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Biochemistry > Endo: Catabolism Of Proteins & AA Nitrogen > Flashcards

Endo: Catabolism Of Proteins & AA Nitrogen Flashcards

0
Q

An excess of ingested over excreted nitrogen.

A

Positive nitrogen balance

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1
Q

Protein and AA catabolism described how

A

Nitrogen is converted to urea

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2
Q

Positive nitrogen balance accompanies

A

Growth and pregnancy

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3
Q

Nitrogen Output exceeds intake

A

Negative nitrogen balance

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4
Q

Negative nitrogen balance accompanies

A

Surgery, Advanced cancer & Marasmus/Kwashiorkor “SAM K”

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5
Q

Ammonia, derived mainly from _______, is highly toxic, tissues covert ammonia to _______ of nontoxic glutamine.

A

a-amino nitrogen of AAs. Amide nitrogen.

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6
Q

Subsequent deamination of glutamine in the liver releases ammonia, which is then converted to

A

Nontoxic Urea

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7
Q

Liver function is compromised in this disease states, elevated ammonia levels generate clinical s/sx

A

Cirrhosis or Hepatitis

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8
Q

_______ turnover occurs in all forms of life.

A

Protein

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9
Q

Each day, humans turn over ____% of their total body protein. Principally __________.

A

1-2%. Muscle protein.

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10
Q

High rates of protein degradation occur in tissue undergoing structural rearrangement such as

A

Uterine tissue during pregnancy

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11
Q

Of the liberated AAs, approximately __% are reutilized

A

75%

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12
Q

Excess of nitrogen forms

A

Urea

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13
Q

Since excess AAs are not stored , those not immediately incorporated into new protein are

A

Rapidly degraded

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14
Q

Degrade protein to AAs

A

Proteases & Peptidases

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15
Q

The susceptibility of a protein to degradation is expressed as its

A

Half life

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16
Q

Half lives of liver proteins range from

A

Under 30mins- over 150hrs

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17
Q

Typical housekeeping enzymes have a half

Iife values of over

A

100hrs

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18
Q

Key regulatory enzymes have a half life of

A

0.5-2hrs

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19
Q

Target some proteins for rapid degradation

A

PEST sequence: Proline, Glutamate, Serine & Threonine

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20
Q

Resulting peptides are then degraded to AAs by ______ that cleave internal bonds.

A

Endopeptidases

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21
Q

Remove AAs sequentially from the amino terminals

A

Aminopeptidases

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22
Q

Remove AAs sequentially from the carboxy terminals

A

Carboxypeptidases

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23
Q

Extracellular, membrane associated and long lived intracellular proteins are degraded in _______ by __________.

A

Lysosomes. ATP-independent processes.

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24
Q

Degradation of abnormal and other short-lived proteins occur in ______ and requires ____ & _______.

A

Cytosol. ATP & Ubiquitin.

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25
Q

Is a small(8.5 kDa) proteinthat targets many intracellular proteins for degradation. The primary structure of this is highly conserved. Only _____ residues differ between yeast and human.

A

Ubiquitin. 3 of 76.

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26
Q

Several molecules of ubiquitin are attached by nonpetide bonds formed between the

A

Carboxy terminal of ubiquitin & amino groups of lysyl residues

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27
Q

The terminal of COOH of ubiquitin forms a ________ bond with an -SH of E1 in a reaction driven by conversion of ___ to ___ and ___. Subsequent hydrolysis of PPi by ________ ensures that reaction 1 will proceed readily.

A

Thioester. ATP. AMP & PPi. Pyrophosphate.

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28
Q

A thioester exchange reaction transfers activated ubiquitin to __.

A

E2

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29
Q

Catalyzes transfer of ubiquitin to amino group of lysyl residues of target proteins.

A

E3

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30
Q

Affects whether a protein is ubitiquinated

A

Residue present at its amino terminal

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31
Q

Amino terminal that retards ubiquitination

A

Met or Ser

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32
Q

Amino terminal that accelerates ubiquitination

A

Asp or Arg

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33
Q

Degradation occurs in a multicalytic complex of proteases known as

A

Proteasome

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34
Q

Proteins are hydrolyzed to this for absorption to make them smaller

A

AAs

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35
Q

Proteolytic enzymes responsible for degrading proteins are in the

A

Stomach, pancreas & small intestine

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36
Q

Contains gastric juices HCL and pepsin

A

Stomach

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37
Q

Kills bacteria

A

HCl

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38
Q

Is from pepsinogen which is activated by HCl

A

Pepsin

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39
Q

Further cleave polypeptides initially digested by the stomach

A

Pancreatic proteases

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40
Q

From the intestine activates pancreatic enzymes such as ________ to its active form.

