ch 11 catabolism: energy release and conservation Flashcards
heterotroph
organisms that use organic molecules as their carbon source for growth
autotrophs
organisms that use carbon dioxide as their sole or principal carbon source
phototroph
use light as their energy source
chemotroph
obtain energy from the oxidation of chemical compounds
lithotrophs
rock eaters
use reduced inorganic substances as their electron source
organotrophs
extract electrons from reduced organic compounds
fueling reactions
the energy, electrons, and carbon that an organism obtains from its environment are used is chemical reactions
- ATP
- reducing power
- precursor metabolites
chemolithoautotrophs
oxidize inorganic compounds such as iron, nitrogen, or sulfur containing molecules to derive both energy and electrons for biosynthesis, and use carbon dioxide as their carbon source
use respiration and fermentation
respiration
an energy-yielding process in which the energy substrate is oxidized using an exogenous or externally derived electron acceptor
- in aerobic respiration the final electron acceptor is oxygen
- in anaerobic respiration the final electron acceptor is a different oxidized molecule such as NO3-, SO42-, Fe3+
fermentation
does not use ETC
an energy-yielding process in which an organic molecule is oxidized without an exogenous electron acceptor. usually pyruvate or a pyruvate derivative serves as the electron acceptor
3 pathways that catabolize glucose to pyruvate in the cytosol
1 Embden-Meyerhof pathway
2 Entner-Doudoroff pathway
3 pentose phosphate pathway
Embden-Meyerhof pathway (EMP)
most common pathway for glucose degradation to pyruvate
found in all major groups of microorganisms, plants and animals, and functions in the presence or absence of O2
provides NADH, ATP
glucose + 2ADP + 2Pi + 2NAD+ -> 2 pyruvate + 2ATP + 2NADH + 2H+
Entner-Doudoroff pathway (EDP)
used by some gram-negative bacteria, especially those found in soil
EDP: glucose + ATP + NADP+ -> pyruvate + glyceraldehyde 3-phosphate + ADP + NADPH + H+
EMP: glyceraldehyde 3-phosphate + 2ADP + NAD+ -> pyruvate + 2ATP + NADH + H+
pentose phosphate pathway
used aerobically or anaerobically
oxidizes glucose 6-phosphate to ribulose 5-phosphate and then converts it to a variety of three to seven carbon sugars
glucose 6-phosphate + 12NADP+ + 6H2O -> 6CO2 + 12NADPH + 12H+ + Pi
tricarboxylic acid cycle
citric cycle/krebs cycle
cycle must turn twice to completely oxidize one molecule of glucose
common in aerobic bacteria, archaea, free-living protists, and fungi
major role is to produce precursor metabolites used in biosynthesis
mitochondrial electron transport chain
a series of electron carriers, operating together to transfer electrons from NADH and FADH2 to a terminal electron acceptor O2
- electrons flow from carriers with more negative reduction potentials to carriers with more positive reduction potentials
two kinds of electron carrier proteins
- flavin: redox active, part of the molecule reduced when electron is accepted and then oxidized when that electron is donated; carry both electron and proton
- quinones (coenzyme Q): no prosthetic group, can directly be reduced and oxidized; carry both electron and proton
- cytochromes and iron sulfur proteins: can only carry protons
bacterial and archaeal ETC aspects
flexible - change components of their ETCs to respond to different environmental conditions; electron carriers can be replaced or different terminal oxidases may be used
bacterial chain ETC
- P. denitrificans
can use one-carbon molecules (methanol) instead of glucose as a source of energy and electrons - E. coli
two branches; one for when oxygen is available, other when oxygen is limited
oxidative phosphorylation
process by which ATP is synthesized using the energy from electron transport, which in turn is driven by the oxidation of a chemical energy source
proton motive force
the combined chemical and electrical potential differences
used to perform work when protons flow back across the membrane, down the conc and charge gradients, and into the cytoplasm
flow is exergonic
also used by many secondary active transport mechanisms
ATP synthase
an enzyme that catalyzes synthesis of ATP from ADP and Pi using energy derived from the proton motive force
anaerobic respiration
chemoorganotrophic process whereby a terminal electron acceptor other than O2 is used for electron transport (nitrate, sulfate, CO2, metals, organic molecules)
generally yields less ATP than aerobic
dissimilatory nitrate reduction
use of nitrate as terminal electron acceptor, making it unavailable to cell for assimilation or uptake
denitrification
reduction of nitrate to nitrogen gas
fermentation
does not require ETC
oxygen not needed
ATP formed by substrate-level phosphorylation
homolactic fermenters
use the EMP and directly reduce almost all their pyruvate to lactate with the enzyme lactate dehydrogenase
- cheese, yoghurt, kimchi
heterolactic fermenters
form products other than lactate (ethanol, CO2)
alcoholic fermentation
fermentation of sugars to ethanol and CO2
pyruvate is decarboxylated to acetaldehyde which is then reduced to ethanol by alcohol dehydrogenase with NADH as the electron donor
- beer, wine
mixed acid fermentation
results in the excretion of a mixture of acids (acetic, lactic, succinic, formic acids) and ethanol
butanediol fermentation
butanediol is the major end product
catabolism of carbs
goal is to convert the carb into a monomer that can be fed into a glycolytic pathway
catabolism of lipids
triglycerides are common energy sources
hydrolyzed to glycerol and fatty acids by lipases, glycerol degraded via glycolytic pathway
fatty acids from triacylglycerols and other lipids can be oxidized in the beta-oxidation pathway after being linked to coenzyme A
protease
hydrolyzes proteins to amino acids
deamination
removal of amino group from amino acid
catabolism of protein and amino acid
deamination accomplished by transamination
resulting organic acids converted to pyruvate, acetyl-coA, or TCA cycle intermediate
chemolithotroph
rock eaters
carried out by certain bacteria and archaea
obtain electrons by oxidizing inorganic molecules
terminal electron acceptor is usually O2
to grow and reproduce, must oxidize a large quantity of inorganic material
three major groups of chemolithotrophs
- oxidize hydrogen
- oxidize nitrogen
- oxidize sulfur
nitrifying bacteria
soil and aquatic bacteria that carry out nitrification - the oxidation of ammonia to nitrate
sulfur-oxidizing bacteria
flexible metabolism depending on environment
ATP can be synthesized by both oxidative phosphorylation and substrate-level phosphorylation
flavin-based electron bifurcation (FBEB)
the conservation of energy by linking an unfavourable endothermic reaction with a favourable exothermic reaction
two parts of photosynthesis
light reaction - light energy is trapped and converted to chemical energy
dark reaction - energy produced in the light reactions is used to reduce CO2 and synthesize cell constituents
oxygenic photosynthesis
oxygen is generated and released when water is reduced
carried out by cyanobacteria and photosynthetic eukaryotes that contain chloroplasts
chlorophyll
large planar molecules composed of four pyrrole rings with a central magnesium atom coordinated to the four nitrogen atoms of the pyrrole rings
major light-absorbing pigments - red and blue absobed
accessory pigments
carotenoids and phycobiliproteins
help chlorophylls harvest light energy but they cannot harvest energy directly
anoxygenic photosynthesis
molecules other than water are used as an electron source and therefore O2 is not produced
different pigments are used
only one photosystem used
different mechanisms used to generate reducing power
carried out by phototrophic green bacteria, phototrophic purple bacteria, heliobacteria
rhodopsin-based phototrophy
microbes that use this live in nutrient depleted environments where organic carbon is limited
uses archaerhodopsin - a deep purple pigment, function as a light-driven proton pump
