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Biochemistry 2300 > Lectures 27/28: Amino Acid Metabolism > Flashcards

Lectures 27/28: Amino Acid Metabolism Flashcards

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1
Q

Nitrogen

A

Essential element found in amino acids, nitrogenous bases and many other molecules
Biologically available nitrogen is scarce

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2
Q

Nitrogen Fixation

A

Reduction of N2 by prokaryotic microorganisms to form NH3
Often rate limiting factor in plant growth
High energy requirement
Nitrogen often rate limiting factor in plant growth
Conversion into amide group of glutamine
Catalyzed by nitrogenase complex

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3
Q

Free-living cyanobacteria

A

Most prominent nitrogen-fixing species

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4
Q

Symbiotic bacteria

A

Most prominent nitrogen-fixing species

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5
Q

Nitrogen assimilation

A

Incorporation of inorganic nitrogen compounds into organic molecules
Roots in plants
NH4+ or NO3- incorporated into amino acids

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6
Q

NO3

A

As nitrogen source, two step reaction is used to convert it to NH4+ by nitrite reductase

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7
Q

Glutamine synthetase

A

Catalyzes ATP-dependent reaction of glutamate with NH4+ to form glutamate
Found in all organisms
Entry point in microorganisms for fixed nitrogen
Uses ATP
Glutamate + ammonium to glutamine: formation of irreversible amide bond

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8
Q

Phytoplankton bloom

A

Can trigger dead zone formation
Decomposition carried out by aerobic bacteria: increased oxygen use by bacteria, O2 levels drop, hypoxic conditions for fish

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9
Q

Glutamate synthase

A

Produces glutamate from glutamine and alpha-ketoglutarate
Only bacteria and plants
Together with glutamine synthase leads to assimilation
Does not use ATP
2 Glutamate yield: Can enter glutamine synthetase reaction
Only in plants and microorganisms

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10
Q

Glutamine

A

Acts as amino group carrier

Synthesis in peripheral tissues and transport to liver also transports amino groups

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11
Q

Amino acids

A

Protein monomeric units
Energy metabolites: can be converted into pyruvate, oxaloacetate, or TCA intermediates
Some can only be converted into acetyl CoA, ketone bodies or fatty acids
Precursors for many biologically active nitrogen-containing compounds
Signalling molecules
Essential and non-essential

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12
Q

Essential amino acids

A

Must be taken up with diet

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13
Q

Non-essential amino acids

A

Can be synthesized by body

Plants and microorganisms have enzymes for the synthesis of all 20 amino acids

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14
Q

Transamination

A

Catalyzed by aminotransferase (transaminase)

Reaction with alpha-ketoacid to yield another amino acid and alpha-ketoglutarate

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15
Q

Transaminase

A

All have pyridoxal phosphates as prothetic group

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16
Q

Pyritical phosphate

A

Derived from pyridoxine VitB6

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17
Q

Aspartate aminotransferase

A

alpha-ketoglutarate + aspartate = glutamate + oxaloacetate

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18
Q

Malate-Asparate shuttle

A

Relies on transamination of aspartate and oxaloacetate
Indirectly transfers NADH into mitochondrial matrix
Malate in exchange for KG, Asp in exchange for Glu

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19
Q

Amination/deamination

A

Catalyzed by glutamate dehydrogenase in mitochondrial matrix
Degradation of amino acid to give KG: reversible
Direction determined by reactant concentrations

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20
Q

Amidation

A

Formation of amide bond: irreversible
Glutamine synthetase converts glutamate + NH4+ to glutamine
Costs ATP

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21
Q

Deamidation

A

Catalyzed by glutaminase
Conversion of glutamine to glutamate
Reverse of glutamine syntheses reaction

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22
Q

Amino acid synthesis

A

Animals synthesize from intermediates of glycolysis and citric acid cycle
Bacteria and plants synthesize with sulfur, branched chains, aromatic groups, histidine, lysine and threonine

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23
Q

Cysteine synthesis

A

Can be made from methionine

Not sufficient: essential aa

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24
Q

Glutamate formation

A

From KG by reductive lamination or transamination

Neurotransmitter in brain: conversion to glutamine prevents overstimulation and neurotoxicity