A

Enteropeptidase. Trypsinogen.

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41
Q

Small intestine contains _______ that cleaves oligopeptides to produce ________.

A

Aminopeptidases. Free AAs.

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42
Q

Absorbed by the intestinal epithelium

A

Free amino acids and dipeptides

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43
Q

Dipeptides are further hydrolyzed in the _______ before being released to the portal system.

A

Cytosol

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44
Q

Excrete ammonia

A

Ammonotelic

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45
Q

Excrete uric acid

A

Uricotelic

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46
Q

Ammonotelic in nature, compels them to excrete water continuously, facilitating excretion of highly toxic ammonia.

A

Teleostean fish

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47
Q

Must conserve water and maintain low weight, uricotelic in nature and excrete uric acid as ___________.

A

Birds. Semisolid guano.

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48
Q

Many land animals, including humans, are _______ and excrete nontoxic, water-soluble urea

A

Ureotelic

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49
Q

A consequence- not a cause- of impaired renal function

A

High blood urea levels

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50
Q

4 stages in Urea biosynthesis

A

-Transamination
-Oxidative deamination of glutamate
-Ammonia transport
-Reactions of the urea cycle
“TOAR”

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51
Q

Transfers a-Amino Nitrogen to a-Ketoglutarate, forming Glutamate. Reaction is readily reversible.

A

Transamination

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52
Q

Transamination interconverts pairs of

A

a-amino acids & a-keto acids

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53
Q

Do not participate in transamination

A

Proline, Hydroxyproline, Lysine & Threonine

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54
Q

Also function in amino acid biosynthesis

A

Aminotransferases

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55
Q

A coenzyme present at the catalytic site of aminotransferases and of many other enzymes that act on AAs

A

Pyridoxal Phosphate

56
Q

During transamination, bound ____ serves as a carrier of amino groups. Following removal of a-amino nitrogen by transamination, the remaining carbon skeleton is _________.

A

PLP. Degraded.

57
Q

2 enzymes that catalyze the transfer of amino groups to pyruvate(forming ______) or to a-ketoglutarate(forming ____)

A

Alanine pyruvate aminotransferase(alanine aminotransferase) & glutamate-a-ketoglutarate aminotransferase(glutamate aminotransferase)
Alanine. Glutamate.

58
Q

Each aminotransferase is specific for _____ of substrates but nonspecific for other pair.

A

One pair

59
Q

Since alanine is also a substrate for ____________, all the amino nitrogen from amino acids that undergo transamination can be concentrated in __________.

A

Glutamate aminotransferase. Glutamate.

60
Q

Is the only AA that undergoes oxidative deamination at an appreciable rate in mammalian tissues.

A

L-glutamate

61
Q

The formation of ammonia from a-amino groups thus occurs mainly via

A

A-amino nitrogen of L-glutamate

62
Q

Occupies a central position in nitrogen metabolism

A

L-glutamate dehydrogenase

63
Q

Transfer of amino nitrogen to a-ketoglutarate forms

A

L-glutamate

64
Q

Release of this nitrogen as ammonia is then catalyzed by hepatic ______________, which can either use ___ or ____.

A

L-glutamate dehydrogenase. NADP NADH

65
Q

Conversion of a-amino nitrogen to ammonia by the concerted action of glutamate aminotransferase and GDH is often termed

A

Transdeamination

66
Q

Liver GDH is allosterically inhibited by

A

ATP, GTP & NADH

67
Q

Liver GDH is allosterically activated by

A

ADP

68
Q

Reaction catalyzed by ____ is freely reversible and functions also in AA biosynthesis

A

GDH

69
Q

Also remove nitrogen as ammonia

A

Amino acid oxidases

70
Q

Convert AAs to an a-amino acid that decomposes to an a-ketoacid with release of ammonium ion.

A

L-amino acid oxidase

71
Q

The reduced _____ is reoxidized by molecular oxygen , forming hydrogen peroxide, which then is split to ___ & ___ by ________.

A

Flavin. O2 & H2O. Catalase.

72
Q

Is life threatening

A

Ammonia intoxication

73
Q

The ammonia produced by enteric bacteria and absorbed into portal venous blood and the ammonia produced by tissues are rapidly removed from the circulation by the _____ and converted ____.

