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x M1 Biochem Quiz 4 > Lectures 43-63 > Flashcards

Lectures 43-63 Flashcards

1
Q

describe the structure of a phophyrin ring

A

4 pyrrole (5-C) rings, large conjugated ring connecting all pyrroles, pocket in center surrounded by N. asymmetrical side chains coming off pyrrole rings

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2
Q

what is the most impt porphyrin?

A

heme

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3
Q

what is the chemical importance of the Nā€™s inside the pocket area?

A

negatively-charged binding pocket, able to bind a metal ion with 2+ charge

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4
Q

besides heme, what are some other porphyrins?

A
  • cobalamin (aka Vit B12) which has Co2+ in center

- chlorophyll (plants only, Mg2+ in center)

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5
Q

what are 4 physiological roles of heme?

A
  1. Electron transport chain
  2. oxygen transport in blood and muscle
  3. drug metabolism via cytochrome P450
  4. removal of H2O2 via catalase
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6
Q

what are the 2 precursors for heme synthesis?

A

Succinyl CoA (TCA precursor) and glycine (AA)

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7
Q

what exactly is heme?

A

porphyrin ring with Fe2+ ion in the center

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8
Q

what is the main feedback for heme synthesis?

A

the product (heme) inhibits the first reaction. synthesis is under ā€˜product feedback controlā€™

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9
Q

are there different isozymes for heme?

A

yes ā€“ different versions of the enzyme exist in liver and blood

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10
Q

what is the first step in heme synthesis? whatā€™s the enzyme?

A

succinyl CoA + glycine -> ALA. enzyme = ALA synthase

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11
Q

what is the committed step and the primary rate-limiting step for heme synthesis?

A

the first step, catalyzed by ALA synthase

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12
Q

what is the second rate-limiting step for heme synthesis?

A

the step where 4 PBGs are attached into an almost-ring structure: enzyme = hydroxymethylbilane synthase

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13
Q

what is unique about the structure of porphyrins that gives them interesting appearance?

A

a lot of conjugated double bonds -> purple color and fluoroscent

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14
Q

what is it called when a metal ion is added to a porphyrin ring?

A

chelation.

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15
Q

what are the sx of Acute Intermittent Porphyria?

A

abdominal pain, psychotic symptoms

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16
Q

what is the cause of AIP? (what enzyme is deficient)?

A

LIVER hydroxymethylbilane synthase (second rate-limiting enzyme in heme synthesis pw).

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17
Q

in AIP, is there increased or decreased heme? increased or decreased ALA?

A
  • heme: decreased due to decreased flow through the pathway.
  • ALA: increased because of decreased repression of pw by heme, and because there are no other metabolic pathways for ALA
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18
Q

what are inducers of CYP? how are they relevant to AIP and other porphyrin diseases?

A

inducers are alcohol/drug use (probably other things) that require heme products to metabolize them. uses up heme, result is less heme, less pathway inhibition, greater ALA buildup

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19
Q

why does AIP cause psych symptoms?

A

the structure of the ALA molecule (remember there is a buildup of ALA with AIP) is very similar to GABA. ALA antagonizes GABA by binding to its normal receptors, so you lose GABA activity (ie you lose inhibition)

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20
Q

how would you test for AIP?

A

urine test for PBG, PCR test for gene mutation

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21
Q

prevention and treatment for AIP?

A
  • prevention: avoid inducers that use CYP and make things worse by further decreasing heme levels
  • treatment use hemin (heme derivative) or glucose to inhibit ALA synthase
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22
Q

what is the major distinction between acute and chronic porphyria?

A

where the blockage in the pathway is: with AIP, its at the 2nd regulatory step. with chronic, itā€™s later on, at the second to last step.

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23
Q

AIP: genetic or acquired?
PCT: genetic or acquired?

A

AIP: genetic
PCT: acquired/induced

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24
Q

what is PCT?

A

one of the most common chronic porphyrias. Porphyria Cutanea Tarda

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25
Q

what are some of the behaviors associated with PCT?

A

EtOH abuse, steroids: damage to liver cells

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26
Q

what is the status of heme levels with PCT?

