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M1 Biochemistry > Exam 2- Amino Acid Metabolism > Flashcards

Exam 2- Amino Acid Metabolism Flashcards

1
Q

Glucogenic amino acids

A

Metabolized to pyruvate, 3-phosphoglycerate, alpha-KG, OAA, fumarate, or Succinyl CoA

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2
Q

Ketogenic amino acids

A

Metabolized to acetyl CoA or acetoacetate

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3
Q

Essential amino acids

A

Amino acids that humans can’t synthesize
Pvt Tim Hall
Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine

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4
Q

Transamination reaction

A

An amino acid donates an amine group to a keto acid

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6
Q

Name the mandatory keto acid and an amino acid in the transamination reaction.

A

Alpha-ketoglutarate - mandatory keto acid

Glutamate - mandatory amino acid

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7
Q

Describe the role of pyridoxal phosphate (vitamin B6) in the transamination reaction.

A

Pyridoxal phosphate is the coenzyme involved in the transamination reaction.

In this reaction, the amine group is transferred from the amino acid to the coenzyme, which transports it to the alpha-keto acid, forming a new amino acid and regenerating the original coenzyme aldehyde.

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8
Q

Describe the role of glutamine with reference to nitrogen catabolism.

A

Glutamine is the transporter of excess nitrogen from the tissues to the liver for the Urea cycle

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9
Q

What are the substrates and products of carbamoyl phosphate synthase.

A

NH4 + HCO3- + 2 ATP —> Carbamoyl phosphate + 2 ADP + 2 Pi

Carbamoyl phosphate synthase I/CPS-1

N-acetylglutamate is a positive affector

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10
Q

Name two cellular compartments where the urea cycle operates.

A

Mitochondrial matrix and cytosol

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11
Q

Name the allosteric affector of carbamoyl phosphate synthase I

A

N-acetyl glutamate

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12
Q

Name a drug that is used for treatment of a urea cycle enzyme deficiency

A

Carbamoylglutamate - Analog of N-acetylglutamate, can also activate CPS-1

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13
Q

In an exercising muscle, name the cycle that utilizes an amino acid & converts it into glucose.

A

Glucose-Alanine Cycle

In the liver, alanine is converted to pyruvate by Alanine transaminase. When blood glucose is low, pyruvate —> GNG —> glucose!

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14
Q

Name 3 neurotransmitters that are derived from tyrosine

A

Dopamine

Epinephrine, norepinephrine

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15
Q

Name 3 types of reactions that are involved in producing a neurotransmitter from an amino acid precursor.

A

Decarboxylation
Hydroxylation
SAM-dependent methylation

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16
Q

Name 3 cathecholeamines

A

Dopamine
Norepinephrine
Epinephrine

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17
Q

Name the rate-limiting step in the biosynthesis of catecholeamines.

A

Tyrosine + O2 + THB —> DOPA + DHB

Tyrosine hydroxylase

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18
Q

Name the cofactors that is required for tyrosine hydroxylase.

A

Tetrahydrobiopterin

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19
Q

Catecholeamine release is stimulated by the neurotransmitter _____________

A

Acetylcholine

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20
Q

Name two enzymes that are involved in catecholeamine catabolism.

A

Catecholeamine O-methyltransferase (COMT)

Monoamine Oxidase (MAO)

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21
Q

Name few functions of catecholeamines.

A

To prepare the body for “fight or flight” response:

Increase cardiac output, glycogen degradation, triglyceride hydrolysis, and release of fatty acids from adipose tissue

Decrease peripheral resistance to blood flow.

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22
Q

Discuss the connection between Parkinson’s disease and dopamine and the drug that is used for patients.

A

Parkinson’s disease is due to a lack of dopamine synthesis. It can be treated by L-Dopa, a precursor of dopamine that can cross the blood-brain barrier.

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23
Q

Name 2 neurotransmitter compounds derived from tryptophan

A

Serotonin and melatonin

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24
Q

What is the hormone that is involved in circadian rhythms?

A

Melatonin

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25
Q

What is the effect of Prozac?

