Biochemistry-Energy Metabolism in the Brain Flashcards
What blood glucose levels define severe hypoglycemia?
Levels below 40mg/100mL
What does the body use glucose for?
85% of it goes to ATP production. 15% of it is used to form neurotransmiters, nonessential amino acids, NADPH, glycogen synthesis and membrane lipids.
Why does the brain really depend on glucose for energy?
Long chain fatty acids cannot cross the blood-brain barrier
Why is the brain the most metabolically active tissue in our body when really all it does it sit there?
It needs lots of ATP to maintain electrochemical gradients via Na/K ATPase and other pumps
How does our body maintain blood glucose levels as you go further and further into a fast?
1) Food 2) Liver Glycogen 3) Glucose from amino acids 4) Ketone bodies
What molecules provide the energy for 75% of ATP in our body during a fasting state?
Ketone bodies, note that they can cross the blood-brain barrier. They provide about 21 ATP/mole from Acetyl CoA going through the citric acid cycle.
Where are ketone bodies formed?
Liver
Why doesn’t paleoman waste away after not eating meat for 20 days?
The body uses ketone bodies to fuel the brain. The decreases the amount of amino acids taken from muscle in gluconeogenesis and spares the muscle.
Why do babies tend to have a more active ketone body production than adults?
Before birth, the child relies on the mother for glucose. At birth glucose levels fall and cause a hormonal stress response. This results in a surge of glucagon, glycogenolysis and gluconeogenesis. Hypoglycemia triggers the need for extra ketone body production.
What is the energy system used by the brain when you have a burst of ATP use from rapidly pumping of ions across the membrane of a neuron during an action potential?
Immediate system. An increase in ADP will cause a decrease in phosphocreatine and create more ATP.
How does your brain recover the phosphocreatine it used during an action potential?
Increased ATP levels causes a decrease in creatine and an increase in phosphocreatine
Where do neurons get most of their ATP from?
Lactate produced by astrocytes. Lactate is oxidized to pyruvate and then pyruvate goes on through the citric acid cycle. Each lactate can produce about 15 ATP!
What is the blood-brain barrier permeable to?
Glucose (GLUT1 & 3 transporters). Ketone bodies, lactate and acetate (monocarboxylate transporter). Select amino acids. Essential fatty acids. It is not permeable to most fatty acids and therefore beta-oxidation is not a significant source of ATP in the brain.
How does the astrocyte provide fuel for the neurons and manage bioactive peptide release and reuptake?
The Na/K ATPase maintains a gradient so glutamate secreted by the neuron can cotransport with Na+ back into the astrocyte. Here it is converted to glutamine where it goes back to the neuron where it is again converted to glutamate. The astocyte also takes blood glucose and oxidizes it to lactate. Lactate is then sent to the neuron as a source for ATP generation.
How do you make glutamate from glucose?
Gluc -> Phosphoglycerate -> Pyruvate -> Acetyl CoA -> Citrate -> Isocitrate -> alpha-ketoglutarate -> Glutamate (via transamination). Glutamate dehydrogenase can also make glutamate from alpha-ketoglutarate with ammonia and a reducing agent.
How do you make glutamine from glutamate?
Replace the carboxyl group with an amide group.
