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Metabolism Flashcards

0
Q

What type of fuel do skeletal muscles prefer at rest?

During activity?

A

Fatty acids at rest

Glucose during exertion

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1
Q

Where does the conversion of pyruvate –> AcCoA take place?

A

The mitochondrial matrix

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2
Q

What type of fuel does cardiac muscle prefer?

A

Fatty acids

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3
Q

How many kcal are in 1g. of carbohydrate?
Protein?
Fat?

A 
Carbs = 4 kcal
Protein = 4 kcal
Fat = 9 kcal

These are according to dry weight. The vast majority (75%) of energy stored in the body is stored as fat.

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4
Q

What is sucrose composed of?

A

Glucose and fructose

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5
Q

What enzyme is responsible for cellulose digestion in humans?

A

Humans can’t digest cellulose (fiber).

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6
Q

What does SGLT1 transport?

A

Sodium-Glucose transporter 1

It transports glucose or galactose
It is a symporter with 2 Na+
It is found in the kidney tubules and intestinal mucosa

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7
Q

What does GLUT2 transport?
Where is it located?
Is is insulin-dependent?

A

GLUT 2 transports glucose.
It is INSULIN INDEPENDENT
It is located in the kidney, intestines, and liver.
It is bidirectional
Serves as the glucose sensor in the pancreas

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8
Q

What does GLUT4 transport?
Where is it located?
Is it insulin-dependent?

A

GLUT4 transports glucose
It is high affinity (higher than GLUT2)
It is located in skeletal muscle, cardiac muscle, and adipocytes.
It is INSULIN-DEPENDENT

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9
Q

Does GLUT2 or GLUT4 have a faster glucose transport rate?

A

GLUT4

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10
Q

What are normal blood glucose levels? (range)

A

60-110 mg/dL

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11
Q

Is hexokinase or glucokinase specific to hepatocytes?

A

Glucokinase is found in the liver.

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12
Q

How is hexokinase allosterically regulated?

A

It is inhibited by its product (Glu-6-P)

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13
Q

How is Glucokinase regulated?

What molecules induce this regulation?

A

It is inhibited by Fructose-6-P & activated by Glucose & Fructose-1-P.
This is accomplished by sequestration in the nucleus or translocation to the cytoplasm.
Insulin induces increased enzyme synthesis

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14
Q

Does Hexokinase or Glucokinase have a higher Km?

A

Glucokinase (liver) has a higher Km. It cannot be saturated at physiological glucose concentrations.

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15
Q

What does PFK-1 catalyze?

A

Phosphofructkinase-1

Fructose-6-P + ATP –> Fructose-1,6-Bisphospate + ADP

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16
Q

How is PFK-1 regulated?

A

It is allosterically activated/inhibited.
Activators: Fructose-2,6-bisphosphate, AMP, ADP
Inhibitors: ATP, Citrate

Fructose-2,6-bisphosphate is the product of PFK-2

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17
Q

Where do PFK-1 and PFK-2 add their phosphates?

A

They both act on Fructose-6-P as substrate.
PFK-1 adds to position 1 –> Fructose-1,6-bisphosphate
PFK-2 adds to position 2 –> Fructose-2,6-bisphosphate

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18
Q

What enzyme catalyzes:

Fructose-2,6-bisphosphate –> Fructose-6-P?

A

Fructose-2,6-bisphosphatase activity is found on the PFK-2 enzyme. It is a bidirectional enzyme.

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19
Q

How is PFK-2 regulated in the liver? What is the overall effect on glycolysis?

A

In the liver, PFK-2 activity is inhibited by glucagon and epinephrine. This leads to less Fructose-2,6-bisphosphate in the cell, so that PFK-1 is less active. This suppresses glycolysis.

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20
Q

Describe the intracellular cascade in liver cells leading to regulation of PFK-2 activity.

A

Glucagon/Epinephrine –> ^cAMP –> ^PKA activity –> phosphorylation (inactivation) of PFK-2 domain –> less Fructose-2,6-bisphosphate –> glycolysis inhibited

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21
Q

Describe the cascade leading to regulation of PFK-2 in heart and skeletal muscle.

A

EPINEPHRINE (only) –> ^cAMP –> ^PKA activity –> phosphorylation (inactivation) of phosphatase domain on PFK-2 –> increased Fructose-2,6-bisphosphate –> glycolysis activation

This is the opposite effect as seen in hepatocytes.

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22
Q

Describe the regulation of hepatic Pyruvate Kinase

A

Glucagon/Epinephrine –> phosphorylation of pyruvate kinase by PKA –> inactivation of pyruvate kinase –> hepatic glycolysis is inhibited

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23
Q

What effect does glucagon have on liver glycolysis?

Heart/skeletal muscle glycolysis?

A

Glucagon (along with epinephrine) inhibits hepatic glycolysis via PFK-2 inhibition and pyruvate kinase inhibition (both phosphorylated).

Glucagon does not inhibit muscle glycolysis. Epinephrine activates muscle glycolysis via inhibition of Fructose-2,6-bisphosphatase (part of PFK-2).

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24
Q

What effect does glucagon/epinephrine have on specific protein synthesis in the liver?

A

Glucagon/epinephrine repress transcription of 3 enzymes:
Glucokinase
PFK-1
Pyruvate Kinase

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25
Q

What enzyme converts pyruvate to lactate?
Where is it located?
What is its purpose?

A

Lactate dehydrogenase
It is found in the cytosol.
It is used to regenerate NAD+ under anaerobic conditions so that glycolysis may continue.

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26
Q

What is a lactate dehydrogenase biomarker for myocardial infarction?

A

LDH-1 > LDH-2 in the blood

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27
Q

What lactate dehydrogenase isozyme is found in skeletal muscle?
What reaction direction does it prefer?

A

The LDH-5 (M4) isozyme

It prefers pyruvate –> lactate for bursts of energy.

