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USMLE1 - Biochemistry > 5. Metabolism 1 > Flashcards

5. Metabolism 1 Flashcards

1
Q

what metabolic reactions occur in the cytoplasm?

A

glycolysis, fatty acid synthesis, HMP shunt, protein synthesis (RER), steroid synthesis (SER), glycogenolysis, glycogenesis

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2
Q

which metabolic reactions require both the mit and cytosol?

A

heme synthesis, urea cycle, gluconeogenesis

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3
Q

what is the difference between a kinase and a phophorylase?

A

both add phosphate; phosphorylase uses no ATP and inorganic phosphate

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4
Q

what is the rate determining enzyme in glycolysis?

A

phosphofructokinase 1

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5
Q

what is the rate determining enzyme in gluconeogenesis?

A

fructose 1,6 bisphosphatase

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6
Q

what is the rate determining enzyme in TCA cycle?

A

isocitrate dehydrogenase

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7
Q

what is the rate determining enzyme in glycogen synthesis?

A

glycogen synthase

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8
Q

what is the rate determining enzyme in glycogenolysis?

A

glycogen phosphorylase

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9
Q

what is the rate determining enzyme in HMP shunt?

A

glucose 6 phosphate dehydrogenase

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10
Q

what is the rate determining enzyme in de novo pyrimidine synthesis?

A

carbomyl phosphate synthetase II

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11
Q

what is the rate determining enzyme in de novo purine synthesis?

A

glutamine PRPP amidotransferase

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12
Q

what is the rate determining enzyme in urea cycle?

A

carbomyl phosphate synthetase I

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13
Q

what is the rate determining enzyme in fatty acid synthesis?

A

Acetyl CoA carboxylase

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14
Q

what is the rate determining enzyme in fatty acid oxidation?

A

carnitine acyltransferase I

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15
Q

what is the rate determining enzyme in steroid synthesis? cholesterol synthesis?

A

HMG CoA synthetase; HMG CoA reductase

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16
Q

what is the rate determining enzyme in galactose metabolism?

A

GALT

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17
Q

what is the rate determining enzyme in fructose metabolism?

A

aldolase B

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18
Q

what type of disease is MELAS? what is the clinical presentation?

A

mit encephalopathy, lactic acidosis, stroke like episodes

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19
Q

what type of disease is MERRF? what is the clinical presentation?

A

myoclonus epilepsy

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20
Q

where is there decreased hydrogen concentration in the mit? increased?

A

matrix; intermembrane space

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21
Q

T/F the outer mit membrane is impermeable to ions

A

false! the inner membrane is

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22
Q

which TCA cycle enzyme is found in the inner mit membrane? where are the rest found?

A

succinate hydrogenase; matrix

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23
Q

other than succinate dehydrogenase what other enzymes are found in the inner mit membrane?

A

ATP synthase, ATP-ADP translocase, ETC

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24
Q

what two processes maintain the plasma glucose levels?

A

1) glycogenolysis (liver only contributes to plasma, muscle keeps it for itself) 2) gluconeogenesis

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25
Q

how many ATP does aerobic metabolism of glucose produce? depending on what? what tissues use which?

A

32 or 30; malate aspartate shuttle or glycerol 3 phosphate shuttle; heart/liver and muscle

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26
Q

what carries activated Phosphate groups?

A

ATP

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27
Q

what carries electrons (as energy)?

A

NADH, NADPH, FADH2

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28
Q

what carries Acyl (as energy)?

A

coenzyme A and lipoamides

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29
Q

what carries CO2 as energy?

A

biotin

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30
Q

what carries 1 carbon units as energy?

A

tetrahydrofolates

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31
Q

what carries methyl groups as energy?

A

SAM

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32
Q

what carries aldehydes as energry?

A

TPP (thiamine pyrophosphate)

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33
Q

T/F NAD + is used in anabolic processes and NADH is used in catabolic processes

A

False! NAD+ is used in catabolic processes and NADPH is used in anabolic processes

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34
Q

Give examples of the anabolic processes that NADPH participates in. From what process is NADPH produced?

