Chapter 15: Glucose Catabolism Flashcards
what is glycolysis
10 enzymatic reactions in which one molecule of glucose is converted to 2 molecules of 3-C compounds (pyruvate), with 2 ATP generated and 2NADH
where does glycolysis occur
cytosol of cells
is glycolysis an anaerobic or aerobic set of reactions?
anaerobic
glycolysis proceeds ______ from equilibrium
far
3 irreversible steps of glycolysis
1) glucose to g-6-P via hexokinase
2) fructose 6 P to fru-1,6-bP via PFK-1
3) PEP to pyruvate vis pyruvate kinase
sequence of glycolysis
1) glucose to glc6P via hexokinase
2) glc 6 p to fructose 6 p via phosphohexose isomerae
3) fructose 6 p to fructose-16bP via PFK-1
4) fructose-16bp to glyceraldehyde-3-phosphate and DHAP via aldose
5) DHAP gets converted to GA3P via triose phosphate isomerase
6) (G3AP and NAD+ and Pi) to (1-3BPG + NADH)via glyceraldehyde 3 phosphate dehydrogenase
7) 1-3BPG and ADP to 3 BPG and ATP via phosphylase kinase
8) 3BPG to 2BPG via phosphoglycerate mutase
9) 2BPG to PEP via enolase, H2o removed
10) PEP to pyruvate and ATP, via pyruvate kinase.
2 ways of making NAD+ from pyruvate
via lactic acid fermenation and alcoholic fermentation
draw mechanism of lactic acid fermentation
keto-pyr to lactate via lactate dehydrogenase, oxidization of NADH to NAD+
draw alcoholic fermentation mechanism
pyr to acetaldehyde via pyruvate decarboxylase, and acetaldehyde to ethanol via alcohol dehydrogenase. Oxidation of NADH it second step.
wich coenzyme is needed inorder for pyruvatedecarboxylase to work (to form acetaldehyde)?
thiamine pyrophosphate
evolutionary pressures of metabolic control
1) to maximize efficiency of fuel utilization
2) partition the flow of metabolites appropriately between competing pathways
3) if more fuel is available in more than one type, choose the one best suited
4) shut down anabolic pathways when product is not required.
reverse reactions have increased reaction flow, there is _____ of enzyme activity in ____ direction
lots of enzyme activity in both directions
irreversible reactions have decreased reaction flow because of _____ in one direction
decreased activity in one direction
T/F net flow is changed by altering enzyme activity in the irreversible reactions
True- irreversible steps are sites of regulation
Substrate cycling and example
the ability of equilibrium and regulation of irreversible reactions (non equilibrium) if a second enzyme catalyzes the regeneration of its substrate from its products in a thermodynamically favorable manner
the pfk-1 cycling in glycolysis vs FBP1 cycling in gluconeogenesis.
hexokinase in the muscle has a ___Km for glucose, meaning that it almost always nearly saturated
low Km
hexokinase is inhibited by _____
its product, glucose-6-phosphate
what will happen to the activity of hexokinase if PFK-1 is turned off?
if PFK-1 is off, its substrate F-6-P will increase, causing glc-6-P to increase, turning off hexokinase.
gluconase-1 in the liver has a ____ km an thus has a lower affinity for glucose
has a high Km, will always operate at a low rate unless glucose concentration is high.
main chemicals that can regulate phosphofructokinase-1
atp, adp, fructo2-6bisphosphate, AMP
at the catalytic substrate site, the ATP can bind to which state?
they can bind equally well, to the T or the R state.
At the inhibitor site, what state does ATP bind to on phosphofructokinase-1
on the T state, thus decreasing the PFK’s affinity for F6P, stalling glycolysis
how does AMP affect PFK1?
amp binds strongly to R state, ACTIVATING PFK 1 and facilitating glycolysis
what amplification reaction allows small amounts of [atp] decrease to create a large increase in AMP in order to increase PFK-1’s activity?
adenylate kinase reaction.
in high concentrations of ATP, PFK1 activity ______
decreases.