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28
Q

What isozyme of lactate dehydrogenase is found in heart cells?
What reaction direction does this enzyme prefer?

A

The LDH-1 (H4) isozyme is found in heart cells.

It prefers the lactate –> pyruvate direction to allow for sustained energy production.

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29
Q

What is the blood serum ratio of lactate:pyruvate typically?

A

10:1, with 10x as much lactate in the blood.

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30
Q

What reaction does Pyruvate Dehydrogenase catalyze?

A

Pyruvate + CoASH + NAD+ –> Ac-CoA + CO2 + NADH + H+

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31
Q

What vitamin cofactors are required for pyruvate dehydrogenase to function?
What are they used to build (functional forms)?

A

Thiamine (B1) –> TPP
Riboflavin (B2) –> FAD
Niacin (B3) –> NAD

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32
Q

How is Pyruvate Dehydrogenase regulated?

A

Its products (NADH & Ac-CoA) cause it to be phosphorylated and thus inhibited.

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33
Q

Where is the first point in glucose metabolism that a cell must be aerobic?

A

Pyruvate dehydrogenase gives off 1 CO2 for every molecule of pyruvate. The TCA cycle gives off 2 CO2 for every molecule of Ac-CoA.

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34
Q

What is the normal pathway to convert

galactose –> glucose-6-P?

A

Galactose –(galactokinase)–> Gal-1-P

–(Gal-1-P uridyltransferase)–> Glucose-1-P –> Glu-6-P

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35
Q

What disease is induced by a deficiency in galactokinase?

A

Galactosemia is the disease.
It manifests as a buildup of Galactitol and galactose.
Symptoms: galactosemia, galactosuria, cataract formation

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36
Q

What is the more severe form of galactosemia caused by?
How is it inherited?
What builds up in the body?
What are the symptoms associated?

A

Gal-1-P Uridyl Transferase deficiency.
It is autosomal recessive (as is galactokinase deficiency)
Galactitol and Gal-1-P accumulate in the body.
Symptoms: Cataracts, galactosemia, galactosuria, elevated
Gal-1-P, hepatic dysfunction (reactions occur in liver), mental retardation.

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37
Q

What is the normal metabolic pathway of fructose?

A

Fructose –(Fructokinase)–> Fructose-1-P
EITHER:
Fructose-1-P –(Aldolase B)–> Dihydroxyacetone-P
OR:
Frucose-1-P –> Fructose-1,6-bisphosphate
–(Aldolase A)–> Glyceraldehyde-3-P

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38
Q

What causes hereditary Fructose intolerance?
How is it inherited?
What are its associated symptoms?

A

Aldolase B deficiency –> hereditary Fructose intolerance.
It is an autosomal recessive disorder.
Aldolase B is normally found in hepatocytes and RBC’s.
Symptoms: Hypoglycemia, jaundice, vomiting, hepatic failure.

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39
Q

What is the only TCA cycle enzyme not located in the mitochondrial matrix?

A

Succinate dehydrogenase. It is located in the mitochondrial inner membrane.

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40
Q

What forms of energy are produced (and amounts) in the TCA cycle, per molecule Ac-CoA?

A

3 NADH
1 FADH2
1 GTP

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41
Q

What steps produce the 3 NADH seen in the TCA cycle?

A

Isocitrate Dehydrogenase (also produces CO2)
alpha-Ketoglutarate Dehydrogenase (also produces CO2)
Malate Dehydrogenase

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42
Q

What step in the TCA cycle is responsible for FADH2 production?

A

Succinate Dehydrogenase

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43
Q

What step in the TCA cycle is responsible for GTP production?

A

Succinyl-CoA Synthetase

aka Succinate Thiokinase

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44
Q

How many ATP equivalents equal one NADH molecule?

FADH2?

A

1 NADH –> 2.5 ATP in ETC
1 FADH2 –> 1.5 ATP in ETC

So 9 total ATP & 1 GTP from 1 molecule Ac-CoA.

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45
Q

How is Isocitrate Dehydrogenase regulated?

A

NADH –> inhibits
ATP –> inhibits
ADP –> activates

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46
Q

How is alpha-Ketoglutarate Dehydrogenase regulated?

A

Ca2+ –> activates
Inhibits: ATP, GTP, Succinyl CoA, NADH

Increased Ca2+ can mean muscle contraction or general stress on the cell.

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47
Q

What is the only TCA cycle enzyme seen to be deficient in some patients?
How is it inherited?
What cannot be catalyzed?
What are the symptoms?

A

Fumarase deficiency
It is autosomal recessive
Fumarate –> Malate cannot be accomplished
Symptoms: Encephalopathy; Dystonia; increased urinary excretion of fumarate, succinate, alpha-ketoglutarate, and, citrate

**This is the only TCA deficiency seen. This is likely because all other deficiencies are lethal in-utero.

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48
Q

Where does gluconeogenesis take place?

Why is this important?

A

It takes place in the liver, intestines, and kidney.

This is important because Glu-6-P is formed, and these organs express Glucose-6-Phosphatase.

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49
Q

What does aspartic acid enter into gluconeogenesis as?

A

Oxaloacetate, whereas alanine enters as pyruvate

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50
Q

Describe the stoichiometry of the Cori cycle.

A

The Cori cycle (Glucose-lactate cycle) takes 2 molecules of lactate and 6 ATP to produce 1 molecule of glucose.

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51
Q

Describe the stoichiometry of the alanine cycle.

A

2 molecules of alanine take 10 ATP in order to produce 1 molecule of glucose. This is because the conversion from 2 pyruvate to 1 glucose takes 6 ATP, and 2 additional ATP must be consumed per round of NH2 –> urea.

Thus, conversion of alanine takes 4 more ATP than the Cori cycle (Glucose-lactate cycle).