A

Liver. Urea.

74
Q

Percent of ammonia always present in peripheral blood

A

10-20g/dL

75
Q

Toxic to the CNS

A

Ammonia

76
Q

Symptoms of ammonia intoxication

A

Tremors, slurred speech, blurred vision, coma & death “TSB CD”

77
Q

Ammonia may be toxic to the brain in part because it reacts with _________ to form _______.

A

a-ketoglutarate. Glutamate.

78
Q

Resulting depleted levels of a-ketoglutarate then impair function of the

A

Tricarboxylic acid(TCA) in neurons

79
Q

Catalyzed the formation of glutamine and fixes ammonia as glutamine.

A

Glutamine synthase

80
Q

Since amide bond synthesis is coupled to the hydrolysis of __ to ___ and ____, the reaction strongly favors glutamine synthesis.

A

ATP. ADP & Pi.

81
Q

Sequester ammonia in a no toxic form.

A

Glutamine

82
Q

Strongly favors glutamate formation. Catalyze the hydrolytic release of the amide nitrogen of glutamine as ammonia.

A

Glutaminase

83
Q

Catalyzes the interconversion of free ammonium ion and glutamine. An analogous reaction is catalyzed by _________.

A

Glutamine synthase & Glutaminase. L-Asparaginase.

84
Q

Formation & secretion of this maintains acid base balance

A

Ammonia

85
Q

Facilitates cation conservation and regulation of acid base balance. Produced by _________.

A

Excretion into urine of ammonia. Renal tubular cells.

86
Q

Ammonia production from intracellular renal AAs, especially glutamine, increases in

A

Metabolic acidosis

87
Q

Ammonia production from intracellular renal AAs, especially glutamine, decreases in

A

Metabolic alkalosis

88
Q

Series of reactions that produce urea from ammonia (NH3). In mammals this cycle occurs in the _____.

A

Urea/Ornithine cycle. Liver.

89
Q

Urea cycle was first discovered by

A

Krebs & Kurt Henseleit, 1932

90
Q

Organisms that cannot easily and quickly remove ammonia usually have to convert it to some other substance, like ___ or ____, which are much less toxic.

A

Urea. Uric acid.

91
Q

Result of liver failure is the accumulation of nitrogenous waste , mainly ammonia, which leads to a neuropsychiatric abnormality

A

Hepatic encephalopathy

92
Q

The urea cycle consists of five reactions.

A

2 mitochondrial, 3 cytosolic

93
Q

Urea cycle: converts two amino groups, one from NH4 and one from Asp, and a carbon atom from HCO3, to relatively nontoxic excretion product, urea at the cost of four high energy phosphate bonds _____ hydrolyzed to ____ & ____.

A

3 ATP. 2 ADP. 1 AMP.

94
Q

Is the carrier of the urea cycle carbon and nitrogen atoms

A

Ornithine

95
Q

Major end product of nitrogen catabolism in humans

A

Urea

96
Q

Synthesis of 1 mol of urea requires ______ plus ______ and _____________.

A

3mol of ATP. 1 mol of each ammonium ion. a-amino nitrogen of aspartate.

97
Q

Initiates urea biosynthesis

A

Carbamoyl Phosphate Synthase

98
Q

Rate limiting enzyme of the urea cycle. Condensation of CO2, ammonia and ATP to form carbamoyl phosphate is catalyzed by mitochondrial

A

Carbamoyl Phosphate Synthase I

99
Q

An allosteric activator of carbamoyl phosphate synthase I. Enhances the affinity of the synthase for ATP.

A

N-acetylglutamate

100
Q

Formation of carbamoyl phosphate requires ________.

A

2mol of ATP

101
Q

Defect in the enzyme carbamoyl phosphate synthase

A

Hyperammonenia type I

102
Q

Carbamoyl phosphate plus ornithine forms

A

Citrulline

103
Q

Catalyze transfer of the carbamoyl group of carbamoyl phosphate to ornithine, forming _____ and ______. Reaction occurs in the _______.

A

L-Ornithine transcarbamoylase. Citrulline & orthophosphate. Mitochondrial matrix.

104
Q

Results from mutation of the ORNT1 gene that encoded the mitochondrial membrane ornithine transporter.

