Chapter 4 Flashcards
Reduction potentials
The reduced substance with the more negative reduction potential donates electrons.
Ex. H donates electrons
The electron tower
Biological systems use electron flow to obtain energy.
Diagrams reduction potentials for biological molecules.
Difference in potential between donors and acceptors expressed as deltaE
Longer the drop of e from donor to recipient, more energy and larger the deltaE.
NAD as a redox e carrier
Redox runs usually involve reactions between intermediates.
e carriers are divided into two classes.
NAD/NADH cycling
Coenzymes make it possible for chemically dissimilar molecules to interact as primary e-donor and terminal e-acceptor.
-coenzyme acts as intermediary.
High energy compounds and energy storage
Redox runs release energy, cell stores it for functioning.
Energy rich compounds and energy storage II
Long term energy storage involves insoluble polymers that can be oxidized to generate ATP.
- Ex. in prokaryotes: glucose and S
- Ex. in eukaryotes: starch
Energy conservation
Two rxn series linked to energy conservation in chemoautotrophs: fermentation and respiration.
Differ in mechanism of ATP synthesis
-Fermentation: substrate level phosphorylation
-Respiration: oxidative phosphorylation.
3 methods of ATP synthesis
Fermentation
Respiration
Photophosphorylation
Terminal e acceptors
Ultimate destination of e is terminal electron acceptor of process.
Type of terminal e acceptor
Terminal e acceptor II
Respiration:externally supplied e acceptor
Fermentation: terminal e acceptor not supplied from the environment.
–Fermentation
Glycolysis
A sequence of enzyme catalyzed runs by which glucose is conveyed into pyruvate.
- Pyruvate can be oxidized further.
- Pyruvate can also be used as a precursor to biosynthesis.
Key facts about glycolysis
Occurs in cytoplasm.
Used by most autotrophs and heterotrophs and both aerobes and anaerobes.
Breaks down glucose.
O2 not required.
Glycolysis II
Two stages:
-Stage 1 catalyzes the splitting of glucose (predatory).
Glycolysis III
Stage 2: catalyzes the oxidation of glyceraldehyde-3-phosphate to pyruvate (payoff phase).
-consists of 5 rxns
-generates 4 ATP’s, net gain of 2 ATP
Generates NADH
Stage 1 summary
Not redox and does not release energy.
2 ATP’s are used to convert glucose to fructose 1,6-biphosphate.
Aldolase splits ructose 1,6-biphosphate
Stage 2 summary
This is when the first redox run occurs.
Each glyceraldehyde 3-phosphate gets another phosphate.
Glycolysis summary
ATP needed
-2 ATP molecules are used to phosphorylate glucose.
ATP produced
-
Fermentation
ATP is produced by a mechanism called substrate level phosphorylation.
The fermentable substrate is both an e donor and e acceptor.
Not all compounds can be fermented.
Regeneration of NAD+
Reduced coenzyme (NADH) produced in stages I and II. -Limited amount of NAD+, for glycolysis to continue NAD+ must be regenerated, fermentation REGENRATES NAD+ FOR REUSE.
Glucose fermentation: Net and practical results
Results of glucose fermentation. -glucose is broken down -fermentation products are produced -Net 2 ATP's Fermentation products may be used for -food production -industrial application Energy yields from fermentation are low -Carbon atoms are only partially oxidized -difference in reduction potentials is small between primary e donor and terminal e acceptor.
Fermentation
Yeast fermentation produces alcohol and CO2 instead of lactic acid.
Alcohol fermentation
CO2 is released from pyruvic acid to form intermediary acetaldehyde.
Acetaldehyde is reduced to ethanol by e from NADH.
Pyruvate end points
Pyruvate produced from carbohydrate metabolic pathways is metabolized in various ways.
- precursor in biosynthetic reactions
- oxidized to CO2
Respiration I
Respirators obtain some energy from glycolysis
Two kinds:
-Aerobic
-Anaerobic
Aerobic respiration
Aerobes undergo aerobic respiration -Kreb's cycle -oxidative phosphorylation Oxidation using O2 as a terminal e acceptor Higher ATP yield than fermentation
Significance of energy transfer
In glycolysis and fermentation, net production of 2 ATP.
Glycolysis+aerobic respiration=38 glucose per glucose.
oxidative decarboxylation of pyruvate
Pyruvic acid from glycolysis can enter cycle but must be converted to acetyl CoA.
-Removes one molecule of CO2
-Transfer of e and NAD
-Addition of coenzyme A
Pyruvate is oxidized to acetyl CoA, CO2 and NADH by pyruvate dehydrogenase.
Acetyl CoA oxidized to CO2 in Kreb’s cycle.
Citric Acid Cycle I
Starts w/ acetyl CoA. Acetyl groups are converted to CO2 H's removed and e transferred to coenzymes that serve as e carriers. Significant events of cycle -oxidation of carbon -removal of e to coenzyme -substarte level energy capture
Citric Acid Cycle II
Pathway through which pyruvate is completely oxidized to CO2.
- Initial steps same as glycolysis
- Per glucose molecule, 6 CO2 released and 38 ATP generated.
- catabolism and biosynthesis
The gist of CAC
Pyruvate is split into 3 CO2
The e produced in the process are put on e carriers.
e are taken to e transport system.
Biosynthesis and CAC
A
Electron transport and oxidative phosphorylation
Series of redox rxn’s to generate a H+ gradient
Electron transport systems
Membrane associated.
Mediate transfer of e from primary donor to terminal acceptor.
Conserve some energy released during transfer and use it to synthesize ATP.
Some e carriers
NADH dehydrogenases:
Flavoproteins:
Cytochromes
Carriers that contain heme prosthetic groups.
Accept and donate single electron via iron atom.
Iron sulfur proteins
Contains clusters
Organization of e carriers in bacteria
Organized into dehydrogenase and oxidase complexes connected by quinones.
Quinones accept e from dehydrogenases.
Generation of proton motive force
e transport system oriented in cytoplasmic membrane so that as e are transported, protons are separated.
Carriers in ETC are arranged in increasingly positive reduction potential.
Final carrier in chain donates e and protons to terminal e acceptor.
The proton motive force
During e transfer, several
Proton motive force and ATP synthesis
ATP synthase complex that converts proton motive force into ATP.
Two components:
-