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52
Q

During an overnight fast, what serves as the primary supply of ATP for gluconeogenesis?

A

Fatty acid oxidation

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53
Q

How many Glucose molecules can be made from one Ac-CoA?

A

None, Ac-CoA cannot participate in gluconeogenesis.

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54
Q

How does Glycerol enter gluconeogenesis?

A

Glycerol –(glycerol kinase)–> Glycerol-3-P
–(Glycerol-3-P Dehydrogenase)–> Dihydroxyacetone-P

NADH is generated in the second step
Dihydroxyacetone-P is an intermediate in glycolysis (1/2 Glu)

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55
Q

What two enzymes are required to reverse pyruvate kinase’s effects?
How are the regulated?
What is required?

A

Pyruvate Carboxylase & PEP Carboxykinase
Pyruvate carboxylase is activated by Ac-CoA & biotin is required for the enzyme’s function.

(gluconeogenesis)

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56
Q

What enzyme can do the reverse reaction of PFK-1?

A

Fructose-1,6-Bisphosphatase
Fructose-1,6-Bisphosphate –> Fructose-6-P
(gluconeogenesis)

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57
Q

What enzyme can perform the reverse reaction of hexokinase?

A

Glucose-6-Phosphatase
Only found in the liver, kidneys, & intestines
(gluconeogenesis)

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58
Q

Pyruvate Carboxylase genetic deficiency.
What reaction cannot occur?
What are the symptoms?

A

Pyruvate –> Oxaloacetate is blocked
Symptoms: Developmental delay; seizures; metabolic acidosis; elevated serum lactic acid; elevated serum alanine.

High blood [pyruvate] is converted to lactate and alanine

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59
Q

How is Fructose-1,6-Bisphosphatase regulated?

A

(gluconeogenesis)
It is inhibited by Fructose-2,6-Bisphosphate (product of PFK-2)
It is also inhibited by AMP

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60
Q

Is Glucose-6-Phosphatase cytosolic?

Why is this important?

A

It is in the LUMEN of the ER (membrane protein).
This means that if the enzyme, OR the transporter is faulty, gluconeogenesis will be backed up.

This leads to glycogen storage disease.

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61
Q 
GSD Type I:
What is its other name?
What is deficient?
How is it inherited?
What are the symptoms?
A

Von Gierke Disease (Type Von)
Glucose-6-Phosphatase is deficient.
It is an autosomal recessive disease.
Symptoms: low tolerance to fasting; growth retardation; hepatomegaly; elevated serum uric acid; elevated serum lactate.

Uric acid is due to increased purine production via Pentose Phosphate pathway & increased purine degradation –> uric acid

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62
Q

How is gluconeogenesis regulated in general?

A

The irreversible steps are generally regulated opposite of their counterparts in glycolysis.

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63
Q

How is Glucose-6-Phosphatase regulated?

A

Glucose inhibits
Insulin inhibits
Glucagon acivates

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64
Q

How is Fructose-1,6-Bisphosphatase regulated?

A

(reverse reaction of PFK-1)
ATP activates
Fructose-2,6-Bisphosphate inhibits
AMP inhibits

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65
Q

How is Phosphoenolpyruvate Carboxykinase (PEPCK) regulated?

A

(part of reverse-pyruvate kinase rxn)
(gluconeogenesis)
Glucagon activates
Insulin inhibits

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66
Q

How is Pyruvate Carboxylase regulated?

A

(gluconeogenesis)
(part of reverse-pyruvate kinase reaction)
Acetyl-CoA activates

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67
Q

What effect do Glucagon & Epinephrine have on gluconeogenic enzyme synthesis?

A 
They promote synthesis of gluconeogenic enzymes.
Pyruvate carboxylase
PEPCK
Fructose-1,6-Bisphosphatase
Glucose-6-Phosphatase
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68
Q

What effect does ethanol have on metabolism?

What can be caused by this?

A

Ethanol metabolism (ethanol dehydrogenase) increases the NADH/NAD ratio. This causes conversion of pyruvate & oxaloacetate to lactate & malate. These cannot participate in gluconeogenesis, so hypoglycemia is often seen.

Pyruvate + NADH –> Lactate

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69
Q

What does a dehydrogenase enzyme do?

A

It transfers a hydride to another molecule. This is an oxidation reaction.

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70
Q

What is a mutase?

A

A mutase is a type of isomerase that transfers a group from one part of a molecule to another.

Ex: Transferring a phosphate from one carbon to another in a ring

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71
Q

What reaction does Pyruvate Carboxylase catalyze?

Where in the cell is this enzyme found?

A

It catalyzes Pyruvate –> Oxaloacetate (fasted state)

It is found in the mitochondria.

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72
Q

How much glycogen can a healthy liver store?

Skeletal muscle?

A

Liver = 100g

Skeletal muscle = 400g

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73
Q

What is the substrate of glycogen synthase?

How does branching enzyme work?

A

Glycogen synthase utilizes UDP-Glucose monomers.

Branching enzyme moves branches over from alpha-1,4 to alpha-1,6 linkages.

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74
Q

What enzymes are involved in glycogen degradation? How do they work?

A

Glycogen Phosphorylase cleaves alpha-1,4 linkages.

Debranching enzyme moves branches over to a nearby branch, leaving one residue in place. It then hydrolyzes the alpha-1,6 linkage to liberate the final residue.

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75
Q

How is glycogen phosphorylase regulated?

A

Second messengers (cAMP, IP3, Ca2+) activate Phosphorylase Kinase. Phosphorylase Kinase activates Glycogen Phosphorylase –> glycogen degradation.

Insulin causes dephosphorylation of Glycogen Phosphorylase –> no glycogen degradation.

AMP can override this phosphorylation regulation when AMP is high, causing activation, even when the enzyme has no P.
ATP can also override this, by binding to the active form and inhibiting it. AMP wins in this battle, but only under conditions when it is high (muscle activity).

