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USMLE > Metabolism > Flashcards

Metabolism Flashcards

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USMLE® Step 1 flashcards
1
Q

Glycolysis Pathway

A

Glucose –> [Hexokinase/Glucokinase] –> G6P –> F6P –> [PFK] –> F-1,6-bP –> DHAP + G3P
DHAP –> G3P
G3P ->->-> PEP –> [Pyruvate Kinase] –> Pyruvate

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2
Q

Glycogen synthesis pathway

Glycogen breakdown pathway

A

G6P –> G1P –> [UDP Glucose Pyrophosphorylase] –> UDP-Glucose –> [Glycogen Synthase] –> Glycogen –> [Branching Enzymes] –> Branched Glycogen
Glycogen –> [Glycogen Phosphorylase] –> G1P –> G6P
Branched Glycogen –> [Debranching enzymes] –> Limit Dextrin –> [Debranching enzymes] –> Linear Glycogen

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3
Q

How does Galactose enter Glycolysis?

A

Galactose –> [Galactokinase] –> Galactose-1-Phosphate –> [Galactose-1-Phosphate Uridyltransferase] –> G1P –> G6P

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4
Q

HMP Shunt pathway

A

G6P –> [G6PD] –> 6-phosphogluconolactone ->->-> Ribulose-5-Phosphate ->->-> [Transketolase + Thiamine] ->->-> F6P

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5
Q

How does Fructose enter glycolysis

A

Fructose –> [Fructokinase] –> F1P –> [Aldolase B] –> DHAP + Glyceraldehyde
Both DHAP and Glyceraldehyde are converted into G3P
OR…
Fructose –> [Hexokinase] –> F6P

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6
Q

Gluconeogenesis pathway

A

Pyruvate –> [pyruvate carboxylase + Biotin] –> Oxaloacetate –> [PEP carboxykinase] –> PEP ->->-> F-1,6-bP –> [F-1,6-bisphosphatase] –> F6P –> G6P –> [G6Phosphatase] –> Glucose

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7
Q

Cholesterol synthesis pathway

A

Acetyl CoA –> Acetoacetyl-CoA –> HMG CoA –> [HMG CoA Reductase] –> Mevalonate ->->-> Cholesterol

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8
Q

β-hydroxybutyrate synthesis pathway

A

2Acetyl CoA –> Acetoacetyl CoA –> HMG CoA –> Acetoacetate
Acetoacetate + NADH –> [β-hydroxybutyrate Dehydrogenase] –> β-hydroxybutyrate + NAD
Reaction is reversed in brain to produce NADH

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9
Q

TCA cycle Pathway

A

“Citrate Is Krebs’ Starting Substrate For Making Oxaloacetate”
Pyruvate –> [Pyruvate Dehydrogenase] –> Acetyl CoA
Acetyl CoA + Oxaloacetate –> [Citrate Synthase] –> Citrate –> Isocitrate –> [Isocitrate dehydrogenase] –> α-ketoglutarate –> [α-ketoglutarate dehydrogenase + Thiamine] –> Succinyl-CoA –> Succinate –> Fumarate –> Malate –> Oxaloacetate

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10
Q

How do odd chain fatty acids and VMIT enter TCA cycle

A

Propinoyl-CoA –> [Biotin] –> Methylmalonyl CoA –> [B12] –> Succinyl CoA

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11
Q

How much ATP does Glucose produce in Heart and Liver

A

Aerobic Metabolism produces 32 ATP via malate-aspartate shuttle

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12
Q

How much ATP does Glucose produce in Muscle?

A

Aerobic Metabolism produces 30 ATP via Glycerol-3-Phosphate shuttle

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13
Q

How much glucose does Anaerobic Glycolysis produce

A

2 ATP per Glucose

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14
Q

Carrier Molecule ATP carries

A

Phosphoryl groups

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15
Q

Carrier Molecules NADH, NADPH, and FADH2 carries

A

Electrons

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16
Q

Carrier Molecules Coenzyme A, Lipamine carries

A

Acyl Groups

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17
Q

Carrier Molecule Biotin carries

A

CO2

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18
Q

Carrier Molecule THF carries

A

1 carbon units

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19
Q

Carrier Molecule SAM carries

A

CH3 groups

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20
Q

Carrier Molecule TPP carries

A

Aldehydes

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21
Q

NADH vs NADPH

A

NAD is Catabolic

NADP is Anabolic

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22
Q

NADPH
What process produces it?
What kind of reaction?
What reactions is it used in?

A

Produces in HMP shunt
Reduction reactions
Used in anabolic processes (Steroid and Fatty Acid Synthesis), Respiratory Burst, P450, Glutathione Reductase

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23
Q 
Hexokinase 
Reaction 
Where is it?
Affinity
Capacity
Regulation
A 
Glucose --> G6P
Ubiquitous 
High Affinity (low Km)
Low Capacity (low Vmax)
Uninduced by insulin. Feedback inhibition by G6P
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24
Q 
Glucokinase 
Reaction 
Where is it?
Affinity
Capacity
Regulation
A 
Glucose --> G6P
Liver and β cells of Pancreas 
Low Affinity (high Km)
High Capacity (high Vmax) "GLUcokinase is a GLUtton, it cannot be satisfied"
Induced by Insulin.
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25
Q

General glucose regulation

A

At low [glucose], hexokinase sequesters glucose in the tissues.
At high [glucose], excess glucose is stored in the liver

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26
Q

Net Glycolysis Reaction

A

Glucose + 2P + 2ADP + 2NAD –> 2Pyruvate + 2ATP + 2NADH + 2H + 2H2O

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27
Q

F-2,6-BP
Reaction that produces it and degrades it
What does it activate and what are the consequences of that?
Pathways in Fed vs Fasting state?