A

normal, because there is both increased flux through the pathway (raising heme) and increased diversion of intermediates to side pathways

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27
Q

what is the dx for PCT? what about treatment?

A

dx: increased urine uroporphyrins (substrate prior to mutated enzyme step)
tx: periodic phlebotomy to remove heme

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28
Q

what is the chemical cause of the symptoms of lead poisoning?

A

lead inhibits the biosynthesis of porphyrins at 2 places in the pw (and in both liver and blood). because of the locations in the pw that are affected, the sx look like AIP.

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29
Q

what part of the pathway is affected by iron deficiency?

A

reduces levels of ALA synthase in blood cells

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30
Q

what are sx of iron deficiency anemia?

A

fatigue, pale thin-rimmed RBCs on blood smear

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31
Q

how does iron deficiency reduce levels of ALA synthase?

A

Fe2+ needed to bind to Iron Repression Protein (on mRNA, blocks translation) to remove it and allow translation. No iron -> IRP sits on mRNA and is not translated. note this control is present on erythrocytes only

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32
Q

what is notable about the degradation of heme?

A

it is colorful ā€“ the various intermediates are different colors. also, it takes place in several different organs

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33
Q

in which organ is bilirubin conjugated?

A

in the liver

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34
Q

what is the general process of degradation of heme?

A

heme -> biliverdin -> bilirubin -> conjugated bilirubin -> urobilinogen -> stercobilin and urobilin

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35
Q

why are bruises different colors?

A

initially they are red (pure heme of RBCs). then macrophages enter the scene and begin at the periphery to remove heme. as macrophages digest heme, heme goes through several different oxidation states and changes color

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36
Q

which is water soluble, conjugated or unconjugated bilirubin?

A

conjugated. is conjugated in the liver, then able to be excreted via urine/feces

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37
Q

jaundice is a sign of what?

A

excess bilirubin in blood

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38
Q

is the presence of jaundice a problem?

A

no, it indicates that there is a problem somewhere

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39
Q

if a patient has jaundice, how will we know if the problem is over production or under degradation?

A

by the amounts of unconjugated v conjugated bili in the blood

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40
Q

very high amounts of unconjugated bili indicates that the problem is what?

A

hemolytic, ie sickle cell anemia or thalessemia. ie, the problem is prior to liver/conjugation

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41
Q

very high amounts of conjugated bili indicates what?

A

obstructive jaundice, ie gallstones. ie problem is after liver/conjugation

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42
Q

if there are increased levels of both conjugated and unconjugated bili, where is the problem likely to be? what kind of disease could cause that?

A

problem is likely in the liver (where conjugation occurs). disease: viral hepatitis.

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43
Q

what is the problem with neonatal jaundice of premature babies?

A

underdeveloped enzyme that converts bilirubin to conjugated bilirubin. that enzyme doesnā€™t typically develop until full-term. therefore will see increased unconjugated bili

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44
Q

How are vitamins classified?

A

by their solubility in water vs fat.

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45
Q

what are some general qualities of water-soluble vitamins?

A

they are usually cofactors in metabolic reactions, they are found in plants, they are usually low body stores and deficiencies appear in weeks. because they are water-soluble, they are easily excreted in urine, hence the low body stores

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46
Q

what is Wernickeā€™s syndrome? what does it progress to?

A

brain disorder due to insufficient thiamine. Progresses to Korsakoff.

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47
Q

what reactions (generally) is thiamine a cofactor for?

A

cofactor for carbohydrate-metabolizing reactions.

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48
Q

in an alcoholic patient with low blood sugar, what should you always administer along with glucose?

A

thiamine

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49
Q

in the developing world, what manifestation of thiamine deficiency are you more likely to see?

A

Beri-beri

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50
Q

is Korsakoffā€™s sx reversible?

A

no. Korsakoffā€™s is end-stage Wernicke

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51
Q

what combination of sx suggests beriberi?

A

peripheral neuropathy and high-output heart failure (ie, heart is moving blood too quickly for body to keep up)

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52
Q

what are clinical manifestations of riboflavin deficiency?

A

angular fissures (mouth), dry skin, smooth, purple tongue

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53
Q

riboflavin is a precursor to what impt coenzymes?

A

FAD, FADH

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54
Q

niacin is a precursor to what impt coenzymes?

