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Medical Biochemistry > Exam II > Flashcards

Exam II Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the name of Complex I? What reactions happen there? What is the net equation?

A 
Complex I is NADH-Q oxidoreductase/NADH dehydrogenase
There are three reactions:
Rx 1: oxidation NADH
Rx 2. Reduction of coenzyme Q
Rx 3: proton pumping

Net reaction:
NADH + Q + 5H+ (matrix)&raquo_space; NAD+ + QH2 + 4H+ (cytosol)

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2
Q

What is the name of complex II? What is the net reaction?

A

Complex II is Succinate dehydrogenase or succinate-Q reductase complex

Net reaction:
succinate + Q&raquo_space;> fumarate + QH2 (without proton pumping)

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3
Q

What is the name of Complex III? What are its prosthetic groups? What are its P site and N site?

A

Complex III is CoQ-cytochrome c oxidoreductase or cytochrome b-c1 reductase

Heme c1, bL, bH, Reiske Iron-sulfur center

Positive site is where electron goes to reduce cytochrome c. Negative site is where electron forms radical.

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4
Q

What is the net reaction of the Q cycle of Complex III?

A

QH2 + 2 Cyt (ox) + 2H+ (matrix)&raquo_space; Q + 2 Cyt c (red) + 4H+ (cytosol) (four protons are pumped out)

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5
Q

What is the name of complex IV? what does it do

A

Complex IV is cytochrome c oxidase or cytochrome oxidase. It transfers electrons to oxygen molecule from cytochrome C, which carries only one electron.

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6
Q

What is the net reaction of complex IV? Per NADH?

A

Net reaction:
4 cyt c (reduced) + O2 + 8H+&raquo_space; 4 cyt c (oxidized) + H2O + 4 H+ (cytosol)

per NADH, however, since cyt is a one electron carrier and we needed four, and each NADH only carries two electrons, we pump 2 H+ into cytosol.

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7
Q

Summary of ETC reaction for NADH

A

NADH + 11 H+ (m) + 1/2 O2&raquo_space; NAD+ + H2O + 10H+ (c)

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8
Q

Summary of ETC reaction for FADH2

A

FADH2 + 6 H+(m) + 1/2 O2&raquo_space; FAD + H2O + 6H+ (c)

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9
Q

What are inhibitors of Complex I (3)?

A

Amytal, barbiturate
Rotenone, insecticide, pesticide and piscicide
MPP+, neurotoxic drug metabolite from MPPP
(ARM)

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10
Q

What is an inhibitor of Complex II?

A

Malonate, a competitive inhibitor of Complex II, from alfalfa leaves (melon)

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11
Q

What is an inhibitor of Complex III?

A

Antimycin A, produced by strep bacteria, binds to N site of Complex III (ANT)

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12
Q

What are inhibitors of Complex IV? (3)

A

cyanide, azide, carbon monoxide (Coconut)

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13
Q

disease caused by mutation to complex I?

A

LHON (blindness), Leigh Syndrome (impaired motor skills), MELAS

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14
Q

disease caused by mutation to complex II?

A

Leigh Syndrome

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15
Q

disease caused by mutation to complex III?

A

LHON, Encephalomyopathy

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16
Q

disease caused by mutation to complex IV?

A

encephalomyopathy, myopathy (muscle dysfunction)

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17
Q

delta G of oxidation of NADH?

A

-52.6 kcal/mol

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18
Q

What is the relationship between Gibbs Free Energy Change and the proton motive force?

A

proton motive force (deltaP) = deltaG/nF

The more deltaG, the more deltaP

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19
Q

What are four inhibitors of ATP synthase? How do they work?

A

oligomycin - binds to Fo, blocking protons from coming in
Aurovertin B - binds to Beta subunit, inhibits conformational change
DCCD - modifies carboxyl groups in protein
IF-1 - (upon onset of myocardial ischemic process) (stroke), what happens is the proton gradient has been flipped, so ATPase will now want hydrolyze ATP. IF-1 binds to the alpha, beta and gamma proteins of F1, preventing their conformation change. This is all under low oxygen conditions.