A

F6P –> [PFK-2] –> F-2,6-BP –> [FBPase2] –> F6P
F-2,6-BP activates PFK1 and pushes balance towards glycolysis
PFK2 is active in fed state
Fasting state: Glucagon –> ↑cAMP –> ↑PKA –> ↑ FBPase2, ↓ PFK2, less glycolysis
Fed state: Insulin –> ↓cAMP –> ↓PKA –> ↓ FBPase2, ↑ PFK2, more glycolysis

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28
Q 
Pyruvate Dehydrogenase Complex 
Reaction 
# of enzymes 
# of cofactors with names 
What activates it?
What complex is similar?
Regulation
A

Pyruvate + NAD + CoA –> Acetyl-CoA + CO2 + NADH
3 enzymes
5 cofactors (TPP, FAD, NAD, CoA, Lipoic Acid) “Tender Loving Care For Nancy”
Activated by ↑ NAD/NADH ratio, ↑ADP, ↑Ca
α-ketoglutarate dehydrogenase complex is similar
Inhibited by ATP, AcetylCoA, and NADH

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29
Q

Arsenic
Mechanism of toxicity
Findings

A

Inhibits Lipoic acid

Vomiting, rice water stool, garlic breath

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30
Q 
Pyruvate Dehydrogenase Complex Deficiency 
Mutation 
PathoPhys
Findings 
Treatment
A

X linked gene for E1-α subunit
Backup of substrates (pyruvate and alanine) –> lactic acidosis
Neurological defects starting in infancy
Intake of ketogenic nutrients (high fat or high in lysine and leucine)
“Lysine and Leucine - the onLy pureLy Ketogenic AA”

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31
Q

Pyruvate Metabolism Pathway

A

Pyruvate ↔ [ALT w/ B6] ↔ Alanine which carries amino groups to liver from muscle
Pyruvate + CO2 + ATP ↔ [Pyruvate Carboxylase w/ Biotin] ↔ Oxaloacetate which can replenish TCA cycle or be used in gluconeognesis
Pyruvate + NAD ↔ [Pyruvate Dehydrogenase] ↔ NADH + CO2 + Acetyl Coa
Pyruvate + NADH ↔ [Lactic Acid Dehydrogenase w/ B3] ↔ NAD + Lactic Acid which is the end product of anaerobic glycolysis (major pathway in RBCs, Leukocytes, Kidney Medulla, Lens, Testes, Cornea)

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32
Q

What does the TCA cycle produce?

A

3NADH, 1FADH2, 2CO2, and 1GTP per 1Acetyl CoA

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33
Q

Where does the TCA cycle occur?

A

In the Mitochondria

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34
Q

Regulation of Citrate Synthase

A

Inhibited by ATP

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35
Q

α-ketoglutarate dehydrogenase regulation

A

Inhibited by SuccinylCoA, NADH, and ATP

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36
Q

What reactions of the Krebs Cycle produce NADH

A

Isocitrate –> α-ketoglutarate
α-ketoglutarate –> Succinyl CoA
Malate –> Oxaloacetate

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37
Q

What reactions of the Krebs Cycle produce GTP

A

Succinyl CoA –> Succinate

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38
Q

What reactions of the Krebs Cycle produce FADH2

A

Succinate –> Fumarate

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39
Q

How does NADH get into the Mitochondria?

A

Malate Aspartate or Glycerol-3-Phosphate shuttle

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40
Q

Malate Aspartate Shuttle

A

Cytoplasm: NADH + OAA –> NAD + Malate
Malate/α-ketoglutarate antiporter transports Malate into matrix
Matrix: NAD + Malate –> OAA + NADH
OAA + Glutamte –> Aspartate + α-ketoglutarate
Asp/Glu antiporter transports Asp into cytoplasm

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41
Q

Glycerol-3-Phosphate Shuttle

A

Cytoplasm: NADH + DHAP –> NAD + G3P
@ Mito inner membrane:
G3P + FAD –> [G3PDH] –> DHAP + FADH2

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42
Q

ETC Complex I
Reaction
Pumping
Inhibitor?

A

NADH –> NAD and CoQ
H pumped out
Rotenone

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43
Q

ETC Complex II
Name
Reaction
Pumping?

A

Succinate Dehydrogenase
FADH2 –> FAD and CoQ
No protons pumped thus lower energy level

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44
Q

Complex III
Reaction
Pumping
Inhibitor

A

CoQ transfers electrons to Cytochrome c
H pumped out
Antimycin A

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45
Q

Complex IV
Reaction
Pumping
Inhibitor

A

2 Cytochrome c gives electrons to 1 O2 to produce H2O
H pumped out
Cyanide and CO

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46
Q

Complex V
Reaction
Pumping
Inhibitor

A

ADP + P –> ATP
H moves into matrix
Oligomycin

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47
Q

How many ATP does NADH produce?

A

2.5

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48
Q

How many ATP does FADH produce?