A

steroid, cholesterol FA synthesis; HMP shunt

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35
Q

Other than anabolic processes what else is NADPH used for?

A

respiratory burst, P450, and glutathione reductase

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36
Q

what do hexokinase and glucokinase do? using what? what pathway is this in?

A

phosphorylation of glucose to yield glucose 6 phosphate; ATP; first step of glycolysis

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37
Q

T/F glucokinase is ubiquitous

A

FALSO! hexokinase is; glucokinase only found in liver and beta cells of pancreas

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38
Q

T/F hexokinase has a low affinity and low Vmax

A

FALSO! hexokinase has a HIGH affinity (low Km) and low Vmax

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39
Q

T/F glucokinase has a high affinity and high Vmx

A

falso! glucokinase has a LOW affinity (high Km) and high Vmax

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40
Q

is hexokinase or glucokinase activated by insulin?

A

glucokinase

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41
Q

T/F hexokinase and glucokinase are inhibited by excess glucose 6 phosphate

A

falso! only hexokinase, glucokinase has no feedback imhibition (its a glutton)

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42
Q

T/F glucokinase is a glutton

A

TRUUUEEEEE. fatty mcfatterson

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43
Q

what is the point of having a gluttonous glucokinase in the liver?

A

so that excess glucose can be stored (phosphorylated glucose cant leave) in the liver and saved as a buffer

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44
Q

what is the net production of glycolysis from one glucose?

A

2 NADH, 2 ATP, 2 pyruvate, 2H+ , 2H20

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45
Q

what is the rate limiting step in glycolysis? what does it do? who activates it? inhibits it?

A

Phosphofructokinase 1; fructose 1 phosphate to fructose 1,6 bisphosphate; enhancers: AMP, fructose 2,6 Bisphosphate; downregulators: citrate, ATP

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46
Q

from what is pyruvate produced in glycolysis? but what enzyme? what enhances that enzyme? downregulates it?

A

phosphoenolpyruvate; pyruvate kinase; fructose 1, 6 BP; ATP, alanine

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47
Q

what ensures that during gluconeogenesis all the ATP wont be used in glycolysis as youre producing it?

A

protein Kinase A inhibits pyruvate kinase also ATP and alanine have negative effects on pyruvate kinase

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48
Q

what control over pyruvate kinase does insulin have?

A

it induces its action!

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49
Q

what converts pyruvate to Acetyl CoA ? what allosterically downregulates this enzyme?

A

Pyruvate dehydrogenase; ATP, NADH, acetyl CoA

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50
Q

by what products are gluconeogenesis and glycolysis linked so that they are not both occurirng at the same time?

A

ATP is an allosteric inhibitor on both phosphofructokinase and pyruvate kinase and pyruvate hydrogenase; and fructose 2,6 BP which is an allosteric enhancer on phosphofructokinase is an allosteric downregulator on fructose 1,6 bisphophatase

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51
Q

what is the first step in glycolysis?

A

phosphorylation of glucose

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52
Q

how does fructose enter glycolysis? galactose?

A

via fructose 1 P by fructokinase in the liver; as glucose 1 by being GALT-ed ;)

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53
Q

T/F galactose is the fastest sugar metabolized. explain.

A

false! fructose because fructokinase in the liver allows it to bypass the rate limiting step in glycolysis (PFK1), and it enters through a different pathway (either through DHAP to glycogenolysis or to glyeraldehyde for glycolysis)

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54
Q

what is fructose 2,6 phosphate? where does it come from? by what enzyme?

A

an allosteric regulator; fructose 1 phosphate; phosphofructokinase 2

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55
Q

what converts fructose 2,6 phosphate back to fructose 2 phosphate?

A

fructose bisphosphatase 2

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56
Q

what two enzymes are the apart of the same complex? what dictates what form they are in? and what dictates that?