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25
Glutamine-glutamate shuttle
In brain Neurons secrete glutamate as NT: too much extracellular is toxic Astrocytes (surrounding neutrons) take up glutamate and convert it to glutamine Glutamine is secreted and taken up by neurons and converted back
26
Aspartate
Synthesized from oxaloacetate by transamination | Asparagine, methionine, threonine, lysine and isoleucine are synthesized from aspartate
27
Asparagine synthetase
Synthesizes aspartate into asparagine
28
Serine
Derives carbon skeleton from glycolytic intermediate 3-phosphoglycerate Served from 3-phosphoglycerate via dehydration, transamination and hydrolysis Precursor for sphingolipids and phospatidylserine Enantiomer D-serine is neuromodulator
29
Glycine
Hydromethyl group transfer reaction from serine | Neurotransmitter
30
Cysteine
Serine plus sulphur group from another amino acid Thiol group is redox active Precursor for glutathione
31
Glutathione
Antioxidant Tripeptide of glutamate of cysteine and glycine Cysteine is lease abundant: supply is rate limiting reacts with peroxide to give non-reactive thiols GSSG in oxidized form
32
One-Carbon metabolism
Describes metabolic pathways that are connected to reactions involving the transfer of single carbons: methyl groups of different oxygen states equivalent of methanol, formaldehyde and formate Includes folate metabolism, methylation cycle and transsulfuration Most important carriers of 1-C groups: folic acid and S-adenosylmethionine
33
Folic Acid
``` B vitamin (B9) Once absorbed by the body, converted to tetrahydrofolate (THF) One of most important carriers of 1-C groups Very important during development Decreased prevalence of neural tube defects following folate fortification of flour ```
34
S-adenosylmethionine
Derivative methionine | One of most important carriers of 1-C groups
35
Tetrahydrofolate
Synthesized from folic acid/folate/vitamin B9, requires NADPH Carrier of 1-C units in several reactions of amino acids and nucleotide metabolism: carrier of methyl groups in different oxidation states Accepts methyl group from serine to convert serine to glycine
36
Serine hydroxymethyltransferase
Catalyzes transfer of methyl-group from serine to tetrahydrofolate to convert serine to glycine
37
Folate metabolism
Required for serine to indirectly supply methyl groups for methionine synthesis, B6 and B12 are also required Methylation requires 3 phosphates
38
Methionine synthase
Works with B12 | Synthesizes methionine from homocysteine by taking methyl group from 5-methyl-THF to convert it to THF
39
Methionine
Converted from homocysteine by accepting methyl group from 5-methyl-THF Converted into S-adenosyl-methionine by using 3 phosphates
40
S-adenosyl-methionine
Converted from methionine | Methylated into S-adenosyl-homocysteine
41
S-adenosyl-homocysteine
Addition of H2O and release of adenosine to give homocysteine
42
DNA methylation
Methylation of cytosine to 5-methyl cytosine Catalyzed by DNA transferases Regulates transcription without changes in DNA sequence
43
Epigenetics
DNA methylation
44
Importance of methylation reactions
DNA methylation (epigenetic) Phosphatidylcholine synthesis (from phosphatidylethanolamine) Thymidine synthesis (dTMP from dUMP) Purine synthesis Synthesis of carnitine, creatine, epinephrine and other products
45
Amino acids and signalling molecules
Glutamate and glycine as neurotransmitters Other neurotransmittedrs/neuromodulators derived form amino acids Catecholamines Nitric oxide
46
GABA
NT derived from glutamate
47
Dopamine
From tyrosine
48
Serotonin
From tryptophan
49
Melatonin
From tryptophan
50
D-Serine
NT | By racemizaton of L-serine
51
D-aspartate
NT | By racemizaton of L-aspartate
52
Catecholamines
Epinephrine, norepinephrine, dopamine | Derivatives of tyrosine
53
Nitric Oxide
From precursor arginine
54
Nitric oxide synthase
Reacts with arginine and NADPH and oxygen to citrulline, NO, NADP+ and water
55
Purine synthesis
AMP and GMP Requires glutamine, glycine, aspartate, bicarbonate and methyl groups ATP promotes GMP synthesis GTP promotes AMP synthesis: two purine will be present in roughly equal amounts
56
Pyrimidine synthesis