A

1.5

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49
Q 
Uncoupling agents 
MoA
PathoPhys
What happens to ATP synthesis and the ETC?
What is produced?
Names
A 
↑ permeability of membrane 
↓ proton gradient and ↑ O2 consumption 
ATP synthesis stops but ETC continues 
Heat is produced 
2,4-DNP, Aspirin (fevers occur after OD), Thermogenin in brown fat
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50
Q

Irreversible Enzymes in Gluconeognesis

Enzyme, Reaction, Location

A

“Pathways Produce Fresh Glucose”
Pyruvate Carboxylase, Pyruvate –> OAA, Mito
PEP carboxykinase, OAA –> PEP, Cytoplasm
F-1,6-bPase, F-1,6,bP –> F6P, Cytoplasm
G6Pase, G6P –> Glucose, ER

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51
Q

Pyruvate Carboxylase
Reaction
Regulation

A

Pyruvate + ATP –> OAA + ADP

Requires Biotin. Activated by Acetyl-CoA

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52
Q

Required cofactor of PEP Carboxykinase

A

GTP

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53
Q

What tissues are capable of gluconeogenesis

A

Occurs primarily in Liver

Also in Kidney and Intestinal Epithelium

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54
Q

What is the result of a deficiency in the enzymes of Gluconeognesis?

A

Hypoglycemia

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55
Q

What tissues care not capable of gluconeogenesis? Why?

A

Muscles because they lack G6Pase

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56
Q

Can fatty acids participate in gluconeogenesis?

A

Odd chain fatty acids yield propinoyl-CoA which enters TCA cycle as succinyl CoA and can undergo gluconeogenesis
Even chain fatty acids cannot produce new glucose since they yield only acetyl CoA equivalents

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57
Q 
HMP Shunt
What does it produce?
What are the phases?
Where does it occur?
ATP?
Sites where it happens?
A

Provides a source of NADPH from G6P and Ribose for nucleotide synthesis and glycolytic intermediates
2 distinct phases (oxidative and nonoxidative)
Occurs in Cytoplasm
No ATP is used or produced
Sites of FA or steroid synthesis: Lactating mammary glands, Liver, Adrenal Cortex
Also RBCs

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58
Q

NADPH in RBCs

A

Glutathione reduction

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59
Q

Oxidative reaction of HMP shunt
Pathway
Regulation
Reversible?

A

G6P + NADP –> [G6PDH] –> NADPH + CO2 + Ribulose-5-Phosphate
Inhibited by NADPH
Irreversible rate limiting step

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60
Q

Nonoxidative reaction of HMP shunt
Pathway
Regulation
Reversible?

A

Ribulose-5-Phosphate –> [Phosphopentose isomerase, Transketolases] ->->-> Ribose-5-Phosphate + G3P + F5P
Requires B1
Reversible

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61
Q 
Respiratory Burst
AKA
Cells that do it?
Role in what system?
Function
A

Oxidative Burst
Neutrophils and Monocytes
Plays an important role in the immune system response
Rapid release of Reactive Oxygen Intermediates

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62
Q

Oxidative Burst Pathway

A

O2 + NADPH –> [NADPH Oxidase] –> O2-* + NADP
O2-* –> [Superoxide dismutase] –> H2O2
H2O2 + Cl –> [Myeloperoxidase] –> HOCl*
HOCl* kills bacteria

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63
Q

Chronic Granulomatous Diseases
Deficiency
Can they fight infection? How?
What are they at risk for?

A

NADPH oxidase deficiency
Can use H2O2 generated by invading organisms to fight disease
At risk for infection by catalase + species (S aureus and Aspergillus)

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64
Q

How is H2O2 neutralized by bacteria?

A

H2O2 –> [bacterial catalases] –> H2O and O2

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65
Q

How is H2O2 neutralized in human cells?

A

H2O2 + Glutathione-SH (reduced) –> [Glutathione Peroxidase] –> H2O + GSSG (oxidized)
GSSG + NADPH –> [Glutathione Reductase] –> GSH + NADP
NADP + G6P –> [G6PDH] –> NADPH + 6-Phosphogluconate

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66
Q

Why is it necessary to keep Glutathione reduced? What keeps it reduced?

A

Reduced Glutathione can detoxify free radicals

NADPH keeps it reduced

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67
Q

G6PDH
Reaction
What happens if there is a deficiency?

A

G6P + NADP –> 6PG + NADPH

Deficiency results in ↓ NADPH

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68
Q

PathoPhys of G6PDH Deficiency

A

Low NADPH in RBCs leads to hemolytic anemia, due to poor RBC defense against oxidizing agents (Fava Beans, Sulfonamides, Primaquine, AntiTB drugs)
Infections can also precipitate hemolysis (free radicals generated via inflammatory response can diffuse into RBCs and cause oxidative damage)

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69
Q 
G6PDH Deficiency 
Inheritance 
Epidemiology 
What does it confer?
Histo
A

X linked recessive
Most common human enzyme deficiency. More prevalent among blacks
Confers Malarial Resistance
Heinz Bodies: Oxidized Hemoglobin precipitated within RBCs
Bite Cells: Phagocytic removal of Heinz bodies by splenic macs
“Bite into some Heinz Ketchup”

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70
Q 
Essential Fructosuria 
Mutation
Inheritance 
Danger?
Symptoms?
Findings
A 
Defect in Fructokinase 
Autosomal Recessive 
Benign
Asymptomatic since fructose is not trapped in cells 
Fructose appears in blood and urine
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71
Q 
Fructose intolerance 
Mutation
Inheritance 
What accumulates and what are the consequences?
Symptoms
Treatment
A