A

fructose bisphosphatase 2 and Phosphofructokinase 2; phosphorylation by protein kinase A; inuslin/glucagon ratio

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57
Q

what does fructose 2,6 bisphosphate regulate?

A

positive on phosphofructokinase 1 and negative on fructose 1,6 bisphosphatase

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58
Q

what does fructose 6 phosphate do, depending on what?

A

this depends on if phosphofructokinase 1 is active and this depends on whether or not fructose 2.6 bisphophate is activating it or not- this can only occur if PFK 2 is on and not FBPase 2. then fructose 6 phosphate will participate in glycolysis. Otherwise FBPase2 is on which will result in fructose 6 phosphate going to gluconeogensis because there is no F26BP to activate PFK1

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59
Q

T/F fructose 1,6 bisphophate in involved in allosteric regulation

A

FALSO - fructose 2,6 bisphophate is involved in allosteric regulation

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60
Q

when is there high levels of cAMP? what does this result in?

A

when there is glucagon; protein kinase A activation and thus phosphorylation of the complex resulting in the activation of fructose 2,6 BPase and no PFK2

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61
Q

when are there low levels of cAMP? what does this result in?

A

where there is insulin; low protein kinase A means dePhosphorylation of the complex which results in increased PFK2 which results in more fructose 2,6 bp and thus more PFK1!!

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62
Q

T/F the result of dephosphorylation of PFK2 is activation of PFK1

A

YES! think it through…

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63
Q

T/F the glycerol phosphate shuttle results more energy than the malate aspartate shuttle.

A

FALSO

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64
Q

other than to glycolysis, where does glucose 6 phosphate get used for? ie what other activated carriers transmit its energy?

A

HMP shunt (to NADPH) and glycogenolysis (as glucose 1 phosphate)

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65
Q

other than glycogenesis and glycolysis, what else is Fructose used for?

A

mannose

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66
Q

what is the pyruvate dehydrogenase complex used for? what is produced in that reaction?

A

conversion of pyruvate to Acetyl CoA; acetyl coA, CO2, and NADH (one of each per pyruvate)

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67
Q

how many enzymes does the pyruvate dehydrogenase complex have? and how many cofactors? where is it located? to what enzyme is it similar to?

A

3; 5; mit matrix; alpha ketoglutarate dehydrogenase complex

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68
Q

what are the cofactors required for pyruvate dehydrogenase?

A

TPP (from B1- pyrophosphate), FAD (B2), NADH2 (B3), CoA (B5, panothenate), Lipoic Acid

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69
Q

what inhibits pyruvate dehydrogenase? what activates it?

A

NADH, Acetyl CoA, ATP; NAD+, ADP and Ca2+

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70
Q

in the fasting state, what ensures that the pyruvate doesnt get used for TCA cycle?

A

the products of FA oxidation (Acetyl CoA and NADH) phosphorylate pyruvate deyhdrogenase which inactivates it

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71
Q

how are fa oxidation and gluconeogenesis linked, ie what compound makes sure that they occur together and that glycolysis doesnt occur?

A

acetyl coA and NADH inhibit pyruvate dehyrogenase

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72
Q

T/F Ca2+ is an inhibitor on pyruvate deyhdrogenase

A

False- activator! this links glycolysis with muscle contraction

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73
Q

what is the product of alpha ketoglutarate dehdrogenase?

A

succinyl coA

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74
Q

what does arsenic do? how is this important?

A

inhibits lipoic acid; lipoic acid is a cofactor for pyruvate dehydrogenase

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75
Q

what are the symptoms of arsenic poisoning?

A

vomiting, rice water stools, garlic breath

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76
Q

what is the result of pyruvate dehydrogenase deficiency? what causes it?

A

back up of pyruvate and alanine and thus lactic acidosis occurs; can be d/t alcoholism (vit B1 def)

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77
Q

what are two reasons why pyruvate would be pushed to lactate in an alcoholic?