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20
Q

What are the four carriers of inner membrane of mitochondria? What do they transport?

A

ATP-ADP translocase (ANT) - ADP into m, ATP into c
Dicarboxylate carrier - Phosphate/Malate
Tricarboxylate carrier - Malate/Citrate + H+
Phosphate carrier - Phosphate/ OH-

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21
Q

What blocks the ATP/ADP exchange, inhibiting ATP/ADP exchange?

A

atractyloside and bonkrekic acid

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22
Q

How many cytosolic ATPs are produced per oxidation of 1 matrix NADH?

A

~2.5 cytoplasmic ATPs

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23
Q

How many cytosolic ATPs are produced per oxidation of 1 matrix NADH?

A

~1.5 ATPs

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24
Q

How does NADH from cytosol get into mitochondrial matrix of heart and liver cells? How many ATPs does it yield?

A

malate-aspartate shuttle

P/O ratio is ~ 2.5 ATPs

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25
Q

How does NADH from cytosol get into mito matrix of cells other than heart and liver? What is important about this carrier yield wise?

A

glycerol-3-phosphate shuttle
P/O = 1.5 ATPs
immediately reduces Q and goes into Complex III and IV

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26
Q

What is total ATP yield from complete oxidation of glucose?

A

Total 30 (or 32) ATPs

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27
Q

what is a chemical uncoupler? Name two examples.

A

A chemical uncoupler dissipates proton gradient across the inner membrane. Examples: aspirin overdose or DNP (2,4-dinitrophenol)

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28
Q

generation of hydroxyl radical

A

O2 + e-&raquo_space; O2-
O2- + e-&raquo_space; H2O2
Fe2+ + H2O2&raquo_space; Fe3+ + OH* + OH-

OH* is hydroxyl radical, which can damage the cell, including DNA, and cause mutations

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29
Q

What are two defense mechanisms against ROS?

A
  1. superoxide dismutase (SOD)
    adds hydrogen ion to radical and makes peroxide
  2. catalase
    turns H2O2 into oxygen and water
    SOD and catalase work together
  3. glutathione peroxidase
  4. antioxidant vitamins E and C
  5. Exercise&raquo_space; ROS up&raquo_space; defense mechanism up
    **intake of antioxidant vitamins blunt exercise benefit
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30
Q

What are two types of Lou Gehrig’s disease? What does the disease do? what does amyotrophic mean?

A

mitochondrial version: manganese containing SOD (Mn-SOD)
cytoplasmic version: copper and zinc dependent SOD (Cu/Zn SOD)
Mutation in gene coding for cytosolic SOD (SOD1) causes familial ALS
this is a fatal neurological disease that attacks the nerve cells
amyotrophic - no muscle nourishment
(amyotrophic lateral sclerosis)

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31
Q

what does an apoptosis imbalance cause disease wise?

A

more new cells than cell death: neurodegeneration, immunodeficiency, infertility
more cell death than new cells: cancer, autoimmunity

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32
Q

what kind of enzyme is an oxygenase? what are the two types of oxygenases? what are their basic reactions?

A 
oxidoreductase
b. monooxygenase and dioxygenase
c. monooxygenase
RH + O2 + ZH2 >> ROH  + H2O + Z
dioxygenase
R + O2 >> RO2
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33
Q

what are the co-substrates of a monooxygenase? a dioxygenase?

A

monooxygenase: NADH, NADPH, FMNH2, FADH2
dioxygenate: ascorbic acid

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34
Q 
cytochrome P450:
What kind of enzyme is it?
What reactions does it catalyze?
Where is it found?
What synthesis does it catalyze?
What kind of interactions does it cause
A

a. monooxygenase
b. hydroxylation, epoxidation and modification of hydrophobic compounds for their detox and excretion
c. in mitochondria and ER of cells in liver and most other tissue
d. it catalyzes the synthesis of steroid hormones and bile acids
e. causes drug interactions

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35
Q

how does cytochrome P450 metabolize ibuprofen?