Defect in Aldolase B
Autosomal Recessive
F1P accumulates –> ↓ in available P –> Inhibition of glycogenolysis and gluconeogenesis
Hypoglycemia, Jaundice, Cirrhosis, Vomiting
↓ intake of fructose and sucrose (glucose + fructose)

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72
Q 
Galactokinase Deficiency 
Mutation 
What accumulates 
Inheritance 
How bad?
Symptoms
A 
Mutation in Galactokinase 
Galactitol accumulates 
Autosomal Recessive
Mild Condition 
Galactose in blood and urine, Infantile Cataracts. May initially present as failure to track objects or to develop a social smile
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73
Q 
Classic Galactosemia 
Mutation?
Inheritance 
What leads to damage?
Symptoms
Treatment
A

Galactose-1-Phosphate Uridyltransferase
Autosomal Recessive
Damage caused by accumulation of toxic substances (including galactitol) which accumulates in the lens of the eye
“I Just Fed Her Milk”
Failure to thrive, Jaundice, Hepatomegaly, Infantile Cataracts, Mental Retardation
Exclude galactose and lactose (galactose + glucose) from diet

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74
Q

How is Galacititol made?

A

Galactose –> [Aldose Reductase] –> Galactitol

Made when [galactose] is high

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75
Q 
Sorbitol
Why is it made?
What is it?
Pathway 
What else can be made into it?
A

Made as an alternative method for trapping glucose in the cell
Alcohol counterpart to glucose
Glucose + NADPH –> [Aldose Reductase] –> Sorbitol + NAD
High galactose can also result into conversion into Sorbitol

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76
Q

What is the fate of Sorbitol
Pathway
What tissues have an insufficient amount of this enzyme?

A

Sorbitol + NAD –> [Sorbitol Dehydrogenase] –> Fructose + NADH
Schwann cells, Retina, and Kidneys only have Aldose Reductase and are thus at risk for osmotic damage (Cataracts, Retinopathy, Peripheral Neuropathy)

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77
Q

Which tissues have both Aldose Reductase and Sorbitol Dehydrogenase?

A

Liver, Ovaries, Seminal Vesicles

78
Q 
Lactase Deficiency
What causes it?
Epidemiology 
Self Limiting Kind?
Symptoms 
Treatment
A

Age Dependent or Hereditary Lactose Intolerance due to loss of brush border enzyme
African Americans and Asians
May follow gastroenteritis
Bloating, cramps, osmotic diarrhea
Avoid dairy products or add lactase pills to diet

79
Q

What kind of AA are found in proteins?

A

Only L form

80
Q 
Essential AA
What are they?
Glucogenic
Glucogenic/Ketogenic
Ketogenic
A

Need to be supplied in the diet
Met, Val, His
Ile, Phe, Thr, Trp “WIFT”
Leu, Lys

81
Q

Acidic AA

A

Asp and Glu

82
Q

Basic AA

A

Arg, Lys, and His
Arg is the most basic
His has no charge at body pH

83
Q

Which AA are required during periods of growth?

A

Arg and His

84
Q

Purpose of Urea Cycle

A

Excrete NH4+ from AA catabolism

85
Q

Urea Cycle Pathway

A

“Ordinary, Careless, Crappers Are Also Frivolous About Urination”
Mito:
NH4 + CO2 + 2ATP –> [Carbamoyl Phosphate Synthase I] –> Carbamoyl phosphate
Carbamoyl Phosphate + Ornithine –> [Ornithine transcarbamoylase] –> Citrulline
Cyto:
Citrulline + Aspartate + ATP –> [Argininosuccinate Synthetase] –> Argininosuccinate (+ AMP) –> [Argininosuccinase] –> Arginine and Fumarate
Arginine + H2O –> Urea + Ornithine

86
Q

What molecules make up Urea

A

NH4+, CO2, Asp

87
Q

Alanine Cycle

A

Muscle: Glucose –> Pyruvate –> Alanine
Liver: Alanine –> Pyruvate –> Glucose

88
Q

Cori Cycle

A

Muscle: Glucose –> Pyruvate –> Lactate
Liver: Lactate –> Pyruvate –> Glucose

89
Q

How does NH3 go from muscles to liver?

What vitamin is important for this process?

A

Muscle:
AA (NH3) + α-ketoglutarate –> Glutamate (NH3) + α-ketoacids
Glutamate (NH3) + Pyruvate –> α-ketoglutarate + Ala (NH3)
Liver:
Ala (NH3) + α-ketoglutarate –> Pyruvate + Glutamate (NH3)
Glutamate –> Urea
BitB6 vital to Alpha Ketoglutarate

90
Q

Hyperammonemia
Etiology
PathoPhys

A

Acquired (liver disease) or Hereditary (urea cycle enzyme deficiency)
Excess NH4+ depletes α-ketoglutarate leading to inhibition of TCA cycle

91
Q

Hyperammonemia
Presentation
Treatment

A

Tremor (Asterixis), Slurring Speech, Somnolence, Vomiting, Cerebral Edema, Blurring Vision
Limit protein diet
Give benzoate or phenylbutyrate which bind AA and lead to excretion
Lactulose to acidify the GI tract and trap NH4 for excretion

92
Q 
Ornithine Transcarbamoylase Deficiency 
Frequency 
Inheritance 
Time of onset
PathoPhys 
Findings
A

Most common urea cycle disorder
X linked recessive (vs other urea cycle enzyme deficiencies which are AR)
Evident in first few days of life but may present with late onset
Body cannot eliminate ammonia. Carbamoyl phosphate builds up and converted into orotic acid (party of pyrimidine synthesis pathway)
Orotic acid in blood and urine, ↓ BUN, Hyperammonemia