A

increased NADH causes lactate production and pyruvate dehydrogenase def causes increased lactate (d/t thiamine def that often occurs with alcoholics)

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78
Q

what are the findings in pyruvate dehydrogenase def? how do you treat it

A

neurologic defects, myopathy, lactic acidosis; giving ONLY ketogenic nutrient high fat content and aa (lysine and leucine)

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79
Q

which aa are only ketogenic?

A

lysine and leucine

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80
Q

what are the four fates of pyruvate metabolism?

A

pyruvate to alanine (to carry amino groups to liver), pyruvate to OAA for gluconeogenesis (or replenish for TCA cycle), acetyl coA (for TCA cycle transition or FA or chol. synthesis), or the end of anaerobic glycolysis

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81
Q

where is anaerobic glycolysis used often?

A

RBCs, renal medulla, leukocytes, lens, testes, cornea

82
Q

what is needed for glycolysis to continue? how is this provided in aerobic glycolysis? anaerobic?

A

NAD+; through ETC you produce NAD+; through production of Lactate from pyruvate you create lactate

83
Q

what is the end of anaerobic glycolysis?

A

pyruvate! (not lactate, that is generate just in order to produce more NAD+)

84
Q

what does the TCA cycle produce?

A

3 NADH, 1 FADH2, 2 CO2, 1 GTP = 12 ATP/acetyl CoA

85
Q

what are the key intermediates in the TCA?

A

Citrate, Isocitrate, alpha ketoglutarate, Succinyl CoA, Succinate, Fumarate, Malate, Oxaloacetate

86
Q

Where does NADH2 enter ETC? FADH2

A

Complex I, Complex II (lower energy)

87
Q

What does the passage of electrons in the ETC result in?

A

formation of a proton gradient that is then used to create ATP through ATP synthase

88
Q

what are three ways to poison Ox phos?

A

electron transport inhibitors, ATPase inhibitors, Uncoupling agents (increase permeability of the membrane- loss of hydrogen gradient)

89
Q

What are rotenon, CN, antimycin A, CO?

A

block Electron transport

90
Q

what does oligomycin do?

A

block ATP synthase resulting in no ATP production and an increased proton gradient

91
Q

what are uncoupling agents? what is the result?

A

they increase the permeability of the inner mit membrane resulting in a loss of gradient and loss of ATP production BUT electron transport continues! heat is generated instead

92
Q

T/F O2 consumption stops with uncoupling agents

A

FALSO! because electron transport continues, O2 consumption (last electron acceptor) gets consumed also

93
Q

list three uncoupling agents

A

2,4 dinitrophenol, aspirin, and thermogenin (in brown fat)

94
Q

what are the only substrates for gluconeogenesis? and what products are convertible to it?

A

pyruvate (through OXA); lactate, alanine, malate (and all other TCA intermediates through OXA), glycerol, odd chain fatty acids yield propionyl coA which can be converted to succinyl coA and enter as TCA cycle

95
Q

T/F acetyl coA is a substrate for gluconeogensis

A

FALSE WE CANT USE even chain fatty acids FOR BLOOD GLUCOSE OR ELSE WE WOULD ALL BE ANOREXIC

96
Q

what are the four irreversible enzymes of gluconeogenesis and where in the cell are they found? which is deficient in von gierkes disease?

A

pyruvate carboxylase (pyruvate to OXA) (mit), PEP carboxykinase (OXA to PEP) (cyt), Fructose 1,6 bisphophatase (fructose 1,6 bisphosphate to fructose 6 P) (cyt) and glucose 6 phosphatase (in ER); glucose 6 phosphatase

97
Q

where does gluconeogenesis occur?

A

liver mit and liver cytosol

98
Q

other than Acetyl coA inhibiting pyruvate dehydrogenase complex, how else is it ensured that gluconeogenesis is occuring during FA oxidation and not glycolysis?

A

Acetyl coA activated pyruvate carboxylase in gluconeogenesis

99
Q

what is a positive allosteric regulator on pyruvate carboxylase? for what reaction is this?

