Glycolysis, TCA, ETC Flashcards
pyruvate carboxylase
enzyme that converts pyruvate to oxaloacetate
oxaloacetate
substrate for gluconeogenesis and a CAC intermediate
when and where does gluconeogenesis occur?
during the fasting state when glucose is in demand, and it occurs in the liver
pyruvate dehydrogenase complex
enzyme that converts pyruvate to acetyl CoA during the fed state (glucose is abundant)
utilizes NAD+ and CoASH and releases NADH and CO2
acetyl CoA can be produced from what?
amino acids, fatty acids, and carbohydrates (by way of pyruvate)
anapleurotic reaction for acetyl CoA
fatty acids
anapleurotic reaction for alpha ketoglutarate
glutamate
anapleurotic reaction for succinyl Co-A
delta-aminolevulinate
anapleurotic reaction for fumarate/oxaloacetate
aspartate
what is pyruvate dehydrogenase activated and inhibited by?
activated by: NAD+ and CoA
inhibited by: acetyl CoA, NADH, and ATP
what is pyruvate decarboxylase activated by?
activated by acetyl CoA
what is citrate synthase inhibited by?
inhibited by ATP, succinyl CoA, and NADH
what is isocitrate dehydrogenase activated and inhibited by?
activated by: ADP
inhibited by: NADH and ATP
what is alpha-ketoglutarate dehydrogenase activated and inhibited by?
activated by: AMP
inhibited by: succinyl CoA and NADH
net reaction of the Kreb’s / Citric Acid Cycle
Acetyl CoA + 3 NAD+ + FAD + GDP + phosphate + 2 H2O –> CoaSH + 3 NADH + FADH2 + GTP + 2 CO2 + 3 H
anapleurotic reactions
many of the intermediates can be synthesized by other enzymes and fed into the TCA cycle to refill it
what molecules leave the CAC and enter the electron transport chain?
NADH and FADH2
electron transport
electrons carried by reduced coenzymes are passed through a chain of proteins and coenzymes to drive the generation of a proton gradient across the inner mitochondrial membrane
oxidative phosphorylation
the proton gradient runs downhill to drive the synthesis of ATP
substrate level phosphorylation
takes an unstable molecule and puts a phosphate onto it
net reaction of glycolysis
Glucose + 2 ADP + 2 NAD+ + 2 Phosphates –> 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O
NADH
carries electrons from catabolic pathways (the break down) and fed into the ETC
NADPH
carries electrons for anabolic pathways (biosynthesis)
what are the key linking molecules between the pathways?
glucose-6-phosphate, pyruvate, and acetyl-CoA
what happens in allosteric regulation of enzymes if the Km is higher?
it would slow down the reactions because the affinity for the substrate is worse
what is the first committed step in glycolysis?
at phosphofructokinase 1
what is the first step in glycolysis where energy is harvested?
at glyceraldehyde 3-phosphate dehydrogenase
hexokinase
takes the gamma phosphate from ATP and puts it onto glucose to generate glucose-6-P
broad substrate specificity
hexokinases can phosphorylate any sugar, meaning EVERY sugar goes through glycolysis (not just glucose!!)
why would we want our brains to have a small Km for glucose?
a smaller Km means a higher affinity and we want our brains to bind to glucose very tightly
why would we want our liver to have a high / larger Km value for glucose?
a higher / larger Km value means a lower affinity which allows the liver to readily release glucose (which would occur during fasting)
glucokinase
has a larger/higher Km value and is active at higher glucose levels which allows the liver to respond to large increases in blood glucose (the enzyme would not bind as tightly to glucose)
reduction potential
the relative ability to give up or accept electrons
it is the voltage (electric potential) at which the redox group is 50% oxidized and 50% reduced!!!!
what happens to a more negative reduction potential?
it is more likely to give up electrons
what happens to a more positive reduction potential?
it is more likely to accept electrons
higher potentials
purely oxidized
lower potentials
purely reduced
complex I
oxidizes NADH and reduces coenzyme Q
complex II
oxidizes succinate and reduces coenzyme Q
complex III
mediates electron transport from coenzyme Q to cytochrome c
UQH2
a lipid soluble electron carrier
cyt c
a water soluble electron carrier that binds on the cytosolic side of complexes 3 and 4
Q cycle
the process by which electrons travel from CoQ to cyt c and pumps a hydrogen ion
one electron is given to cyt c and the other electron is given to cyt b which prevents the formation of a dangerous free radical
cytochromes
proteins that contain heme groups that can bind and transfer electrons
complex IV
transfers electrons from cyt c to reduce oxygen on the matrix side
what is the terminal acceptor of electrons in the ETC? what is the driving force?
oxygen!
reactive oxygen species
some electrons can “escape” the ETC and combine with oxygen to form a superoxide radical (an unstable form of oxygen)
chemiosmotic theory
Peter Mitchell proposed the idea that a proton gradient across the inner mitochondrial membrane could drive ATP synthesis
how does a proton gradient drive the synthesis of ATP?
proton diffusion from an area of higher concentration to lower concentration through the protein drives the synthesis of ATP!
how does ATP synthase work?
assuming there are three interactive and conformationally distinct active sites, ADP and P bind to an active site which causes an energy-driven conformational change among the sites, eventually producing ATP
how were vesicles used to demonstrate the chemiosmtic theory?
reconstituted vesicles containing ATP synthase and bacteriorhodopsin (a protein that acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane); using light, protons were issued across a membrane and then it entered the ATP synthase and ATP was produced
where do inhibitors affect the electron transport chain?
they can affect it at complexes I, II, III, IV, and at the ATP synthase
what are uncouplers?
hydrophobic molecules with a dissociable proton that shuttle back and forth across the membrane, carrying protons to dissipate the gradient
what do uncouplers do?
they dissipate the proton gradient across the inner mitochondrial membrane and therefore destroy the tight coupling between electron transport and the ATP synthase reaction
how is uncoupling related to brown fat?
brown fat contains a ton of mitochondria (and thus cytochromes) and it has an uncoupler protein that pokes holes in the mitochondrial membrane thereby allowing H to leave, but it generates heat in lieu of ATP
the protein dissipates the H gradient and therefore ATP can’t be made, but heat is made instead (this is why bears hibernate!)
how does the cell transport things like NADH?
NADH can’t cross the mitochondrial membrane, but that’s okay because we only need the electrons
shuttle systems
move electrons across membranes when we can’t move the molecule; effects electron movement without actually carrying the molecule that can’t cross the membrane
when are 2 reactions used that use pyruvate decarboxylase and alcohol dehydrogenase?
in the metabolism of pyruvate to ethanol (in yeast in anaerobic systems)
why are 2 steps necessary in ethanol formation?
recall that in glycolysis, glyceraldehyde 3-P dehydrogenase reduces an NAD+ to NADH and in alcohol dehydrogenase this NADH is oxidized to NAD+ again
in anaerobic conditions there is no CAC cycle to burn up the reduced NADH, so alcohol dehydrogenase is needed to regenerate NAD+, otherwise glycolysis would stop!!!!
why is alcohol dehydrogenase crucial?
it is needed to regenerate NAD+ for glycolysis
NADH-CoQ Reductase
complex I
Succinate-CoQ Reductase
complex II
CoQ Cytochrome c Reductase
complex III
Cytochrome c Oxidase
complex IV
