Carbohydrates (Lecture 3) Flashcards
how is creatine phosphate an immediate reservoir for ATP?
cells can’t store free ATP (as for this would inhibit ATP synthase)
the ATP is stored by generating Creatine-P which can remobilize ATP
steps involved in ATP production via creatine
- ETC will create a proton gradient
- ATP synthase uses this gradient to generate ATP
- ATP will be transporter via AAC ATP/ADP carrier into the inner mitochondrial matrix
- creatine kinase can convert creatine into creatine-P with ATP
when ATP is in low amount, the creatine kinase can partake in the reverse reaction, thus the accumulation of ADP will convert creatine-P into creatine and produce ATP
what is the regulatory step of glycolysis?
Hexokinase
the first step
what happens once glucose enters the cell?
the glucose will be phosphorylated by hexokinase (the regulatory step)
what is the first step in glycolysis?
glucose + ATP + Mg 2+ are converted into glucose-6-phosphate (G6P) via hexokinase
what are the advantages of hexokinase phosphorylation?
glucose sequestration, by trapping glucose inside the cell
thermodynamically, this keeps the glucose concentrations low within the cell (cytoplasmic), thus promoting passive diffusion of more glucose into the cell
hexokinase has a substrate specificity for…
hexoses
which enzyme has higher affinity for glucose? (hexo/gluco-kinase)
hexokinase
what is hexokinases modulator?
G6P (product inhibition)
where is glucokinase found and what does it do?
found in the liver/pancreas and it converts glucose and ATP into G6P and ADP
what is glucokinases modulator?
glucokinase regulatory protein (GKRP)
what is GKRP and how does it work?
binding partner that sequesters glucokinase in the nucleus when glucose levels are low
, therefore when glucose levels are high, the GKRP will release the enzyme in order to promote the production of G6P and promote the production of energy
what is the second step fo glycolysis?
the first reversible step converting G6P into F6P via phosphoglucose isomerase
how is phsophoglucose isomerase (PGI) driven?
by substrate concentration
what is the third step in glycolysis?
F6P is converted to fructose 1,6 bisphosphate (F1,6BP) with the addition of ATP and the enzyme phosphofructokinase (PFK)
this is the committing step for metabolizing glucose
how is PFK activated?
PFK is regulated by AMP and F26P
how is PFK inhibited?
ATP and citrate
explain the allosteric regulation of PFK
in the presence of ATP, PFK1 will be in the T (tense) inactive state. this is because ATP inhibits PFK
in the presence of high AMP, thus low ATP, PFK1 will shift to the R (relax) state. the relax state will trigger the conversion of F6P to F1,6P
is AMP or ATP more potent at regulating PFK?
PFK is more sensitive to AMP, as for AMP overcomes the ATP inhibition of PFK1
what is the function of ADK (adenylate kinase)?
regeneration of ATP
2ADP –> ATP +AMP
ADENYLATE KINASE can keep ATP abundant for exercise, but it can also regenerate AMP in order to activate the PFK, thus stimulating glycolysis and the production of energy
how is PFK regulated with Fructose-1,6-bisphosphate.
substrate cycling, where there is differential regulation
what occurs with PFK during exercise?
during exercise, glycolysis will be favoured in order to generate more energy
the conversion of G6P to F6P is favoured and the conversion of F6P to F1,6BP is favoured with the addition of an ATP molecule
this in turn will also allow F1,6BP to be converted into GAP and DHAP
the ADP generated in this reaction will b e converted to ATP and AMP via ADK, thus activating PFK further
explain F2,6 bisphosphate’s role in glycolysis?
F2,6P is a potent activator of PFK, but it is not a substrate of glycolysis
F2,6BP also functions to inhibit FBPase-2 (which converts F1,6BP into F2,6BP.
F2,6BP is made via PFK2
what are the regulators of PFK2?
glucagon (liver) and epinephrine (heart muscle)
what occurs in the differential hormonal regulation of PFK2 enzyme in the liver isozyme?
during fasting/prolonged exercise:
the sensing of low glucose by pancreatic alpha cells secretes glucagon, which increases cAMP and allows PKA activity
decrease in blood glucose, promotes gluconeogenesis by inactivating PFK2 (via phosphorylation by PKA) and activating FBPase in order to convert F2,6BP into F1,6BP and then further into F6P and then G6P
what occurs in the differential hormonal regulation of PFK2 enzyme in the heart muscle isozyme?
in conditions of stress:
epinephrine levels are high, cAMP levels ar also high and PKA is active
this promotes glycolysis and activates PFK1 to form GAP + DHAP
