biochem exam 5 Flashcards
(186 cards)
1
Q
what are the three classes of genetic disorders that affect metabolic pathways?
A
lysosomal storage, toxin-generating, and energy production
2
Q
what is lysosomal storage disorder?
A
caused by deficiencies in lysosomal enzymes or function –> substrates will accumulate over time, leading to swollen lysosomes and impaired cell structure and function
most LSDs present after 2-3 months of age and involve PROGRESSIVE DEGENERATION of neurologic function and skeletal deformities –> enzyme replacement therapy is used as treatment
ex: I-cell disease, Pompe disease, Gaucher, Tay-Sachs, Niemann-Pick
3
Q
what is toxin-generating disorder?
A
result in accumulation of toxic substances –> treatment = avoiding unnecessary activation of affected pathway and/or inactivating or eliminating toxin
ex:
neurotoxin-generating: urea cycle defects, phenylketouria, maple syrup disease, organic acidurias, Refsum disease
other toxin-generating: G6PDH deficiency, hereditary fructose intolerance, galactosemia, dyslipidemias, primary oxaluria, homocystinuria
4
Q
what is energy production disorder?
A
results in FASTING hypoglycermia, few are limited to muscle metabolism and result in muscle weakness with little or no association with faster metabolism (very FEW affect both fed and fasting metabolism, like pyruvate kinase deficiency in erythrocytes)
treatment = avoiding precipitating events (fasting, illness, exercise), ACUTE decompensation is treated by administration of IV glucose (to go back to fed state), some disorders of fasting metabolism become less severe as one reaches adulthood
ex: glycogen storage disorders (EXCEPT Pompe disease), defects in gluconeogenesis, MCAD deficiency
5
Q
what are the 4-carbon non-essential AAs?
A
asparagine and aspartate (differ by one amide group)
OAA –> asp –> asn
6
Q
what are the 2 or 3 carbon non-essential AAs?
A
glycine, serine, cysteine, and alanine
glucose –> 3-phosphoglycerate –> serine <–> glycine and serine –> cysteine, 3-phosphoglycerate –> 2-phosphoglycerate –> pyruvate <–> alanine
7
Q
what are the 5 carbon non-essential AAs?
A
glutamine, glutamate, proline, and argnine
citrate –> isocitrate – alpha-KG <–> glutamate –> glutamine or glutamate –> glutamate semialdehyde –> proline and arginine
8
Q
what do glucogenic AAs produce?
A
pyruvate or TCA intermediates
use for gluconeogenesis
9
Q
what do ketogenic AAs produce?
A
acetyl CoA
10
Q
what AAs are ONLY ketogenic?
A
lysine and leucine
some AA may appear in both groups like tyrosine
11
Q
how are the 2-3 carbon non-essential AAs degraded?
A
glucose <–> 3-phosphoglycerate which can convert to serine <–> glyine, serine –> 2-phosphoglycerate, or serine –> cysteine
2-phosphoglycerate + cysteine –> pyruvate <–> alanine
12
Q
how is ser made and degraded?
A
from 3-PG and degraded to 2-PG
synthesis
begins with OXIDIZING alcohol side chain of 3-PG to ketone making alpha-keto acid –> TRANSAMINATION making alpha-AA –> HYDROLYSIS of phosphate –> SERINE
degrade
SERINE –> TRANSAMINATION –> REDUCTION –> PHOSPHORYLATE –> 2-PG –> glycolysis
13
Q
how is gly made?
A
it is interconverted with ser by SERINE HYDROXYMETHYLTRANSFERASE and can also be degraded by glyoxylate pathyway or glycine cleavage enzyme
serine <–> glycine via serine hydroxymethyltransferase, glycine –> CO2, NH4+, and methyl attached to tetrahydro-folate via glycine cleavage enzyme OR transaminase and D-AA oxidase –> glyoxylate –> oxalate
both serine hydroxymethyltransferase and glycine cleavage enzyme use FH4 as a cofactor
14
Q
what are serine hydroxymethyltransferase and glycine cleavage enzyme important?
A
these reactions are important because they provide carbons for the cofactor tetrahydro-folate (B9)
15
Q
why is the oxalate produced from glycine important?
A
it can precipitate with calcium and form kidney stones
about 40% of oxalate production in the body is via this reaction
16
Q
what happens when there’s a deficiency in the pyruvate-alanine aminotransferase in the glycine pathway?
A
can lead to PRIMARY OXALURIA type I because transaminase is not converting glycoxylate back to glycine, instead glycoxylate will build up and form oxalate = kidney stones
17
Q
what is calcium oxalate?
A
a strong irritant, contain need-like crystals that cause pain and edema after coming into contact with lips, tongue, oral mucosa, conjunctiva, or skin –> lasts up to 2 weeks
18
Q
how is cys made?
A
made from serine with sulfur coming from methionine in form of homocysteine
19
Q
what can a deficiency in cystathinone beta-synthase cause? what are the symptoms?
A
type 1 homocystinuria
patients will experience PREMATURE VASCULAR DISEASE with 25% dying from thrombic complications
signs = subluxation (dislocation) of lenses in eyes, mental retardation, and osteroporosis in childhood
20
Q
how is cys degraded?
A
catabolized to pyruvate and sulfate, also route for catabolism of met
- sulfyhydryl group oxidized to sulfinic acid then transamination with alpha-KG produces pyruvate, glutamate, and sulfite
- sulfite oxidized to sulfate which can be incorporated into PAPS or excreted in urine
serine + homocysteine –> cystathinone via beta-cystathionine synthetase using PLP as cofactor –> cystathionine –> cysteine + alpha-ketobutyrate via cystathionase using PLP as cofactor –> cysteine sulfinic acid (this step produces glutamate, pyruvate, and uses PLP) –> sulfite –> sulfate –> PAPS or urine
note: alpha-ketobutyrate can be converted to propionyl CoA –> methymalonyl CoA –> succinyl CoA
21
Q
how is alanine made?
A
alanine aminotransferase of amino group from glutamate to pyruvate –> alanine and alpha-KG
22
Q
how are glu, gln, pro, and arg made?
A
they’re all made from and degraded to alpha-KG
23
Q
what is the significance of his?
A
it is also degraded to alpha-KG, but CANNOT be synthesized by the body so it is an ESSENTIAL aa
HOWEVER, it is not rapidly degraded, so dietary requirements are low because it can be efficiently recycled
24
Q
how is glu and gln made?