What inhibits pyruvate kinase?
inhibited by high energy status of the cell (increased ATP conc), and the presence of alternative fuels.
in liver, it is also regulated by glucagon
galactose is converted to ____ before entering glycolysis
glucose-6-phosphate
mannose and muscle fructose is converted to ____ before entering glycolysis
fructose-6-phosphate
liver fructose is converted to ____ before entering glycolysis
glyceraldehyde-3-phosphate
why is over consumption of high fructose containing sugars a problem?
because in the liver, fructose to GA3P by passes PFK-1, which is supposed to be a key regulatory step in how much glucose is broken down to energy.
fructo kinase does what to fructose
make fructose to fructose one phosphate
fructose 1 phosphate aldolase catalyzes fructose 1 phosphate to what
fructose 1 phosphate open chain glyceraldehyde
glyceraldehyde in the liver can made into either
glycerol or glyceraldehyde 3 phosphate via alcohol dehydrogenase or glyceraldehyde kinase
glycerol gets converted into______ via glycerol kinase
glycerol 3 phosphate
glycerol 3 phosphate gets converted into ______ via glycerol 3 phosphate dehydrogenase
Dehydroxyacetone
DHAP from fructose liver metabolism turns into GA3P, which can be put into the glycolysis cycle, via _______
triose phosphate isomerase
in order for galactose to be used in glycolysis, it must first be converted into
glucose 6 phosphate
draw galactose
4th carbon is up instead of down (down down up up)
during the metabolism of galactose: galactose is phosphorylated by ATP via galactokinase to make ______,
galactose 1 phosphate
galactose 1 phosphate gets a uridyl group via transferase to yield ______
GLUCOSE 1 phosphate and UDP-galactose
what enzyme converts UDP galactose to UDP glucose? which energy rich compound is associated with this transfer?
UDP galactose-4-EPIMERASE, NAD+
phosphoglucomutase converts glucose 1 phosphate to _____ in the last step of the galactose metabolism
glucose 6 phosphate, then gets put into glycolysis
mannose is an _____ of glucose
an epimer at the second carbon (down up up down)
mannose must get converted into _____ before proceeding to glycolysis
fructose 6 phosphate
mechanism of mannose metabolism to fructose 6 phosphate
mannose gets phosphorylated via hexokinase to mannose 6 phosphate, and then gets converted to fructose 6 phosphate via phosphoMANNOSE isomerase
cutting a glucose molecule off a long chain (glycogen) via glycogen phosphorylase results in the molecule _____
glucose 1 phosphate
after being cut off the glycogen chain, glucose 1 phosphate turns into _____ via phosphoglucomutase
glucose-6-phosphate
how is lactose broken down?
broken down into galactose and glucose. galactose goes through gal metabolism (gal–>gal1p—>UDPgal–> UDPglu—>glu1P—>glu6P–>rest of glycolysis
how is sucrose broken down?
into glucose and fructose
In liver, fructose–>fruc 1 P–> glyceraldehyde—> GA3P
What does the pentose phosphate pathway do?
burns glucose to make NADPH for reductive biosynthesis.
Is the oxidation branch irreversible or reversible?
irreversible.
purpose of oxidation branch
makes ribuolos5 Phosphate and CO2 and 2NADPH out of glucose 6 phosphate
What does the non-oxidative branch do?
converts 6 ribulose 5 phosphates into 6 FRUCTOSE6phosphates or GA3P (glycolytic intermediates)
where does pentose phosphate pathway occur in the cell?
