Amino Acids: Metabolism of Carbon Skeletons. Flashcards
What is pyridoxial phosphate also known as?
Vitamin B6.
What is an essential amino acid?
An amino acid that must be obtained through the diet as the body cannot make it.
What is a non essential amino acid?
An amino acid that can be synthesised by the body.
The bodys pool of amino acid is topped up by what processes?
Amino acids from protein turnover.
Amino acids from dietary proteins.
Non-essential amino acids that are synthesised by the body.
The amino acids in the body’s amino acid pool can be used for what processes?
Protein synthesis.
The synthesis of specialised products.
Amino acid catabolism.
Amino acid catabolism leads to what?
The release of ammonia in urea.
The release of carbon skeletons.
The carbon skeletons that are released by the catabolism of amino acids can be used for what processes?
Making glucose.
Making ketone bodies.
Are excess amino acids ever stored in the body?
No.
How many amino acids does the body need?
20.
What stereoisomer of amino acids will the body use?
Always the L form.
How many of the 20 amino acids are essential?
10.
How many of the 20 amino acids are non-essential?
10.
Cant the carbon skeleton be used to classify amino acids?
Yes.
What are the 2 classifications of amino acids by their carbon skeletons?
Glucogenic amino acids.
Ketogenic amino acids.
What does the catabolism of glucogenic amino acids yield?
Carbon skeletons that form pyruvate or intermediates of the TCA cycle.
The carbon skeletons of glucogenic amino acids can be used as what precursors?
As gluconeogenic precursors.
The catabolism of ketogenic amino acids will yield what?
A carbon backbone that forms acetoacetate, ACoA or acetoacetyl CoA.
The carbon skeletons of ketogenic amino acids can be converted to what?
To fatty acids and ketone bodies.
Can ketogenic amino acids be converted to glucose?
No.
What are the 10 essential amino acids?
PVT TIM HALL.
Phenylalanine.
Valine.
Tryptophan.
Threonine.
Isoleucine.
Methionine.
Histidine.
Arginine.
Lysine.
Leucine.
Which essential amino acid is essential in children?
Arginine.
Why is arginine only essential in children?
As it is made in the urea cycle which is more active in adults than in children.
What are the 10 non-essential amino acids?
AGA CAPS GAG.
Asparagine.
Glycine.
Aspartate.
Cysteine.
Arginine.
Proline.
Serine.
Glutamine.
Alanine.
Glutamate.
Does every amino acid give a corresponding keto acid?
Yes.
What is the keto acid of alanine?
Pyruvate.
What is the keto acid of glutamate?
Alpha ketogluterate.
What is the keto acid of aspartate?
Oxaloacetate.
What 2 amino acids are always keto acids?
Leucine.
Lysine.
What are the 15 glucogenic amino acids?
PATHS GAG CAMP GAV.
Proline. Aspartate. Threonine. Histidine. Serine.
Glycine.
Arginine.
Glutamine.
Cysteine.
Alanine.
Methionine.
Proline.
Glutamate.
Asparagine.
Valine.
What are the 5 amino acids that are both glucogenic and ketogenic?
TIP TT.
Tyrosine.
Isoleucine.
Phenylalanine.
Tryptophan.
Threonine.
What can the carbon skeletons of glucogenic and ketogenic amino acids yield?
ACoA or fumarate.
What does the catabolism of amino acids involve?
The removal of the amino group from the amino acid and then breaking down the carbon skeleton.
What are the glucogenic products of amino acid catabolism?
SOAP F.
Succinyl CoA.
Oxaloacetate.
Alpha ketogluterate.
Pyruvate.
Fumarate.
What are the ketogenic products of amino acid catabolism?
AA.
Acetyl CoA.
Acetoacetyl CoA.
Which 2 amino acids form oxaloacetate?
Asparagine (ASN).
Aspartate.
How does asparagine form oxaloacetate?
It is hydrolysed by asparaginase to give NH3 and aspartate.
Aspartate gives OAA after transamination by aminotransferase (AST).
What 4 amino acids form alpha keto-gluterate?
GAPH.
Glutamate.
Arginine.
Proline.
Histidine.
What 5 amino acids form pyruvate?
G CATS.