A

Inhibits reuptake process of serotonin

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26
If you suffer from jet lag, what pathway would you target for drug therapy?
Melatonin
27
Name the enzyme that catalyzes the formation of histamines.
Histidine carboxylase
28
Name 3 functions of histamines
Mediate allergic and inflammatory reactions Vasodilation & drop in BP Constriction of bronchioles Stimulates excretion of HCl
29
What are the substrates and products of glutamate decarboxylase?
Glutamate —> GABA (E: glutamate decarboxylase) Requires Pyridoxal Phosphate (vitamin B6)
30
In general, decarboxylases require the coenzyme _________
Pyridoxal phosphate
31
L-DOPA is used for ___________ disease treatment
Parkinson’s
32
Name a synthetic compound that limits serotonin reuptake.
Prozac
33
Describe pheochromocytoma.
Tumors of chromaffin tissue that produce large amounts of catecholeamines.
34
Describe the clinical correlation between Huntington’s disease and GABA metabolism.
Low levels of GABA and GABAnergic neurons result in the uncontrolled movements of Huntington’s disease
35
Melanins are synthesized in ___________
Melanocytes
36
Tyrosinase deficiency causes _____________
Albinism
37
Under oxidative conditions, in order to maintain reducing environment inside the cell, which compound is invoked?
Glutathione
38
Name the methyl group donor compound that is used in the majority of methyl transfer reactions
S-adenosylmethionine (SAM)
39
Name 2 functions of glutathione.
Maintains protein sulfuhydryl groups in reduced form. Detoxifies xenobiotics (peroxides and free radicals) in the liver
40
Nitric oxide is derived from the amino acid _____________
Arginine | Uses THB
41
Name the substrate and products of acetylcholinesterase
ACh + H2O —> Acetate + Choline | E: Acetylcholine esterase
42
Explain the action of DIPF on acetylcholinesterase
DIPF is a component of nerve gas. It covalently modifies acetylcholinesterase and knocks the enzyme activity
43
Name some xenobiotics that inhibit acetylcholinesterase.
Physostigmine | Neostigmine
44
Name the channel that is opened up by acetylcholine.
Na+/K+ ion channels
45
Discuss the mechanism of action of nerve gas.
DIPF is a component of nerve gas. It covalently modifies acetylcholinesterase and knocks the enzyme activity.
46
Excitatory neurotransmitters
Excitatory: - Acetylcholine - Aspartate - Dopamine - Histamine - Norepinephrine - Epinephrine - Glutamate - 5-hydroxytryptamine
47
Name Excitatory and Inhibitory neurotransmitters
Inhibitory: - Glycine - GABA - Taurine - 4-aminobutyrate Excitatory: - Acetylcholine - Aspartate - Dopamine - Histamine - Norepinephrine - Epinephrine - Glutamate - 5-hydroxytryptamine
48
Name the 3 stages of nerve transmission:
Resting Excitation Termination
49
What is the action of GABA?
GABA is inhibitory neurotransmitter. Upon binding to its Beta subunits, it increases membrane permeability of postsynaptic membranes to chloride ion. This can lead to hyperpolarization and increased threshold of triggering an action potential.
50
What is the function of phenobarbital?
Inhibits action potentials when bound to GABA receptors. Tx for epilepsy
51
Name the catabolic products of GABA.
Succinate semialdehyde | Succinate
52
What is an ion-gated channel?
A channel that allows ions to pass through when a neurotransmitter binds to its receptor.
53
Name 2 ion channels.
Cholinergic nicotinic receptors GABA receptors (More generally, Na and K channels)
54
Diisopropylphosphoflouridate (DIPF) inhibits the enzyme ___________
Acetylcholinesterase
55
Name two inhibitors of the ACh receptor
Tubocurarine Alpha-bungarotoxin Cobra toxin m
56
Name two linear compounds in the proline biosynthetic pathway.
Glutamate and glutamate semialdehyde
57
Describe the role of hydroxyprolines?
Collagen stability - stable collagen triple helix
58
Name the amino acid that is required for selenocysteinyl tRNA synthesis.
Selenocysteine (21st amino acid)
59
What is the cofactor that is required for phenylalanine hydroxylase synthesis?
Tetrahydrobiopterin (THB)
60
What enzyme deficiency causes phenylketonuria?
Phenylalanine hydroxylase
61
Name two disorders of tyrosine metabolism.
Alcaptonuria, Albinism.
62
What enzyme deficiency causes albinism?
Tyrosinase
63
Methionine adenosyltransferase catalyzes the synthesis of _______________