A

acetyl coA; gluconeogenesis

100
Q

what two substrates (other than pyruvate) does pyruvate carboxylase require?

A

ATP and biotin

101
Q

what does PEP carboxykinase require? and for what reaction is this?

A

GTP: gluconeogenesis- OXA to phosphoenolpyruvate

102
Q

what regulates Fructose 1,6 bisphosphatase? what reaction is it found in?

A

citrate is positive on it, AMP and fructose 2,6 bisphosphate is negative on it; gluconeogenesis

103
Q

other than in the kidney, where else are gluconeogenesis enzymes found?

A

kidney and intestinal epithelium

104
Q

why cant muscle participate in gluconeogenesis- what key enzyme does it lack?

A

glucose 6 phosphatase

105
Q

T/F all products of fats can not enter gluconeogenesis.

A

False! odd chain fatty acids yield one proprionyl coA which can enter the TCA cycle as succinyl coA (and then to OXA)

106
Q

T/F even chain fatty acids can not produce new glucose since they only yield acetyl coA

A

TRUE

107
Q

what is one steroid that increases gluconeogenesis? what else does cortisol do that yields hyperglycemia?

A

cortisol; inhibits insulin action

108
Q

what is the purpose of HMP shunt?

A

to provide NADPH since there is an abundance of glucose 6 phosphate; also yields ribose for nucleotide synthesis and glycolysis intermediates

109
Q

how many stages are there in HMP shunt? where do they occur? how much energy does HMP shunt use up?

A

2 oxidative and nonoxidative; cytoplasm (both); none (none produced either- you are simply switching carriers of energy- from glucose 6 phosphate to NADPH)

110
Q

where does the HMP (pentose phosphate pathway) occur other than in the liver?

A

lactating mammary glands, adrenal cortex (sites of fatty acid or steroid synthesis), RBCS (for glutathione reduction for FR injury)

111
Q

what enzyme is used in the oxidative phase of HMP shunt? nonoxidative?

A

G6PD dehydrogenase; transketolases

112
Q

how does lactate contribute to gluconeogenesis?

A

gets converted to pyruvate via the Cori cycle in the liver

113
Q

name three glucogenic AA and how they enter gluconeogenesis. through what cycle do they enter gluconeogenesis?

A

alanine (through pyruvate), aspartate (through OXA), glutamate (alpha ketoglutarase); TCA

114
Q

how does glycerol from triacylglycerols in adipose tissue used for gluconeogenesis?

A

gets converted to glycerol 3 P which is then converted to DHAP which then can enter glycolyis

115
Q

T/F glycogen makes up the back wall of triacylglycerol in fat (TG)

A

false! glycerol; glycogen is what glucose is stored as

116
Q

What is the first step in the respiratory burst/oxidative burst? in what disease is this deficient?

A

NADPH oxidase; CGD

117
Q

in what cells does the Respiratory burst occur? where is NADPH located in the cell? what is this reaction important for?

A

Neutrophils and monocytes; membrane bound; immune response by generating Reactive oxygen species

118
Q

what is this reaction dependent on?

A

oxygen!

119
Q

what are the first three enzymes in the first three steps in respiratory burst? where do they occur? what do they result in? what does it do?

A

NADPH oxidase, superoxide dismutase, myeloperoxidase; in the phagolysosome; HOCl (bleach); kills!

120
Q

what are the last three steps of the respiratory burst? why do they need to occur? where do they occur?

A

glutathione peroxidase (catalase) reduces H202 to H20 with glutathione; oxidized glutathione gets reduced by glutathione reductase with NADPH; NAP+ is regenerated to NADPH with Glucose 6 phosphate dehydrogenase; because H2O2 from the resp burts in the phagolysosome- some gets leaked into cell; in the cytosol

121
Q

how do WBCs of CGD patients do some damage?