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76
Q

Describe insulin and glucagon’s effect on the phosphorylation state of glycogen synthase and glycogen phosphorylase.
What effect does this have on glycogen content in the cell.

A

Insulin causes dephosphorylation of both glycogen synthase and glycogen phosphorylase. Glucagon causes phosphorylation of both enzymes.

Glycogen synthase is inactive when phosphorylated, glycogen phosphatase is active when phosphorylated.

Insulin –> glycogenesis
Glucagon –> glycogenolysis

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77
Q

What is cAMP’s effect in liver cells?

Muscle cells?

A

cAMP promotes glycogen degradation and inhibits glycogenesis in both tissues.

In liver, cAMP inhibits glycolysis, however in muscle, cAMP stimulates glycolysis (via PFK regulation).

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78
Q

What is the effect of excess Glu-6-P on glycogen content?

A

Glu-6-P can allosterically activate dephosphorylated glycogen synthase, even in the absence of insulin. This is generally in pathogenic situations, such as GSD’s.

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79
Q

Which 4 glycogen storage diseases have the same symptoms?
What are the symptoms?
Which is the most severe?

A

GSD’s: I, III, VI, VIII

Symptoms:
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis

GSD I is the most severe form

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80
Q

What is GSD Type I called?
What is its deficiency?
What organ does it affect?
What are its symptoms?

A

Von Gierke’s
Glucose-6-Phosphatase deficiency
Transporter can also be deficient, since this enzyme is in the ER.
Affects the liver

Symptoms (I, III, VI, VIII the same):
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis
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81
Q

What is GSD Type II called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Pompe’s Disease
1,4-Glucosidase deficiency
Affects all organs

Symptoms:
Cardiomegaly
Cardiorespiratory failure (early in life)
Hypotonia

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82
Q

What is GSD Type III called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Cori’s Disease
Amylo-1,6-Debranching Enzyme deficiency
Affects muscle & liver

Symptoms (I, III, VI, VIII):
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis
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83
Q

What is GSD Type IV called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Anderson’s Disease
Branching Enzyme Deficiency
Affects liver & spleen

Symptoms:
Cirrhosis of liver
Liver failure before age 2

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84
Q

What is GSD Type V called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

McArdle’s Disease
Phosphorylase deficiency
Affects muscle

Symptoms (V & VII the same):
Limited exercise ability
Painful muscle cramps

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85
Q

What is GSD Type VI called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Hers’ Disease
Phosphorylase deficiency
Affects the liver

Symptoms (I, III, VI, VIII the same):
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis
86
Q

What is GSD Type VII called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

No given name
PFK-1 deficiency
Affects muscle

Symptoms (V & VII the same):
Limited exercise ability
Muscle cramps

87
Q

What is GSD Type VIII called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

No name given
Phosphorylase Kinase deficiency
Affects the liver

Symptoms (I, III, VI, VIII, but this is least severe):
Mild hypoglycemia
Mild hepatomegaly

88
Q

What are the symptoms of Glycogen Synthase deficiency?

A

The liver is affected mostly. Glycogen levels are decreased.
Hypoglycemia
Postprandial lactic acidemia
Fasting ketosis

89
Q

What enzyme deficiency can lead to hemolytic anemia?
How is it inherited?
How does this deficiency lead to hemolytic anemia?

A

Glucose-6-P Dehydrogenase deficiency (pentose phosphate path)

It is X-linked inheritance

Normally G6PD yields NADPH. NADPH keeps glutathione in a reduced state that protects RBC’s from oxidative damage by detoxifying H2O2 and other ROS.

This is usually exacerbated by oxidizing drugs, favism, or infection (produces free radicals).

90
Q

What is the rate-limiting enzyme in the Pentose Phosphate Pathway?

A

Glucose-6-P Dehydrogenase

91
Q

How are fatty acids transported in the fed state?

Fasted state?

A

Fed –> transported as triacylglycerols on lipoproteins

Fasted –> transported bound to albumin

92
Q

What are the essential fatty acids?

A 
omega-3 = alpha-Linolenic Acid
omega-6 = Linoleic Acid
93
Q

What is the overall reaction for fatty acid biosynthesis?

A

Acetyl-CoA + 7 Malonyl-CoA + 14 NADPH + 14 H+ —>

Palmitate + 7 CO2 + 8 CoASH + 14 NADP+ +6 H2O

94
Q

What is Citrate’s role in FA biosynthesis?

A

Citrate transports acetyl groups from the mitochondrial matrix to the cytoplasm. Its presence also stimulates Acetyl-CoA carboxylase.

It is eventually recycled back into the mitochondria as pyruvate.

95
Q

What is the rate-limiting enzyme in fatty acid synthesis?
What reaction does it catalyze?
How is it allosterically regulated?
How is it hormonally regulated?

A

Acetyl-CoA Carboxylase
Acetyl-CoA —> Malonyl-CoA
Allosteric Activators: Citrate
Allosteric Inhibitors: Palmitoyl-CoA
Hormonal Activators: Insulin (dephosphorylation)
Hormonal Inhibitors: Glucagon; Epinephrine (phosphorylation)

96
Q

What enzyme is responsible for adding Malonyl groups to a growing fatty acid?
How many cycles are performed per fatty acid?

A

Fatty Acid Synthase

It performs the reaction 7 times to yield a 16C palmitate.

97
Q

What enzyme is implicated in splitting TAG’s into glycerol and FA’s?

A

Hormone-sensitive Triacylglycerol Lipase

98
Q

What enzyme is required for HSTL to successfully translocate to the surface of lipid droplets?

A

Perilipin

99
Q

What hormones affect TAG breakdown?

How does this occur?

A

Epinephrine –> ^cAMP –> PKA –> phosphorylation of HSTL and Perilipin –> TAG breakdown.
ACTH also has this effect.

