Metabolism 3

Question 1

What are the general precursors and fates of acetyl CoA? Draw.

Answer 1

p 3 or slide 2

Question 2

Where and how is pyruvate formed?

Show eq.

Answer 2

Pyruvate is formed from the oxidation of glucose in the cytosol

Glucose + 2 NAD+ -> 2 pyruvate + 2 NADH + 2 H+

Question 3

Where and how is pyruvate oxidized to acetyl-CoA?

Show eq.

Answer 3

Pyruvate is oxidized to acetyl-CoA in the mitochondrial matrix via the action of pyruvate
dehydrogenase (PDH).

2 Pyruvate + 2 NAD+ + 2 CoA PDH> 2 NADH + 2 H+ + 2 Acetyl-CoA

Question 4

Where and how are fatty acids oxidized to acetyl-CoA?

Answer 4

Fatty acids join to CoA in the cytosol and are oxidized to acetyl-CoA in the mitochondrial
matrix via beta-oxidation.

C-16 fatty acyl-CoA + 7 NAD+ + 7 FAD + 7 H2O + 7 CoA B-oxidation>
7 NADH + 7 H+ + 7 FADH2 + 8-Acetyl-CoA

Question 5

What is coenzyme A?

Answer 5

the universal carrier of acyl groups

Question 6

What does the oxidation of acetyl-CoA lead to?

Answer 6

The oxidation of Acetyl-CoA leads to the production of

NADH, FADH2, and GTP.

Question 7

Draw an overview of the Citric Acid cycle.

Answer 7

P 5

Question 8

It is important to make sure patients have optimal dietary intake and nutritional status.

If a patient has low citrate, cis-aconitate and isocitrate, what does this mean?

Answer 8

amino acid insufficiencies

a need for arginine, lipoic
acid, magnesium, or amino acid supplementation

Question 9

It is important to make sure patients have optimal dietary intake and nutritional status.

If a patient has elevated alpha ketoglutarate, what do they need?

What if low ketoglutarate?

Answer 9

high - need for vitamins B1, B3, and B5.

low- have aa insufficiences and need alpha ketoglutarate

Question 10

What if a patient has elevated succinate, fumarate, and malate? What is insufficient?

Answer 10

then they have a coenzyme Q10 insufficiency

Question 11

What if a patient had elevated succinate?

low succinate?

Answer 11

insufficiency of coenzyme Q10, vitamin B2 and magnesium

low- low aa, specifically leucine and isoleucine

Question 12

What if a patient had low fumarate?

Answer 12

low tyrosine and phenylalanine

Question 13

What are the important outer membrane, inner membrane, and matrix enzymes for fatty acid metabolism?

What are the important inner membrane and matrix membrane CAC enzymes?

Answer 13

fatty acid metabolism:

outer membrane- fatty acyl-CoA synthetases
inner membrane- camitine: acyl-CoA transferase
matrix- fatty acid B oxidation system

CAC enzymes:
inner membrane: succinate dehydrogenase
matrix:
-citrate syntehase
isocitrate dehydrogenase
alpha ketoglutarate dehydrogenase
aconitase
fumarase
succinyl-CoA synthetase
malate dehydrogenase

Question 14

Where are CAC enzymes located?

Answer 14

matrix and inner mitochondrial membrane

Question 15

What provides the energy to synthesize ATP?

Show drawing diagram

Answer 15

The transfer of electrons from substrates to molecular
oxygen provides the energy to synthesize ATP

P 9

Question 16

How many high energy phosphates are generated for each cycle of citric acid cycle?

Where do these come from?

Answer 16

10 high energy phosphates generated for each cycle of the citric acid cycle

reoxidation of 3 NADH at 2.5 ATP/NADH =7.5

reoxidation of 1FADH2 at 1.5 ATP/FADH2 =1.5

GTP (GTP + ADP …GDP +ATP) =1

10 total

Question 17

What is coarse control? What exerts the level of course control? Why?

What is the rate limiting factor? How does this relate to coarse control?

Answer 17

Coarse control is exerted by the level of ADP, because it is necessary to reoxidize NADH and FADH2 to regenerate NAD+ and FAD. The mitochondrial reoxidation of NADH or FADH2 is coupled to ATP synthesis from ADP. Consequently, the supply of ADP for ATP synthesis is usually rate limiting.