A

they use the H2O2 produced by some bacteria to produce bleach with myeloperoxidase which they still have

122
Q

What kind of bugs are CGD patients screwed with? why do they call it chronic granulamotous disease?

A

catalase positive because they reduce their H2O2 and WBCs cant use that to make bleach; because the way they protect is by building a wall around the organisms with granulomas

123
Q

what are some catalase positive bugs?

A

s. aureus, Aspergillus

124
Q

other than the H2O2 produced from the resp burst in infections, what other things does G6PD reproduce NADPH for glutathione reduction for? what cells are particularly vulnerable to these oxidizing agents?

A

sulfonamides, primaquine, dapsone, antiTB drugs, fava beans, LDL; RBCs

125
Q

what happens in RBCs after their membranes get oxidized?

A

hemolytic anemia due to heinz bodies which are oxidized hemoglobin precipitating within the RBCs

126
Q

what is the presentation of G6PD deficiency?

A

hemolytic anemia with a blood smear with heinz bodies and bite cells (phagocytic removal of heinz bodies)

127
Q

what is the most common human enzyme deficiency? why? what is the mode of inheritance of this deficiency?

A

G6PD; provides malarial resistance; X linked recessive

128
Q

what are the titles of the two types of fructose disorders? which is more serious>

A

essential fructosuria and fructose intolerance; fructose intolerance

129
Q

T/F fructose disorders are worse than galactose disorders.

A

FALSE

130
Q

T/F galactose can not get inside cells

A

false; fructose cant get inside cells

131
Q

what is the metabolism of fructose?

A

fructose gets phosphorylated into fructose 1-P by fructokinase and then fructose 1P gets metabolized into DHAP or glyceraldehyde by aldolase B

132
Q

what enzyme is deficient in Essential fructosuria? what are the symptoms?

A

fructokinase; benign- fructose in the blood and urine

133
Q

what enzyme is deficient in Fructose intolerance? what is the result of the enzyme def? what are the symptoms?

A

Aldolase B; Fructose 1 phosphate accumulates which uses up Phosphate and the result is inhibition of gluconeogenesis without phosphate; hypoglycemia, jaundice, cirrhosis, vomitting

134
Q

how do you treat fructose intolerance?

A

decrease intake of fructose and sucrose (fructose and glucose)

135
Q

what are the two disorders of galactose metabolism? which is worse?

A

galactokinase deficiency and classic galactosemia; classic galactosemia

136
Q

what is the metabolism of galactose like?

A

galactose gets converted to galactose 1 Phosphate by galactokinase which then gets turned into glucose 1 phosphate by Galactose 1 Uridyl Transferase (GALT) which also produces UDP Gal which is used for lactose production in the breast; the fate of glucose 1 depends on fasting (glycolysis) or fed state (glycogenesis)

137
Q

what tissues contain aldose reductase? what does this enzyme do to what?

A

lens and neural tissue; converts galactose to osmotically active galactitol

138
Q

where does a majority of galactose in our diet come from?

A

lactose (glucose and galactose)

139
Q

what causes cataracts in a galactose metabolism deficiency?

A

aldose reductase in the lens converts built up galactose to galactitol which is osmotically active

140
Q

what enzyme is deficient in galactokinase deficiency? what are the symptoms?

A

galactokinase; galactose appears in blood and urine, sometimes infantile cataracts may present as failure to track objects or lack of a social smile

141
Q

what enzyme is deficient in classic galactosemia? symptoms? treatment?

A

galactose 1 phosphate uridyltransferase (GALT) results in an accumulation of toxic substances; failure to thrive, jaundice, hepatomegaly, infantile cataracts, mental retardation; exclude galactose and lactose from diet

142
Q

why does galactose def present in newborns>

A

lactose in mothers milk contains galactose

143
Q

what is another way to trap glucose in cells but not by phosphorylating it? what enzymes are used?

A

by turning it into fructose, but sorbitol first; glucose to sorbitol via aldose reductase and sorbitol to fructose sorbital dehydrogenase

144
Q

in what tissues can sorbitol accumulate? why?