A

basically, it adds a hydroxyl group to it.

ibuprofen&raquo_space;P450 in liver&raquo_space;add hydroxyl group to it

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36
Q

how does cytochrome P450 metabolize acetaminophen?

A

P450 oxidizes acetaminophen by turning its hydroxyl group into a ketone. This becomes N-Acetyl-p-bensoquinine imine. N-acetyl-p-bensoquinine imine needs glutathione to not remain thiolated (after reacting with another chemical) and become toxic to the liver. Via glutathione S-transferase, the thiol is turned in to S ether with glutathione. If there is too much of this, we run out of glutathione.

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37
Q

How does cyp 450 turn benzopyrene into a carcinogen?

A

We start with benzo(a)pyrene. CYP turns in into an epoxide, Benzo(a)pyrene 7,8 epoxide.
Epoxide hydrolase removes the epoxide and turns the molecule into a diol, Benzo(a)pyrene 7,8 diol.
CYP then takes that molecule and adds an epoxide to it, so it becomes Benzo(a)pyrene 7,8 diol,-9,10 epoxide.

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38
Q

Describe tyrosine synthesis. What enzyme is responsible and what kind of enzyme is it?

A

Phenylalanine hydroxylase, a monooxygenate, turns Phenylalanine into tyrosine

It adds O2 and results in H2O and tyrosine.

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39
Q

Describe phenylketonuria? What mutation causes it?

How is phenylalanine digested instead?

A

a. caused by mutation to phenylalanine hydroxylase

b. phenylalanine is digested via an alpha-ketoacid, making a phenylpyruvate, which becomes a phenylketone (in urine)

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40
Q

Describe serotonin synthesis. What enzyme is responsible and what kind of enzyme is it? what is the result of lowered serotonin levels in body?

A

Tryptophan hydroxylase, a monooxygenate, turns tryptophan into serotonin
low serotonin has been linked with depression

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41
Q

what two monooxygenases work in synthesis of catecholamines and how?

A

Tyrosine hydroxylase turns tyrosine into DOPA.

DOPA then becomes dopamine through a decarboxylase. Dopamine Beta hydroxylate turns dopamine into norepinephrine.

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42
Q

what monooxygenase plays a role in cholesterol synthesis and how?

A

In a long process that starts with FAs, squalene monooxygenase turns squalene to squalene epoxide.

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43
Q

what monooxygenases work in vitamin D synthesis? What disease is caused by Vitamin D deficiency?

A

a. in the liver, 25-hydroxylase adds a hydroxyl group to previtamin D3, making Vitamin D3 b. in the kidney, 1alpha hydroxylase adds a hydroxyl group at first carbon of vitamin D3, making calcitriol.
Rickets is caused by vitamin D deficiency.

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44
Q

what monooxygenase participates in nitric oxide synthesis and how?

A

nitric oxide synthase (NOS) turns arginine into N-omega-Hydroxyarginine by adding a hydroxyl group to it. This eventually becomes citrulline and nitric oxide.

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45
Q

what are the three types of nitric oxide synthases?

A

neuronal NOS: nNOS -signaling
endothelial NOS: eNOS - vasodilation
inducible NOS : INOS - immune reaction

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46
Q

what are the co-substrates of dioxygenases?

A

reducing agents such as ascorbic acid

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47
Q

what dioxygenase is involved in the inflammatory response?

A

Prostaglandin H2 Synthase = COX
by cyclo-oxygenase activity it turns Arachidonate into Prostaglandin G2.
by peroxidase activity, it turns Prostaglandin G2 into Prostaglanding H2

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48
Q

How do NSAIDS block inflammation?

A

NSAIDS inhibit prostaglandin H2 synthase, which is responsible for COX-2 activity. This activity is upregulated at the site of inflammation, causing pain and fever. NSAIDS block the COX-2 activity.

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49
Q

How do aspirin and ibuprofen inhibit COX? How does acetaminophen work?