A
glu is made from and converted to alpha-KG, gln is made from and converted to glu
glu <–> alpha-KG via GDH and aminotransferases
glu <–> gln via glutamine synthetase and glutaminase
25
how is pro and arg made?
glutamate semialdehyde is an intermediate in synthesis and degradation of pro and arg
side chain of glut can be reduced to aldehyde --> glu semialdehyde --> semialdehyde SPONTANEOUSLY CYCLIZE and be reduced to pro or ornithine via ornithine aminotransferase
via urea cycle, ornithine can be converted arg (undergo whole urea cycle to generate arg)
all processes are REVERSIBLE
26
how is asp and asn made?
asp and asn are converted and made from OAA
OAA <--> asp via transamination using PLP
asp <--> asn via asparagine synthetase or reversed using asparaginase
asp --> asn uses N group from glutamine for transamination
this reaction is analogous to alpha-KG, glu, gln reaction
27
how is fumarate formed?
asp, phe, and tyr generate fumarate during their catabolism
recall: fumarate can be generated in urea cycle from asp
phe and tyr are both degraded to fumarate and acetoacetate
28
how is succinyl CoA formed?
met, thr, ile, and val are all degraded to succinyl CoA via propinyl CoA
recall: propionyl CoA is also made in oxidation of odd-chain FAs
conversion of propionyl CoA to succinyl CoA requires B7 (for propionyl CoA carboxylase) and B12 (for methylmalonyl mutase)
29
what happens when there's a deficiency in methylmalonyl mutase (B12 metabolism)?
results in methylmalonic acidemia (accumulation of methylmalonyl CoA, BCAA, thr, OCFA, VOMIT)
infants begin to develop symptoms when first introduced to solid foods or with first viral or bacterial infection (because this triggers fasting state which will result in protein catabolism)
treatment = low protein diet (decrease protein catabolism), often supplemented with B12 or carnitine
30
what are met and thr degraded to?
they're degraded to alpha-ketobutyrate which is converted to propionyl CoA
met --> homocysteine (add serine) --> cystathionine, cysteine is released via PLP; deamination of thr--> alpha-ketobutyrate --> propionyl CoA
rxn of alpha-ketobutyrate --> propionyl CoA is similar to the reaction catalyzed by pyruvate dehydrogenase and alpha-KG dehydrogenase (uses coenzymes TPP, lipoic acid, CoA, FAD, NAD+)
31
how is met made from homocysteine?
via met synthetase using B12 and tetrahydrofolate-CH3
homocysteine is methylated by FH4-CH3, using B12 as a cofactor --> converts to met
32
what are the branched amino acids and what are they degraded to?
val, ile, and leu
VAL is degraded to propionyl CoA, ILE to propionyl CoA and acetyl CoA, LEU to acetyl CoA and acetoacetate also ONLY ONE OF TWO AAs THAT IS SOLELY KETOGENIC
about 20% of AA in proteins are branched chain, and BCAAs have lots of oxidizable carbon so they play a large role in ENERGY PRODUCTION in fasting state
33
explain the reaction of BCCAs
val, ile, and leu are all first transaminated (reversible) and then undergo oxidative decarboxylation via branched chain alpha-ketoacid DH
deficiency in alpha-ketoacid DH results in MAPLE SYRUP URINE DISEASE --> build up of BCAAs
34
what is the maple syrup urine disease?
MSUD is caused by deficiency in branched-chain alpha-ketoacid DH
acute PRESENTATION occurs when protein catabolism INCREASES due to fasted metabolism or consumption of BCAAs
35
what can alpha-ketoisocaproic acid trigger?
derived from leu and triggers neuronal apoptosis
leu, ile, and val compete with other large neutral AA (like phe and trp) for entry into brain --> leads to depletion of AA needed for neurotransmitter synthesis
36
what are the treatments for MSUD?
based on prevention of acute episodes and remediation of neural AA deficits (reversal of catabolic state; IV glucose initially then high calorie intake)
prevention of acute episodes
- tight regulation of BCAA consumption
- weekly AA monitoring
- early detection and treatment of infections or other physiologic stresses
remediation of neural AA deficits
- supplementation with tyr, trp, met, phe, his, thr, gln
37
what is organic aciduria?
inherited disorders caused by deficiencies in enzymes involved in AA carbon skeleton degradation
alpha-ketoacids accumulate and contribute to development of metabolic acidosis, hyperammonemia, and neurologic damage
38
what is the presentation of organic aciduria?
acute presentation with metabolic compensation = vomiting, metabolic acidosis, hypoglycemia, hyperammonemia (some cases it's caused by inhibition of N-acetylglutamate synthase which makes N-acetylglutamate that activates CPSI)
39
what are the long-term consequences of organic aciduria?
developmental delay, ataxia, heart, kidney, and pancreatic problems
40
what are the treatments of organic aciduria?
- restriction of triggering AA (branched AA)
- avoidance of fasting and monitoring of illness
- supplementation with carnitine or glycine to facilitate production and elimination of acid-conjugates
- vitamin supplementation
- treatment of hyperammonemia as needed
41
what is the function of ketogenic AAs?
they produce acetyl CoA or acetoacetate
trp catabolism is complex -- it can be converted to nicotinamide portion of NAD/P, it's ketogenic (acetyl CoA) AND glucogenic (can be converted to alanine --> pyruvate --> glucose), also generate formate
lys --> acetyl CoA
thr has two metabolic routes -- one generates propionyl CoA via alpha-ketobutyrate and another generates glycine and acetate/acetyl CoA
42
what happens when there's defects in phe and tyr catabolism?
associated with many diseases
phe is hydroxylated to tyr by PHENYLALANINE HYDROXYLASE --> deficiency in hydroxylase or cofactor (tetrahydrobiopterin) results in phenylketouria (PKU)
tyr aminotransferase also transaminates phe, explaining accumulation of phenylketone in PKU
43
what is the function of homogenitsate oxidase?
phe --> tyr via phe hydroxylase --> hydroxyphenylpyruvate --> homogentisate via decarboxylation --> fumarate and acetoacetate via homogentisate oxidase
deficiency in homogentisate oxidase result in ALKAPTOURIA
44
what is the difference between classic and nonclassic PKU?
classic = deficiency in phe hydroxylase
nonclassic = deficiency in cofactor tetrahydrobiopterin (BH4)
45
what can PKU cause?
accumulated phe inhibits transport of other large hydrophobic AAs to brain, causing altered neurotransmitter synthesis leading to problems in PSYCHOMOTOR development
decreased synthesis of CATECHOLAMINES may cause mood disorders in older patients
phenylpyruvate (phenyllactate and phenylacetate) , produced by transamination of phe, accumulates in serum and urine (musky or mousy odor)
46
what is tyr a precursor for?
tyr is precursor of melanin (lack of melanin results in albinism)
47
what is the treatment for PKU?
restriction of dietary phe and sometimes supplementation with large hydrophobic AAs
nonclassical PKU can be treated with TETRAHYDROBIOPTERIN which can also benefit some individuals with classic PKU
48
what is alkaptonuria?
results from deficiency in homogenitsate oxygenase
accumulation of homogentisic acid in urine causes it to turn black upon air oxidation
over time --> homogentisic acid accumulates in various body fluids/tissues, causing large joint arthritis and black pigmentation (ochronotic)
49
how is tetrahydrofolate made?
synthesized from folic acid and requires dihydrofolate reductase to convert from folate --> dihydrofolate --> tetrahydrofolate (cofactor for serine hydroxymethyl transferase and glycine cleavage enzyme)
folate has 3 parts -- pteridine ring, PABA, and glutamate
50
what are sulfa drugs and their significance?
they're used to treat certain bacterial infections
analogs of p-aminobenzoic acid (PABA)
substrate for synthesis of folic acid in bacteria (inhibit synthesis of folic acid in bacteria --> necessary for growth and reproduction)
51
what is the most OXIDIZED form of tetrahydrofolate?
formyl-tetrahydrofolate
52
what is the most REDUCED form of tetrahydrofolate?
methyl-tetrahydrofolate
53
what is the IRREVERSIBLE step in the oxidation of tetrahydrofolate?
methylene-tetrahydrofolate to methyl-tetrahydrofolate
54
what is important about the carbon which tetrahydrofolate carries?
it is used in the synthesis of many biomolecules like nucleotides and neurotransmitters
55
what happens when there's a folate deficiency in pregnancy?
can lead to neural tube defects
56
what happens to the fully methylated form of tetrahydrofolate?
the ONLY possible fate is donation of methyl group to homocysteine to make methionine
methyl-tetrahydrofolate transfers its methyl group to homocysteine via met synthetase using B12 as cofactor --> forms met -- formation of the methyl species for this reaction is IRREVERSIBLE
57
what AAs use tetrahydrofolate?