UMP and CMP Requires glutamine, aspartate, bicarbonate dUMP is methylated to generate dTMP CTP inhibits pyrimidine synthesis (negative feedback) ATP is feedforward activator for pyrimidine synthesis
57
Deoxyribonucleotide synthesis
ATP, GTP, CTP and UTP are dephosphorylated, then reduced to deoxyribonucleotides by ribonucleotide reductase and phosphorylated again: requires NADPH
58
Ribonucleotide reductase
Reduces dephosphorylated ATP, GTP, CTP and UTP to deoxyribonuceotides Two regulatory sites: 1 to regulate overall activity, and one to regulate substrate specificity (overall synthesis and relative amount of the different dNTP) Activated by ATP dATP decreases activity Binding of purine ATP: reductase prefers pyrimidines Binding of pyrimidine dTTP: reductase prefers purine GDP
59
Protein degradation
By proteasome or lysosomal proteases Each protein has a biological half-life Most amino acids are degraded to precursors for gluconeogenesis: carbon skeleton of amino acids resemble energy metabolites and can be oxidized for energy
60
Lysosomes
Internal vesicular organelles that have very low pH Contain many different proteases Usually takes place after endocytosis of extracellular and membrane material Intracellular material and whole organelles can also be packaged into large double-membrane vesicles which fuse with lysosomes for degradation: autophagy
61
Autophagy
Intracellular material and whole organelles can be packaged into large double-membrane vesicles which fuse with lysosomes for degradation
62
Proteasomal degradation
Breaks down single proteins Proteins are tagged with small 76aa protein ubiquitin and degraded by large multi protein complex proteasome Important quality control mechanism: breaks down misfiled and damaged proteins
63
Both glycogenic and ketogenic amino aicds
``` Isoleucine Phenylalanine Threonine Tryptophan Tyrosine ```
64
Ketogenic amino acids
Leucine | Lysine
65
Branched chain amino acids catabolism
First two steps for all are transamination and decarboxylation BCKD
66
Maple Urine Syrup Disease
Caused by defects in BCKD
67
Degradation of aa carbon skeleton
Carbon skeleton of glycogenic amino acids are used for pyruvate of TCA cycle intermediates: useful for anaplerosis and glucogneogenesis Of ketogenic amino acids: converted to acetyl-CoA energy substrate but not for gluconeogenesis or anapldrotic reactions
68
Negative N balance
Nin less than Nout Starvation Serious illness Insufficient essential amino acids
69
Postitive N balance
Nin less than Nout Growth Pregnancy Recovery illness or starvation
70
Excretion of excess nitrogen
Amino acid transamination does not eliminate nitrogen form the body Some reactions set free ammonium, which can be directly eliminated form the body High ammonium concentrations are cytotoxic (especially for the brain) Terrestrial animal secrete nearly 80% excess N as urea Some eliminated as ammonium salts or uric acid Purines are broken down to uric acid
71
Lysine
Only amino acid that cannot be transaminated
72
Urea
Highly water soluble Non-Toxic pH neutral Eliminates two amino groups per molecule urea Highly efficient nitrogen disposal Terrestrial animal secrete nearly 80% excess N as urea Direct precursor is arginine
73
Arginine
Direct precursor of urea | Intermediate in urea cycle
74
Direct substrates of urea cycle
Aspartate and carbamoyl phosphate
75
Products of urea cycle
Urea and fumarate | Fumarate is covered to oxaloacetate through TCA cycle reactions
76
Carbamoyl phosphate synthesis
Investment of energy to generate a transferable amino group | Controls urea production
77
Carbamoyl phosphate synthetase
Controls the urea cycle and is activated by N-acetylglutamate: controls urea production
78
N-acetylglutamate
Allosteric activator | Formed when degradation of amino acids lead to high concentration of acetyl-CoA and glutamate
79
Urea
Formed from cyclic pathway in liver Intermediates are not used up One amino group stamps from ammonia, one from aspartate, carbon comes from bicarbonate Enters blood stream and is filtered out by kidney into urine: requires large quantities of water to be excreted

Biochemistry 2300 (10 decks)

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