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46 Cards in this Set

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glutamate dehydrogenase
◊ In the liver mitochondria matrix, the amino group on glutamate can be directly removed by glutamate dehydrogenase (liver has glutamate transporters).
glutamine synthetase
Glutamate is converted into glutamine by glutamine synthetase first before being transported into the liver.
glutaminase
After glutamine is transported to the liver, it is converted back to glutamate by glutaminase.
Modified Cori Cycle
The modified cori cycle, also known as the glucose-alanine cycle, is used by the body to transport excess NH4+ to the liver.

First, pyruvate is transaminated using glutamate, forming α-ketogluterate and alanine. Alanine is transported to the liver and transaminated back using α-ketogluterate, forming glutamate and pyruvate. Glutamate can be deaminated by glutamate dehydrogenase and pyruvate can be converted to glucose by gluconeogenesis. The glucose can then be shipped back to the muscle.
Ammoniotelic
organisms that excrete soluble ammonia
Ureotelic species
secrete ammonia in the form of urea
Uricotelic species
secrete ammonia in the form of uric acid
3 prep steps before entering the urea cycle
Bicarbonate is phosphorylated by ATP to form carboxyphosphate (reactive) and ADP. NH3 displaces the phosphate, forming carbamic acid. Carbamic acid is phosphorylated by ATP to form carbomoyl phosphate and ADP
carbamoyl phosphate synthetase I
Carbamoyl phosphate is synthesized from NH3+ and bicarbonate (HCO3) by carbamoyl phosphate synthetase I
ornithine transcarbamoylase
Carbamoyl phosphate is added to the amino acid ornithine, forming the amino acid citrulline.
argininosuccinate synthetase
Citrulline reacts with the amino acid aspartate to form argininosuccinate.
argininosuccinate synthetase
Citrulline reacts with the amino acid aspartate to form argininosuccinate.
argininosuccinase
Argininosuccinate is cleaved into fumarate and arginine
Glucogenic
Intermediates that can give rise to glucose through gluconeogenesis. Namely pyruvate, oxaloacetate, a-ketogluterate, succinyl CoA, and fumarate.
Ketogenic
Intermediates that can be used to make ketone bodies or fatty acids. Namely acetyl CoA and acetoacetyl CoA.
name 2 amino acids skeletons that are both glucogenic and ketogenic
phenylalanine and tyrosine
phenylalanine hydroxylase
Uses O2 and a co-factor called tetrahydrobiopterin to hydroxylate phenylalanine into tyrosine,converting the co-factor into Quinoid dihydrobiopterin.
Tyrosine transaminase
Uses α-ketogluterate to transaminates tyrosine, forming p-hydroxyphenylpyruvate (α-keto acid of tyrosine)
4-fumarylacetoacetate is hydrolyzed to?
fumarate and acetoacetate
Phenylketonuria (PKU)
Genetic defects in the gene encoding phenylalanine hydroxylase can lead to the inactivation of the enzyme, resulting in ↑[phenylalanine] and ↑[phenylpyruvate], which is the α-keto acid of phenylalanine.
Alcaptonuria
mutations in the gene encoding the enzyme needed to open the ring homogentisate.
Parkinson's disease
Patients that fail to produce enough dopamine in the brain
three ketone bodies
Acetoacetate, acetone, and β-hydroxybutyrate
thiolase
In the reverse of thiolysis, 2 acetyl CoA units are joined by thiolase to form acetoacetyl CoA. (reversible)
HMG-CoA synthase
Adds another acetyl CoA to acetoacetyl CoA, forming HMG-CoA
HMG-CoA lyase
Acetyl CoA is cleaved off in an irreversible reaction yielding acetoacetate.
β-hydroxybutyrate dehydrogenase
Uses NADH to reduce acetoacetate to β-hydroxybutyrate (reversible).
CoA transferase
Acetoacetate is converted to acetoacetyl CoA through the transfer of a CoA group from succinyl CoA (yielding succinate).
Hyperglycemia
↑ blood [glucose] long term can lead to neurological, cardiovascular, and renal damage.
Hypoglycemia
↓ blood [glucose] can cause unconsciousness, brain damage, and even death.
Glucagon
a peptide hormone released when glucose is scarce
Epinephrine
a catecholamine that is also released when glucose is needed.
Insulin
peptide hormone released when glucose levels are high
GLUT 3 and GLUT 1
Found in he brain at high levels.