- serine via serine methylhydroxy transferase
- glycine via glycine cleavage enzyme
- histidine
- tryptophan
58
describe the activated methyl cycle
methyl-tetrahydrofolate donates its methyl group to B12, methylated B12 is donated to homocysteine to make met via met synthetase (note: deficiency in methyl-hydrofolate can disrupt this cycle)
met is used in protein synthesis or to generate S-adenosylmethionine (SAM) using ATP --> SAM dontas methyl group to various molecules, generating S-adenosylhomocysteine (SAH) which is cleaved to form homocysteine and adenosine (homocysteine can be used to make cysteine or met)
Some molecules that SAM donates methyl group to are norepinephrine to make epinephrine, nucleotides to make methylated nucleotides
59
what does a deficiency in MTR (met synthetase) cause?
Type II homocysteinEMIA
recall cystathionine beta-synthetase deficiency causes homocystinURIA
60
what is B12?
cobalamin
complex molecule synthesized only in bacteria --> humans obtain B12 from animals --> animals obtain them from bacteria
structural similarity to heme, also coordinated by porphyrin ring and adenosyl group (X group that ligand binds to can be CN, CH3, or 5'-doxyadenosine)
61
what are the only two enzymes in humans that use B12?
methionine synthetase and methylmalonyl mutase
62
what happens when there's a deficiency in B12?
disrupts the activated methyl cycle and ELEVATED methylmalonic acid levels --> this is important in determining whether it is a B12 or B9 deficiency
B12 = methylmalonyl CoA mutase
B9 and B12 = met synthetase
can also result in macrocytic anemia and neurological dysfunction
63
what is the cause of pernicious anemia?
caused by genetic or age-related problems with dietary B12 absorption
64
explain the absorption and transport pathway of B12
dietary B12 is bound by R-binders (salivary and gastric proteins) as it passes through the stomach
intrinsic factor (another gastric protein) binds to B12 in intestine, after R-binders are degraded (DEFICIENCY in intrinsic factor is PRIMARY cause of pernicious anemia because intrinsic factor is important in absorption of B12) --> in ileum, B12-intrinsic factor complex is taken into enterocytes by specific receptors
in enterocytes, B12 forms complexes with transcobalamin II which transports 50% to tissues and 50% to liver which stores enough B12 to supply the body's needs for 3-6 years (B12 deficiency doesn't become symptomatic until 3-6 years after store begins to deplete)
65
what happens in B12 deficiency resulting in anemia?
anemia associated with B12 deficiency is due to depletion of METHYLENE-FH4 which is required for nucleotide biosynthesis
deficiency results in defects in erythrocyte development and bone marrow releases megaloblasts
methylene to methyl is an irreversible step that can lead to depletion of methylene and increase methyl that is stuck as methyl-tetrahydrofolate (METHYL TRAP) because there's no B12 to catalyze met synthetase
build up of methyl-tetrahydrofolate can also create SECONDARY FOLATE DEFICIENCY because the body will be low on folate since it's stuck as methyl-tetrahydrofolate
66
what happens in B12 deficiency resulting in neurological deficiency?
can cause peripheral neuropathy, professing to spastic gait disturbance
B12 deficiency due to depletion of SAM (required for the synthesis of some neurotransmitters)
accumulation of methylmalonyl CoA in nervous system is also thought to be contributing factor
67
recall: how is tyrosine made?
derived from phenylalanine in a BH4 (tetrahydrobiopterin) dependent reaction catalyzed by phenylalanine hydroxylase
68
recall: how is PKU caused?
deficiency in conversion of phe --> tyr -- either in hydroxylase or metabolism of BH4 (tetrahydrobiopterin)
69
explain the process of generating tetrahydrobiopterin (BH4) and its use in phenylalanine hydroxylase
BH4 is synthesized from GTP --> it's oxidized with phe, each providing 2 elections for reduction of O2 --> generates tyr and dihydrobiopterin --> BH2 is reduced back to BH4 using DIHYDROPTERINE REDUCTASE
70
what are the catecholamines?
dopa, dopamine, norepinephrine, and epinephrine are all synthesized from tyr
71
explain the process of generating catecholamines
phe generates tyr via phe hydroxylase --> tyr is hydroxylated to dopa via tyr hydroxylase (uses BH4 as a cofactor) --> dopa is decarboxylated to dopamine in the neuron via dopa decarboxylase (uses PLP/B6 as a cofactor) --> dopamine is hydroxylated by dopamine beta-hydroxylase (mixed function oxidase) that requires Cu+2 and vitamin C (deficiency of vitamin C = scruvy, microcytic anemia, and this reaction) to norepinephrine
in adrenal medulla, norepinephrine is methylated using SAM which then generates epinephrine (adrenal medulla releases primarily epi but also some norepi)
72
explain Parkinson's disease
substantia nigra in the brain controls movement
Parkinson's disease - dopaminergic cells in the substantia nigra STOP producing dopamine --> as these cells die, brain does not receive necessary messages for movement
symptomatic relief from Parkinson's is obtained by administration of L-dopa which is the precursor for dopamine --> this helps the enzyme work faster and generate more dopamine
73
how do recreational stimulants affect dopamine?
it inhibits the reuptake of dopamine in specific regions of the brain, increasing the synaptic gap levels of dopamine -- prolonging its effects
74
how do schizophrenia and ADHD affect dopamine?
schizophrenia is linked to an OVERPRODUCTION of dopamine
ADHD is linked to REDUCED levels of dopamine
75
how are catecholamines degraded?
they are inactivated by oxidative deamination and O-methylation
begins with catecholamine like norepinephrine which has two pathways (are reverse pathways of each other)
1. undergoes monoamine oxidase (MAO) --> catalyzes oxidative DEAMINATION then it's methylated using COMT and SAM (MAO inhibitors are used to treat depression and Parkinson's because they prevent degradation of dopamine, norepinephrine, serotonin, and other transmitters)
2. undergoes methylation using COMT AND SAM, then oxidized using MAO
both pathways produce VANILLYLMANDELIC ACID (VMA) which is secreted in the urine (high levels in the urine tell us we're making enough catecholamines while low levels tell us we're not)
76
what are MAO inhibitors used for?