Glycine. Cysteine. Alanine. Threonine. Serine.
What glycolytic intermediate can serine be made from?
2-phosphoglycerate.
What process can be used to form pyruvate from alanine?
Transamination by ALT.
Which amino acids can form fumarate?
TP.
Tyrosine.
Phenylalanine.
The amino acids that can form fumarate can also form what?
Acetoacetate.
Which 4 amino acids for succinyl CoA?
V TIM.
Valine.
Threonine.
Isoleucine.
Methionine.
Is methionine a ketogenic or glucogenic amino acid?
Both.
Which amino acids from ACoA or acetoacetyl CoA?
LILT.
Leucine.
Isoleucine.
Lysine.
Tryptophan.
What molecule will leucines ketoacid form?
Acetoacetate as it is strictly ketogenic.
What molecule will isoleucines ketoacid form?
Acetyl CoA, also known as propionyl CoA.
What molecule will lysines ketoacid form?
ACoA as it is strictly ketogenic.
What molecule will tryptophans ketoacid form?
ACoA.
Which amino acids can form acetoacetate and fumarate during their catabolism?
Tyrosine and phenylalanine.
Which essential amino acid is required for the synthesis of all proteins within the body?
Methionine.
Which amino acid is used as a pre-cursor to make cysteine?
Methionine.
What is step 1 of the metabolism of methionine?
Dietary methionine will be added to an adenosine group from an ATP molecule to form S-adenosylmethionine (SAM).
What enzyme is used in step 1 of the metabolism of methionine?
S-adenosylmethionine synthase.
Why is S-adenosylmethionine (SAM) a very important molecule in biological reactions?
As it can donate its methyl group to form many methylated products.
What is step 2 of the metabolism of methionine after SAM has been formed?
The methyl group is removed from SAM forming the molecule S-adenosylhomocysteine (SAH).
What enzyme removes the methyl group from SAM in step 2 of the metabolism of methionine?
Various methyltransferases.
What is step 2 of the metabolism of methionine after SAH has been formed?
The adenosine group is removed from adenosylhomocysteine to form homocysteine.
What enzyme removes the adenosine group in step 3 of the metabolism of methionine?
Adenosylhomocysteinase.
Why is homocysteine an important molecule?
It can be used in a number of pathways or it can be used to re-synthesise methionine.
What enzyme is used to re-synthesise methionine from homocysteine?
Methionine synthase.
What coenzymes are used with methionine synthase to re-synthesise methionine?
Methyltetrahydrofolate and methyl B-12.
What do the co enzymes do when methionine synthase is re-synthesising methionine?
They are responsible for carrying the methyl group that is replaced onto homocysteine to make methionine.
What does a deficiency in B12 or methyltetrahydrofolate (folic acid) result in?
In an accumulation of homocysteine in the bloodstream and in the urine.
Where does the methyl group that is transferred onto homocysteine in the re-synthesis of methionine taken from?
From methyltetrahydrofolate (folic acid).
What happens in step 4 of the metabolism of methionine, once homocysteine has been formed?
Homocysteine is combined with serine to make cystathionine.
What enzyme is used to combine homocysteine with serine in step 4 of the metabolism of methionine?
Cystathionine β-synthase.
What co-enzymes does cystathionine β-synthase use in step 4 of the metabolism of methionine?
Vitamin B6.
What happens in step 5 of the metabolism of methionine, once cystathione has been formed?
Cystathionine is broken down to form L-cysteine.
What enzyme is used to break down cystathione in step 5 of the metabolism of methionine?
Cystathionase
What co-enzymes are used by cystathionase to break down cystathione in step 5 of the metabolism of methionine?
Vitamin B6.
What 2 enzymes and coenzymes required for the final 2 steps of the formation of cysteine from methionine?
Cystathionine β-synthase. Vitamin B6.
Cystathionase. Vitamin B6.
What enzyme and coenzymes are required for the formation of methionine from homocysteine?
Methionine synthase. Methyltetrahydrofolate (folic acid) and methyl B-12.
What is a tyrosinase deficiency?
An inherited deficiency in tyrosinase resulting in the inability to make melanin which results in albinism.
What is a homogentisate oxidase deficiency?