Have a low Km: 1mM
GLUT 2
Found in the liver and pancreas.

Very high Km: 15-20mM.
GLUT4
Found in muscles and adipocytes.

Km is 5mM, meaning that it is 50% saturated at normal blood glucose concentrations.
fructose-2,6-bisphosphate (F26BP) stimulates ? and inhibits ?
stimulates phosphofructokinase I and inhibits fructose-1,6-bisphosphatase
When glucose is abundant, ? is active; when glucose is scarce, ? is active.
When glucose is abundant, PFK2 is active; when glucose is scarce, FBPase2 is active.
When PFK2 is phosphorylated, it?
it is inactive and FBPase2 is active
When PFK2 is not phosphorylated
it is active and FBPase2 is inactive
cAMP cascade
When glucose levels are low, this causes a cAMP cascade, leading to the activation of protein kinase A (PKA). PKA phosphorylates PFK2, and thus fructose-2,6-bisphosphate levels drop, and glycolysis is no longer stimulated and gluconeogenesis is no longer inhibited.
Insulin cascade
Increased uptake of glucose, increased hexokinase activity, activation of protein phosphatase. This protein phosphatase (phosphoprotein phosphatase) dephosphorylates PFK2, thus activating it and inhibiting FBPase 2. This lead to the activation of glycolysis and inactivation of gluconeogenesis.
Urea Cycle Steps
1. Carbamoyl phosphate is added to the amino acid ornithine, forming the amino acid citrulline.
2. Citrulline reacts with the amino acid aspartate to form argininosuccinate, catalyzed by argininosuccinate synthetase.
3. Argininosuccinate is cleaved into fumarate and arginine by argininosuccinase.
4. Arginine is hydrolyzed to generate urea and ornithine by arginase, and ornithine is transported to the matrix.
Ketone Body Synthesis
1. In the reverse of thiolysis, 2 acetyl CoA units are joined by thiolase to form acetoacetyl CoA.
2. HMG-CoA synthase adds another acetyl CoA to form HMG-CoA.
3. Acetyl CoA is then cleaved off in an irreversible reaction catalyzed by HMG-CoA lyase, yielding acetoacetate.
4. a. Acetoacetate can be decarboxylated spontaneously to produce acetone (not that useful)
4. b. β-hydroxybutyrate dehydrogenase uses NADH to reduce acetoacetate to β-hydroxybutyrate (more stable)
Ketone Body Breakdown
1. In the reverse of 4b, β-hydroxybutyrate is oxidized back to acetoacetate by β-hydroxybutyrate dehydrogenase, generating an NADH.

2. Acetoacetate is converted to acetoacetyl CoA through the transfer of a CoA group from succinyl CoA (yielding succinate) as catalyzed by CoA transferase. Where was the price paid?
§ The conversion of succinyl CoA to succinate can produce enough energy to generate one GTP molecule. Instead, the CoA transferase uses this energy to convert acetoacetate to acetoacetyl CoA.
3. Thiolase catalyzes the thiolysis of acetoacetyl CoA to 2 acetyl CoA units.
Phenylalanine Breakdown
1. Phenylalanine is converted to tyrosine
2. Tyrosine transaminase uses α-ketogluterate to transaminates tyrosine, forming p-hydroxyphenylpyruvate (α-keto acid of tyrosine).
3. A whole molecule of O2 is added to p-hydroxyphenylpyruvate, while CO2 is removed, forming homogentisate.
4. The phenyl ring is opened with the addition of another O2, forming 4-maleylacetoacetate, which is the wrong isomer
5. 4-maleylacetoacetate is isomerized to 4-fumarylacetoacetate.

6. 4-fumarylacetoacetate is hydrolyzed to fumarate and acetoacetate.