A

aspirin esterifies the enzyme via covalent modification.
Ibuprofen binds to the active site of COX without covalent modification.
The target of acetaminophen is unclear.

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50
Q

What are three specific COX-2 inhibitors?

A

Celebrex
Vioxx -= off market for increased risk of cardiovascular events
Bextra - off market, cardiovascular events

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51
Q

what dioxygenase plays a role in collagen modification? what does it do? what happens if there is a deficiency in the enzyme’s co-substrate?

A

Prolyl 4 hydroxylase
with the cosubstrate ascorbate, it turns alpha-ketoglutarate to 4-hydroxyprolyl residue
cosubstate vitamin deficiency causes scurvy.

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52
Q

what kind of enzyme turns beta-carotene into vitamin A and Rhodopsin? What are diseases associated with vitamin deficiency?

A

dioxygenase

night blindness, xerophthalmia (pathologic dryness of the conjunctive and cornea)

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53
Q

What is MEOS? How is cytochrome 450 involved?

A

microsomal ethanol oxicizing system in liver;

cyp 450 2E1 metabolizes alcohol and generates reactive species like superoxide anion radical, peroxide, etc.

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54
Q

what are two types of mtDNA mutations?

A

DNA insertion or deletion mutations

  • frameshift mutations/chain termination
  • total or partial loss of genes

DNA base substitution mutations

  1. in proteincoding genes
    - amino acid substitution
    - polypeptide chain termination
  2. in tRNAs or rRNAs
    - protein synthesis compromised globally
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55
Q

what is LHON? what causes it?

A

maternally inherited form of an acute adult onset blindness due to the death of optic nerve

primary: complex I
other: Complex III, IV, V

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56
Q

what is T8993G(leu to arg)? what does it cause?

A

this is a mutation in Complex V (ATPase6);
at low percentages: NARP
at high percentages: Leigh syndrome

57
Q

NARP

A

mito disease characterized by decreased muscle strength, regional brain degenheration and retinal deterioration

58
Q

Leigh Syndrome

A

degenerative neurological condition, commonly occuring during childhood. charac. by CNS degeneration, dev delay, seizures, etc.

59
Q

What is MELAS? What causes it?

A

causes periodic stroke-like episodes with mitochondrial myopathy

80% is caused by mutation in tRNA,Leu

60
Q

What is MERFF? what causes it?

A

maternally inherited epilepsy caused by a mutation in tRNA’Lys

61
Q

diseases with % OxPhos capacity, highest to lowest

A

optic track, basal ganglia/cortex, heart/muscle, kidney

62
Q

Steps of Lipogenesis

A

a. acetyl CoA carried out of Mito to cytosol by Citrate via Citrate/Malate transporter
b. Need NADPH from pentose phosphate pathway and malic enzyme
c. carboxylate acetyl Coa to malonyl CoA via acetyl CoA carboxylase
d. add ACP to acetyl and malonyl
e. go through fatty acid synthase process
condense acetyl acp and malonyl acp to acetoacetyl acp
reduce acetoacetyl acp via nadhp to D-3-Hydroxybutyryl ACP
dehydrate above to crotonyl ACP
reduce above via nadph to butyryl acp
repeat cycle seven times, adding malonyl ACP each time, and end up with palmitoyl acp, which is hyrolized to ACP and palmitate

63
Q

what is the comitted step in fatty acid biosynthesis?

A

formation of malonyl CoA

64
Q

what prosthetic group does carboxylation need?

A

biotin

65
Q

how is acetyl coa carboxylase regulated?