A

Hyperornithinemia, hyperammonemia and homocitrullinuria “HHH syndrome”

105
Q

Failure to import cytosolic ornithine into the mitochondrial matrix renders the ________ inoperable.

A

Urea cycle

106
Q

Citrulline olus aspartate forms

A

Argininosuccinate

107
Q

Links aspartate and citrulline via the amino group of aspartate and provides the second nitrogen of urea. The reaction requires ___.

A

Argininosuccinate synthase

108
Q

Subsequent displacement of AMP by aspartate forms

A

Citrulline

109
Q

Cleavage of Argininosuccinate forms

A

Arginine & Fumarate

110
Q

Cleavage of argininosuccinate, catalyzed by ______, proceeds with retention of nitrogen in ______ and release of the aspartate as _______.

A

Argininosuccinase. Arginine. Fumarate.

111
Q

Fumarate is recycled back to

A

Aspartate

112
Q

Addition of water to fumarate forms ________ and subsequent NAD+dependent oxidation of malate forms ________. Analogous to reactions of the citric acid cycle but are catalyzed by __________ & ___________.

A

L-malate. Oxaloacetate. Cytosolic fumarase & malate dehydrogenase.

113
Q

Transamination of oxaloacetate by ________ then re forms ______.

A

Glutamate aminotransferase. Aspartate.

114
Q

Arginine is produced from

A

Argininosuccinate

115
Q

ASL gene is located on chromosome

A

7

116
Q

Deficiency in argininosuccinase which is accompanied by elevated levels of argininosuccinate in blood, CSF and urine.

A

Argininosucciniaciduria

117
Q

Argininosucciniaciduria is associated with friable & tufted hair

A

Trichorrhexis nodosa

118
Q

Cleavage of arginine releases ____ & Re forms ____.

A

Urea. Ornithine.

119
Q

Hydrolytic cleavage of the guanidino group of arginine, catalyzed by liver ______, releases _____.

A

Arginase. Urea.

120
Q

Re enters liver mitochondria for additional rounds of urea synthesis.

A

Ornithine

121
Q

Are potent inhibitors of arginase, competitive with arginine.

A

Ornithine & Lysine

122
Q

Arginine also serves as the precursor of the potent muscle relaxant __________ and catalyzed by ___________.

A

Nitric oxide. Nitric oxide synthase.

123
Q

Is an autosomal recessive defect in the gene for arginase. Symptoms of this appear until age __ to __ years.

A

Hyperargininemia. 2-4

124
Q

Is the pacemaker enzyme of the urea cycle

A

Carbamoyl Phosphate Synthase I

125
Q

The activity of carbamoyl phosphate synthase I is determined an allosteric activator

A

N-acetylglutamate

126
Q

N-acetylglutamate level is dictated by its rate of synthesis from _____ & ______ and its rate of hydrolysis to ______ & _______. These reactions are catalyzed by __________ & _________

A

Acetyl CoA & Glutamate. Acetate & Glutamate. N-acetylglutamate synthase & hydrolase.

127
Q

Defects in NAGS gene result in

A

Hyperammonemia

128
Q

Elevate enzyme levels to cope with the increased production of ammonia

A

Starvation

129
Q

All defects in urea synthesis results in

A

Ammonia intoxication

130
Q

The effects are more severe when the metabolic block occurs at reactions

A

1 or 2

131
Q

Clinical symptoms common to all urea cycle disorders include

A

Vomiting, avoidance of high protein foods, intermittent ataxia, irritability, lethargy and severe mental retardation

132
Q

Significant improvement and minimization of brain damage accompanies

A

Low CHON diet & Small frequent meals

133
Q

Offers promise for correcting defects in urea biosynthesis

A

Gene therapy

134
Q

2ATP+HCO3+NH4. Name product, Enzyme and Location

A

Carbamoyl phosphate. Carbamoyl phosphate synthase. Mitochondria.m

135
Q

Carbomoyl phosphate+ornithine. Name product, Enzyme and Location

A

Citrulline. Ornithine transcarbamoylase. Mitochondria.

136
Q

Citrulline+aspartate+ATP. Name product, Enzyme and Location

A

Argininosuccinate. Argininosuccinate synthase. Cytosol.

137
Q

Argininosuccinate. Name product, Enzyme and Location

A

Arg+fumarate. Argininosuccinate lyase. Cytosol.

138
Q

Arg+H2O. Name product, Enzyme and Location

A

Ornithine+urea. Arginase. Cytosol.

Biochemistry (20 decks)

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