A

NAD, NADP

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55
Q

why is niacin an essential vitamin if we can synthesize it ourselves?

A

the pathway for synthesis (tryptophan -> niacin) is not efficient

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56
Q

what are the sx of a niacin deficiency?

A

the 4 Ds: dermatitis, diarrhea, dementia, death.

possibly due to poor nutrition (not consuming either niacin or its precursor, tryptophan).

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57
Q

What vitamin is a component of Coenzyme A?

A

Pantothenic Acid

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58
Q

what is a cofactor for enzymes that metabolize amino acids?

A

pyridoxine (B6)

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59
Q

what drug is a molecular antagonist of pyridoxine?

A

isoniazid (TB medication)

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60
Q

what vitamin binds tightly to raw eggs?

A

Biotin (B7)

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61
Q

what vitamin is involved in carboxylation reactions?

A

Biotin (B7)

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62
Q

what vitamin is critical for synthesis of purines, thymidine, and amino acids?

A

folate

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63
Q

what is the form of folate that is used in one-carbon metabolism?

A

THF

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64
Q

why is folate important during pregnancy?

A

essential for cell division, since it helps synthesize purines/thymidine

65
Q

what does methotrexate do?

A

blocks the conversion of folate to THF, blocks DNA synthesis in rapidly-dividing cells (ex cancer, hair)

66
Q

how is B12 (cobalamin) an exception to the general qualities of water-soluble vitamins?

A

only water-soluble vitamin not found in plants, body stores exceed several weeks (stores actually last several years)

67
Q

B12 is a precursor of 2 different coenzymes: where are they located? what processes are the enzymes involved in?

A

blood cells and neurons. involved in DNA/AA synthesis (folate trap) and metabolizing FAs.

68
Q

deficiencies of what 2 things can cause megaloblastic anemia?

A

folate and B12.

69
Q

symptoms of fatigue, megaloblastic anemia, and decr sensation in feet suggest what?

A

pernicious anemia

70
Q

what is pernicious anemia?

A

autoimmune disorder. destruction of parietal cells means loss of intrinsic factor (made by those cells) which leads to inability to absorb B12 through gut.

71
Q

why does the sx of decreased vibratory sense in the feet suggest B12 defiency rather than folate?

A

folate def does not present in neurons.

72
Q

what is the argument against fortifying certain foods with folate?

A

folate supplementation may mask a deficiency of B12 (the dx used to be megaloblastic anemia), since they are both involved in the reaction in RBCs. But B12 deficiency is harder to diagnose (involves lack of sensation on feet due to nerve degeneration) yet is irreversible

73
Q

what is the tx for B12 deficiency, if the cause is due to pernicious anemia?

A

since pt canā€™t bring in B12 via GI, give IM B12

74
Q

what is Vitamin C required for?

A

connective tissue: promotes cross-linking in collagen

75
Q

some sx of Vit C deficiency?

A

hemorrhaging around hair follicles (due to connective tissue loss), swelling/bleeding of gums

76
Q

a few generalizations abour fat-soluble vitamins?

A

body stores last for months, stored in adipose tissues, possible to have a toxic dose, deficiencies seen in patients with fat malabsorption disorders

77
Q

what are the 3 impt forms of Vitamin A? what are their functions?

A

Retinol: required for reproduction
Retinoic Acid: differentiation of epithelial cells, teratogenic
11-cis-retonol: visual pigment rhodopsin

78
Q

what is the major cause of blindness worldwide? what is a symptom indicating early deficiency?

A

Vit A deficiency. presents first as night blindness, then with dry eyes, Bitotā€™s spots.

79
Q

what are symptoms of an overdose of Vit A?

A

dry skin liver damage, raised intracranial pressure

80
Q

what are sx of thiamine deficiency?

A

impaired eye movements, impaired motor coordination

81
Q

in what dietary sources is Vitamin D found?

A

D2 is found in plants (we convert to D3). D3 found in animal sources.

82
Q

what does Vit D do?

A

is converted to calcitriol, increases Ca2+ absorption in the intestine.

83
Q

what is the likely clinical profile of a Vit D deficient pt?