93
Q

Products made from Phenylalanine

A

Phe –> [BH4] –> Tyrosine –> [BH4] –> DOPA –> [B6] –> DA –> [VitC] –> NE –> [SAM] –> Epi
Tyrosine –> Thyroxine
DOPA –> Melanin

94
Q

Products made from Tryptophan

A

Trp –> [B6] –> Niacin –> NAD

Trp –> [BH4] –> 5HT –> Melatonin

95
Q

Products made from Histidine

A

His –> [B6] –> Histamine

96
Q

Products made from Glycine

A

Gly –> [B6] –> Porphyrin –> Heme

97
Q

Products made from Arginine

A

Arg –> Creatine
Arg –> Urea
Arg –> Nitric Oxide

98
Q

Products made from Glutamate

A

Glu –> [B6] –> GABA

Glu –> Glutathione

99
Q

Catecholamine Synthesis Pathway

A

Phe + THB –> [Phe Hydoxylase] –> Tyr + DHB
Tyr + DHB –> [Tyr Hydroxylase] –> DOPA + DHB
DOPA –> [DOPA Decarboxylase w/ VitB6] –> DA –> [DA-β-Hydroxylase w/ VitC] –> NE –> [Phenylethanolamine N-methyltransferase] –> Epi

100
Q

Phenylethanolamine N-methyltransferase
Reaction
Regulation

A

NE –> Epi

Activated by Cortisol

101
Q

Tetrahydrobiopterin
Names
What replenishes it?

A

THB or BH4

DHB + NADPH –> [Dihydropteridine Reductase] –> THB + NADP

102
Q

Breakdown of Catecholamines
Enzymes
Products

A

MAO and COMT
DA –> HVA
NE –> NorMetanephrine –> VMA
Epi –> Metanephrine –> VMA

103
Q 
Phenylketonuria 
Mutation 
Consequences Re AAs
What builds up?
Inheritance
A

Mutation in Phe Hydroxylase
Tyr becomes essential
Phe builds up leading to excess phenylketones in urine
Autosomal Recessive

104
Q

Malignant Phenylketonuria
What causes it?
Findings

A

Decreased THB

PKU symptoms, but after treatment pt will have elevated prolactin levels (because of low DA)

105
Q

Phenylketonuria
Findings
Treatment
Screening

A

Mental Retardation, Growth Retardation, Seizures, Fair Skin, Eczema, Musty Body Odor
Treat with ↓ Phe (contained in aspartame) and ↑ Tyr in diet
Screened 2-3 days after birth (normal at birth because of maternal enzyme)

106
Q

Phenylketones

A

Phenylacetate, Phenyllactate, Phenylpyruvate

107
Q

Maternal PKU
Cause
Findings

A

Lack of proper dietary therapy during pregnancy

Microcephaly, Mental retardation, Growth retardation, Congenital heart defects

108
Q 
Alkaptonuria 
AKA
Mutation 
Inheritance
Danger?
Findings
A

Ochronosis
Deficiency of Homogentisic Acid Oxidase in the degradative pathway of Tyr to Fumarate
AR and Benign
Dark connective tissue, Brown pigmented sclera, Urine turns black on prolonged exposure to air, Debilitating arthralgias (homogentisic acid is toxic to cartilage

109
Q

Albinism
Defect
Inheritance
Risk

A

Defective Tyrosinase which converts Tyr –> Melanin. AR
Defective Tyr transporter (low amounts of Tyr and thus melanin)
Lack of migration of Neural Crest Cells
Variable inheritance
Risk of Skin Cancer

110
Q

Inheritance of ocular albinism

A

X linked recessive

111
Q

Homocystinuria
Inheritance
Cause w/ Treatment

A

AR

  1. Cystathionine Synthase Deficiency. ↓ Met and ↑ Cys, B12, and Folate in diet
  2. ↓ affinity of cystathionine synthase for B6 (Pyridoxal Phosphate). ↑ B6 in diet
  3. Homocysteine Methyltransferase Deficiency
112
Q

Homocysteine Pathways

A

Homocysteine –> [Homocysteine Methyltransferase w/ B12] –> Methionine
Homocysteine + Serine –> [Cystathionine Synthase w/ B6] –> Cystathionine –> Cysteine

113
Q 
Homocystinuria
What builds up?
What happens Re AAs?
Findings 
Test
A

Homocysteine builds up
Cysteine becomes essential
Homocysteine in urine, Mental Retardation, Osteoporosis, Tall stature, Kyphosis, Lens Subluxation (downward and inward), and atherosclerosis (Stroke and MI)
Nitroprusside Cyanide Test

114
Q 
Cystinuria 
PathoPhys
Findings 
Inheritance 
Treatment
A

Defect of renal tubular AA transporter for cysteine, ornithine, lysine, and arginine in PCT of kidney
Cystine in urine –> Precipitation of hexagonal crystals and renal staghorn calculi
AR
Hydration and Urinary Alkalinization

115
Q

What is Cystine

A

2 cysteines connected by a disulfide bond

116
Q 
Maple Syrup Urine Disease 
PathoPhys
Findings 
What does it lead to?
Inheritance
A

“I Love Vermont Maple Syrup from trees with Branches”
↓ in α-ketoacid dehydrogenase (B1) –> Blocked degradation of branched AA (Ile, Leu, Val)
↑ α-ketoacid in blood (especially Leu), Urine smells like maple syrup (burned sugar)
CNS defects, Mental Retardation, Death
AR