A

schwann cells, lens, retina, kidneys because they only have aldose reductase and no sorbital dehydrogenase

145
Q

what is osmotic damage and what molecules cause it? give some examples of osmotic damage- in what disease state do you see these?

A

when water is pulled in; polyols (sugar alcohols); cataracts, retinopathy, peripheral neuropathy all seen in chronic hyperglycemia in diabetes

146
Q

T/F osmotic damage can not occur in the blood

A

false- high blood levels of fructose, galactose, glucose can result in conversion to osmotically active alcohol forms by aldose reductase!

147
Q

what is the result of lactase deficiency? in what nationalities is it seen the most?

A

lack of lactase (brush border enzyme) so can not break down lactose (a dissaccharide of galactose and glucose); African Americans and Asians

148
Q

what are the symptoms involved in lactase deficiency?

A

osmotic diarrhea, bloating, cramps

149
Q

what is unique about the diarrhea in lactase deficiency?

A

bacteria produce lactate acid and gases from lactose and produce acidic diarrhea and bloating

150
Q

other than being hereditary, what are two other ways you can have a lack of brush border enzymes?

A

following gastroenteritis and kwashiokor (protein deficiency)

151
Q

T/F amino acids are found in both L and D forms

A

false- only L form

152
Q

what are the ketogenic amino acids?

A

leucine and lysine

153
Q

what are the glucogenic amino acids?

A

met, arg, val, his

154
Q

what are the glucogenic and ketogenic amino acids?

A

Ile, Phe, Thr, Trp

155
Q

which amino acids are acidic? are they negatively or positively charged at body pH?

A

asp and glu; negatively

156
Q

which amino acids are basic? are they negatively or positively charged at body pH?

A

arg, lys, his; positive except His has no charge at body pH

157
Q

which amino acid is the most basic?

A

arg

158
Q

which amino acids makes up histones?

A

lys and arg

159
Q

which amino acids are required during periods of growth?

A

arg and his

160
Q

what happens in an aminotransferase reaction

A

an aminotransferase enzyme transfers an amino group from an amino acid on to alpha ketoglutarate making it a glutamate (to join the urea cycle or excreted in the kidney) and the amino acid that lost the amino group is then turned into a glycolytic intermediate (pyruvate or oxaloacetate!)

161
Q

how are nonessential amino acids made?

A

…

162
Q

what are the two most common aminotransferase and what amino acids do they turn to what glycolytic intermediates?

A

alanine aminotransferase (ALT) and aspartate aminotransferase (AST); alanine to pyruvate and aspartate to oxaxloacetate

163
Q

where do aminotransferase reactions occur? and what vitamin cofactor do they require?

A

in hepatocytes; B6

164
Q

how is excess nitrogen taken care of?

A

excreted from the kidney in the form of urea in hepatocytes

165
Q

how is urea measured

A

as BUN (blood urea nitrogen)

166
Q

which are the mitochondrial reactions of the urea cycle?

A

carbomyl phosphate synthetase I turns N acetyl glutamate into carbomyl phosphate and then ornithine transcarbomyalse turns carbomyl phosphate into citrulline (using ornithine)

167
Q

which is the rate limiting step of the urea cycle?

A

carbomyl phoshpate synthetase I

168
Q

what two compounds provide the two N’s of urea? what else is in urea other than two NH2’s?

A

glutamate and aspartate; CO2 provides an ketone

169
Q

after citrulline is produced and in the cytoplasm what happens next in the urea cycle?

A

citrulline is combined with aspartate to make arginosuccinate which is then split into fumarate (which leaves to enter TCA) and arginine. Arginine is then converted to Ornithine (via arginase) giving off Urea which then goes to the kidney and ornithine reenters the urea cycle (combined with carbomyl phosphate to make citrulline)

170
Q

what is the most common disorder of the urea cycle? what is the result? what is its mode of inheritance? what is the mode of inheritance of the other urea cycle enzyme def?

