TRICARBOXYLIC ACID CYCLE AND PYRUVATE DEHYDROGENASE COMPLEX

Question 1

• aerobic pathway
• final pathway where the oxidative catabolism of carbohydrates, amino acids, and fatty acids converge, their carbon skeletons being converted to CO2
• responsible for producing most of the energy that cells need to function

Answer 1

The tricarboxylic acid (TCA) cycle/ Citric acid cycle/ Kreb’s cycle

Question 2

Functions: Krebs Cycle

Answer 2

Energy production:
Intermediates for biosynthesis

Question 3

The cycle begins with the condensation of _____, which is derived from the breakdown of carbohydrates, amino acids, and fatty acids, with oxaloacetate to form citrate.

Answer 3

acetyl-CoA

Question 4

____ is then converted to a series of other intermediates, including isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, and malate.

Answer 4

Citrate

Question 5

____ is converted back to oxaloacetate to complete the cycle

Answer 5

malate

Question 6

The cycle ends with the regeneration of ______, which can then be condensed with another molecule of acetyl-CoA to start the cycle again

Answer 6

oxaloacetate

Question 7

The _____ catalyzes the oxidative decarboxylation of pyruvate to acetyl-CoA.

Answer 7

pyruvate dehydrogenase complex (PDH complex)

Question 8

The PDH complex is located in the mitochondrial matrix and contains five coenzymes:

Answer 8

TPP, lipoic acid, CoA, FAD, and NAD+.

Question 9

The PDH complex is regulated by two enzymes:

Answer 9

pyruvate dehydrogenase kinase (PDH kinase) and

pyruvate dehydrogenase phosphatase (PDH phosphatase).

Question 10

PDH kinase phosphorylates the PDH complex, which ____ it.

Answer 10

inactivates

Question 11

PDH phosphatase dephosphorylates the PDH complex, which ___it.

Answer 11

activates

Question 12

____ is activated by high-energy signals, such as ATP, acetyl-CoA, and NADH.

Answer 12

PDH kinase

Question 13

___ is an inhibitor of PDH kinase.

Answer 13

Pyruvate

Question 14

___ activates PDH phosphatase

Answer 14

Calcium

Question 15

can cause serious central nervous system problems.
brain cells are unable to produce sufficient ATP (via the TCA cycle) if the PDH complex is inactive.

Answer 15

Thiamine or niacin deficiency:

Question 16

an encephalopathy -psychosis syndrome due to thiamine deficiency, may be seen with alcohol abuse

Answer 16

Wernicke-Korsakoff

Question 17

is a rare genetic disorder that affects the way the body converts food into energy.

deficiency results in an inability to convert pyruvate to acetyl CoA

can cause a variety of symptoms, including developmental delays, muscle weakness, seizures, and intellectual disability.

Answer 17

Pyruvate dehydrogenase complex (PDH) deficiency

Question 18

rare, progressive, neurodegenerative disorder caused by defects in mitochondrial ATP production

Answer 18

Leigh syndrome (subacute necrotizing encephalomyelopathy)

Question 19

can interfere with glycolysis at the glyceraldehyde 3- phosphate step, thereby decreasing ATP production. this particularly affects the brain, causing neurologic disturbances and death.
inhibit enzymes that require lipoic acid as a coenzyme.

Answer 19

Arsenic poisoning

Question 20

The condensation of acetyl CoA and oxaloacetate (OAA) to form citrate (a tricarboxylic acid) is catalyzed by ____

Answer 20

citrate synthase.

Question 21

Citrate is isomerized to isocitrate by the enzyme ____ .

Answer 21

aconitase

Question 22

___ catalyzes the oxidative decarboxylation of isocitrate to alphaketoglutarate.

Answer 22

Isocitrate dehydrogenase

Question 23

The oxidative decarboxylation of α-ketoglutarate to succinyl CoA is catalyzed by the ___

Answer 23

α - ketoglutarate dehydrogenase complex.

Question 24

Succinate is oxidized to fumarate by ___

Answer 24

succinate dehydrogenase.

Question 25

Fumarate is hydrated to malate by _____.

Answer 25

fumarase

Question 26

Malate is oxidized to oxaloacetate by ___

Answer 26

malate dehydrogenase.

Question 27

When the ATP/ADP ratio is ___high, the TCA cycle is downregulated. This is because the cell has enough energy and does not need to produce more.

Answer 27

high

Question 28

When the ATP/ADP ratio is ___, the TCA cycle is upregulated. This is because the cell needs more energy and needs to produce more.

Answer 28

low