Thyroid hormones and adrenal cortical hormones do not stimulate TAG breakdown but are permissive of it (required).

Insulin & prostaglandins inhibit HSTL (dephosphorylated)

100
Q

What is the fate of FA’s released from TAG’s by HSTL?

A

They are released and transported bound to albumin in the bloodstream. Once at their target tissue (liver, muscle, etc.) they will undergo beta-Oxidation.

101
Q

What is glycerol’s fate once liberated from TAG’s by HSTL?

A

It is transported to the liver and kidneys. Glycerol Kinase phosphorylates it to Glycerol-3-P, which can participate in gluconeogenesis.

102
Q 
Complete beta-Oxidation of Palmitate yields:
NADH?
FADH2?
Acetyl-CoA?
Final total ATP?
A

7 NADH
7 FADH2
8 Acetyl-CoA
106 total ATP

103
Q

What is carnitine responsible for?

A

Carnitine carries long chain FA’s into the mitochondrial matrix for beta-Oxidation. Deficiency results in less beta-Oxidation and less ATP production.

104
Q

What enzyme transports acyls across the mitochondrial outer membrane?
How is this enzyme regulated?

A

Carnitine Palmitoyltransferase-I (CPT-1)

It is inhibited by Malonyl-CoA. Malonyl-CoA is high during the fed state.

105
Q

What are the two ketone bodies produced in the body?

Where are they produced?

A

Acetoacetic Acid
beta-Hydroxybutyric Acid

They are produced in liver mitochondria.

106
Q

Describe Acetoacetate production, beginning with Acetyl-CoA

A

2 Acetyl-CoA —> Acetoacetyl-CoA

Acetoacetyl-CoA + Acetyl-CoA —(HMG-CoA Synthase) —>
HMG-CoA

HMG-CoA —> Acetoacetate + Acetyl-CoA

So 2 Acetyl-CoA are utilized to make Acetoacetate, and one additional one is used and then regenerated.

107
Q

What enzyme is the rate-limiting enzyme in ketone body formation?

A

HMG-CoA Synthase

108
Q

What enzyme is required for utilization of ketone bodies?
What reaction does it catalyze?
Where is it found?

A

Acetoacetate:Succinyl-CoA Transferase (or Thiophorase)

Transfers CoA from succinyl-CoA to acetoacetate, to yield acetoacetyl-CoA and succinate.

Found in extrahepatic tissues, but not in the liver.

109
Q

How is beta-Oxidation regulated?

A

Carnitine Palmitoyltransferase-I (CPT-1) is regulated.
This enzyme is responsible for transferring acyls into the mitochondria.
It is inhibited by malonyl-CoA (an intermediate of FA synthesis)

110
Q

How is ketone body production regulated?

A

Indirectly via availability of Acetyl-CoA from

lipolysis/beta-Oxidation or hepatocyte glycolysis.

111
Q

How is synthesized cholesterol transported in the blood?

A

As VLDL

112
Q

What is the rate-limiting enzyme in cholesterol synthesis?

What reaction does it catalyze?

A

HMG-CoA Reductase

HMG-CoA + 2 NADPH –> Mevalonic Acid + 2 NADP+ + CoASH

113
Q

How is HMG-CoA Reductase regulated?

What drug type can inhibit this enzyme?

A

Transcription: inhibited by cholesterol sterols
Translation: Inhibited by Mevalonate sterols
Stability: Degradation promoted by both types
Phosphorylation: Phosphorylated (inhibited) due to AMP/Glucagon

STATINS can inhibit it

114
Q

What is the rate-limiting enzyme in bile acid synthesis?

How is it regulated?

A

7-alpha-hydroxylase

It is activated by cholesterol

115
Q

What enzyme is responsible for cholesterol storage?

How is it regulated?

A

ACAT
Acyl-CoA Cholesterol Acyl-Transferase

It is activated by cholesterol

116
Q

What occurs with excess of cholesterol?

What occurs with shortage of cholesterol?

A

Excess:
Decreased synthesis (HMG-CoA Reductase inhibited)
Increased bile acids (7-alpha-hydroxylase activated)
Increased storage (ACAT activated)

Shortage = the opposite

117
Q

What is larger, HDL or LDL lipoproteins?

A

LDL is larger.

Chylomicrons > VLDL > LDL > HDL

118
Q

What type of apolipoproteins are found in VLDL?

A

B-100, A, C, E

119
Q

What is the main transport function of VLDL?

A

Transports synthesized TAG’s from the liver to adipose & muscle tissue.

120
Q

What is the transport function of LDL?

A

Transports cholesterol to the liver and other steroidogenic cells.

121
Q

How are LDL’s formed?

A

They are processed in the circulation from IDL’s, which are processed from VLDL’s.

122
Q 
What type(s) of apoproteins does LDL contain?
HDL?
A

LDL: B-100 only
HDL: A, C, E

123
Q

What are the functions of HDL?

A

Accepts cholesterol from peripheral tissues, esterifies it, and delivers it to the liver.

Exchanges Cholesterol esters for TAG’s in VLDL, IDL, & LDL

Reservoir for apoproteins

Atheroprotective by preventing oxidation of VLDL

124
Q

What type of apoproteins are found in IDL?

A

B-100, E

125
Q

What type of B apoprotein is found in chylomicrons?

Other apoproteins?

A

Chylomicrons: B-48
Other: B-100

126
Q

What is the function of ApoB-100?

A

It binds the LDL receptor.

127
Q

What is the function of Apo A-I?

A

It binds the HDL receptor & is a cofactor for Lecithin:Cholesterol Acyl Transferase (LCAT).

128
Q

What is the function of Apo C-II?

A

It is a cofactor for lipoprotein lipase.

129
Q

What is the function of Apo E?

A

It is the remnant receptor. It binds to LDL receptors.