117
Q

Hartnup Disease
Inheritance
PathoPhys
Presentation

A

AR
Defective Neutral AA transporter on renal and intestinal epithelial cells
Trp excretion in urine and ↓ absorption in gut –> pellagra

118
Q

Glucagon/Epi Pathway

A

Glucagon/Epi –> AC –> cAMP –> PKA –> Glycogen Phosphorylase Kinase –> Glycogen Phosphorylase –> Glycogenolysis

119
Q

Insulin Pathway

A

Insulin –> RTK –> Protein Phosphatase –/ Glycogen Phosphorylase Kinase and Glycogen Phosphorylase

120
Q

Glycogen
Branch points
Linkages

A

α(1,6) Branches

α(1,4) Linkages

121
Q

Fate of Glycogen in Skeletal Muscle

What regulate Glycogenonlysis during exercise?

A

Undergoes Glycogenolysis –> G1P –> G6P which is rapidly metabolized during exercise
Ca –> glycogenolysis

122
Q

Glycogen in Hepatocytes

A

Glycogen is stored and undergoes glycogenolysis to maintain blood sugar at appropriate levels

123
Q

Debranching Enzyme Type III

A

Acts on Limit Dextrin (4 glucose residues in branched configuration) to produce Glucose

124
Q

How is Glycogen degraded in lysosomes?

A

α-1,4-glucosidase

125
Q

Glycogen Storage Disorders
Names
What do they result in?

A

“Very Poor Carb Metabolism”
Von Gierke’s, Pompe’s, Cori’s, McArdle’s
Accumulation of glycogen within cells

126
Q 
von Gierke's Disease 
Type
Deficient enzyme
Findings 
Inheritance
A

Type I
G6Pase
Fasting hypoglycemia, ↑ glycogen in liver, ↑ lactate in blood, hepatomegaly
AR

127
Q 
Pompe's Disease 
Type
Deficient enzyme
Findings 
Inheritance
A

“Pompe trashes the Pump”
Type II
Lysosomal α-1,4-glucosidase (acid maltase)
Cardiomegaly and systemic findings leading to early death (Liver, Muscle)
AR

128
Q 
Cori's Disease 
Type
Deficient enzyme
Findings 
Inheritance
A

Type III
Debranching Enzyme (α-1,6-glucosidase
Milder form of type I with normal blood lactate levels. Gluconeogenesis intact
AR

129
Q 
McArdle's Disease 
Type
Deficient enzyme
Findings 
Inheritance
A 
McArdle's = Muscles 
Type V
Skeletal muscle glycogen phosphorylase 
↑ glycogen in muscle that cannot be broken down leading to painful muscle cramps, myoglobinuria with strenuous exercise 
AR
130
Q 
Fabry's Disease 
Kind of disease 
Deficiency 
What accumulates 
Findings 
Inheritance
A

Sphingolipidoses Lysosomal Storage Disease
α-galactosidase A
Ceramide Trihexoside accumulates
Peripheral neuropathy of hands/feet, angiokeratomas, CV/Renal disease
XR

131
Q 
Gaucher's Disease 
Kind of disease 
Deficiency 
What accumulates
Frequency  
Findings 
Histo
Inheritance
A

Sphingolipidoses Lysosomal Storage Disease
Glucocerebrosidase
Glucocerebroside
Most common
Hepatosplenomegaly, Aseptic necrosis of femur, Bone crises, Pancytopenia, Thrombocytopenia
Gaucher’s cells (macs that look like crumpled tissue paper)
AR. More common in Ashkenazi Jews

132
Q 
Niemann-Pick Disease
Kind of disease 
Deficiency 
What accumulates 
Findings 
Histo
Inheritance
A

“No man picks his nose with his SPHINGer”
Sphingolipidoses Lysosomal Storage Disease
Sphingomyelinase
Sphingomyelin
Progressive neurodegeneration, Hepatosplenomegaly, Cherry-red spots on macula
Foam cells
AR. More common in Ashkenazi Jews

133
Q 
Tay-Sachs Disease  
Kind of disease 
Deficiency 
What accumulates 
Findings 
Histo
Inheritance
A

“Tay-SaX lacks heXosaminidase”
Sphingolipidoses Lysosomal Storage Disease
Hexosaminidase A
GM2 Ganglioside
Progressive neurodegeneration, Developmental delay, Cherry-red spots on macula, No hepatosplenomegaly
Lysosomes with onion skin
AR. More common in Ashkenazi Jews

134
Q 
Krabbe's Disease 
Kind of disease 
Deficiency 
What accumulates 
Findings 
Histo
Inheritance
A

Sphingolipidoses Lysosomal Storage Disease
Galactocerebrosidase
Galactocerebroside
Peripheral neuropathy, Developmental delay, Optic atrophy
Globoid cells
AR

135
Q 
Metachromatic Leukodystrophy  
Kind of disease 
Deficiency 
What accumulates 
Findings 
Inheritance
A

Sphingolipidoses Lysosomal Storage Disease
Arylsulfatase A
Cerebroside Sulfate
Central and peripheral demyelination with ataxia, dementia
AR

136
Q 
Hurler's Syndrome 
Kind of disease 
Deficiency 
What accumulates 
Findings 
Inheritance
A

Mucopolysaccharidoses Lysosomal Storage Disease
α-L-iduronidase
Heparan sulfate, Dermatan sulfate
Developmental delay, Gargoylism, Airway obstruction, Corneal clouding, HSM
AR

