Gluconeogenesis and The Pentose Phosphate Pathway Flashcards
What molecule do we convert to glucose first when we have not consumed any glucose for awhile
Glycogen
How long does it take for glycogen stores to be depleted
10-18hours
Why can we not produce glucose from fat
We can’t turn acetyl CoA to pyruvate as the reaction is irreversible
Apart from glycogen what else can be converted to glucose
Ketone bodies
What are ketone bodies derived from
Excess fatty acid oxidation in the liver
Where does gluconeogenesis only take place
The liver
What substrates are converted to glucose in the liver via gluconeogenesis
Amino acids (glutamine and alanine), lactate, glycerol
What is the difference between lactic acid and lactate
Lactic acid is lactate and a H+
How is lactate formed
In glycolysis from the oxidation of pyruvate in acetyl CoA
What enzyme catalyses lactate production
Lactate dehydrogenase (LDH)
When is lactate production upregulated and why
During high intensity exercise as glycolysis is occurring rapidly and lactate is needed as a safety net to be reconverted back to pyruvate for glucose if aerobic oxidation is not possible (ensures continuation of anaerobic glycolysis during HI exercise)
What is lactate used for at rest
Conversion of glucose to glycogen for storage
How many irreversible reactions in glycolysis does gluconeogenesis have to overcome to produce glucose
3 irreversible reactions
What is the ATP cost of gluconeogenesis
6 ATP
What substrates can pyruvate be derived from in step 1 gluconeogenesis
Alanine, glutamine, lactate and glycerol
What enzyme catalyses the conversion of pyruvate to Oxaloacetate
Pyruvate carboxylase
Why does pyruvate need to be converted to Oxaloacetate first before we can generate PEP
As the reaction of PEP to pyruvate is irreversible
What is the the second irreversible reaction of glycolysis that must be overcome in gluconeogenesis
Fructose 1,6- bis to fructose 6-phosphate which is catalysed by fructose1-beta biophosphotase
What is the final irreversible reaction glycolysis that is overcome in gluconeogenesis
Glucose 6-phosphate to glucose, catalysed by glucocorticoids 6 phosphotase
Why can gluconeogenesis only occur in the liver
skeletal muscle doesn’t have G-6-Phosphotase enzyme so therefore gluconeogenesis cannot occur in SM.
When is gluconeogenesis activated
When glucose is not consumed e.g when fasting (10-18hrs), during sleep, after 30-45 minutes of steady state exercise and when insulin is low
What molecule does a our liver take from circulation for gluconeogenesis
Glycerol and alanine and glutamine
What is the Pentose phosphotase pathway
Pathway used to oxidise glucose to produce the sugars needed for DNA
How many ATP does the Penrose phosphotase pathway generate
None
What are the end products of the Penrose phosphotase pathway
Penrose and phosphate
Where does the Pentose phosphotase pathway occur
Mostly the cytosol of the liver and adipose tissue
Which reaction does the Pentose phosphotase run parallel to
Glycolysis
Describe the main step of the Pentose phosphotase pathway
Glucose 6 phosphate shunted away from glycolysis is converted to ribulose 5C, 2 NADPH are generated during this process
What are the function of ribulose-5-C
Important in the development of DNA and RNA
OR
Alternatively, the ribulose-5-C can be converted to fructose 6-phosphate or glyceraldehyde-3-P
What determines does whether ribose 5-c predominates or fructose-6-P and glyceralshedye -3-p does at the the end of the PP
The NADPH content of the cell as if more NADPH is needed more fructose-6-p is needed to generate more glucose 6-P for glycolysis, which can then be used to restart the PP pathway and generate more NADPH
Why is NADPH important
NADPH is used to make glutathione which is an important antioxidant to prevent oxidative stress
Why is glutathione production important
Glutathione is an important antioxidant, because several processes that involve high levels of 02 turnover generates potentially damaging free radicals. The ETC and aerobic exercise increases free radicals production
What molecule upregulated the Pentose phosphate pathway
NADP+
What else can fructose-6-P be used for
To produce new fatty acids