130
Q

What do STATINS inhibit?

What effects are seen?

A

They inhibit HMG-CoA Reductase (cholesterol formation).

Less cholesterol, more LDL receptors, more removal of circulating cholesterol.

131
Q

What are foam cells?

A

Macrophages that have taken up oxidized lipids. They are indicative of excessive cholesterol in the blood.

132
Q

What Apoproteins are found on nascent HDL?

Mature HDL?

A

Nascent: Apo A-I, Apo E, Apo C-II.
Mature: Apo A-I

133
Q

What enzyme facilitates the exchange of HDL cholesterol esters for VLDL/IDL/chylomicron triacylglycerols?

A

CETP
Cholesterol Ester Transfer Protein

This is important because this is one method of getting cholesterol back to the liver.

134
Q

What enzymes are involved in glycogen degradation? How do they work?

A

Glycogen Phosphorylase cleaves alpha-1,4 linkages.

Debranching enzyme moves branches over to a nearby branch, leaving one residue in place. It then hydrolyzes the alpha-1,6 linkage to liberate the final residue.

135
Q

How is glycogen phosphorylase regulated?

A

Second messengers (cAMP, IP3, Ca2+) activate Phosphorylase Kinase. Phosphorylase Kinase activates Glycogen Phosphorylase –> glycogen degradation.

Insulin causes dephosphorylation of Glycogen Phosphorylase –> no glycogen degradation.

AMP can override this phosphorylation regulation when AMP is high, causing activation, even when the enzyme has no P.
ATP can also override this, by binding to the active form and inhibiting it. AMP wins in this battle, but only under conditions when it is high (muscle activity).

136
Q

Describe insulin and glucagon’s effect on the phosphorylation state of glycogen synthase and glycogen phosphorylase.
What effect does this have on glycogen content in the cell.

A

Insulin causes dephosphorylation of both glycogen synthase and glycogen phosphorylase. Glucagon causes phosphorylation of both enzymes.

Glycogen synthase is inactive when phosphorylated, glycogen phosphatase is active when phosphorylated.

Insulin –> glycogenesis
Glucagon –> glycogenolysis

137
Q

What is cAMP’s effect in liver cells?

Muscle cells?

A

cAMP promotes glycogen degradation and inhibits glycogenesis in both tissues.

In liver, cAMP inhibits glycolysis, however in muscle, cAMP stimulates glycolysis (via PFK regulation).

138
Q

Which 4 glycogen storage diseases have the same symptoms?
What are the symptoms?
Which is the most severe?

A

GSD’s: I, III, VI, VIII

Symptoms:
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis

GSD I is the most severe form

139
Q

What is GSD Type I called?
What is its deficiency?
What organ does it affect?
What are its symptoms?

A

Von Gierke’s
Glucose-6-Phosphatase deficiency
Transporter can also be deficient, since this enzyme is in the ER.
Affects the liver

Symptoms (I, III, VI, VIII the same):
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis
140
Q

What is GSD Type II called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Pompe’s Disease
1,4-Glucosidase deficiency
Affects all organs

Symptoms:
Cardiomegaly
Cardiorespiratory failure (early in life)
Hypotonia

141
Q

What is GSD Type III called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Cori’s Disease
Amylo-1,6-Debranching Enzyme deficiency
Affects muscle & liver

Symptoms (I, III, VI, VIII):
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis
142
Q

What is GSD Type IV called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Anderson’s Disease
Branching Enzyme Deficiency
Affects liver & spleen

Symptoms:
Cirrhosis of liver
Liver failure before age 2

143
Q

What is GSD Type V called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

McArdle’s Disease
Phosphorylase deficiency
Affects muscle

Symptoms (V & VII the same):
Limited exercise ability
Painful muscle cramps

144
Q

What is GSD Type VI called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

Hers’ Disease
Phosphorylase deficiency
Affects the liver

Symptoms (I, III, VI, VIII the same):
Enlarged liver
Hypoglycemia
Hyperuricemia
Hyperlipidemia
^ Lactate
Mental Retardation
Gouty Arthritis
145
Q

What is GSD Type VII called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

No given name
PFK-1 deficiency
Affects muscle

Symptoms (V & VII the same):
Limited exercise ability
Muscle cramps

146
Q

What is GSD Type VIII called?
What is its deficiency?
What organs does it affect?
What are its symptoms?

A

No name given
Phosphorylase Kinase deficiency
Affects the liver

Symptoms (I, III, VI, VIII, but this is least severe):
Mild hypoglycemia
Mild hepatomegaly

147
Q

What are the symptoms of Glycogen Synthase deficiency?

A

The liver is affected mostly. Glycogen levels are decreased.
Hypoglycemia
Postprandial lactic acidemia
Fasting ketosis

148
Q

What enzyme deficiency can lead to hemolytic anemia?
How is it inherited?
How does this deficiency lead to hemolytic anemia?

A

Glucose-6-P Dehydrogenase deficiency (pentose phosphate path)

It is X-linked inheritance

Normally G6PD yields NADPH. NADPH keeps glutathione in a reduced state that protects RBC’s from oxidative damage by detoxifying H2O2 and other ROS.

This is usually exacerbated by oxidizing drugs, favism, or infection (produces free radicals).

149
Q

What is the rate-limiting enzyme in the Pentose Phosphate Pathway?

A

Glucose-6-P Dehydrogenase

150
Q

How are fatty acids transported in the fed state?

Fasted state?

A

Fed –> transported as triacylglycerols on lipoproteins

Fasted –> transported bound to albumin

151
Q

What is the suggested dietary protein intake for a 70kg person?
What does this translate into per kg?

A

55 g/day

0.76 g/kg/day

152
Q

How much protein is obligatorily degraded each day?

A

55 g./day for a 70kg person.

This must be replaced by dietary protein intake in order to remain in nitrogen equilibrium.