MAO inhibitors are used to treat depression and Parkinson's because they prevent degradation of dopamine, norepinephrine, serotonin, and other transmitters
77
what are melanins derived from?
tyrosine in melanocytes
78
what are melanins?
large polymers, and in skin, they are produced by melanocytes
skin color is determined by the level of gene expression in melanocytes
- eumelanins are either black or brown
- pheomelanins are pink
some enzymes in the biosynthetic pathways are UV-dependent
79
what is trp a precursor for?
serotonin and melatonin
80
explain the process of making serotonin and melatonin
trp is hydroxylated via trp hydroxylase to hydroxytrp --> decarboxylation (via dopa decarboxylase) makes serotonin --> acetylation makes acetyl-serotonin --> methylation with SAM makes melatonin
serotonin can under the MAO-A pathway to be degraded (to treat depression, you'd block this pathway to increase serotonin levels -- includes tricyclic antidepressants and selective serotonin uptake inhibitors)
81
what is creatine?
it stores high-energy phosphate in muscle tissue and is synthesized from GLYCINE and ARGININE, with methyl group provided by SAM
when ATP levels are high, creatine is phosphorylated, when ATP levels are low, creatine-P donates it's phosphate to ADP to generate ATP
82
what is the importance of creatinine?
phosphocreatine is spontaneously cyclized to creatinine which is excreted in the urine
creatinine levels in the urine remain constant and are measured in urine drug tests to determine if urine has been diluted --> serum creatinine levels are measured to assess renal function
amount of creatinine in the blood and urine reflects how much creatine is being used by muscles and, therefore, can be indirectly related to muscle mass.
83
what are the purine bases?
adenine and guanine
PURe As Gold
A has only an AMINE
84
what are the pyrimidine bases?
cytosine, thymine, and uracil
T is ONLY METHYLATED base
U has ONLY O function groups
85
what is the difference between ribonucleotide and deoxyribonucleotide?
ribonucleotide has 2 hydroxy groups while deoxyribonucleotide has ONE
86
what is the difference between a nucleoside and a nucelotide?
nucleoside has nitrogenous based linked via N-glycosidic bond to a sugar, usually ribose or deoxyribose
nucleotide is a nucleoside with phosphate groups attached to sugar
87
where are purines synthesized?
primarily in the liver and brain
purine produced in the liver are transported to extrahepatic tissues by erythrocytes
only 5% come from the diet (requires 6 high-energy bonds, so that's why most cells use salvage)
88
how is the purine ring structure built?
onto the ribose base, using carbons from bicarb, glycine, and FH4, and nitrogen from asp and gln
89
what is the common intermediate in purine synthesis?
inosine monophosphate (IMP) is converted to either AMP or GMP
90
what initiates the purine biosynthetic pathway? explain the purine synthesis pathway
an activated form of ribose --> ribose-5-P (from PPP) is activated at C1 by addition of pyrophosphate --> this reaction is catalyzed by PRPP synthetase (regulated but not committed) --> makes PRPP (golden star)
gln donates its side chain N to PRPP, forming 5-phosphoribosyl 1-amine (reaction catalyzed by glutamine phosphoribosyl amidotransferase = COMMITTED STEP) --> glycine is added --> makes inosine monophosphate (IMP) with purine base called hypoxanthine (this reactions costs 6x ATPs)
91
what is the committed step of the purine synthesis pathway?
glutamine phosphoribosyl amidotransferase
92
how is IMP converted to AMP?
asp is condensed with IMP forming ADENYLOSUCCINATE (reaction requires GTP, making pathway sensitive to cellular [GTP] and helping balance the A:G ratio) --> uses adenylosuccinate synthetase
fumarate is released from adenylosuccinate, producing AMP --> uses adenylosuccinate lyase
LIKE UREA CYCLE
93
how is IMP converted to GMP?
IMP requires NAD+ and is oxidized --> generates xanthosine monophosphate (XMP) occurs via IMP dehydrogenase --> XMP accepts amide from nitrogen from gln forming GMP, reaction requires ATP making it sensitive to [ATP] and is catalyzed by GMP synthetase
94
what is the function of nucleoside monophosphate kinase?
monophosphate kinases are SPECIFIC for NUCLEOTIDE BASE but NOT for sugar
they work equally well with ribonucleotides and deoxy-nucleotides
ATP + NMP <--> ADP + NDP
95
what is the function of nucleoside diphosphate kinase?
nucleoside diphosphate kinase is NONSPECIFIC for NUCLEOTIDE BASE and sugar
it works equally well with ALL nucleotides
96
how is purine synthesis regulated?
net effect of regulation is to maintain a constant G:A ratio and to inhibit synthesis when purine concentrations are high
PRPP synthetase and glutamine phosphoribosyl amidotransferase exhibit sigmoidal kinetics are sensitive to [ribose 5-P] and [PRPP]
GMP and AMP inhibit their own synthetases (GMP synthesis is inhibited by low [ATP] and AMP synthesis is inhibited by low [GTP]
97
what is IMP dehydrogenase inhibited by?
GMP
98
what is adenylosuccinate synthetase inhibited by?
AMP
99
what is PRPP synthetase inhibited by?
ADP and GDP
100
what is glutamine PRPP amidotransferase inhibited by?
AMP, GMP, IMP
101
what are the 4 key enzymes in the purine salvage pathway?
5' nucleotidase = converts nucleotides to nucleosides
APRT (adenine phosphoribosyltransferase) or HGPRT (hypoxanthine-guanine phosphoribosyltransferase)
deaminases = convert AMP to IMP or adenosine to inosine
102
what does a deficiency in HGPRT result in?
- Lesch Nyhan Syndrome
- mental impairment (probably due to imbalance of A:G during development and/or inability to make BH4)
- self mutilation
- hyperuricemia
all due to INCREASED degradation of purines
103
explain the purine salvage pathway
adenine is converted into AMP using PRPP and PPi, reaction catalyzed by APRT --> AMP is converted to adenosine cleaving off Pi, catalyzed by 5'nucleotidase --> adenosine can undergo deaminase to make inosine --> converted to hypoxanthine via purine nucleoside phosphorylase --> uses HGPRT to make IMP --> IMP can't be converted to AMP or GMP (GMP undergoes the same pathway as AMP)
ADENOSINE CAN BE CONVERTED BACK TO AMP VIA ADENOSINE KINASE (only A can do it)
slide 27 of purine lecture
104
what is the Lesch-Nyhan syndrome?
HGPRT deficiency which results in accumulation of hypoxanthine and guanine --> can make uric acid by purine degradation
105
what are the symptoms of Lesch-Nyhan syndrome?
