Nitrigen III Flashcards
Contrast essential and nonessential
Dietary essential- cannot be synthesized by the cell(it must be provided by the diet)
Dietary nonessential- can be synthesized by the cell
What are glucogenic amino acids?
Catabolism yields Pyruvate (an alpha keto acid) or one of the intermediates of the citric acid cycle
-these are substrates for gluconeogenesis
What are ketogenic amino acids?
Yields acetoacetate, Acetyl CoA or acetoacetyl CoA
-these may be substrates for ketones body synthesis
Which amino acids are conditionally dietary essential?
Cysteine (Cys)
Tyrosine
Arginine
Why is arginine conditionally essential?
Arg is conditionally essential, its biosynthesis May not keep up with a rapidly growing individual
-children who are in positive nitrogen balance
- gaining protein weight, or muscle mass
Why is tyrosine conditionally essential?
Tyrosine is conditionally essential: if Phe is limited in the diet Tyr becomes essential
-Phe has an aromatic ring
Why is Cys conditionally essential?
Cys is condition essential: if Met is limited in diet, Cys becomes essential
-Met contains the sulfur
What are the glucogenic nonessential amino acids ?
- Alanine
- Arginine
- Asparagine
- Aspartate
- Cysteine
- Glutamate
- Glutamine
- Glycine
- Proline
- Serine
What are the glucogenic nonessential amino acids?
- Histidine
- Methionine
- Threonine
- Valine
What is the glucogenic AND ketogenic nonessential amino acid?
Tyrosine
What amino acids are essential Glucogenic AND ketogenic amino acids?
- Isoleucine
- Phenylalanine
- Tryptophan
What are the essential ketogenic amino acids?
Leucine
Lysine
What are the essential amino acids?
PVT TIM HALL
phenylalanine
Valine
Tryptophan
Threonine
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine
What are the amino acids that are strictly ketogenic? What does this mean?
Lysine and leucine
The degradation of Leu or Lys does not produce a molecule that can support gluconeogenesis
Isoleucine, phenylalanine and tryptophan are ketogenic and Glucogenic, what does this mean?
Isoleucine
Phenylalanine
Tryptophan
Why did mammals lose the ability to synthesize all the amino acids?
- warm blooded animals must produce an enormous amount to heat to stay alive
- Amino acids are part of the diet (calories), so we get all we need from our diet (hopefully)
- We must eat a lot to survive.
- With disuse, the pathways were ‘retired’ or lost over time
The end products of amino acid catabolism feed into:
- Glycolytic intermediates
- TCA cycle intermediates
- Substrate for ketone body
What are alpha keto acids? How are they formed?
Amino acids are blocked from catabolism by the alpha amino group
- when the alpha amino group is removed, we call what is left behind the “carbon skeletons “
- this is an alpha keto acid
What 2 ways can cells remove the alpha amino group from an amino acid?
- Transamination
2. Deamination
Describe the amino acceptor/donor in transamination
Alpha keto glutarate and glutamate always participate as an amino acceptor/donor pair
Describe deamination of the alpha amino group
There are many reactions that can deaminate the various amino acids
-we don’t have to be concerned with most of them
For us, the most important deamination reaction is catalyzed by the glutamate dehydrogenase enzyme
- Reversible enzyme
- Conversion of Glu to a-KG is oxidative deamination
WHat products are formed from amino acid catabolism
- Pyruvate
- Oxaloacetate
- a-ketoglutarate
- Fumarate
- Succinyl CoA
- Acetyl CoA (ketogenic)
- Acetoacetyl CoA (ketogenic )
The end products of catabolism of phenylalanine and tyrosine are fumarate and acetoacetyl CoA
What is the first step of Phe degradation?
Phe degraded to tyrosine
Enzyme: phenylalanine hydroxylase
Needs tetrahydrobiopterin and oxygen
Converted to: dihydrobiopterin (BH4)+ H2O
Tyrosine converted to fumarate( glucogenic precursor )
Or acetoacetate (ketone body precursor)
When phenylalanine is converted to tyrosine, what can the tyrosine be used for?
- tissue proteins
- thyroid hormone
- melanin
- Catecholamines
- fumarate
- acetoacetate
What is phenylketonuria?
PKU. I (Classic PKU) : deficiency of phenylalanine hydroxylase
-simple enzyme deficiency
- phenylalanine accumulates
- tyrosine is deficient
How can PKKU be treated ?
Individuals who have PKU must be put on a diet restricted for phenylalanine within the first few days after birth
Highlights the importance of newborn screening
What Catecholamines can tyrosine be converted to?
Hormones, neurotransmitters: dopamine, norepinephrine, epinephrine
What causes Alkaptonuria?
Deficiency of homogenistic acid oxidase (homogentisate oxidase) causes alkaptonuria
What causes tyrosinemia type I?
The disease is due to a deficiency in fumaryl-acetoacetate hydrolase
What is the last step in tyrosine catabolism?
The last step of tyrosine catabolism is cleavage of fumarylacetoacetate
Enzyme: fumarylacetoacetate hydrolase
Products (fumarate which is glucogenic)
Acetoacetate which is ketogenic
What is PKU II? What causes it?
Malignant PKU/PKU II caused by:
-deficiency of biopterin (BH2) synthesis (any step)
- deficiency of dihydrobiopterin reductase (inability to convert BH2 —> BH4)
- cofactors deficiency
- BH4 is the coenzyme for phenylalanine hydroxylase (and other ring hydroxylation reactions)
- so BH4 deficiency causes dopamine, norepinephrine, epinephrine (the 3 Catecholamines) and serotonin deficiency
How is BH4 formed? What is BH4 used from?
BH2 uses NADPH to create BH4+ NADP+ H+
BH4 is required for aromatic ring hydroxylation reactions (formation of serotonin from Trp,L-dopa from Tyr, Tyr from Phe), and some other reactions
What is “the catechol “ ?
- has two hydroxyl groups next to each other on an aromatic (arene) ring (benzene ring)
- So L-Dopa is an amino acid that contains a catechol on its side chain
- Decarboxylation of L-dopa (CO2 comes off), forms dopamine (a catecholamine)
What 3 Catecholamines are formed from the PHE/TYR pathway?
- Dopamine
- Norepinephrine
- Epinephrine
Norepinephrine converted to epinephrine by adding methyl group via SAM replacing the norepinephrine NH3
How is serotonin formed ?
The amino acid tryptophan is hydroxylase on its aromatic ring
Serotonin is derived from the amino acid tryptophan
- Requires BH4 for ring hydroxylation
- Serotonin is an amine
- Important hormone and neurotransmitter