A

lactose intolerant, lack of sun (or wears burka, has a lot of melanin), may have bone microfractures

84
Q

what is a result of deficient Vit D in adults? kids?

A

adults: osteomalacia. kids: ricketts

85
Q

what overall process is Vit K involved in?

A

clotting cascade (K: german word = Klotting)

86
Q

what is Vit Kā€™s involvement in the clotting cascade?

A

adds - charges to glutamate, causes it to locate to cell membrane of platelets, where clotting will occur

87
Q

where is Vit K produced?

A

by the endogenous intestinal bacteria

88
Q

why might newborns have trouble with clotting?

A

if sterile gut (common) gut bacteria wonā€™t yet be making Vit K. see this effect via elevated PTT.

89
Q

deficiency of Vit K leads to what?

A

hemorrhage.

90
Q

what is a drug that counters the effects of Vit K?

A

Coumadin/warfarin

91
Q

the fenestrated epithelium of the liver allows passage of what?

A

proteins, lipoproteins, and chylomicron remnants

92
Q

what is unique about the parenchymal cells of the liver and how they have various functions?

A

liver cells are zonated based on proximity to portal input (periportal) or portal vein (perivenous)

93
Q

what are the 6 major functions of the liver?

A
  1. maintain blood glucose levels
  2. nitrogen metabolism
  3. lipid metabolism
  4. bile secretion/circulation
  5. processing/excreting bilirubin
  6. oxidizing lipid-soluble substances (via CYPs)
94
Q

does insulin affect glucose transport in the liver?

A

no, gluc transport is high in all directions, all the time

95
Q

what are the general effects of insulin in the liver?

A
  • stimulation of protein synthesis & glycogen synthesis

- inhibition of protein degradation, gluconeogenesis, lipogenesis (??)

96
Q

does liver contain hexokinase? glucokinse?

A

yes ā€“ both

97
Q

what do hexokinase/glucokinase do?

A

phosphorylate glucose for use in TCA or lipogenesis

98
Q

what happens to glucokinase during starvation?

A

it is repressed (makes sense because glucokinase phosphorylates glucose for use in glycolysis or lipogenesis)??

99
Q

in what food is galactose found?

A

milk

100
Q

what 3 enzymes are required for metabolism of galactose?

A
  1. galactose kinase (to phosphorylate galactose)
  2. P-galactose uridyltransferase (to change galactose-1P to glucose-1P)
  3. UDP galactose epimerase (UDP-galactose to UDP glucose)
101
Q

what is a generality about disorders of conversion of sugars to glucose?

A

worse to have a deficiency/mutation of the second enzyme of a pathway that the first, due to the accumulation of toxic intermediates

102
Q

what are the 2 possible pathways for fructose to join glycolysis?

A
  1. hexokinase phosphorylates fructose to fructose-6P (intermediate in glycolysis)
  2. fructokinase phosphorylates fructose to fructose-1P, and then fructose-1P aldolase turns it to glyceraldehyde, which can join glycolysis as glyceraldehyde-3P
103
Q

of the 2 enzymes involved in fructose uptake, which is rate-limiting?

A

fructose-1P aldolase is rate limiting. so a mutation of this enzyme can lead to fructose poisoning (too much fructose -1P is toxic to the liver)

104
Q

what are the 3 precursors for gluconeogenesis?

A

lactate, amino acids, glycerol

105
Q

gluconeogenesis from amino acids is increased under what conditions?

A

starvation or a protein-rich meal

106
Q

7 enzymes critical to gluconeogenesis?

A
  1. alanine aminotransferase (AA to pyruvate)
  2. lactic dehydrogenase (lactate to pyruvate)
  3. pyruvate carboxylase
  4. malate dehydrogenase (mito)
  5. malate dehydrogenase (cyto)
  6. PEP carboxykinase
  7. fructose 1,6 bisphosphatase
107
Q

gluconeogenesis depends on the availability of NAD (which NAD?)

A

cytosolic NAD that is a cofactor in malate -> oxaloacetate

108
Q

why will a combination of starvation and ethanol lead to hypoglycemia?

A

gluconeogenesis and ethanol metabolism compete for the same cytosolic NAD cofactor. ethanol therefore inhibits liver gluconeogenesis

109
Q

increase urea synthesis results from what?