An inherited deficiency in homogentisate oxidase which leads to alcaptonuria.
What is a phenylalanine hydroxylase deficiency?
An inherited deficiency in phenylalanine hydroxylase that results in phenyl-ketone urea (PKU).
What is phenylalanine hydroxylase responsible for?
Making tyrosine from phenylalanine.
How many types of phenyl-ketone urea syndrome?
2.
What are the 2 types of phenyl-ketone urea syndrome?
Classic PKU.
Malignant PKU.
What deficiency will result in classic PKU syndrome?
A deficiency in phenylalanine hydroxylase.
What deficiency will result in malignant PKU syndrome?
A deficiency in the co-enzyme for phenylalanine hydroxylase or in the enzyme that makes the co-enzyme.
What is the co-enzyme for phenylalanine hydroxylase?
Dihydrobiopterin (BH4).
What makes the coenzyme for phenylalanine hydroxylase (BH4)?
Dihydropterin reductase.
What can amino acid will not be synthesised as a result of PKU syndrome?
Tyrosine.
PKU syndrome means that anything that needs to be made from which amino acid cannot be made?
Tyrosine.
What is one of the most common deficiencies in amino acid metabolism?
A PKU disorder.
What enzymes normally produce tyrosine from phenylalanine?
Phenylalanine hydroxylase.
An inability to make tyrosine from phenylalanine will result in what?
A build up of phenylalanine which must be converted to phenyl pyruvate and this leads to health problems.
What is one of the major outcomes of an untreated PKU disorder?
Mental retardation in infants and improper development.
A deficiency in vitamin B12 results in what?
An accumulation of homocysteine meaning that THF is trapped in its methyl-THF form.
Why will a vitamin B-12 deficiency result in THF being trapped in its methyl form?
Because THF donates its methyl group to vitamin B-12 to pass on to homocysteine to re-form methionine.
What happens to THF once it has donated its methyl group to homocysteine?
It can use a variety of carbon sources to replace it, allowing THF to take up many forms.
This allows THF to play a key role in many biological processes such as nucleic acid metabolism and amino acid metabolism.
A B12 deficiency prevents THF from donating what?
Its methyl group, meaning that THF is stuck in the methyl form.
What is homocysteinemia?
An inherited enzyme deficiency of cystathione synthase or homocysteine N-methyl transferase.
What are the symptoms of homocysteinemia?
Lens dislocation after the age of 3 as well as other ocular abnormalities.
Children will also develop osteoporosis and mental retardation.
How can homocysteinemia be acquired?
As a result of a vitamin B12 deficiency.
What is an α-keto acid dehydrogenase deficiency?
A deficiency in the enzyme, branched chain α-keto acid dehydrogenase which some amino acids require for their metabolism.
Which amino acids require the enzyme, branched chain α-keto acid dehydrogenase for their metabolism?
Leucine.
Isoleucine.
Valine
A deficiency in branched chain α-keto acid dehydrogenase results in what?
A condition called maple syrup urinary disease (MSUD).
What are the symptoms of maple syrup urinary disease (MSUD)?
Urine that smells like maple syrup due to the accumulation of amino acids that cannot be metabolised.
What are the 4 co-enzymes required by branched chain α-keto acid dehydrogenase?
FAD.
NAD.
Lipoic acid.
Thiamine CoA.
The biosynthesis of non-essential amino acids is often the reverse of what process?
The reverse of their degradation.
What is alanines carbon skeleton and how does it form it?
Carbon skeleton. Pyruvate.
Formation. Transamination of precursor via ALT.
What is arginines carbon skeleton and how does it form it?
Carbon skeleton. Orthinine.
Formation. Arginiosuccinate lyase reaction in urea cycle.
What is asparagines carbon skeleton and how does it form it?
Carbon skeleton. OAA.
Formation. Amide reaction from glutamine.
What is aspartates carbon skeleton and how does it form it?
Carbon skeleton. OAA.
Formation. Transamination of precursor via AST.
What is cysteines carbon skeleton and how does it form it?
Carbon skeleton. Serine.
Formation. Sulphur group from methionine.
What is glutamates carbon skeleton and how does it form it?
Carbon skeleton. Alpha K-G.
Formation. Transamination of precursor.