137
Q 
Hunter's Syndrome 
Kind of disease 
Deficiency 
What accumulates 
Findings 
Inheritance
A

“Hunter see clearly (no corneal clouding) and aim for the X”
Mucopolysaccharidoses Lysosomal Storage Disease
Iduronate Sulfatase
Heparan sulfate, Dermatan sulfate
Mild Hurler’s + Aggressive behavior, No Corneal Clouding
XR

138
Q

Lysosomal Pathways

A

GM2 –> [Hexosaminidase A] –> GM3 –> Glucocerebroside –> [Glucocerebrosidase] –> Ceramide
Sphingomyelin –> [Sphingomyelinase] –> Ceramide
Sulfatides –> [Arylsulfatase A] –> Galactocerbroside –> [Galactocerebrosidase] –> Ceramide

139
Q

Where does Fatty Acid degradation occur?

A

In Mitochondria

140
Q

Acyl-CoA Dehydrogenase Deficiency produces…

A

↑ Dicarboxylic acids, ↓ glucose and ketones

141
Q

Carnitine Deficiency
PathoPhys
Presentation

A

Inability to transport LCFA into Mito resulting in toxic accumulation
Weakness, Hypotonia, Hypoketoic hypoglycemia

142
Q

Fatty Acid Synthesis Pathway

A

Citrate transported out of Mito via Citrate shuttle
Citrate –> [ATP citrate lyase] –> AcetylCoA
AcetylCoA + CO2 (biotin) –> MalonylCoA –> Palmitate (16 carbons)

143
Q

Fatty Acid Degradation Pathway

A

Cytoplasm:
Fatty Acid + CoA –> [FA CoA synthetase] –> Acyl-CoA
Carnitine Shuttle into Mito
Acyl-CoA –> β-oxidation (breakdown to AcetylCoA groups) –> Ketone Bodies or TCA Cycle

144
Q

Regulation of Carnitine Shuttle

A

Malonyl CoA –/ Carnitine Shuttle

145
Q 
Ketone Bodies
Where are they produced 
What are they produced from?
Names?
Where are they used?
A

Produced in liver from Fatty Acids
Acetoacetate and β-hydroxybutyrate
Used in muscles and brain

146
Q

Circumstances that lead to ketone body formation?
PathoPhys?
What are they metabolized into?
What is it excreted into?

A

Prolonged starvation and diabetic ketoacidosis: OAA is depleted for gluconeogenesis
Alcoholism: Excess NADH shunts OAA to Malate
Low OAA –> stalled TCA cycle, which shunts glucose and FFA towards production of ketone bodies
Metabolized into 2 molecules of AcetylCoA
Excreted in urine

147
Q

Urine test for ketone bodies?

A

Does not detect β-hydroxybutyrate which is favored by high redox state

148
Q

Energy sources during exercise
Seconds?
Minutes?
Hours?

A

Stored ATP drops. Creatinine Phosphate rises and falls
Rise in Anaerobic glycolysis and Aerobic metabolism and FA oxidation with Anaerobic glycolysis larger percentage
Rise in Anaerobic glycolysis and Aerobic metabolism and FA oxidation with latter having larger percentage

149
Q

Metabolism during fed state
What processes?
Hormones?

A

Glycolysis and Aerobic Respiration

Insulin stimulates storage of lipids, protein. and glycogen

150
Q

Metabolism during fasting between meals
Processes
Hormones

A 
Hepatic Glycogenolysis (major), Hepatic gluconeognesis, Adipose release FFA (minor)
Glucagon, Adrenaline stimulate use of fuel reserves
151
Q

Metabolism During Starvation Days 1-3

A

Blood glucose levels maintained by:

  1. Hepatic glycogenolysis
  2. Adipose release FFA
  3. Muscles and Liver shift from using glucose to using FFA
  4. Hepatic gluconeogenesis from peripheral tissue lactate and Ala, and from adipose tissue glycerol and propionyl-CoA (from add chain FFA)
152
Q

How long to glycogen reserves last?

A

Depleted after 1 day

153
Q

Can RBC use ketone bodies?

A

No, they lack mito

154
Q

Metabolism of Starvation after day 3

A

Adipose stores produce ketone bodies which become the main source of energy for the brain and heart. After these are depleted, protein degeneration accelerates leading to organ failure and death

155
Q

What determines survival time during starvation?

A

Adipose stores

156
Q

How much cholesterol is esterified?

A

2/3 of plasma cholesterol is esterified by lecithin-cholesterol acyltransferase (LCAT)

157
Q

Lipid intake pathway

A

Chylomicrons –> [LPL] –> FFA and Chylomicron remnant
FFA taken up by adipose and peripheral tissue
Remnant taken up by liver via Apolipoprotein E

158
Q

Hormone Sensitive Lipase

A

Degrades TG stores in adipocytes

159
Q

HDL production

A

Liver or Intestines produce Nascent HDL
Lecithin-Cholesterol Acyltransferase (LCAT) turns nascent HDL into Mature HDL by esterification of cholesterol
Cholesterol Ester Transfer Protein (CETP) mediates transfer of cholesterol esters from HDL to VLDL, IDL, and LDL

160
Q

Apolipoprotein E
Function
What is it in?

A

Mediates remnant uptake

In Chylomicron, Chylomicron Remnant, VLD, IDL, and HDL. Not LDL

161
Q

Apolipoprotein A1
Function
What is it in?