153
Q

How much protein is turned over per day in the body?

Protein synthesis = protein degradation

A

300 g/day

154
Q

What do all transaminases use as an amino acceptor?

What does this form?

A

All use alpha-Ketoglutarate.

This forms glutamate.

155
Q

What cofactor is required for transamination reactions?

A

Pyridoxal Phosphate (Vit. B6)

Transamination is the first step in amino acid degradation.

156
Q

What is ALT?
Why is it clinically relevant?
What are its products?

A

Alanine Transaminase

It indicates tissue damage when found at high serum titer. Usually indicated liver/renal/pancreatic damage.

It produces glutamate and pyruvate.

157
Q

What is AST?
Why is it clinically relevant?
What are its products?

A

Aspartate Transaminase

It indicates tissue damage. Can indicate damage to a variety of organ systems.

Its products are glutamate and oxaloacetate.

158
Q

What reaction does AST catalyze?

Why is this important?

A

Glutamate + OAA alpha-Ketoglutarate + Aspartate

This is important because in the second step of A.A. degradation, half of the glutamate produced by transaminases is converted to Aspartate (& regenerated alpha-Ketoglutarate)

The other half of the glutamate is used to form ammonia.

159
Q

What reaction does Glutamate Dehydrogenase catalyze?

Why is this important?

A

Glutamate + NADP+ + H2O –> NH4+ + alpha-Ketoglutarate + NADPH

This reaction takes up half of the glutamate formed during the transamination seen during protein degradation. The ammonia produced will form urea.

160
Q

What substrates can enter the urea cycle?

A

Aspartate and ammonia

161
Q

What is the major regulated step in the urea cycle?

What activator is required?

A

Carbamoyl Phosphate Synthetase I
N-acetylglutamate

N-acetylglutamate is high when glutamate is plentiful

162
Q

What is the overall reaction of the urea cycle?

A

Aspartate + NH3 + CO2 + 3ATP + 3H2O —->

Urea + Fumarate + 2ADP + AMP

163
Q

What is the enzyme that catalyzes the formation of Urea?

A

Arginase

Arginine + H2O —> Urea + Ornithine

164
Q

Where do Urea cycle reactions take place?

A

Generation of Carbamoyl Phosphate and Citrulline = mitochondria
All others = cytosol.

Ornithine and Citrulline are exchanged via a transporter.

165
Q

What two AA’s are present in higher serum titers than other AA’s?
Why?

A

Alanine and Glutamine

They serve as transporters of nitrogen to the liver

166
Q

Define glucogenic and ketogenic.

What are the amino acids that are strictly ketogenic?

A

Glucogenic: Carbon skeletons produce TCA intermediates or pyruvate. Gluconeogenesis follows.

Ketogenic: Carbon skeletons produce Acetyl-CoA, Acetoacetyl-CoA, or Acetoacetate. Ketogenesis follows.

Leucine and Lysine are strictly ketogenic. Others are either glucogenic or mixed.

167
Q

How long are protein half lives?

A

10 mins to 2 weeks

168
Q

How is net protein turnover controlled in the fed & fasted state?

A

Fed: Insulin –> Net protein synthesis

Overnight fast: Glucagon –> Net protein degradation & gluconeogenesis

169
Q

What enzyme is deficient in phenylketonuric patients?
What builds up if too much phenylalanine is ingested?
What should a PKU patient’s diet look like?

A

Phenylalanine Hydroxylase
Phenylpyruvic Acid builds up in the blood
These patients now need Tyrosine as an essential AA and should limit Phenylalanine but not eliminate it fully.

170
Q

What is the major regulated enzyme in purine synthesis?

What are its allosteric regulators?

A

Glutamine PRPP Amidotransferase
5-Phosphoribosyl-1-Pyrophosphate –> 5-Phosphoribosylamine
Activator: PRPP
Inhibitors: IMP, AMP, GMP

171
Q

What drug inhibits Purine biosynthesis?

A

6-Mercaptopurine
It is an adenine with a sulfur instead of a Nitrogen.
It inhibits Glutamine PRPP Amidotransferase and other steps in the pathway.

172
Q

What enzyme dephosphorylates glycogen synthase and glycogen phosphorylase in response to insulin?

A

Phosphoprotein Phosphatase

173
Q

What enzyme catalyzes Acetyl-CoA –> Malonyl-CoA
What cofactor does this require?
What are its allosteric effectors?

A 
Acetyl-CoA Carboxylase
First step in FA synthesis
Requires Biotin
Activator: Citrate
Inhibitor Palmitoyl-CoA

Insulin & Glucagon/Epinephrine also affect its activity

174
Q

What is Wernicke’s encephalopathy?
What causes it?
Symptoms?

A

Caused by a Thiamine deficiency, it prevents Pyruvate Dehydrogenase activity.

Symptoms:
Retardation, poor muscle tone, poor coordination.

175
Q

What does arsenic poisoning affect?

A

Pyruvate Dehydrogenase complex. Inhibits the third reaction.

176
Q

What cofactor do carboxylase enzymes typically require?

A

Biotin

177
Q

What enzymes is citrate an effector for?

A

Activates:
Acetyl-CoA Carboxylase (Acetyl-CoA –> Malonyl-CoA) (FA Synth)

Inhibits:
PFK-1

178
Q

What enzyme catalyzes the formation of dTMP?

What drug inhibits this enzyme?

A

Thymidylate Synthase
5-fluorouracil

This enzyme normally catalyzes dUMP –> dTMP.
It requires N5,N10-methylene Tetrahydrofolate.

179
Q

What enzyme catalyzes Dihydrofolate –> Tetrahydrofolate?

What drug inhibits this?

A

Dihydrofolate Reductase
Methotrextate inhibits it

This creates an effective folate deficiency, inhibiting
dUMP –> dTMP and preventing DNA synthesis.