Hyperuricemia (can be severe enough to result in renal complications and accumulation of orange "sand" - sodium urate crystals
Gout
Pugnacious
Retardation
dysTonia
106
explain the purine nucleotide cycle
begins with asp donating amino group to make adenylosuccinate from IMP, AS lyase releases fumarate for the TCA cycle/energy production and makes AMP --> AMP is rapidly produced during exercise --> AMP then undergoes AMP deaminase and forms ammonia which may help to buffer increase [H+] from glycoslysis
this is an IMPORTANT anaplerotic reaction cycle in brain and exercising muscle
107
what inhibits cystathione beta-synthetase?
cysteine
108
how does pyrimidine biosynthesis differ from purine biosynthesis?
pyrimidine ring is assembled PRIOR to attachment to the ribose ring (not ON the ring like purines)
109
what are the precursors for the pyrimidine ring formation?
asp, gln (supplies amido nitrogen), and bicarb
110
what happens in the first reaction of pyrimidine biosynthesis?
carbamoyl phosphate is made from ATP, bicarb, and amido nitrogen from gln
reaction is catalyzed by CYTOSOLIC version of CPSII (recall CPSI is involved in urea cycle and is a MITOCHONDRIAL ENZYME that uses free ammonia)
111
when will CPSII be used?
when carbamoyl phosphate levels in mitochondria increase due to defects in OTC, carbamoyl phosphate leaks into cytosol and is used by CPSII
112
what is the key regulatory point in pyrimidine biosynthesis?
CPSII where amido nitrogen from gln, ATP, and bicarb combine to make carbamoyl phosphate
CPSII is inhibited by UTP (one of its products) and activated by PRPP
113
what happens to the carbamoyl phosphate produced in the first reaction of pyrimidine biosynthesis?
it is condensed with asp, ring is closed by DIHYDROOROTASE and oxidized to for OROTATE
reaction is catalyzed by ASP TRANSCARBAMOYLASE
114
what enzyme is used to the close the ring for carbamoyl asp?
DIHYDROOROTASE closes the ring
115
what happens when orotic acid accumulates?
orotic acid accumulates and is eliminated in the urine of patients with OTC DEFICIENCY and in HEREDITARY OROTIC ACIDURIA
primary symptoms of hereditary orotic aciduria = GROWTH RETARDATION and MACROCYTIC ANEMIA (like B9 and B12 deficiency)
116
what happens after the formation of orotic acid?
PRPP provides the ribose ring for orotic acid forming OMP which is DECARBOXYLASE to UMP --> this will ONLY OCCUR when PRPP is available (hence the accumulation of orotate rather than OMP or UMP in OTC deficiency) --> reaction is catalyzed by orotate phosphoribosyltransferase
117
what enzyme has the greatest catalytic efficiency?
orotidylate decarboxylase
118
what are the blocks in the pyrimidine biosynthesis pathway that leads to hereditary orotic aciduria?
blocks in orotate phsophoribosyltransferase --> leads to build up of orotic acid
orotidylate decarboxylase --> leads to build up of OMP
DECREASE UMP, which is a precursor for pyrimidine synthesis, leads to impaired DNA and RNA synthesis = results in hereditary orotic aciduria
119
how is CTP synthesized?
1. UMP is phosphorylated by nucleotide kinases to form UTP
2. UTP is converted to CTP using amido nitrogen from glutamine, reaction catalyzed by CTP SYNTHASE
CTP is dependent on the concentrations of UTP
120
what is CTP synthase inhibited by?
by CTP (product inhibited)
121
what is the first committed step in pyrimidine synthesis?
aspartate transcarbamoylase
122
what is significant about the salvage pathway for pyrimidine biosynthesis?
because pyrimidine levels within cells are MUCH LOWER than purine levels and their synthesis is LESS COSTLY --> pyrimidine salvage pathway is not heavily used
123
how are deoxyribonucleotides produced?
purine and pyrimidine biosynthetic pathways produce NTPs --> we need dNTPs for DNA synthesis
reaction begins with NDP --> ribonucleotide reductase catalyzes the reduction of the 2' carbon --> enzyme is specific for NDPs and is tightly regulated to maintain optimal dNTP ratios in cell
reducing equivalents required for this reaction are provided by 2 SULFHYDRYL groups on the enzyme which are oxidized to form DISULFIDE --> THIOREDOXIN or Trx = small protein that reduces the disulfide bonds in ribonucleotide reductase and other enzymes --> it will form its own disulfide bonds which are reduced by NADPH via Trx reductase
dNDP is formed
124
what is the final molecule that inhibits RNR?
dADP
125
how is RNR regulated?
rATP is needed to ACTIVATE the enzyme
when [deoxyATP] reaches key level, enzyme is inhibited (dATP is the 4 of 4 dNTPs made)
126
how do uracil and thymine differ from each other?
thymine has a methyl group
127
what is the importance of thymidine?
it is the base used in DNA
UMP produced by de novo or salvage synthesis must be converted to dTMP for REPLICATION and CELL DIVISION to occur
128
explain the process of making dTMP
methylation of dUMP by THYMIDYLATE SYNTHASE requires METHYLENE-H4-folate --> dTMP is formed
unlike other reactions that use FH4, this one transfers 3 Hs from FH4 --> results in formation of FH2 which must be reduced back to FH4 by DIHYDROFOLATE REDUCTASE --> makes FH4 --> undergoes serine hydroxymethyltransferase using PLP cofactor to make methylene-FH4 for thymidylate synthase
129
explain the uptake of purines and pyrimidines
dietary uptake of purines and pyrimidines is MINIMAL (most foods contain only small amounts of nucleotides and most of those are salvaged or degraded by intestinal epithelial cells
130
how are nucleotides digested?
1. dietary nucleic acids are DENATURED in the stomach and HYDROLYZED to oligonucleotides and free nucleotides by NUCLEASES secreted by the pancreas
2. oligonucleotides are further hydrolyzed by phsophodiesterases (also released by pancreas) --> makes mononucleotides
3. mononucleotides are DEPHOSPHORYLATED to nucleosides by nucleotidases
4. nucleosidases produce ribose or deoxyribose and free nitrogenous bases ---> they enter circulation or are converted to uric acid and excreted through urine
131
how are purine nucleotides degraded?
purine nucleotides are degraded to uric acid --> occurs in intestinal mucosal cells and most other cell types
1. AMP is converted to IMP then inosine (same process occurs in the purine synthesis pathway) via adenosine deaminase
2. purine nucleoside phosphorylase removes ribose rings, leaving the bases guanine and hypoxanthine
3. guanine and hypoxanthine are converted to xanthine; guanine by DEAMINATION and hypoxanthine by OXIDATION
4. XANTHINE OXIDASE oxidizes xanthine to form uric acid (same enzyme that oxidizes hypoxanthine) --> allopurinol is used to inhibit uric acid levels
132
what are the diseases associated with purine degradation?
- gout (hyperuricemia) --> results in formation of urate crystals in the joints of extremities, gout can be caused by decreased urinary excretion or uric acid or overproduction and/or increased degradation of purines
- adenosine deaminase (ADA) deficiency --> results in increased intracellular [dATP] and [ATP] which results in
1. inhibition of RIBONUCLEOTIDE REDUCTASE (essential for dNTP synthesis and nucleic acid formation)
2. inhibition of SAH, leading to decreased [SAM]
3. increased [cAMP] --> alters cell signaling pathways
these factors are detrimental to T-cells and B-cells, ADA deficiency causes a form of SEVERE COMBINED IMMUNODEFICIENCY (SCID) = bubble babies, untreated children will die due to infection before 2 y/o
133
what is the function of allopurinol?