A

allosteric and hormonal regulation
allosteric: citrate activates/ lonc chain fatty acyl coa deactivates
hormonal: insulin: phosphorylates and activates
corticosteroids and glucagon: camp dep. pka dephosphorylate and inactivate

66
Q

how does ACP activate acetyl coa and malonyl coa

A

provides SH group

67
Q

odd numbered FA are synthesized starting with

A

propionyl CoA

68
Q

fatty acid synthase complex does

A

seven different enzyme activities and domain covalently binds 4-phosphopantheine

69
Q

FA ox vs. synt. / intracellular location

A

mito/cytosol

70
Q

FA ox vs. synth; carrier

A

CoA / ACP

71
Q

FA ox vs synth coenzymes for electron transfer

A

FAD,NAD/ NADPH

72
Q

FA ox vs. synt, bicarb dependence

A

no/yes

73
Q

FA ox vs. synt energy state favoring the process

A

high ADP/high ATP

74
Q

FA ox vs. synt. citrate activation

A

no, but malonyl CoA/ yes

75
Q

FA ox vs. synt. Acyl CoA inhibition (long chain)

A

no/yes

76
Q

FA ox vs synt. higheste activity

A

fasting, starvation/carbohydrate fed

77
Q

FA ox vs. synt hormonal state

insulin/glucagon ratio

A

low/high

78
Q

FA ox vs. synt carrier of acyl/acetyl group

A

carnitine cyto mito/ citrate mito to cyto

79
Q

FA ox vs synt product

A

acetyl Coa/Palmitate

80
Q

three types of complex lipids

A

acylglycerols, phosphoglyceridews and sphingolipids

81
Q

how are FA esteirified? what do they form?

A

carboxyl groups/ neutral fat

82
Q

How are FAs activated prior to TG biosynthesis?

A

attached to CoA

83
Q

what precursors are required for TG biosynthesis?

A

fatty acyl CoAs and L-glycerol-3-phosphate

84
Q

where does L-glycerol-3-phosphate come from?

A

liver or adipose tissue
in both liver and adipose tissue, dihydroxyacetone phosphate is reduced to glycerol phosphate by glycerol P dehydrogenase and NADH
in only liver, glycerol goes through glycerol kinase with ATP to make glycerol phosphate

85
Q

when do adipocytes take up glucose?

A

in presence of insulin, so limit ability to synthesize glycerol 3 phosphate

86
Q

steps of TG biosynthesis

A

a. start with glycerol phosphate
b. acylation of free OH groups of glycerol by 2 molecules of fatty acyl CoA
MAKES lysophosphatidic acid and then phosphatidic acid
via glycerol phosphate acyltransferase
c. phosphatidic acid undergoes hydrolysis by phsphatidate phsphatase for form diacyl glycerol
d. dyacylglycerol reacts with 3rd FA CoA molecule via diacylglycerol acyltransferase to yield TG

87
Q

what is key molecule in phospholipid biosynthesis?

A

diacylglycerol

88
Q

clinical correlation: what is primary phospholipid in surfactant and is used in respiratory distress syndrome in newborns?

A

phosphatidylcholine (lecithin)

89
Q

steps of biosynthesis of glycerophospholipids

A

a. get to phosphatidic acid (seen before in TG synthesis)
or start with diacylglycerol and phosphorylate it
(basically add alcohol to phosphatidic acid in smooth ER)

there are two strategies:

  1. start with diacylglycerol
  2. activate with CDP
  3. add alcohol (glycerol or inositol)
  4. add glycerol - P if added glycerol
  5. yield phophatidylinositol or physphatidyl glycerol

strategy 2

  1. start with diacylglycerol
  2. activate alcohol with DCP (CDP-choline or CDP-ethanolamine)
  3. yield phosphatidyl choline or phosphatidylethanolamine
90
Q

what are the most abundant phospholipids?

A

PC and PE

91
Q

source of choline and ethanolamine?

A

from diet or from turnover of the body’s phospholipids

92
Q

what is phosphatidyl glycerol a precursor of? how is it made?

A

cardiolipin/ take PG and add to CDP diacylglycerol

93
Q

how is phosphatidyl inositol formed? what is PI a reservoir of?

A

from free myo-inositol and CDP-diacylglycerol

arachidonic acid in membranes

94
Q

how is phosphatidylserine synthesized?

A

base exchange reaction with phosphatidylethanolamine

95
Q

where can de novo synthesis of PC take place?