What is glutamines carbon skeleton and how does it form it?
Carbon skeleton. Alpha K-G.
Formation. Amide group from free NH4+.
What is glyines carbon skeleton and how does it form it?
Carbon skeleton. 3-phosphoglycerate.
Formation. From serine via transfer of methylene group.
What is prolines carbon skeleton and how does it form it?
Carbon skeleton. Glutamate.
Formation. Cyclisation of glutamate semialdehyde.
What is serines carbon skeleton and how does it form it?
Carbon skeleton. 3-phosphoglycerate.
Formation. Oxidation to keto acid, transamination, hydrolysis of phosphate.
What is tryrosines carbon skeleton and how does it form it?
Carbon skeleton. Phenylalanine.
Formation. Hydroxylation of phenylalanine by phenylalanine hydroxylase.
Which amino acids can only be synthesised when methionine and phenylalanine are available from the die?
Tyrosine.
Cysteine.
Which 2 amino acids are interconvertible?
Glycine.
Serine.
What is transferred between glycine and serine to interconvert them?
A hydroxymethyl group.
What enzyme transfers the hydroxymethyl group between glycine and serine?
Hydroxymethyltransferase.
How does hydroxymethyltransferase transfer the hydroxymethyl group between glycine and serine?
It will take a methyl group from methylene-tetrahydrofolate and transfer it to glycine to form serine or vice versa.
How is glutamate produced from histidine?
Histidine is deaminated to form N-formiminogluterate (FIGLU) which then donates a formimino group to THF to produce glutamate.
The active form of folic acid in the body is called what?
Tetrahydrofolate (THF).
What enzyme is responsible for activating THF?
Dihydrofolate reducatase
What co-enzymes does dihydrofolate reducatase require to produce THF?
2 NADPH molecules.
THF can be thought of as a carrier of what atom?
Carbon.
Or carbon containing compounds.
The different carbon forms of THF can be used for what?
A number of reactions such as the synthesis of purines and pyrimidines that are used to make nucleotides.
A deficiency in folic acid can result in what neurological defect?
Spina bifida.
Can humans make folic acid?
No.
It must be obtained from the diet.
Can microbes make folic acid?
Yes.
How is folic acid that is obtained in the diet activated?
By an enzyme called dihydrofolate in a 2 step reaction.
Why is THF incredibly important in all organisms?
It will synthesise important precursors for nucleotides.
Why do anticancer drugs inhibit dihydrofolate reductase
So that purines and pyrimidine synthesis stops, this prevents the cancer cells from obtaining them and slows cell division.
How do microorganisms make folate?
They can make it from PABA.
What family of drugs will inhibit the synthesis of folic acid in microorganisms?
Sulphonamides.
What enzyme will will sulphonamides inhibit?
Dihydropteroate synthetase.
B12 is only found in what organisms?
Animals.
What 2 enzymes require vitamin B12 as a coenzyme?
Homocysteine N-methyltransferase (methionine synthase).
Methyl manolyl CoA mutase.
Is vitamin B12 required for the re-synthesis of methionine from homocysteine?
Yes.
Along with THF.
What is methyl manolyl CoA mutase used for?
The metabolism of amino acids and odd chain fatty acids.
What is the final product of the beta oxidation of odd chain fatty acids?
Propionyl CoA.
What happens to the propionyl CoA that is produced by the beta oxidation of odd chain fatty acids?
It is converted to methyl-malonyl CoA.
What enzyme converts propionyl CoA to methyl-malonyl CoA?
Propionyl CoA carboxylase.
Does propionyl CoA carboxylase require any coenzymes when it converts propionyl CoA to methyl-malonyl CoA?
Biotin.
What happens to methyl malonyl CoA that is formed from the from the breakdown of odd chain fatty acids?
It can is converted to succinyl CoA.
What enzyme converts methyl malonyl CoA to succinyl CoA?
Methyl manolyl CoA mutase.
What coenzyme does methyl manolyl CoA mutase require when it converts malonyl CoA to succinyl CoA?
B12.
What happens to the succinyl CoA that is produced in the final step of the breakdown of odd chain fatty acids?
It is a glucogenic carbon skeleton and enters the TCA cycle.