IRREVERISBLE inhibitor of xanthine oxidase and commonly used to treat gout
when hyperuricemia is caused by overproduction and/or increased degradation of purines, allopurinol can provide relief
in addition to decreasing amount of uric acid formed, it also increases cell concentrations of hypoxanthine and xanthine --> used in salvage pathy and consume PRPP (lower [PRPP] inhibits de novo purine biosynthesis = less uric acid)
134
how are pyrimidines degraded?
pyrimidine nucleotide bases are degraded to beta-alanine and beta-aminoisobutyrate
beta-alanine (from URACIL) can be used in biosynthesis of CARNOSINE (by addition His) and ANSERINE (with 3MethHis) --> molecules act as buffers and antioxidants
beta-aminoisobutyrate (from thymine) is excreted in urine
135
what is the function of 6-mercaptopurine?
6-MERCAPTOPURINE is an anti-tumor drug --> it is converted, using HGPRT, to ribonucleotide monophosphate that ALLOSTERICALLY INHIBITS glutamine phosphoribosyl amidotransferase (purine synthesis) and IMP dehydrogenase --> 6-mercaptopurine is oxidized and inactivated by xanthine oxidase
136
which drug might be administered alongside 6-mercaptopurine to prevent its oxidation?
allopurinol (which is also used to inhibit xanthine oxidase)
137
what is the function of 5-fluorouracil?
it is an ANTIMETABOLITE
5-FLUOROURACIL is also another anti-tumor drug --> converted by pyrimidine salvage pathway to fUMP and to FdUMP by rionucleotide reductase --> FdUMP is SUICIDE INACTIVATOR OF THYMIDYLATE SYNTHASE (makes dTMP for DNA replication)
138
what is the function of cytosine arabinoside?
it is an ANTIMETABOLITE
CYTOSINE ARABINOSIDE is another anti-tumor drug (stereochem at C2 is inverted) --> after phosphorylation by cell kinases it is incorporated into growing DNA strands --> DNA poly will NOT elongate the strand after the arabinoside is incorporated, so replication is halted
used to terminate DNA replication
139
what is the function of acycloguanosine?
it is an ANTIMETABOLITE
ACYCLOGUANOSINE (acyclovir) is used to TREAT INFECTIONS caused by HERPES VIRUS (HSV) --> HSV genome encodes a protein that phosphorylates acycloguanosine which is then incorporated into replicating viral DNA strands --> lack of 3'-OH group terminates replication and inhibits the infection
140
what is the function of 3'-azido-3'-deoxythymidine?
3'-AZIDO-3'-deoxythymidine (AZT) is used in treatment of HIV-AIDS --> it is phosphorylated by human nucleotide kinases but AZTTP is recognized almost exclusively only by HIV DNA poly --> lack of 3'-OH group will terminate replication
141
what are the chemotherapeutic agents that interfere with nucleotide biosynthesis?
a number of drugs that target nucleotide synthesis has been developed for treatment of infection, cancer, and graft rejection
- antimetabolites = structural analogs of PURINE or PYRIMIDINE bases that interfere with specific metabolic reactions
- antifolates = interfere with ability of FH4 to participate in nucleotide biosynthesis
- hydroxyurea = inhibits ribonucleotide reductase
142
what are antifolates and their function?
they're folate analogs that inhibit DIHYDROFOLATE REDUCATSE and interferes with use of FH4 as a carbon donor
METHOTREXATE, aminopterin, and trimethoprim are ANTI-TUMOR drugs that COMPETITIVELY inhibit dihydrofolate reductase, also used in treatment of AUTOIMMUNE DISORDERS such as rheumatoid arthritis, they starve cells of FH4 needed for de novo purine biosynthesis and for reaction catalyzed by thymidylate synthase
143
what is the function of other agents related to FH4?
several anti-tumor drugs currently in development use folate or folate analogs to target delivery of chemotherapeutic agents to tumor cells --> tumor cells express large numbers of folate receptors, binding of folate (or analogs) to these receptors initiate endocytosis (new drugs can be targets specifically to tumor cells)
VINTAFOLIDE
VINBLASTINE inhibits formation of microtubules
144
explain how the O2 kinetic chain functions
O2 is delivered to skeletal muscle from the lungs, via circulatory system
O2 is inspired into the lungs, goes through pulmonary circulation to the heart, then through peripheral circulation to the muscle --> O2 is used for oxidation of fuels in the mitochondria to generate ATP --> CO2 is produced by mitochondrial oxidation and is transported by the same pathway as O2 circulatory system to be expired
145
what is VO2?
how much O2 is consumed by the skeletal muscle
VO2 = Q (cardiac output) x (CaO2 - CvO2)
cardiac output and VO2 difference improve with exercise training
cardiac output is also rate limiting factor for max VO2
146
what effects do COPD, CHF, and PAD have on the O2 kinetic chain/muscle metabolism?
COPD will affect the lungs = can't deliver O2 to the muscles, leading to lower VO2
CHF affects the heart = decrease cardiac output also decreasing VO2
PAD affect peripheral circulation = decrease blood flow to tissues, leading to a decrease in (CaO2-CvO2) and VO2
147
what do you need for muscle contraction?
You need ATP and Ca2+
within sarcomeres, there are fibrous proteins like myosin and actin that help facilitate contraction --> Ca2+ will bring to actin fibers for contraction while the heads on myosin will bend to contract
148
what does muscle do with ATP and Ca2+?
during CONTRACTION, if there is a low [Ca2+] then the actin-binding site is unavailable but if there is HIGH [Ca2+] then Ca2+ will bind to troponin on actin, making the actin-binding site available --> myosin heads will attach to the binding sites making a cross-bridge attachment in the presence of Ca2+ --> myosin heads creates a POWERSTROKE that moves actin inward, shortening the sarcomere and contracting
during RELAXATION, ATP will bind to myosin ATPase to detach the myosin from actin (also remove Ca2+ via Ca2+ ATPases to restore Ca2+ to sarcoplasmic reticulum, and rigor mortis) --> ATP hydrolysis in myosin ATPase begins again
process continues over and over again until we are fully shortened
149
what is rigor mortis?
2-6 hrs after death, starting from jaw moving to extremities, stiffness occurs
stiffness = sarcoplasmic reticulum leaks Ca2+ out, no ATPase to bring it back in
if any ATP is hydrolyzed = binding sites are opened --> myosin will attach and dow power stroke --> end in contracted state --> dead body has no ATP to displace myosin
150
simply, why do we need ATP?
energy for contraction = myosin powerstroke
energy for relaxation = myosin detachment and Ca2+ ATPases
151
what are the types of muscle fibers?