A

incr supply of AAs to liver, from diet or muscle degradation

110
Q

over days of starvation or protein-rich diet, how does the liver adapt?

A

upregulation of all urea cycle enzymes

111
Q

what is the problem with having high blood NH3?

A

toxic to the brain!

112
Q

what tissues donā€™t use FA for energy?

A

brain and RBCs

113
Q

what organ uses FA almost exclusively as an energy source?

A

liver

114
Q

can hepatocytes oxidize ketone bodies?

A

no, can synthesize them but not oxidize

115
Q

what promotes ketogenesis in starvation?

A

in adipocytes, promoted by cAMP

in hepatocytes, promoted by inhibition of ACC, lower malonyl CoA, and increased carnitine-linked transport of FAs

116
Q

what effect does citrate have on the activity of ACC? insulin? glucagon?

A

citrate: increase
insulin: increase
glucagon: decrease

117
Q

what are a few conditions that could lead to the accumulation of hepatic triglycerides (fatty liver)?

A

excessive FFA uptake, excessive lipogenesis, decreased FA oxidation, impaired synthesis of VLDL (due to drugs, liver failure, choline deficiency)

118
Q

where is bile synthesized and stored?

A

synth in liver, stored in gallbladder

119
Q

in what organ is heme degraded to bilirubin?

A

spleen (macrophages)

120
Q

how is bilirubin transported in the plasma?

A

bound to serum albumin

121
Q

in what types of jaundice do fecal pigments tend to increase?

A

hemolytic. ie, sickle cell anemia, thalessemia. because of increased flux through bilirubin degradation pathway

122
Q

in what types of jaundice to fecal pigments tend to decrease?

A

hepatocellular (ie, liver damage maybe due to hepatitis) and obstructive (ie due to gallstones). also due to neonatal jaundice, because of decr flow through the bili degradation pw

123
Q

what do CYPs do?

A

metabolize drugs and hormones. in most cases this involves inactivation by hydroxylation (makes them soluble, can be excreted). use O2 and Fe2+. there are dozens of them, each broadly specific for different substrates.

124
Q

what is the structure of a CYP?

A

stands for cytochrome P450. heme-containing, with a reactive Fe2+ in the heme pocket.

125
Q

what functions use up about 90% of muscle energy?

A

Ca2+ pump and myosin ATPase

126
Q

what are the type of energy stores in muscle fibers?

A

lipid droplets and glycogen granules

127
Q

which type of muscle filament is the one with the moving flippers? which is thicker?

A

myosin: both flippers and thicker. actin has the tropomyosin wrapping around it, and the troponin complex (T, I, C)

128
Q

what are the characteristics of Type I muscle?

A

slow twitch. aerobic. high vascularization, lots of mitochondria (for more oxidative phos (ETC), beta-oxidation), higher intramuscular triglyceride, higher LPL

129
Q

what are the characteristics of Type II muscle?

A

fast twitch. anaerobic. low vascularization, fewer mitochondria, high conc of glycolytic enzymes, major source of energy is glycogen, not TGs

130
Q

what are the characteristics of cardiac muscle?

A

lots of mitos. lots of blood supply, rarely goes anoxic. little glycogen, low capacity for glycolysis, oxidizes both FA and lactate well.

131
Q

what are the 2 major fuel sources to the heart?

A

Fatty acids, lactate

132
Q

can the heart work anaerobically?

A

no, both FAs and lactate require O2 to be metabolized

133
Q

can ATP be transported through the blood?

A

NO!

134
Q

what are the 7 sources of ATP for muscle?

A
  1. glucose catabolism (anaerobic to lactate, or aerobic to CO2)
  2. glycogen
  3. FA catabolism (b-oxidation)
  4. ketone catabolism
  5. AA catabolism
  6. creatine phosphate
  7. ADP conversion through adenylate kinase (ADP + ADP -> ATP + AMP)
135
Q

for those 7 sources of ATP for muscle, where does each come from?

A
  1. glucose (blood/liver)
  2. glycogen (local)
  3. FA (local, adipose)
  4. ketone catabolism (liver)
  5. AA catabolism (blood, liver)
  6. creatine phosphate (local)
  7. ADP (local)
136
Q

what is the deal with creatine phosphate as an energy source (aka phosphocreatine)?

