Poolman lectures 1 and 2: metabolism Flashcards
Why do electrons entering at complex I result in greater energy conservation than electrons entering at complex II?
Because complex I translocates an additional 4 H+ for every 2 electrons transported. Complex II doesn’t pump protons across the membrane.
What are other names for complexes I and II and from which substances do they get their electrons?
Complex I: NADH dehydrogenase. NADH deposits two electrons into complex I.
Complex II: succinate dehydrogensae, gets its electrons from FADH2.
Why do strictly fermentative organisms still contain ATPases, even though they lack electron transport chains and don’t carry out oxidative phosphorylation?
Because the action of ATPase is reversible; it can cause protons to be transported out of the cytoplasm, generating (rather than dissipating) a pmf. Many important reactions in the cell (including flagellar rotation and transport) are driven by this pmf.
what is the main difference between respiration and fermentation?
Respiration requires an external electron acceptor (whether it’s oxygen or not) and ATP is produced by oxidative phosphorylation (pmf).
Fermentation does not require an external electron acceptor, and ATP is generated by substrate-level phosphorylation.
What does it mean when the delta G of a reaction is negative?
When it is positive?
When the delta G of a reaction is negative, it yields energy and is exergonic.
When the delta G of a reaction is positive, the reaction requires energy and is endergonic.
What are catabolic pathways?
What are anabolic pathways?
Catabolic pathways are exergonic processes in which cells generate free energy by transferring reactants into products.
Anabolic pathways are endergonic processes in which the synthesis of cellular material from simple precursors requires an input of energy.
How many ATP molecules are produces in the aerobic respiration of a mole of glucose under clelular conditions?
38 ATP
91 ATP under standard conditions
What is reducing power?
Reducing power is the ability to donate electrons during electron transfer reactions.
What happens when a substance gets reduced?
What happens when a substance gets oxidized?
When an electron is added to a substance, it gets reduced, when an electron is removed from a substance, it gets oxidized.
How do chemoorganotrophs obtain their energy? How do chemolithotrophs do this?
Chemoorganotrophs obtain their energy and reducing power from organic molecules, while chemolithotrophs obtain their energy and reducing power from inorganic molecules.
NADP+/NADPH participates in many … reactions, while NAD+/NADH typically participates in… reactions.
Anabolic … catabolic
What is the standard free energy of formation?
The standard free energy of formation of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states.
Why is the oxidation of propionate to H2 and CO2 a good example of why delta G is better dan deta G0?
Because propionate oxidation becomes more favourable as reactant concentrations go up, and product concentrations go down.
Cells need compounds whose delta G0 of phosphate hydrolisis exceesd … to synthesize ATP.
-31.8 KJ/mol
Through which three mechanisms do cells generate ATP?
- Substrate-level phosphorylation: the energy-rich bond of a substrate is hydrolized to directly drive the formation of ATP. This is the dominant mechanism of energy conservation in fermentative organisms.
- Oxidative phosphorylation: The movement of electrons from donor to acceptor generates a proton motive force, which is used to synthesize ATP. Oxidative phosphorylation is the defining feature of respiration reactions.
- Photophosphorylation: light energy is used to form the proton motive force that powers ATP synthesis.
What is the difference between prosthetic groups and coenzymes?
Prosthetic groups bind tightly to their enzymes, covalently and permanently. (Example: heme group of cytochrome C).
Coenzymes are loosely and transiently bound to enzymes. A single coenzyme may associate with multiple enzymes. (Examples: NADH and ATP).
What does the enzyme aldolase do?
Aldolase splits fructose 1,6-bisphosphate into two 3-carbon molecules: glyceraldehyde 3-phosphate, and dehydroxyacetone phosphate, which is also converted into glyceraldehyde 3-phosphate.
What is the first redox reaction of glycolysis?
The first redox reaction of glycolysis is when glyceraldehyde 3-phosphate is oxidized to 1,3-bisphosphoglycerate. In this reaction, the enzyme glyceraldehyde 3-phosphate dehydrogenase reduces NAD+ to NADH.
Simultaneously, each glyceraldehyde 3-phosphate molecule is phosphorylated by the addition of an inorganic phosphate, which sets the stage for energy conservation, since 1,3-bisphosphoglycerate is an energy-rich compound.
Through which two mechanisms is ATP synthezided during glycolysis?
- When 1,3-bisphosphoglycerate is converted into 3-phosphoglycerate
- When each molecule of phosphoenolpyruvate is converted into pyruvate
Both are substrate-level phosphorylation
Why is glycolysis on its own not sufficient to sustain life?
Because glycolysis lacks redox balance: it produces NADH, but it lacks an electron acceptor and therefore the ability to regenerate the NAD+ needed to oxidize glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate
What is the net yield of the citric acid cycle?
The citric acid cycle produces a net yield of: 1 ATP, 4 NADH, 1 FADH2, and 3 CO2 per molecule of pyruvate.
What are some important intermediates of the citric acid cycle that are used for biosynthesis?
- a-ketoglutarate and oxaloacetate. These are precursors for many amino acids. Oxaloacetate can also be converted to phosphoenolpyruvate (a precursor of glucose) when needed
- succinyl-CoA, to form cytochromes and chlorophyll
- acetate: provides the raw material for fatty acid biosynthesis
Why does an organism need the enzyme pyruvate carboxylase
to enable growth if pyruvate is its sole source of energy and
reducing power?
Because a cell growing on the 3 carbon compound pyruvate cannot regenerate the oxaloacetate needed to accept the acetyl group from acetyl-CoA.
Pyruvate carboxylase allows cells to regenerate oxaloacetate, making them able to grow on only pyruvate.
In eukaryotes, from where to where are protons pumped to create a proton gradient?
In eukaryotes, this happens in mitochondria. Protons are pumped from the mitochondrial matrix into the intermembrane space.
What does the F1 complex of ATPase do? What does the F0 complex do?
F1 sticks into the cytoplasm and is the catalytic site where ADP + Pi are converted into ATP.
F0 is imbedded into the membrane and carries out proton translocation from outside the membrane to inside.
When establishing a proton gradient, protons are pumped from … to ….
During ATP synthesis, these protons are transported from … to …
In the electron transport chain (establishing a proton gradient) protons are pumped from inside the cytoplasmic membrane to outside the cytoplasmic membrane.
During ATP synthesis, ATPase pumps these protons back in from the outside.
Explain why Paracoccus denitrificans would outcompete E. coli if both organisms were competing for glucose
in the presence of O2
Because E.coli lacks complex III. This means that for every two electrons that pass through the electron transport chain, E.coli pumps 8 H+ across the membrane, while P. denitrificans pumps 10 H+, conserving more energy.
What form of activated glucose is used in the biosynthesis of glycogen by bacteria?
Uridine diphosphoglucose (UDPG) or adenosine diphosphoglucose (ADPG)
Through the activity of which protein are fatty acids synthesized?
Fatty acids are synthesized two carbons at a time by the acyl carrier protein (ACP)