A

Activates LCAT

HDL

162
Q

Apolipoprotein C2
Function
What is it in?

A

Lipoprotein Lipase Cofactor

Chylomicron, VLDL, HDL

163
Q

Apolipoprotein B48
Function
What is it in?

A

Mediates Chylomicron Secretion

Chylomicron, Chylomicron remnant

164
Q

Apolipoprotein B100
Function
What is it in?

A

Binds LDL receptor

VLDL, IDL, LDL

165
Q

What are lipoproteins composed of?

A

Cholesterol, TG, Phospholipids

166
Q

What lipoproteins carry most cholesterol?

A

LDL and HDL

167
Q

LDL
Function
How is it formed
How is it taken up?

A

Delivers hepatic cholesterol to peripheral tissues
Formed by hepatic lipase modification of IDL in peripheral tissue
Taken up by target cells vai receptor mediated endocytosis

168
Q

HDL
Function
Repository for what?
What secretes it?

A

Mediates reverse cholesterol transport from periphery to liver
Acts as a repository for apoC and apoE (which are needed for chylomicron and VLDL metabolism)
Secreted from both liver and intestine

169
Q

Chylomicron
Function
What secretes it?

A

Delivers dietary TG to peripheral tissue and Delivers cholesterol to liver in the form of remnant (which is depleted of TGs)
Secreted by intestinal epithelial cells

170
Q

VLDL
Function
What secretes it?

A

Delivers hepatic TG to peripheral tissue

Secreted by liver

171
Q

IDL
How is it formed
Function

A

Formed in the degradation of VLDL

Delivers TG and cholesterol to liver

172
Q 
I-Hyper-Chylomicronemia 
Inheritance 
PathoPhys
Blood test?
Presentation
A

AR
LPL deficiency or altered apoC2
↑ chylomicrons, TG, cholesterol
Pancreatitis, HSM, Eruptive/Pruritic Xanthomas, No ↑ risk for atherosclerosis

173
Q 
IIa-Familial-HyperCholesterolemia 
Inheritance 
PathoPhys
Blood test?
Presentation
A

AD
Absent of decreased LDL receptor
↑ LDL and cholesterol
Accelerated atherosclerosis, Achilles tendon xanthomas, Corneal arcus

174
Q 
IV HyperTriglyceridemia 
Inheritance 
PathoPhys
Blood test?
Presentation
A

AD
Hepatic overproduction of VLDL
↑ VLDL and TG
Pancreatitis

175
Q 
Abetalipoproteinemia 
Inheritance 
PathoPhys
Onset
Presentation
Histo
Presentation
A

AR
Defective Microsomal TG Transfer Protein (MTP) –> ↓B48 and B100 –> ↓ chylomicron and VLDL synthesis and secretion
Symptoms appear in the 1st few months of life
Biopsy shows lipid accumulation in enterocytes. Blood shows Acanthocytosis
Failure to thrive, Steatorrhea, Ataxia, Night blindness

176
Q

What happens in Mitochondria

A

Fatty acid oxidation (β oxidation), Acetyl-Coa Production, TCA cycle, Oxidative Phosphorylation

177
Q

What happens metabolically in the Cytoplasm?

A

Glycolysis, Fatty Acid Syntesis, HMP shunt, Protein Synthesis (RER), Steroid Synthesis (SER), Cholesterol Synthesis

178
Q

What reactions occur in both the Mitochondria and the Cytoplasm?

A

“HUGs take 2”

Heme synthesis, Urea cycle, Gluconeogenesis

179
Q

Rate limiting step of Glycolysis

Regulators

A

PFK1
+: AMP, F2,6BP
-: ATP, Citrate

180
Q

Rate limiting step of Gluconeognesis

Regulators

A

Fructose 1,6 bisphosphatase
+: ATP
-: AMP, F2,6BP

181
Q

Rate limiting step of TCA cycle

Regulators

A

Isocitrate Dehydrogenase
+: ADP
-: ATP, NADH

182
Q

Rate limiting step of Glycogen Synthesis

Regulators

A

Glycogen Synthase
+: Glucose, Insulin
-: Epinephrine, Glucagon

183
Q

Rate limiting step of Glycogenolysis

Regulators

A

Glycogen Phosphorylase
+: AMP, Epinephrine, Glucagon
-: Insulin, ATP

184
Q

Rate limiting step of HMP shunt

Regulators

A

G6PD
+: NADP
-: NADPH

185
Q

Rate limiting step of de novo pyrimidine synthesis

A

Carbamoyl Phosphate Synthetase II

186
Q

Rate limiting step of de novo purine synthesis

Regulation

A

Glutamine PRPP aminotransferase

Inhibited by AMP, IMP, and GMP

187
Q

Rate limiting step of urea cycle

Regulation

A

Carbamoyl Phosphate Synthetase I

Activated by N-acetylglutamate

188
Q

Rate limiting step of Fatty Acid Synthesis

Regulation

A

Acetyl-CoA Carboxylase (ACC)
+: Insulin, Citrate
-: Glucagon, Palmitoyl-CoA

189
Q

Rate limiting step of Fatty Acid Oxidation

Regulation

A

Carnitine Acyltransferase

Inhibited by Malonyl-CoA

190
Q

Rate limiting step of Ketogenesis

A

HMG CoA Synthase

191
Q

Rate limiting step of Cholesterol Synthesis

Regulation

A

HMG CoA Reductase
+: Insulin, Thyroxine
-: Glucagon, Cholesterol

USMLE (25 decks)

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