in the cytosol
in the first step of the oxidative branch PPP, glucose 6 phosphate, with the help of glc-6-P dehydrogenase, gets turned into ____
6-phosphoglucono lactone
in the oxidative PPP, 6-phosphoglucono lactone gets turned into ____with the help of lactonase
6phosphogluconate
in the oxidative PPP, 6phosphogluconate gets turned into ____ with the help of 6 phosphogluconate dehydrogenase
ribulose 5 phosphate, which can make more glucose 6 phosphate via the non oxidative branch
in the final step of the oxidative branch of the PPP, ribulose 5 phosphate gets converted into ____ via ____
ribose 5 phosphate, which can make nucleotides and stuff. ribulose 5 phosphate —>ribose 5 phosphate is catalyzed via phosphopentose isomerase
what happens to the oxidative branch of the PPP when NADPH conc is high?
it gets turned off, glucose 6 phosphate goes to glycolysis
what happens when the body WANTS ribose and NADPH conc is low?
glucose-6-phosphate dehydrogenase is active and makes 6phosphoglucanolactone, initiating oxidative PPP to make ribose
what happens when u want NADPH but not ribose?
oxidative branch will run, making nadph and ribose. excess ribose will funnel into glycolysis by making glycolytic intermediates through non-oxidative phosphate pentose pathway
what happens whn you want NADPH, but NOT RIBOSE, but ATP is high?
NADPH is wanted, there for oxidative pathway is running, making ribose as well. PPP intermediates cannot go to glycolysis because it is turned off due to high ATP, so they route through the GLUCONEOGENESIS pathway, which can also form g6p and such
with inhibitory proteins that can regulate hexokinase/glucokinase in the liver, how are they upregulated? down regulated?
upregulated ALLOSTERICALLY by increased levels of fructose 6 phosphate, which increases with glucokinases’ product glc 6 up
downregulated by increase levels of glucose, which signals “time to make glycogen,” because high levels of glucose turn into G6P, which is needed for glycogen
with no large amount of ATP in the system, fructose phospho kinase 1 will assume a _____ shape
bell shape, there will be no inhibitor
with large amount of ATP in the system, fructose phospho kinase 1 will assume a _____ shape
sigmoidal shape, ATP allosterically inhibits PFK by binding to T state on the inhibitor site.
what happens when you want ribose, but the concentration of NADPH is high?
You cannot go through the oxidative PPP because NADPH is too high, so you use glycolytic intermediates (gA3p, fru6p), pull them out of glycolysis and make them undergo the nonoxidative pathway with transaldolases and transketolases to form ribose-5-phosphate
How many pyruvates, NADH and ATP is made in glycolysis
2 pyruvate, 2 NADH and 2 Net ATP
How many ATP is spend during the energy investment stage of glycolysis
2, converting glucose into G3p in a series of steps
Steps where atp is invested in glycolysis
1) converting glucose to glucose6p
2) converting glucose6p into fructose 1, 6, biphosphate. via phosphofructokinase
two anaerobic methods to generate NAD+ from NADH
1) lactate formation –> Homolactic fermentation
2) alcoholic fermentation
Draw tauteromerization of pyruvate into enol form
reference notes
two enzymes in alcoholic fermentation
pyruvate decarboxylase and alcohol dehydrogenase
T/F: Conversion of glucose to lactate is an net oxidation
false. Converting glucose first forms 2 pyruvates (+2 NADH), and then makes 2 lactates from the 2 pyruvates. (-2NADH). thus there is no net of NADH formation. nothing was net oxidized.
fructo2-6bisphosphate is an allosteric _____ of PFK-1.
allosteric ACTIVATION
during fructose metabolism, fructose is broken down to Fruc-___-phosphate in the muscle, whereas it is broken down into Fruc-____ phopshate in the liver.
Fruc-6-phosphate in the muscle, Fruc-1-phosphate in the liver.
What is galactose’s relationship to glucose?
they are epimers. the configuration is switched at one carbon.
lactose is made of:
galactose and glucose
sucrose is made of
glucose and fructose
phosphate pentose pathway burns ___ to make ____
burns glucose to make NADPH