S-adenosylmethionine (SAM) ATP —-> SAM (E: Methionine adenosyltransferase- MAT)
64
What compound is the precursor for cysteine synthesis?
Methionine
65
Name a disorder of cysteine metabolism.
Homocystinuria and Cystathionuria
66
Name the oxidized form of homocysteine
Homocystine - consists of 2 molecules of homocysteine linked together by a disulfide bond
67
Name the amino acid precursor for NMP synthesis
Tryptophan Trp —> other steps —> —> niacin —> NMP
68
Name an enzyme that requires a Vitamin B12 derivative as a coenzyme
Methionine synthase (in converting homocysteine to methionine) Methyl Malonyl CoA Mutase (converting propionyl CoA to Succinyl CoA)
69
Name a disorder of branched chain amino acid metabolism.
Maple syrup urine disease (MSUD)
70
Name the amino acid that is required for carinitine biosynthesis.
Lysine
71
Name two amino acids that are required for creatine biosynthesis.
Glycine and Arginine
72
Name the components of folate.
Pterin, PABA, and Polyglutamine
73
Name 2 active centers of THF.
N5 and N10
74
Name the 3 reactions that use THF.
Purine synthesis Thymidine synthesis Methionine synthesis
75
Name the amino acid and the vitamin derivative that is required for glycine synthesis.
Serine and THF Serine + THF —> (E: Serinehydroxy methyl transferase) Glycine + N5-N10-Methylene THF
76
Name two amino acid degradative pathways that require THF.
Histidine —> Glutamate Serine —> Glycine
77
Name two reactions that require Tetrahydrobiopterin as a cofactor.
Phenylalanine (Phenylalanine Hydroxylase) —> THB Tyrosine (Tyrosine Hydroxylase) —> DOPA Tryptophan (Tryoptophan Hydroxylase) —> Serotonin
78
Describe how homocysteine is converted into methionine
Homocysteine —> methionine | Vit B12 derivative; E: Methionine synthase
79
Lysine is required for the synthesis of _________
Carnitine
80
Name the vitamin derivative that is required for the prolyl hydroxylase reaction.
Collagen | Vitamin C
81
Why is the element selenium essential?
Activation of selenocysteine to tRNA
82
Describe in detail the pathway of SAM and cysteine.
Methionine + ATP —> SAM —> Homocysteine (B6) —> Cystathione (B6) —> Cysteine + alpha ketobutyrate —> Propionyl CoA
83
Biochemical basis of Phenylketonuria
- Classical PKU is an autosomal recessive deficiency of phenylalanine hydroxylase - The accumulated phenylpyruvate and phenylketone are excrete in the urine - Since tyrosine production is affected, all the related compounds that are derived from tyrosine are also blocked (Ex. DA, NE/epinephrine) - In some individuals biopterin deficiency causes PKU
84
Biochemical basis of Alkaptonuria
- Deficiency of hemogentisate oxidase results in the accumulation of homogentisic acid - Upon accumulation, this compound is oxidized into a dark brown polymer and is deposited in joints, causing arthritis
85
Biochemical Albinism
- Tyrosinase deficiency results in defective melanin production - Skin is susceptible to the damaging effects of sunlight such as skin cancer
86
The biochemical basis for Homocystinuria, Cystathionuria, Cystinuria
Issues with the cysteine biosynthetic pathway - Vitamin B6 deficiency can block overall cysteine synthesis, as two steps in the pathway require B6 as cofactor 1) Homocystinuria: - Cystathione beta-synthase deficiency causes homocysteine accumulation - Vitamin B6 (pyridoxal phosphate) deficiency can exacerbate the condition 2) Cystathionuria: - Gamma-cystathionase deficiency —> accumulated cystathionine for excretion - Also requires Vitamin B6 3) Cystinuria - Defect in membrane transport of dietary cysteine through epithelial cell membrane results in the accumulation of cysteine in the urine
87
Maple syrup urine disease
Defect in catabolism of branched amino acids | Deficiency in branched chain keto acid dehydrogenase
88
Histidinemia
Deficiency in the enzyme histidase Histidine + THF —> Uroconate —> Glutamate
89
Can folic acid be synthesized by humans?
No
90
What step is inhibited by sulfamethoxazole?
Inhibits the conversion of para-amino benzocaine acid (PABA) —> folic acid Folic acid synthesis is inhibited by sulfonamides Only in prokaryotes
91
The role of folate in relation to one carbon metabolism
Folate —> DHF —> THF (tetrahydrofolate) With addition of a 1-carbon unit (tryptophan, hisitidine, serine/glycine) —> active folate active folate —> purines, thymidine, and methionine
92
Biosynthesis of carnitine