A

when plenty of ATP available, phosphorylate creatine to store energy as phosphocreatine. energy source that can be activated very quickly.

137
Q

describe the Cori Cycle. how many ATP are needed, and how many are generated?

A

muscle uses glucose, turns to lactate and gains 2 ATP. lactate moves to liver via blood. liver returns lactate to glucose, using 6ATP. glucose then travels back to muscle via blood

138
Q

what energy sources does the brain use?

A

ketones, glucose. both from liver

139
Q

why will we see the effects of hypoglycemia in brain before muscles?

A

because muscles can burn FAs, and brain relies strongly on glucose for energy.

140
Q

what are the relative rates at which fatty acids and glucose are able to provide energy?

A

FAs are a lot slower; unable to provide sufficient energy at high intensity

141
Q

muscle: endogenous fuel sources

A

glycogen, triglyceride, phosphocreatine, AMP

142
Q

muscle: exogenous fuel sources

A

glucose (liver), FAs (adipose), ketone (liver), AAs (diet)

143
Q

what are the enzymes that mobilize local ATP availability?

A

creatine kinase (phosphocreatines) and adenylate kinase (AMP)

144
Q

what is a key metabolic difference between heart muscle and skeletal? what accounts for this difference?

A

heart muscle can use lactate for energy during exercise (skel cannot). reason: heart has a special isozyme of lactate dehydrogenase that promotes quick conversion from lactate to pyruvate

145
Q

resting muscle burns mostly what?

A

fatty acid

146
Q

what is the general trend of fuel source at low intensity and high intensity?

A

low: mostly fatty acids
high: glucose oxidation becomes more impt

147
Q

metabolically, what does it mean to hit the wall?

A

means that your muscles ran out of glycogen, and CAT I cannot keep up with FA demand of muscles. CAT I = rate limiting step, will become saturated.

148
Q

in muscle, what is the function of malonyl-CoA?

A

used as a switching mechanism between use of glucose and use of FAs

149
Q

if malonyl-CoA is high in muscle, what is the effect on FA oxidation?

A

high malonyl-CoA means less CAT-1 activity, means less FAs brought to mito matrix, less FA oxidation

150
Q

in muscle, what is the direct effect of Malonyl-CoA?

A

inhibits CAT-1

151
Q

what is the effect of insulin on Malonyl-CoA?

A

insulin upregulates ACC which makes more Malonyl CoA, which inhibits CAT-1

152
Q

what is an insulin-independent way to increase FA oxidation?

A

Exercise. 2 ADPs are reconfigured via adenylate kinase to AMP and ATP. The AMP decr ACC activity (phosphorylates it), less malonyl-CoA, CAT-1 is activated, FAs are oxidized

153
Q

what is the best way to avoid hitting the wall?

A

have fully-stored glycogen in muscle, and become more efficient at using IMTG (intra-muscular triglyceride)

154
Q

what are the 4 supplies of ATP for a sprint?

A

phosphocreatine, adenylate kinase, glycolysis, increased glycolytic flux

155
Q

during the first 10 secs of a sprint, what energy sources are used?

A

ATP (1 sec), phosphocreatine (4 secs), then glycolysis

156
Q

what happens to ATP levels during a 10 sec sprint? what about levels of phosphocreatine?

A

ATP is steady. phosphocreatine decreases rapidly (being used quickly)

157
Q

what is unusual about muscle glycogenolysis?

A

muscle can perform rapid glycogenolysis, skipping a few steps via Ca2+ (rather than using the GCPR in the membrane). This Ca2+ allows quick contraction of fibers via myosin, and also activates glycogen phosphorylase ā€“> glycolysis

158
Q

how would s sprint increase flux through the glycolytic pathway?

A

there are activators of PFK created in the first 5 secs of a sprint (AMP, phosphate, ammonia). also, after about 5 secs, there is a fall in the levels of PFK inhibitors (ATP, phosphocreatinine)

159
Q

what are 2 ways to increase the number of GLUT 4 receptors on a muscle cell?

A

insulin, and AMP

x M1 Biochem Quiz 4 (1 decks)

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