Type I (slow twitch, slow ox) = slow contraction speed, low force/power, HIGH fatigue resistance due to high mitochondria and capillary density/myoglobin (cap deliver O2 to muscle, more of them and more O2 to muscle), MAJOR FUEL SOURCE = TG - can still use other sources but TG is main source (ex: endurance performance)
Type IIA (fast twitch, fast ox) = fast contraction speed, high force/power, MODERATE fatigue resistance due to high mitochondria and intermediate cap. density/myoglobin, MAJOR STORAGE FUEL = PCr and GLYCOGEN (ex: 200m, 400m, 800m sprints) --> diff from type IIB because it can break gown glycogen using O2 or ANAEROBICALLY
Type IIB (fast twitch, fast glycolysis) = VERY fast contraction speed, VERY high force/power, LOW fatigue resistance due low mitochondria and cap. density/myoglobin, MAJOR STORAGE FUEL = PCr and GLYCOGEN (ex: short distance sprinters, lineman, weight lifting) --> favor ANAEROBIC glycolysis because use of short term fuel like glycogen
152
what is the sequence of recruitment of muscle fiber type?
type I (walking) --> type IIa (running) --> type IIb (sprinting)
Increasing exercise intensity (increase VO2) requires more FT muscle fiber recruitment
153
you are asked to sprint as fast as possible for 30s. rank the depletion of ATP from lowest to highest by fiber type
type I
type IIa
type IIb
154
what are the bioenergetic systems of skeletal muscle?
1. all systems create ATP, they VARY IN RATE AND AMOUNTS
2. always a blend of systems, but ONE PREDOMINATES (depending on exercise and fiber type used during it)
3. at rest: primarily use aerobic lipolysis
4. initiation of activity = ATP> CP>An.gly>Aero.gly>Aero.lip
5. increase intensity = greater CHO use because Type II fibers were be used and their main fuel source is glycogen
aerobic lipolysis produces the most ATP while CP and anaerobic glycolysis produce the least amount of ATP
high intensity/shorter duration = more ANAEROBIC glycolysis, low intensity/longer duration = more AEROBIC glycolysis
155
explain training specific energy states
as max power decreases, your typical exercise time increases, and work:rest ratio decreases (you begin with PCr and glycogen then use oxidative - aerobic glycolysis and aerobic lipolysis)
156
what does it mean to have an O2 deficit?
use of phosphagen system (PCr) consumes energy stores that were initially generated by aerobic metabolism --> results in an "ANAEROBIC DEBT" that must be paid back via AEROBIC METABOLISM (EPOC) after exercise ends
at the start of exercise, you're in O2 deficit because muscle's consumption of O2 increases but body cannot meet its demands --> leads to use of store ATP and CP aka anaerobic glycolysis
in the steady state, O2 needs of muscle is met because aerobic metabolism can provide sufficient amount of energy (steady state will be using glucose first then fat over longer periods
at end of exercise, you'll undergo EPOC = aerobic repayment of anaerobic metabolism, O2 remains elevated above resting levels, O2 consumption for hours after exercise to repay O2 deficit, EPOC primarily uses fat, but also little carb
ex: 5x2 min sprints with 1 minute rest would create large O2 debt and EPOC
157
what are the sources of CHO and fat during steady-state exercise?
source of CHO or fat used for energy production depends on level of O2 uptake by tissue
at LOW O2 uptake = plasma free FAs are PRIMARY energy source
at HIGH O2 uptake = muscle glycogen becomes the dominant energy source
muscle TG are more favorable than plasma form because it is more efficient to access
ex: powerlifting = glycogen and CP will be used
158
explain the significance of CHO and lipid oxidation during exercise
at ONSET of exercise, CHO oxidation dominates
DURING exercise, lipid oxidation becomes more abundant
during EPOC, lipid oxidation is the most abundant (EPOC can last up to 24 hrs with high intensity internal training, lipid oxidation helps repay all ATP and CP stores)
159
how do you move from anaerobic (O2 deficit) to aerobic (steady state) metabolism?
use AMPK --> key regulator of aerobic metabolism --> during anaerobic work, AMP levels increase and activate AMPK, AMPK will stimulate aerobic oxidative pathways to utilize sugar and fat
inactive AMPK will be activated by high [Cr], high [AMP], and low pH --> active AMPK will increase aerobic oxidation and decrease synthesis (protein, FA, glycogenesis synthesis) leading to more ATP
AMPK is inactivated by high [PCr] and high [ATP]
persistence of activity requires a "steady state" of aerobic metabolism:
1. liberate more nutrients and deliver more O2
2. slow down aerobic metabolism
3. utilize both strategies
160
how does AMPK alter skeletal muscle glucose metabolism during exercise?
AMPK stimulates glucose uptake by activating --> glut 4 transporters (increases), glycogen phosphorylase (increase glycogenolysis), HK and PFK-1 (increase glycolysis)
these effects are EXERCISE (AMPK) SPECIFIC and INDEPENDENT of insulin
muscle activity will activate AMPK (due to increase in AMP) --> AMPK activates glycogenolysis, glycolysis, and glut 4 transporters while glycogenesis and protein synthesis are INHIBITED
161
what determines lactate vs. pyruvate output from glycolysis?
anaerobic (fast glycolysis) or aerobic (slow glycolysis)
162
how does AMPK alter skeletal muscle fat metabolism during exercise?
Acutely = AMPK stimulates fat metabolism by inhibiting ACCase, decreasing [malonyl CoA] --> AMPK inhibits free FA synthesis and allows mitochondrial oxidation of FAs (FFAs transported in by Fat/CD36, synonymous to glut 4, combines with TG to make fatty acyl CoA --> CPTI --> fatty acylcarnitine --> into mitochondria --> under FA oxidation to make ATP
Chronically = AMPK promotes mitochondrial biogenesis using PGC1a, leads to mitochondrial fusion --> more and bigger mitochondria, able to improve CaVO2 difference due to more mitochondrial enzymes
163
what determines CHO or fat utilization during exercise?
CHO use increases and fat use decreased with increasing exercise intensity
1. HIGH intensity (>65-70%) = greater CHO use, fat is still used but CHO will dominate
2. PROLONGED LOW intensity (<65-70%) = greater LIPID, carbs still used by lipid dominates
164
why does increased intensity increase CHO use while lower intensity increase fat use?
increase intensity = use of type II muscle fibers which are dependent on glycogen, glucose, and CP
lower intensity = use of type I muscle fibers which are dependent on fats
165
what are the 2 primary stressors that alter hormones?
time and intensity
as exercise increases in intensity or duration = increase in epi and decrease in insulin --> change in metabolic profile increases the activity of HSL, thus releasing more FFA for oxidation
166
if insulin is low, how do we take up glucose?
it doesn't matter that insulin is low because AMPK causes an increase in glut 4 transporters for glucose uptake (which is independent of insulin)
epi also ensures glucose and FFA metabolism with stress
167
what is increase epi doing to skeletal muscle metabolism during exercise?
increased epi also stimulates HEPATIC GLYCOGENOLYSIS and GLUCONEOGENESIS and ACTIVATES skeletal muscle AEROBIC GLYCOLYSIS
epi stimulates liver to undergo gluconeogenesis to increase blood glucose --> increase blood glucose stimulates skeletal muscle to undergo glycolysis
epi activates ADENYLATE CYCLASE --> produces cAMP, increase in [cAMP] will activate PKA --> PKA will activate phosphorylase a for glycogenolysis, PFK-1 and PDH to make acetyl CoA for TCA (PKA's effect on PDH activation appears to be indirect by providing enhanced pyruvate delivery)
168
what is low insulin doing to skeletal muscle metabolism?