Lysine —> N-trimethyl lysine —> carnitine | E: Methyl transferase, 3SAM
93
What are some organism specific dihydrofolate reductase inhibitors?
Methotrexate- eukaryotes Epiroprim (type of trimethoprim)- bacteria Pyrimethamine - protozoan (amoeba) DHF (E: Dihydrofolate reductase) —> THF
94
Trimethoprim, methotrexate, and pyrimethamine inhibits __________
They all inhibit Dihydrofolate reductase ! Methotrexate- eukaryotes Epiroprim- bacteria Pyrimethamine- protozoans/amoeba
95
3 amino acid specific transaminase:
``` Alanine aminotransferase (ALT): Alanine to pyruvate Aspartate aminotransferase (AST): aspartate into OAA Alpha KG —> Glutamate ```
96
Name 3 glial cells and their functions n
Oligodendrocytes: provide mullein sheaths that insulinate axons Astrocytes: integral parts of synapses, regulate molecules necessary for interneuron communication. Clear most of glutamate and stop neurotransmission. Also release growth factors and can take up other monoamine nt’s (serotonin and dopamine) Microglia: closely related to macrophages, fight infections, and release inflammatory substances (may damage neurons) in response to injury
97
ACh is not metabolized by reuptake process. Explain which cell would catabolize the ACh after the action potential.
Astrocytes
98
Explain the differences between endogenous proteolysis (protein degradation) versus digestion related degradation.
Endogenous proteolysis = ubiquitination —> degradation by proteasome Digestion related (dietary protein in excess) = proteolysis into amino acids which undergo transamination reactions producing nitrogen. Nitrogen taken to liver by glutamine, and nitrogen are fed into urea cycle and excreted
99
Normal blood creatine levels
< 1.5 mg/dL
100
Describe the lactate dehydrogenase catalyzed reaction.
Cori Cycle: Muscle: Pyruvate —> Lactate (E: LDH-M) Liver: Lactate —> Pyruvate (E: LDL-L) —> glucose (through GNG) Glucose then transferred back to the muscle
101
When lactate accumulates in the blood it is a problem. Why?
This can lead to lactic acidosis, which can cause a decrease in pH and muscle weakness
102
Explain why vitamin B6 deficiency can cause brain related problems.
Glutamate —> GABA ``` Other reactions that use B6: Histidine —> Histamine Dopa —> Dopamine Trp —> Serotonin Homocysteine —> Cystathione —> Cysteine ```
103
Reactions that use THB
Phenylalanine —> Tyrosine Tyrosine —> Dopa Trp —> Serotonin Arginine —> NO
104
Describe the biosynthesis of creatine phosphate and its degradation.
Synthesis: Glycine + Arginine (SAM) —> creatine phosphate (E: creatine kinase) Degradation: Creatine Phosphate —> (spontaneous!) creatinine —> excreted through urine!
105
Which vitamin derivative is required for many of the decarboxylases?
Pyridoxal phosphate
106
Describe the 3 NO synthases
Endothelium derived: diffuse out of endothelial cells into vascular smooth muscle, activates cytosolic guanylate cyclase which increases cGMP which up regulates PKG —> phosphorylation of smooth muscle contractile proteins leading to relaxation of vascular smooth muscles (vasodilation) Brain derived: Receptors for NO in neurons upregulate cytosolic guanylate cyclase increases cGMP which upregulates PKG —> phosphorylates proteins (not well understood) Macrophage derived: Stimulated after bacterial infection, NO toxic to bacteria
107
Biochemical basis for Parkinson’s
Substantial Nigeria degraded —> decreased dopamine
108
Biochemical basis for depression
Increased serotonin uptake and degradation (less serotonin)
109
Pheochromocytomas
Tumors that increase production of catecholeamines —> HTN
110
Huntington’s
Low GABA (inhibitory) leading to uncontrolled movements (chorea)
111
Normal BUN levels
10-20 mg/dL
112
Glucose-Alanine Cycle
In low oxygen conditions, alanine is transferred from the muscle to the liver Alanine is converted to Pyruvate by alanine deaminase in the liver Pyruvate can then re-enter the GNG cycle Glucose returned to the muscle
113
Describe the connection between dicarboxylate and the urea cycle
Fumarate leaves the Urea cycle in the arginosuccinate lyase step which converts arginosuccinate to arginine Fumarate can enter the dicarboxylate cycle and become aspartate which is necessary for the previous step in which citrulline becomes arginosuccinate using the enzyme arginosuccinate synthase

M1 Biochemistry (17 decks)

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