Gluconeogenesis and the Pentose Phosphate Pathway Flashcards
What is essential for the well-being of organisms?
well regulated glucose metabolism
Tumour cells are frequently_______–> generates less__ per glucose molecule, requiring a lot of it
ATP
What is Gluconeogenesis?
a metabolic pathway that converts pyruvate into glucose
Where is Gluconeogenesis especially important?
during prolonged periods of of fasting or starvation (or periods of increased need of energy).
What are non carbohydrate precursors first converted into?
pyruvate or enter the pathway at later stages
What are the major precursors?
-lactate
-amino acids
-glycerol (but not in animal cells)
What enzyme regularly converts lactate into pyruvate?
lactate dehydrogenase
Amino acids___ from proteins which are broken down e.g. skeletal muscle
derive
Where does Gluconeogenesis mainly occur?
the liver (with a small amount taking place in the kidney)
What does Gluconeogenesis in the liver and kidney help with?
helps to maintain the glucose level of the blood
What does this mean for the brain and muscles?
that they can extract sufficient glucose to meet their metabolic demands
What type of pathway is Glycolysis?
a catabolic pathway
What type of pathway is gluconeogenesis?
an anabolic pathway
Reactions of both pathways are____ in both organisms
similar
What is the first bypass step of Glyconeogenesis?
conversion of pyruvate to oxaloacetate
What is the second bypass of Gluconeogenesis?
conversion of oxaloacetate to PEP (PEP carboxykinase).
What do both of these steps require?
the use of high energy phosphate molecules (ATP and GTP).
What does the PEP formation pathway depend on?
the starting molecule
Why are enzymes required for conversion of oxaloacetate to PEP in both the mitochondria and the cytosol?
because NADH is much lower in the cytosol and required for further processes in the pathway
What are the 2 enzymes catalysing the two other “bypass” reactions?
-FBPase-1
-Glucose-6-phosphatase
(these reactions do not use up high energy molecules)>
Synthesis of glucose from pyruvate is energetically____.
What is this to ensure
expensive
To ensure the irreversibility of glujconeogenesis
Gluconeogenesis and Glycolysis have reciprocal _____
regulation
It is possible for both to occur_______ due to_____ as both of them are highly_______.
Why does this not occur?
simultaneously, thermodynamics, exergonic
It would waste energy
Describe how the pathways are coordinated
when one is highly active the other is inactive
How are the enzymes regulated? Why is this important?
using allosteric mechanisms
This allows the balance between gluconeogenesis and glycolysis to ensure stable blood glucose concentration
What is an alternative metabolic fate for glucose-6 phosphate instead of the glycolysis pathway?
Pentose phosphate pathway
Why is the Pentose phosphate pathway crucial?
-crucial source of NADPH
-protection against oxidative stress
What is a major product of the PPP? What is it used for?
pentose-5 phosphate
-used to make RNA, DNA and coenzymes such as NADH, ATP etc.
What is the PPP an important reaction for?
rapidly dividing cells
e.g.) bone marrow, skin, tumours etc.
How many stages of the PPP are there?
2
1st stage of PPP
Oxidative reactions of pathway generate pentose molecules important for fast dividing cells
2nd stage of PPP
Non-oxidative reactions used in tissues requiring a lot of NADP (as formed during the oxidative phase).
What type of reactions are these?
reversible reactions used to inter-convert pentose and hexose molecules
What does NADPH help decide?
fate of glucose-6-phosphate
What happens if NADPH forms faster than it is used? What does this do?
it feeds back to inhibit the first enzyme in the pathway
This makes more glucose 6-phosphate available for glycolysis