A

ornithine transcarbomyalse; orotic aciduria; X linked recessive; autosomal recessive

171
Q

how is the nitrogen of amino acids transferred to the liver for the urea cycle? explain this process.

A

as alanine; amino acids donate their amino group to alpha ketoglutarate making it glutamate and the aa then becomes an alpha ketoacid (joins TCA cycle); glutamate then converts pyruvate to alanine by donating its amino group to pyruvate (with ALT); alanine then travels through the blood and in the liver gets reconverted back to pyruvate (gluconeogenesis) while giving its amino group to an alpha ketoglutarate which makes glutamate which then joins the urea cycle

172
Q

what is the primary source of nitrogen in the urea cycle

A

glutamate

173
Q

T/F all glutamate goes to liver to be turned into urea

A

false; goes to kidney and ammonia is used as a buffer in urine

174
Q

how can hyperammonia be hereditary? acquired?

A

urea cycle enzyme deficiency (mc: ornithine transcarbamoylase); liver disease- alcoholic cirrhosis and reye’s

175
Q

what does the excess NH4+ in hyperammonia eat up? what is the result?

A

alpha ketoglutarate; no TCA cycle intermediates

176
Q

what is the treatment of hyperammonia?

A

limit protein in diet; give benzoate or phenylbutyrate which bind amino acids and lead to excretion, lactulose (hydrogen ion binds to ammonia to make excretable ammonium) and neomycin (to kill bacteria that release ammonia from aa)

177
Q

what are the clinical symptoms of hyperammonemia?

A

tremor (asterixis), slurring of speech, decrease temperature, somnolence, vomitting, cerebral edema, blurring of vision, neural focal deficits

178
Q

what is the result of arginase deficiency?

A

chorea and spastic paresis

179
Q

what are the lab findings see in hyperammonemia?

A

increased blood levels of ammonia, decreased BUN

180
Q

what are the findings in ornthinie transcarbamoylase?

A

orotic acid in blood and urine (from pyrimidine synthesis), decreased BUN, and symptoms of hyperammonemia

181
Q

what aa does tyrosine come from?

A

phenylaline

182
Q

from what aa does dopa come from?

A

tyrosine

183
Q

what converts dopa into melanin?

A

tyrosinase

184
Q

from what aa does thyroxine come from?

A

tyrosine

185
Q

from what aa do the catecholamines come from? and what aa does that aa come from?

A

tyrosine; phenylaline

186
Q

what aa does melanin come from? melatonin?

A

tyrosine; tryptophan

187
Q

from what aa does niacin come from? with what vitamin cofactor?

A

tryptophan; B6

188
Q

from what aa do NAD+ and NADP+ come from?

A

tryptophan

189
Q

from what aa does serotonin come from? what NT is serotonin a precursor for?

A

tryptophan; melatonin

190
Q

from what aa does histamine come from? with what vitamin cofactors help?

A

histidine; B6

191
Q

from what aa does porphyrin come from? what is porphyrin the precursor of?

A

glycine; heme

192
Q

for what three enzymes is arginine a precursor for?

A

Nitric Oxide, creatinine, Urea

193
Q

what aa (other than glutamate) is a precursor for urea?

A

arginine

194
Q

what aa is the precursor for NO?

A

arginine

195
Q

what aa is the precursor for creatinine?

A

arginne

196
Q

from what aa does glutathione come from?

A

glutamate

197
Q

from what aa does GABA come from? with what enzyme? and what vit cofactor? what does GABA stand for?

A

glutamate; glutamate decarboxylase; B6; gamma aminobutyrate

198
Q

what are the three branched aa?

A

isoleucine, valine, leucine

199
Q

what enzyme is deficient in maple syrup disease? what does it result in?

A

branched chain alpha keto acid dehydrogenase; inability to break down branched chain aa

200
Q

what aa is the ultimate precursor of catecholamine synthesis?

A

phenylalanine

USMLE1 - Biochemistry (6 decks)

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