A

in cell membrane

96
Q

why are sphingolipids important?

A

they confer:

a. blood group specificity
b. organ and tissue specificity
c. tissue immunity
d. cell-cell recognition

97
Q

where are sphingolipids abundant?

A

in brain, nerve tissue

98
Q

what is ceramide? what is special about it?

A

built from sphingosine plus saturated or unsaturated long chain fatty acyl group and amide linkage on the amino group
ti has 2 nonpolar tails and is similar in structure to diacylglycerol

99
Q

what are the most abundant sphingolipids in higher animals?

A

sphingomyelins, cererosides (glycosphingolipids), gangliosides

100
Q

what is Guillain-Barre syndrome

A

autoimmune neuritis. antibodies “attack” myelin sheath of peripheral nerves

101
Q

what is multiple sclerosis?

A

autoimmune demyelinating disease in CNS. nerves lose conduction and degenerate

102
Q

what are sphingomyelins?

A

sphingosine plus PE or PC

103
Q

what are glycosphingolipids?

A

no phosphate, jsut sugar attached by a beta-glycosidic linkage a 1-OH group of sphingosine in a ceramide.

104
Q

what are cerebrosides?

A

subgroup of glycosphingolipids. contain either a galactose or glucose attached to ceramide.

105
Q

where are galactocerebrosides found? glucocerbrosides?

A

neural tissue/ non neuronal cell plasma membrane

106
Q

what are gangliosides?

A

sphingolipid with oligosaccharide head group and one or more residues of sialic acid at termini. sialic acid imparts a negative charge to gangliosides.

107
Q

ganglioside nomenclature. what is Gm and Gd

A

Gm has one sialic acid. Gd has 2 (di) etc.

108
Q

how do we make sphingolipids?

A

a. use sphingosine backbone
b. add long chain acyl CoA and convert to ceramide
c. substitute terminal hydroxyl group
- sphingomyelin: ceramide plus phosphorycholine
- cerebroside: glucose or galactose
- ganglioside: oligosaccharide

109
Q

an abnormal accumulation of certain complex lipids in specific tissues is termed lipid storage disease or ? what does it involve?

A

lipidoses
lysozomal storage disease
lysozomal enzyme deficiency
sphingolipidose

involves absence or deficiency of specific glucosidases

110
Q

what enzyme therapy is used to treat Gaucher’s glucocerebrosidase)

A

imiglucerase (cerezyme)

111
Q

what enzyme therapy is used to treat Fabry’s (alpha galactosidase)?

A

agalsidase

112
Q

Name six sphingolipidoses? what is the theory behind them? what is the result?

A

Niemann-Pick disease, Fabry’s Disease, Krabbe disease, Gaucher’s disease, Tay-Sachs disease, Metachromatic leukodystrophy.
due to enzyme deficiency. may be addressed with enzyme therapy. result in death for infant affected.

113
Q

what are eicosanoids? name three kinds? what are they derived from?

A

paracrine hormones involved in functions essential to health/diseases
three types are prostaglandins, leukotrienes, thromboxanes
derived from C20 polyunsaturated acids, like arachidonic acid

114
Q

carbon number of eicosanoids

A

prostaglandin is 5 carbons
thromboxane is six carbons
leukotriene is three carbons

115
Q

what do glucocorticoids inhibit?

A

steroidal drugs inhibit phospholipase A2, which harvests arachidonic acid from plasma membrane so it can go through cyclocoxygenase process of COX. That means they inhibit leukotrienes, thromboxanes and prostaglandins.

116
Q

what do NSAIDS inhibit?

A

they inhibit the cyclooxygenase process, so inhibit prostaglanding and thromboxane but NOT leukotriene

117
Q

how does asaspirinpirn inhibit cyclooxygenease activity of COX?

A

aspirin inhibits by acetylating essential Ser. It is an irreversible inhibitor.

118
Q

How does ibuprofen inhibit COX cyclooxygenase process?

