fermentation?
An anaerobic process where energy substrates are oxidized without using exogenous electron acceptors.
Is fermentation efficient in generating ATP?
No, it generates very little ATP (only 2 per glucose).
What is aerobic respiration?
Oxidation of substrates using oxygen as the terminal electron acceptor.
Why is aerobic respiration efficient?
It produces large amounts of ATP via the electron transport chain (ETC).
Where does the ETC occur in eukaryotes?
In the inner mitochondrial membrane.
Where does the ETC occur in prokaryotes?
In the plasma membrane
What is the main role of the ETC?
To transfer electrons and create a proton gradient for ATP synthesis.
What are the two components of oxidative phosphorylation?
The electron transport chain and ATP synthase.
What is the chemiosmotic hypothesis?
A theory that ETC activity creates a proton gradient (PMF) used to drive ATP synthesis.
What is PMF (proton motive force)?
The energy stored as a proton gradient across a membrane.
What enzyme uses PMF to make ATP?
ATP synthase.
What are the parts of ATP synthase?
F0 drives the oxidative phosphorylation
F1 is free floating
What do blockers of ETC do?
Inhibit electron flow (e.g., cyanide blocks oxygen binding).
What do uncouplers do?
Allow electron flow, but disconnect it from oxidative phosphorylation
Which yields more ATP: fermentation or aerobic respiration?
Aerobic respiration.
What is the Pasteur effect?
Decrease in sugar metabolism rate when switching from anaerobic to aerobic conditions due to higher ATP yield per sugar.
Why do bacteria often produce less ATP than eukaryotes?
Their ETCs may be shorter, branched, or less efficient.
What is anaerobic respiration?
A form of respiration where a terminal electron acceptor other than oxygen is used.
How does anaerobic respiration differ from fermentation?
Anaerobic respiration uses the electron transport chain; fermentation does not.
Why does anaerobic respiration yield less energy than aerobic respiration?
Because alternative electron acceptors have a lower redox potential (E₀) than oxygen.
What is dissimilatory nitrate reduction?
The use of nitrate as a terminal electron acceptor
Is dissimilatory nitrate reduction energy efficient
No, it’s energetically less efficient than using oxygen.
What is denitrification?
The stepwise reduction of nitrate (NO₃⁻) to nitrogen gas (N₂).
Why is denitrification ecologically important?
It returns nitrogen to the atmosphere and reduces soil nitrate levels.
What types of carbohydrates can microbes use for energy?
Monosaccharides, disaccharides, polysaccharides.
What are monosaccharides converted into before being used?
Intermediates that enter the glycolytic pathway.
How are disaccharides and polysaccharides broken down?
Using hydrolases (with water) or phosphorylases (with phosphate).
How do microbes digest large polysaccharides in the environment?
They secrete hydrolytic enzymes to break them into smaller sugars.
Why do microbes use external enzymes for carbohydrate digestion?
To break down large molecules too big to be transported into the cell.
What are reserve polymers?
Stored internal energy sources used when external nutrients are unavailable.
Give two examples of reserve polymers.
Glycogen and PHB starch.
Q: How are glycogen and starch broken down?
A: By phosphorylases into glucose-1-phosphate
Q: What is PHB broken down into?
A: Acetyl-CoA.
Q: What enzyme breaks down triglycerides?
A: Lipases.
What are the two products of triglyceride hydrolysis?
Glycerol and fatty acids.
How is glycerol metabolized?
It enters the glycolytic pathway.
How are fatty acids often oxidized?
Via the β-oxidation pathway.
What happens to acetyl-CoA produced from β-oxidation?
It enters the TCA cycle or is used for biosynthesis.
What enzyme breaks proteins into amino acids?
Protease
What is deamination?
Removal of the amino group from an amino acid.
What happens to amino acids after deamination?
The remaining organic acid is converted into pyruvate, acetyl-CoA, or a TCA intermediate.
What is transamination?
Transfer of an amino group from one amino acid to an α-keto acid.
What can deaminated amino acid products be used for?
