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Biochem Exam 6

Protein & Amino Acid Metabolism and The Urea Cycle

Can amino acids be stored No
What are amino acids borwken down and used for Fuel or as building blocks for glucose and lipid synthesis
The break down of amino acids generates what Ammonia
What are the chemical formulas for ammonia and ammonium NH3, NH4+
Which is membrane permeable ammonia or ammonium Ammonia
At a pH less then the pK the equation is going to shift to the Protonated form
Why is ammonia so toxic It increases pH which alters redox balanc and can disrupt protien structure function and it inhibits ox phos by breaking down the H+ gradient
Where do whe get our amino acids Dietary protein, endogenous proteins turnover, endogenous AA synthesis
What do we do with amino acids Synthesis of other N containing molecules, degrade it into C which is used fo synthesis of glucose, fatty acids, ketones and N which is excreted in urea
Amino acids are important for the CNS because Somone amino acids act as neurotransmitters and many neurotransmitters are synthesized from amino acids
What is nitrogen balance Nitrogen input = nitrogen output
What is Positive nitrogen balance N input > N output
Who would be seen in positive N balance Children, Pregnant women
What is Negative nitrogen balance N input < N output
Who would be seen in negative N balance Those with a dietary deficiency or those with catabolic stress such as an infection
What are essential amino acids Phenylalanine, Valine, Tyrptophan, Threonine, Isoleucine, Methionine, Histidine, Arginine, Lysine, Leucine
Alanine is synthesized from Pyuvate
Aspartate is synthesized from Oxaloacetate
Glutamate is syntehsized from Alpha keto gluterate
What amino acid is essention only for growth and is generated int eh urea cycle Arginine
The S in cysteine comes from where Methionine
Tyrosine is made from Phenylalanine
What are the three cofactors important for amino acid synthesis Pyridoxal phosphate, Tetrahydrofolate, Tetrahydrobiopterin (BH4)
Pyridoxal phosphate is made from Vitamin B6
A defect in a transporter for cystine and basic amino acids which can result in kidney stones Cystinuria
A defect in the transporter for neutral amino acids and generaly asymptomatic Hartnup disease
Amino acids cant be further catabolized until the amino group has been removed
The nitrogen component of degraded amino acids is excreted as Urea
Transamination is catalyzed by Aminotransferases (transaminases)
How does transamination work The amion acid gives its amino group to alpha-ketoglutarate producing glutamate. The original amino acid has been converted to its corresponding keto acid.
The enzyme that catalyzes the transamination of Aspartate to Oxaloacetate is Aspartate aminotransferase (AST)
The enzyme that catalyzes the transamination of Alanine to Pyruvate is Alanine aminotransferase (ALT)
Aminotransferases are intracellular proteins and are not usually found in the Plasma
High serum levels of ALT and AST would indicate A liver disease
What cofactor do aminotransferases require Pyridoxal phosphate
What is pyridoxal phosphate synthesized from by the liver Vitamin B6
Glutamate is deaminated by Glutamate dehydrogenase (GDH)
What are the products of Glutamate deamination Ammonia and alpha-ketoglutarate
Where does glutamate deamination primarily occur Liver and kidneys
Free ammonia is produced by what other metabolic processes Purine metabolism, bacterial metabolism in the gut, metabolism of serine and threonine
What can carry two ammonia molecules to the liver Glutamine
Ammonia can be tranpsorted to the liver as what amino acid Alanine
Amino acids are classfied into what two groups depending on what happens to the carbons Glucogenic or ketogenic
Amino acids that are ultimately degraded to pyruvate or TCA cyle intermediates are classified as Glucogenic
Amino acids that are ultimately degraded into acetyl CoA or acetoacetate are classified as Ketogenic
What two amino acids are strictly ketogenic Lysine and leucine
Aspartate, alanine, and glutamate are strictly Glucogenic
Insulin promotes Amino acid uptake and protein synthesis
Glucocorticoids induce Ubiquitin synthesis
Glucagonand cortisol stimulate Uptake of amino acids into the liver
The brain needs amino acids for synthesis of Neurotransmitters
Muscle is a major source of amino acids in the Fasted state
Teh liver uses a lto of amino acids in the Fasted state
A state of increased fule usage in which the body needs energy and precurs to mount a defense against infection heal wounds, ect Hypercatabolic state
A hypercatabolic state results in what type of nitrogen balance Negative nitrogen balance
The disposal form of ammonia Urea
Where does the urea cycle primarily occur Liver
Where is urea excreted Kidneys
Where do the two nitrogens of urea come from Ammonia and aspartate
What is the precurso of both ammonia and aspartate Glutamate
HCO3 + NH4 --> Carbamoyl phosphate Carbamoyl phosphate synthase 1 (CPS1)
Carbamoyl Phosphate + Ornithine --> Pi + Citrulline Ornithine transcarboylase (OTC)
Is the synthesis of urea reversible No
The first two steps of the urea cycle take place in the Mitochondria
The nitrogen in the first step comes from ... and this is catylzed by ... Ammonia, CPS1
What is the rate limiting step of the urea cycle CPS1
The second nitrogen in urea comes from Aspartate
What links the TCA cycle to the urea cycle Fumarate
Is arginine produced from the urea cyle Yes
Is ATP used inteh urea cycle Yes
What is regenerated and transported back inot the mitochondria where OTC uses it to make citrulline Ornithine
Regulation of the urea cycle is primarily based on what Substrate availability
Transcripton/translation of the urea cycle enzymes is induced by High protein diet or prolonged fasting
What stimulates carbamoyl phosphate synthase 1 (CPS1) N-acetylglutamate (NAG)
What is NAG synthesized from Acetyl CoA and glutamate
Acetyl CoA + Glutamate --> NAG NAG synthase
Can ura cross membranes and diffuse into the blood Yes
Where is urea filtered and excreted Kidneys, urine
Some urea diffuses inot the ... and is cleaved by ... Intestines, bacteria
What is the measure of urea concentration in the blood Blood Urea Nitrogen (BUN)
BUN levels reflect the function of the Kidney and liver
BUN levels depend on Diet
Urea cycle impairment results in Hyperammonemia
What is hyperammonemia Increased blood levels of ammonia
Tremors, agitation, slurring of speech, blurred vision, vomiting, hypotonia, seizures, mental retardation, cerebral edema and coma are symptoms of Hyperammonemia
Kidney failure can lead to hyperammonemia
All hereditary urea cycle disorders are ... except for ornithine transcarbamoylase deficiency Autosomal recessive
Ornithine transcarbamoylase deficiency is X-linked
What is the most common urea cycle disorder Ornithine transcarbamoylase (OTC) deficiency
Created by: mhaynes