A

it may inhibit COX by mimicking the structure of the substrate

119
Q

How are leukotrienes synthesized?

A

arachidonic acid is converted by lipoxygenases to hydroperoxy acids and then to a series of leukotrienes.

120
Q

what do leukotrienes do? what drug antagonizes them?

A

cause broncho-constriction; implicated in asthmal/airway reactivity. LT receptor antagonists used. MONTELUKAT (singulair)

121
Q

how does baby aspirin therapy work?

A

1/4 the dose of regular aspirin, baby aspirin inhibits thromboxane A2 and platelet aggregation, which can lead to stroke. this is a cardio protective effect.

122
Q

what are simple lipids? two categories?

A

those that do not contain fatty acids

terpenes and steroids

123
Q

what are terpenes? major classes?

A

multiple 5 carbon isoprenes. major classes: fat soluble vitamins, A,E, K 2. ubiquinone or coenzyme Q

124
Q

features of cholesterol

A

OH group at C3 of ring A
branched aliphatic chain of 8 or more carbons at C-17
27 carbons

125
Q

two kinds of bile acids?

A

cholic acid and deoxycholic acid

126
Q

what five hormones is cholesterol the precursor for?

A

testosterone, estradiol estrone, cortisol, and aldosterone

127
Q

what are aromatase inhibitors?

A

attenuate estrogen production in postmenopausal women. converts androgen into estrogens. less estrogen- less stimulated growth of hormone-receptor-positive breast cancer cells. only effective in postmenopausal.

128
Q

how is cholesterol biosynthesized?

A

acetyl CoA via thiolase becomes Acetoacetyl Coa
Acetoacetyl Coa via HMG CoA synthase becomes beta-hydroxy-beta-methylglutaryl-CoA, which becomes mevalonate,
mevalonate becomes isopentenyl pyrophosphate, which eventually becomes squalene and then cholesterol

129
Q

what is the rate limiting step of cholesterol biosynthesis?

A

the reduction of HMG CoA to mevalonate

130
Q

at what point can product become cholesterol synthesis can lead either to ketone bodies mevalonate?

A

Beta-hydroxy-beta-methylglutaryl-CoA
at that point, it can face HMG CoA Lyase in mitochondria and become ketone bodies OR face HMG CoA reductase in cytosol and become mevalonate

131
Q

How is HMG CoA reductase regulated?

A

feedback inhibition by cholesterol
hormonal regulation:
-starvation: glucagon causes phosphorylation and activation of the enzyme
-well fed: insulin causes dephosphorylation and activation of the enzyme
-sterol mediation regulation of transcription

132
Q

sources of liver cholesterol and routes by which cholesterol leaves the liver

A

sources: dietary cholesterol&raquo_space; chylomicron remnants, denovo synthesis in liver, cholesterol synthesized in extrahepatic tissue&raquo_space; HDL
exit: VLDL, free cholesterol secreted in bile, conversion in bile acids/salts

133
Q

primary source of cholesterol not from liver or instetine?

A

LDL

134
Q

how does LDL get cholesterol to nonhepatic tissue?

A

Apo B-100 on LDL surfaces bind to receptors. the LDL receptor and everything in it is endocytosed. LDL receptors are recycled to the PM.

135
Q

What does PCSK9 enzyme do? How do its levels reflect recycle progress of LDL receptors.

A

regulates LDL-R cycling
Low PCSK9 good, means LDL R recycled, more cholesterol removed from blood
High is bad, LDL-R not recycled

136
Q

How do PCSK9 inhibitors work? Adverse effects?

A

increeases expressionof LDL receptor so more cholesterol can be taken up and excreted by liver.
adverse effects include injection site reactions and maybe neurocognitive effects.

137
Q

What is ACAT

A

acyl CoA cholesterol acyl transferase? esterifies cholesterol for storage inside cell

138
Q

what does mipomerser treat? how?

A

treats homozygous familial hypercholesteremia? inhibits Apo B100 synthesis

Medical Biochemistry (3 decks)

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