Energy via the TCA cycle or for biosynthesis.
What do chemolithotrophs use as an energy source?
Inorganic molecules (e.g., NH₃, H₂, H₂S, Fe²⁺)
How do chemolithotrophs generate ATP?
Through oxidative phosphorylation using the electron transport chain.
What types of terminal electron acceptors can be used in chemolithotrophy?
O₂ (aerobic), oxidized exogenous molecules (anaerobic), or oxidized endogenous organic molecules.
What is the role of nitrifying bacteria in the nitrogen cycle?
They oxidize ammonia to nitrate .
Which two genera of bacteria are required for complete nitrification?
Nitrosomonas and Nitrobacter
What is a well-known sulfur-oxidizing bacterium?
Thiobacillus
How do sulfur-oxidizing bacteria synthesize ATP?
Via both oxidative phosphorylation and substrate-level phosphorylation.
What does metabolic flexibility mean for chemolithotrophs?
They can switch between chemolithotrophic and chemoorganotrophic metabolism.
What two carbon metabolisms can many chemolithotrophs switch between?
Autotrophic (fixing CO₂) and heterotrophic (using organic carbon).
What is reverse electron flow?
An energy-requiring process where electrons move “uphill” to reduce NAD⁺ to NADH
What are the two stages of photosynthesis?
Light reactions and dark reactions.
Name four types of prokaryotic photosynthesizers.
Cyanobacteria, green bacteria, purple bacteria, Prochloron.
What are chlorophylls?
The main light-absorbing pigments in photosynthesis.
What are accessory pigments?
Transfer light energy to chlorophylls
Give examples of accessory pigments.
Carotenoids, phycobiliproteins.
What is an antenna complex?
A group of pigments that captures and funnels light to the reaction center
What is a photosystem?
An antenna complex and its associated reaction-center chlorophyll.
What wavelength does PSI absorb?
Light with wavelengths longer than 680 nm.
What wavelength does PSII absorb?
Light with wavelengths shorter than 680 nm.
What does noncyclic electron flow produce?
ATP, NADPH, and O₂.
What does cyclic electron flow produce?
ATP only
What is anoxygenic photosynthesis?
Photosynthesis that does not use water or produce oxygen.
Which bacteria carry out anoxygenic photosynthesis?
Green sulfur bacteria and purple nonsulfur bacteria.
Q: What is anabolism?
A: The synthesis of complex molecules and cellular structures using energy.
Q: What is turnover in anabolism?
A: The constant breakdown and resynthesis of cellular components.
Q: Why are macromolecules made from a limited number of monomers?
A: It saves genetic storage space, raw materials, and energy.
Q: How are anabolic and catabolic pathways related?
A: They share enzymes but operate independently and often use different cofactors.
Q: What cofactor is used in anabolism?
NADPH
Q: How is ATP used in biosynthesis?
A: Its breakdown drives unfavorable biosynthetic reactions to completion.
Q: Which organisms can use CO₂ as their sole carbon source?
A: Autotrophs.
Q: What are the three phases of the Calvin cycle?
Carboxylation, Reduction, Regeneration.
Where does the Calvin cycle occur in eukaryotes?
In the stroma of chloroplasts.
Q: What enzyme catalyzes CO₂ fixation in the Calvin cycle?
Rubisco
Q: What is gluconeogenesis?
A: The synthesis of glucose and fructose from non-carbohydrate precursors.
Q: What enzyme catalyzes fatty acid synthesis?
A: Fatty acid synthetase.
Q: What molecule assists in fatty acid synthesis?
A: Acyl carrier protein (ACP).
Q: What are the products of fatty acid biosynthesis used for?
A: Membranes (phospholipids) and energy storage (triacylglycerols).
Q: What forms the cross-links in peptidoglycan?
Transpeptidation
Q: What are autolysins?
A: Enzymes that digest parts of the peptidoglycan to allow for new unit insertion.
Q: What are the two patterns of bacterial cell wall growth?
A: Localized growth at the septum and dispersed growth along the cell.