high levels of insulin inhibit FA transport across plasma and mitochondrial matrix membranes
insulin levels decline = inhibition also declines, thus facilitating oxidation of fat which inhibits glycolysis
high insulin inhibits FA oxidation and stimulates glycolysis
low insulin inhibits glycolysis and stimulates FA oxidation
remember fat/CD36 transports fat into muscles
169
how are inactive people metabolically inflexible?
untrained subjects DO NOT have metabolic flexibility, even when faced with lipid overload provided during clamp, they CANNOT effectively decrease glucose oxidation and increase FT oxidation compared to exercise trained group
170
why do inactive people suffer from the curse of "thrifty genes"?
during famine activity there is decrease glycogen and TG stores --> contracting skeletal muscle increase glut 4 and AMPK --> eventually reach feast where there is intake of glucose and fat --> physical inactivity will build thrifty storage = replenish skeletal muscle glucose and TG, more efficient storage of excess glucose and TG in adipocytes
in active individuals --> they will be able to store and oxidize nutrients in their skeletal muscle BUT in inactive individuals --> they have less muscle storage and utilization, leading to obesity and increased risk for non-alcoholic fatty liver disease
171
what is the MET equation? (metabolic equivalent of task)
1 MET = VO2 of 3.5 ml/kg/min
172
what are the general rules to chronic exercise-mediated biochem adaptations?
1. fitness = metabolic flexibility (ability to use the more efficient fuel store)
2. specificity of adaptations (do lots of aerobic training = increase aerobic enzymes)
3. soon to ripe = soon to rot (ex: if you're sick for a few days and don't exercise, you'll lose some stability, but can build it back)
4. interval training (increasing anaerobic and aerobic enzymes) vs endurance (building anaerobic enzymes)
173
what is creatine?
creatine is a nitrogenous orgo acid
creatine can be made through an ENDOGENOUS pathway from arginine and glycine --> using AGAT (in kidney) --> convert arginine and glycine to guanidino acetate --> using GAMT (in liver) to make creatine --> creatine involves phosphate energy transfer and is metabolized to CREATININE to be cleared by kidney (reaction is IRREVERSIBLE) --> MOST CREATINE is made via this pathway
creatinine is a waste product cleared from plasma, ONLY by the KIDNEY, creatinine is also a clinical marker of renal function
creatine can come from dietary intake via EXOGENOUS pathway --> its absorbed --> then transfer to muscle and undergo the same non-enzymatic, irreversible reaction to make creatinine for excretion (vegans and vegetarians will take creatine supplements) --> increase in exogenous creatine can give false positive results for renal function decline
174
how does the PCr system work?
PCr donates its P to ADP to make ATP and creatine via creatine kinase --> muscle contraction will convert ATP back to ADP (there's more myosin ATPases than creatine ATPases)
another pathway will use 2 ADP (mainly when lots of ADP is present) --> one ADP transfers its P to the other and converts it to ATP and AMP using adenylate kinase (myokinase) --> AMP will activate AMPK and thus activating glycolysis while ATP provides energy for muscle contraction
175
what happens to cytoplasmic ATP, PCr, ADP, AMP, Pi as you exercise to exhaustion? How might these products regulate CK/MK?
ATP decrease (used for muscle contraction)
PCr decrease (P used to make ATP)
ADP increase (made from ATP)
AMP increase (exercising increases [AMP])
Pi increases as muscle contraction dephosphorylates ATP
CK is activated by AMP, Pi, and ADP
MK is only activated by ADP
176
how do you replenish the CP system?
exercise utilizes PCr stores to help maintain ATP levels in cells and drive muscle contraction
during recovery, mitochondria replenishes PCr and ATP stores using aerobic metabolism
Cr will go to mitochondria --> mtCK will phosphorylate CR using ATP to regenerate PCr (ADP is produced) --> exits the mitochondria and undergoes the PCr cycle again, ADP undergoes oxidative phosphorylation to regenerate ATP
177
where does ingested protein go when a person is at rest?
ex: first a person ingests milk-based protein --> 50% of ingested protein is extracted by splanchnic tissues (like LIVER) prior to entering circulation --> remaining 40% is catabolized (energy ureagenesis and neurotransmitter production) --> 10% that is left is used for de novo protein synthesis in skeletal muscle
178
explain the molecular pathways that regulate protein turnover
resistance exercise (RE) will activate FAK/integrins (receptors in muscle cell membrane that can detect tension and stretch in muscles) --> concurrent exercise, RE, AAs (leucine) will activate mTORC1 --> mTORC1 will activate p70S6K and inhibit 4EBP1 --> p70S6K activates eEF2 for ELONGATION and RPS6 for initiation --> both results in protein synthesis
endurance exercise and concurrent exercise will increase ADP:ATP ratio --> activates AMPK (endurance exercise also activates AMPK) --> AMPK activates FOXO and PGC1a (for mitochondrial biogenesis) --> FOXO activates MaFBx and MuRF-1 for protein breakdown --> used for kreb cycle intermediates
179
how important is mTOR for muscle hypertrophy?
conditional activation of mTOR regulator Akt (activated by muscle contraction or AA, upstream of mTOR) rapidly induces muscle hypertrophy in adult mice --> this demonstrates that mTOR is a very powerful regulator of muscle protein synthesis
180
how does feeding affect muscle protein synthesis?
natural fluctuations in muscle protein synthesis and breakdown with meals, where muscle building is limited to the fed state
effect of RE increasing MPS and improving body's ability to use dietary protein for muscle growth, leading to a more substantial net gain in muscle protein over time
181
how do trained and untrained people have diff responses to protein turnovers in RE?
untrained focus on REPAIRING large amount of muscle damage --> as person becomes more trained, they are less suscpetible to muscle damage, so more of their efforts in turnover lead to muscle hypertrophy (muscle will eventually become protected against damage)
trained people are less susceptible to muscle damage and recover more quickly than untrained people
182
how does chronic resistance training increase resting MPS?
this may help offset decreases MPS induced by RE
muscle growth is a chronic adaptation from cumulative exercise which improves MPS at rest, but NOT during the stimulated MPS response to RE, which seems to get smaller with time
183
what causes the increase in resting MPS in trained people?
acute effects of RE = intracell anabolic signaling transduction --> increase short-term protein synthesis rates and increased RIBOSOME BIOGENESIS --> increased translation efficiency
chromic effect of RE can lead to increased ribosome content from increase ribosome biogenesis --> increase protein synthesis rate at rest --> increase tranlation capacity
184
does an increase in MPS translate into myofibrillar protein or just form other muscle enzymes?
increases in MPS seem to correlate very well with increase in myofibrillar protein synthesis (actin and myosin)
185
how much protein should we eat each day to max fat free mass (FFM)?
US RDA 0.8 g/kg/d
segmental linear regression shows that the delta FFM plateaus about 1.62 g/kg/d
186
how many grams of protein will max protein synthesis?
20-40 grams per meal
