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Lecture 31
Urea Cycle and NO synthesis
Question | Answer |
---|---|
What carbon sources can be broken down for energy? | Carbohydrates, proteins, and fatty acids |
What are the sources for amino acids for energy generation in the body? | Dietary protein |
What organs don't use amino acids for energy? | Brain and the Red blood cells |
What two amino acids specifically breakdown to form Acetyl-CoA? | Lysine and Leucine |
What three amino acids can be used in the liver to make glucose? | Alanine, aspartate, and glutamate |
What are two fates of an alpha keto acid? | Kreb's cycle or gluconeogenesis |
What enzyme transfers the amine from amino acids in the muscle to pyruvate? What are the products? Co-factor? | Pyruvate + Glutamate --> Alanine and A-ketoglutarate; Alanine aminotransferase; PLP |
How does alanine get to the liver? | Travels in the blood |
What is Alanine the amino acid that travels in the blood? | Alanine is a stable molecule. Free ammonia is too toxic and other amino acids are more reactive |
What amino acid releases ammonia in the muscle? | Glutamate |
What does ALT stand for? | Alanine aminotransferase |
What reaction does ALT catalyze? | The transamination from alanine to glutamate |
Why is alanine converted to glutamate in the liver? | Glutamate carries the free amine which is later released to the urea cycle |
What are two fates for glutamate in the liver? | It can enter the citric acid cycle through alpha keto glutarate or it can do transamination with OAA to form Aspartate which enters the urea cycle |
What are two types of amines that enter into the urea cycle? | The amine from aspartate and the amine from glutamate |
What is the carbon backbone that free ammonia attaches to? | Bicarbonate- HCO3 |
What is the first molecule that enters the urea cycle? Why does it take 2 ATPs to form this product? | Carbomoyl phosphate; it takes 1 ATP to do the reaction and 1 ATP to phosphorylate it |
Where does the amine from aspartate enter the urea cycle? | After the citrulline intermediate |
What carbon skeleton is released by the urea cycle and enters the citric acid cycle? | Fumarate |
What amino acid is synthesized in the urea cycle? | Arginine |
Where do the two amines and the carbonyl of urea originate from? | the two amines come from aspartate and glutamate; the carbonyl comes from bicarbonate |
What are the substrates, source of oxygen and products of NO synthesis? | Substrate(arginine and NADPH)Products(NADP+, Citrulline, and NO) |
What second messenger is increased in the presence of NO? | cGMP |
What affect does cGMP have on blood vessels? | Relaxes smooth muscles and increases vasodilation |
What enzyme cleaves cGMP to form 5' GMP? | cGMP phosphodiesterase |
What happens to the NO formed in the endothelial cell? | It leaves the endothelial cell and enters the smooth muscle to affect guanylyl cyclase |
What reaction does guanylyl cyclase catalyze? | GTP to cGMP |
What does viagra do? | Inhibits the penile form of PDE so cGMP levels stay high |