Question 18

What is the supply of acetyl-CoA related to? (2 things)

Answer 18

The supply of Acetyl-CoA is related to the activity of pyruvate dehydrogenase and to the transport of fatty acids into the mitochondria The latter process is affected by the
availability of carnitine and the activity of carnitine acyl transferase-1/ carnitine palmitoyl
transferase-1

Question 19

How are oxaloacetate levels affected?

What type of reactions replenish CAC intermediates?

Answer 19

Oxaloacetate levels are affected by biosynthetic pathways that deplete CAC intermediates;
anaplerotic reactions replenish CAC intermediates.

Question 20

What exerts fine control?

Answer 20

Fine control is exerted by the allosteric effectors in the figure above (p. 10). Additional allosteric effectors may regulate a specific purified enzyme, but their physiological relevance has not been established.

Question 21

Citric acid cycle provides intermediates for biosynthetic reactions. The TCA cycle is a source of
precursors for amino acid, fatty acid, and glucose synthesis.

Show this on a figure… what are precurosors for aa synthesis or fatty acid and sterol synthesis/ gluconeogensis?

Answer 21

p 11

citrate- fatty acid and sterol syntehsis

alpha-ketoglutarate- aa synthesis (to neurotransmitters)

succinyl CoA- heme synthesis

malate- gluconeogensis

oxaloacetate- aa synthesis

Question 22

Citric acid cycle intermediates of the TCA cycles can be replenished by anaplerotic (filling in)
reactions. Which are these intermediates?

Answer 22

p 11

aa to glutamate for alpha ketoglutarate

valine and isoleucine to propionyl CoA to succinyl CoA

aa to fumarate

asparate to oxaloacetate

aa to pyruvate to acetyl CoA or oxaloacetate

Question 23

What does the pyruvate dehydrogenase complex do?

What does it contribute to/ accomplish?

Answer 23

The pyruvate dehydrogenase complex contributes to transforming pyruvate into acetyl-
CoA by a process called pyruvate decarboxylation.

Acetyl-CoA may then be used in the TCA
cycle to carry out cellular respiration, so pyruvate dehydrogenase contributes to linking
the glycolysis metabolic pathway to the citric acid cycle and releasing energy via NADH.

Question 24

Describe the pyruvate dehydrogenase complex. What is it made up of?

Answer 24

The pyruvate dehydrogenase complex is made up of multiple copies of several enzymes
called E1, E2, and E3, each of which performs part of the chemical reaction that converts
pyruvate to acetyl-CoA.

Question 25

What is the most common form of PDH deficiency? How is it inherited?

Answer 25

The most common form of pyruvate dehydrogenase deficiency is caused by mutations in
the E1 alpha gene, and is inherited in an X-linked dominant manner; all other forms are
caused by various genes and are inherited in an autosomal recessive manner.

Question 26

What do children with PDH deficiency exhibit clinically?

What does treatment include?

Answer 26

Children with pyruvate dehydrogenase deficiency exhibit elevated serum levels of lactate,
pyruvate and alanine, which produce a chronic lactic acidosis.

Treatment typically includes dietary supplementation with thiamine, carnitine, and lipoic
acids.

Some patients have been treated with dichloroacetate, an inhibitor of the protein kinase
subunit of pyruvate dehydrogenase complex.

Question 27

Describe fumarase (Fumarase Hydratase) Deficiency or fumaric aciduria or Polygamist Down’s.

How is it inherited?
What characterizes the disease symptomatically? What will urine contain

Describe the mutations and effect.

What are treatment options?

Answer 27

It is an autosomal receive metabolic disorder, which is extremely rare.

• The disease characterized by severe neurological impairment, encephalomyopathy and
  dystonia developing soon after birth. Urine contains abnormally high amounts of fumarate
  and elevated levels of succinate, alpha-ketoglutarate, citrate and malate.
• Mutations in the fumarase (fumarate hydratase) gene disrupt the enzyme’s ability to convert
  fumarate to malate, interfering with the function of this reaction in the citric acid cycle.

-The first mutation characterized in the gene for fumarase contains a glutamine (Gln or Q)
substituted for a glutamic acid (Glu or E) residue 319.

-There is no effective treatment available for fumarate hydratase deficiency. Nutritional
intervention (e.g., feeding gastrostomy) may be appropriate. Physical therapy and wheelchairs
can be useful for some individuals.

Question 28

What is fluoroacetate?

Answer 28

fluoroacetate=rat poison

fluoroacetate is converted to fluorocitrate

FA is lethal in small dose; 0.2mg/kg of body weight rats

fluorocitrate inhibits aconitase and consequently it inhibits the CAC