180
Q

What enzyme is responsible for the formation of DNA from RNA?
What cofactor is required?
What drug inhibits this?

A

Ribonucleotide Reductase
Thioredoxin is required
Hydroxyurea inhibits it

181
Q

What percent of purines are “salvaged” rather than degraded?

A

90% are salvaged

182
Q

What causes Lesch-Nyhan Syndrome?

What are its symptoms?

A

HGPRT deficiency (purine salvage)

Symptoms: mental retardation, compulsive self-mutilation, gout.

183
Q

What is the enzyme involved in degradation of purines?
What drug inhibits it?
What is this a treatment for?

A

Xanthine Oxidase
Allopurinol inhibits it
Used as a treatment for gout and renal uric acid stones.

184
Q

What is ABCA1?

Its function?

A

ATP-binding cassette transporter A-1

It transports cholesterol from tissues into HDL’s.

185
Q

What is LCAT?

Function?

A

Lecithin-cholesterol Acyltransferase

Esterizes cholesterol in HDL’s

186
Q

Are purine or pyrimidine bases built onto the ribosyl group or built and then added later?

A

Purines are built onto a ribosyl group.

Pyrimidines are built completely and then added onto the sugar.

187
Q

What is the major regulated enzyme in pyrimidine synthesis?

A

Carbamoyl Phosphate Synthetase II

Glutamine + CO2 + 2ATP are inputs

188
Q

What carbon is acted on by ribonucleotide reductase?

A

2’ hydroxyl is replaced by a hydrogen

189
Q

What enzyme is the regulated step in Heme synthesis?
How is it regulated?
What is the reaction?

A

ALA Synthase

Inhibited by heme (ALAS1 only; liver only)

Succinyl-CoA + Glycine –> ALA (first step)

190
Q

What ALA Synthase isoform is found in the liver?
In bone marrow?
Which is regulated?

A

Liver = ALAS1
Bone marrow = ALAS2

ALAS1 (liver) is inhibited by heme. ALAS2 is not.

191
Q

Where in the cell does heme synthesis occur?

A

Begins in mitochondria
Steps 2-5 in cytosol
Steps 6-8 in mitochondria again

192
Q

What are porphyrias?

A

Diseases due to deficiencies in heme synthesis enzymes. The symptoms are due to buildup of intermediates, not heme deficiency. Sunlight can exacerbate, since it converts porphyrinogens to porphyrins.

193
Q

What are the fates of the components of hemoglobin?

A

Globin –> free AA’s
Heme –> Fe (reused) & biliverdin

Biliverdin will be converted to bilirubin & excreted

194
Q

How is unconjugated bilirubin transported?

Where is it transported to/from?

A

It is found attached to Albumin.

It is transported from the reticuloendothelial system (macrophages) to the liver, to be conjugated.

195
Q

What gives poop its brown color?

What is reabsorbed and then excreted in urine?

A

Stercobilins give poop its color.

Some urobilinogen is reabsorbed and then excreted in urine.

196
Q

What group is added to unconjugated bilirubin (multiple times) to yield conjugated bilirubin?

A

Glucuronic acid

Yields bilirubin diglucuronide

197
Q

How can porphyrinogens be converted (non-enzymatically) into porphyrins?
What is the difference?

A

By light.

Porphyrinogens are colorless and have no double bonds at bridging carbons.

198
Q

What intermediates are elevated in Acute Intermittent Porphyria?

A

ALA and PBG

199
Q

Acute Intermittent Porphyria:
Inheritance?
Symptoms?

A

Autosomal dominant - incomplete penetrance

Acute, intermittent attacks of abdominal pain, cardiovascular symptoms, seizures, psychiatric symptoms, muscle weakness.

200
Q

What is another name for unconjugated bilirubin?

Conjugated?

A

Indirect bilirubin = unconjugated

Direct = conjugated

201
Q

How is vitamin A (retinol) stored?
How is it transported to the liver?
From the liver?

A

Stored as an ester of long-chain FA’s.
It is transported as an ester to the liver in chylomicrons.
When mobilized from the liver, it is hydrolyzed from its ester and then binds to Retinol-Binding Protein (RBP) to be secreted into the blood.

202
Q

Where is Vit. D stored?

A

Adipose & muscle

203
Q

What is the active form of Vit. D?

Where does this occur?

A

25-Hydroxycholecalciferol

It is activated within the liver.

204
Q

What are the names associated with each GSD?

A 
I -Von Gierke's
II - Pompe's
III - Cori's
IV - Anderson's
V - McArdle's
VI - Hers'

Very Pretty Chicas At My House

205
Q

What is a TIPS procedure?

A

Transjugular Intrahepatic Portosystemic Shunt.

Used to bypass a cirrhosed liver

206
Q

What is hepatorenal syndrome?

What is it caused by?

A

The rapid shutdown of the kidneys in response to cardiovascular changes seen secondary to liver cirrhosis. The kidneys themselves are functioning, however they are not perfused well enough.

207
Q

What are the symptoms of Cholangitis?

A

Charcot’s triad:

RUQ pain
Fever
Jaundice

208
Q

What receptor does Apo A-I bind to?

A

Scavenger Receptor Protein BI

SR-BI

209
Q

Where are chylomicrons formed?
HDL?
VLDL?

A

CM: Intestines

HDL & VLDL: Liver

210
Q

What is the difference between chylomicron and VLDL triacylglycerol transport?

A

Chylomicrons transport ingested TAG to the liver.

VLDL transport synthesized TAG to the tissues.

211
Q

What is a normal serum albumin level?

A

3.5-5 mg/dL

212
Q

What do increased levels of AST & ALT in the blood indicated?
Alkaline Phosphatase levels?

A

High Alkaline Phosphatase means a problem with the biliary tree, whereas high AST/ALT indicate a problem with the hepatocytes themselves.

FHB (8 decks)

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