Carbohydrates (Lecture 5) Flashcards
can galactosemic mothers produce milk?
yes, only in types 1 and 2
galactosemia
this is done by converting glucose into galactose
how do galactosemic mothers produce milk?
using the energy provided from the addition of UTP to G1P (release of PPi) to synthesize UDP-glucose
the energy provided from the liberation of 2Pi will be invested in inverting the epimerase reaction, the UDP glucose can be converted into UDP galactose ]
which substrate is used in the PPP?
NADP(H)
how does NADPH protect against hemolysis?
rbcs produce hydrogen peroxide, which is a toxic substrate that will react with fatty acid residues in the cell membrane and create organic hydroperoxides
hydroperoxides cleave FA bonds, thus damaging the cell membrane and causing cells to lyse
organic peroxidase is eliminated through the action of glutathione peroxidase
glutathione (GSH) prevents peroxidase mediated hemolysis
NADPH maintains the pool of GSH, thus preventing peroxide mediated call lysis
what is the salvaging reaction?
the salvaging reaction involved the input of NADPH
the organic hydroperoxide must be eliminated form the cell, as for it can cause cell membrane damage and in turn cell lysis
the organic hydroperoxides are eliminated via glutamine peroxidase
when GSSG us produced, the salvaging reaction occurs to produce GSH and push the reaction equilibrium away from generating organic hydro peroxide
NADPH provides the necessary protons for this reduction reaction
what are the 3 major steps in the PPP?
- oxidation
- isomerase/ wpimerase reaction
- recycling reactions
what is the regulatory step of the PPP?
G6P dehydrogenase is the regulatory step
G6PDH is highly sensitive to ___ and this molecules serves to _____
NADPH
inhibit G6PDH allosterically, in cases of surplus (product inhibition)
what are the oxidative steps of the PPP? (3)
G6P –> 6-phosphoglucono delta lactone (via G6PDH and NADP+)
6-phosphoglucono delta lactone –> 6-phospho-gluconate via 6-phosphoglucono lactonase
6-phospho-gluconate –> Ribulose-5-phosphate (Ru5P) via 6-phosphogluconate dehydrogenase
NOTE: 3 Ru5P are generated
what is the purpose of the oxidative reactions in the PPP?
production of NADPH
what are the steps in the isomerization and epimerization reactions?
Ru5P –> R5P via ribulose-5-phosphate isomerase
Ru5P –>(2) Xu5P via ribulose-5-phosphate epimerase
what’s the purpose of the isomerization and epimerization reactions?
production of Ribose-5-phosphate
what is the purpose of CC bond cleavage and formation reactions in the PPP?
recycle R5P and Xu5P
what are the products of the recycling steps that are used for glycolysis?
F6P and GAP
which enzymes are responsible for the recycling reactions in the PPP?
transkelotase
transaldolase
what can R5P (ribose-5-phosphate) be used for?
nucleotide synthesis
the fate of G6P depends on the activity of…
PFK, which is inhibited by ATP (if inhibited PPP)
G6PDH, inhibited by NADPH (if inhibited, then glycolysis)
cellular needs in ATP, NADPH and ribose-5-phosphate
what are the 3 situations of the PPP?
cells needs both NADPH and nucleotides
cell needs NADPH
cell needs nucleotides
what occurs in the case that cells need NADPH and nucleotides?
Both NADPH and R5P are generated
G6P will be converted into Ru5P via G6PDH
Ru5P will then form Xu5P and R5P, which are sued for the synthesis of F6P and GAP via the recycling pathways
R5P is also used fun the synthesis of nucleotides
what occurs in the case that cells need NADPH?
G6PDH will be activated to form NADPH via G6P
in turn this will generate Ru5P which will produce Xu5P and R5P
these products will feed into the intermediates of glycolysis, that being F6P and GAP
what occurs in the case that cells need nucleotides?
in this case, there is an excess of NADPH, which will inhibit the G6PDH enzyme. therefore the accumulation of F6P and GAP will encourage the reverse reaction to allow for the synthesis of R5P, which will then be utilized for nucleotide synthesis
the reverse reaction is accomplished via the recycling steps involving traskelotase and tansaldolase
what it the starting point for gluconeogenesis?
oxaloacetate and or lactate
when does gluconeogenesis occur?
when fasting, since the blood glucose levels are low , thus the liver must generate more glucose to allow for energy production
how are the intermediates for gluconeogenesis generated?
amino acids will be converted into CAC intermediates
do FA contribute to the formation of gluconeogenesis intermediates?
no, however once broken down, they can generate ATP for energy consumption
the irreversible steps in gluconeogenesis require:
Pyruvate carboxylase
PEPCK
FBPase
Glucose-6-phosphatase
gluconeogenesis consumes____ and requires :
NADH ATP
what is the importance of pyruvate carboxylase and PEPCK?
pyruvate carboxylase will perform a carboxylation reaction to form a 4C molecule from a 3C molecule
pyruvate carboxyalse will synthesis oxaloacetate from pyruvate and an investment of ATP
PEPCK will then decarboxylate oxaloacetate to form the 3C molecule, PEP
the formation of PEP requires the input of GTP
how are the carboxylation and de-carboxylation reactions able to proceed?
the carboxylation generates a high energy intermediate (oxaloacetate), which provides the energy for PEP synthesis
what occurs after PEP is synthesized?
PEP is converted into F1,6BP and then to F6P via FBPase
then F6P is converted to G6P and G6P is converted into glucose via Glucose-6-phosphatase
what regulates FBPase?.
F2,6P
where is Glucose-6-phosphatase found and why is this relevant?
online the liver
this is why gluconeogenesis is only performed in the liver
what regulates pyruvate carboxylase and PEPCK?
allosterically activated by Acetyl-CoA
PEPCK can be regulates at the transcriptional level via glucagon and other hormones
substrate cycling between ____ and ___ cause…
FBPase and PFK1 cause and inverse coordination
how many ATP, GTP and NADH does gluconeogenesis come (per pyruvate)
4 ATP
2 GTP
2 NADH
