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BIOCHEM 405 > Lecture 19 > Flashcards

Lecture 19 Flashcards

1
Q

where does cellular respiration occur?

A
  • Glycolysis – cytosol

* Respiration – mitochondria

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2
Q

where does ATP generation occur?

A

inner membrane of mitochondrion

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3
Q

where does pyruvate oxidation and CAC occur?

A

matrix of mitochondrion

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4
Q

cristae

A

folds in the inner mitochondrial membrane that project into the mitochondrial matrix. The enzymes of the ETC and oxidative phosphorylation are located mainly on the cristae

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5
Q

how is pyruvate transported from the cytosol into the mitochondria? and what is it converted to?

A
  • mitochondrial pyruvate carrier (MPC)
  • converted to acetyl CoA
  • pyruvate is a “mono carboxylate”
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6
Q

rxn for conversion to acetyl CoA

A

pyruvate + CoA + Nad+ —> Acetyl CoA + CO2 + NADH

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7
Q

what is an oxidative decarboxylation catalyzed by?

A

pyruvate dehydrogenase complex

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8
Q

what family does pyruvate dehydrogenase complex belong to?

A

family of α-keto Dehydrogenases

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9
Q

what is the ΔGº’ of the pyr–> CoA rxn?

A

Pyruvate + CoA + NAD+ —> Acetyl CoA + CO2 + NADH

-33.5 kJ/mol

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10
Q

What three enzymes catalyze the 5 rxns

A

E1- pyruvate dehydrogenase
E2- dihydrolipoamide transacetylase
E3- Dihydrolipoamide dehyrdogenase

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11
Q

The 3 enzymes require which 5 cofacors?

A
  • Thiamine Pyrophosphate (TPP)
  • Lipoic Acid
  • Coenzyme A (CoA or CoA-SH)
  • Flavin Adenine Dinucleotide (FAD)
  • Nicotinamide Adenine Dinucleotide (NAD+)
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12
Q

which cofactor stabilizes carboanions?

A

thiamine pyrophosphate

thiamine (vitamin b1)

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13
Q

The 3 enzymes require which 5 cofactors?

A
  • Thiamine Pyrophosphate (TPP)
  • Lipoic Acid
  • Coenzyme A (CoA or CoA-SH)
  • Flavin Adenine Dinucleotide (FAD)
  • Nicotinamide Adenine Dinucleotide (NAD+)
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14
Q

which cofactor stabilizes carboanions?

A

thiamine pyrophosphate

thiamine (vitamin b1

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15
Q

what are coenzymes?

A

Coenzymes are small molecules. They cannot by themselves catalyze a reaction but they can help enzymes to do so. In technical terms, coenzymes are organic nonprotein molecules that bind with the protein molecule (apoenzyme) to form the active enzyme (holoenzyme)

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16
Q 
Pyruvate Dehydrogenase (PDH) 
what are the methods to identify
A

is a large multisubunit complex.

Use Crystallography and NMR to solve structures of domains, subunits, and enzymes

Use Electron Microscopy to determine how they are organized

Not easy – Complex is somewhat flexible

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17
Q

Pyruvate Dehydrogenase Complex

What’s the advantage?

A
  • Substrate Channeling- int. of multistep pathway are handed off form one active site to the next w/o diffusing complex- makes smooth
  • Effective Concentration-
  • A + B <==> A-B + A-B
  • tethering can increase the effective concentration

• Regulation-

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18
Q

TPP- Location and function

A
  • tightly bound to E1

- decarboxylates pyruvate, yielding hydroxyethyl- TPP

19
Q

Lipoic Acid- location and function

A
  • covalently bound to E2 via lysine (“swinging arm”)

- accepts hydroxyl carbanion from TPP as acetyl group

20
Q

Coenzyme A (CoA)- location and function

A
  • dissociable substrate for E2

- accepts acetyl group from lipoamide

21
Q

FAD- location and function

A
  • tightly bound to E3

- accepts pair of e- from reduced lipoamide

22
Q

NAD+ - location and function

A
  • dissociable substrate for E3

- accepts pair of e- from reduced FADH2

23
Q

Enzymes of the Krebs cycle

A

Pyruvate Dehydrogenase & α-Ketoglutarate Dehydrogenase are in the same enzyme family.

24
Q

ReWhat is PDH inhibited by?

A

acetyl CoA, NADH

compete for binding with substrates CoA and NAD+

25
Q

what is PDHG regulated by?

A

covalent modifcation:

• PDH kinase (inhibits) (phosphorylates E1)
–kinase activated by NADH and acetyl CoA
–kinase inhibited by NAD+ and pyruvate

• PDH phosphatase (activates)
–phosphatase activated by insulin and Ca2+

26
Q

Transcriptional regulation of PDH kinase

A

Expression of many glucose metabolism genes is regulated by a specific transcription factor HIF-1.

low O2–> stabilized HIF –> DNA –> RNA–> Protein –> PDH Kinase

27
Q

what is HIF-1 and what is it stabilized by?

A

transcriptional factor

hypoxia

28
Q

hydroxylation

A

is a signal to degrade HIF-1 by a proteolysis pathway (ubiquitin pathway)

29
Q

HYPOXIA (low O2) –> HIF1 stabilized

low or high

PDH
PDH activity
pyruvate consumed
acetyl CoA made
glycolytic enzymes
CAC activity
A 
More PDH Kinase
PDH Phosphorylation Increases
PDH Activity Decreases
Less Pyruvate is consumed
Less Acetyl CoA is made
More glycolytic enzymes made
Less Citric Acid Cycle Activity
30
Q

More lactic acid production rxn:

A

Pyruvate + NADH —-> Lactate + NAD+

31
Q

Hypoxia-Inducible Factor (HIF) is important for:

A

-(HIF-1 also stimulates production of specific types of Growth Factors (VEGF and EPO))
•Adaptation to high altitudes
•Survival and growth of cells in low O2 environments.
•Tumor growth

32
Q

VEGF

A

(Vascular Endothelial Growth Factor and Erythropoietin)

VEGF stimulates formation of new blood vessels.
• EPO stimulates production of new erythrocytes

33
Q

Erythropoietin (“EPO”)

A
  • made in kidneys (and liver)
  • heavily glycosylated
  • stimulates survival of red blood cell progenitors

The “JAK/STAT” pathway is another type of signaling pathway that uses reversible phosphorylation of proteins.

34
Q

high altitude training

A

“Through the production of normobaric hypoxic (oxygen reduced) air, we can simulate altitudes of up to 21,000ft/6,400m. As a result, athletes, fitness enthusiasts and health conscious individuals worldwide can take advantage of the benefits associated with altitude training while at sea-level”.

35
Q

too much EPO can be dangerous - WHY?

A

increase the thickness (viscosity) of the blood, raising the risk for blood clots, heart attacks, and strokes

36
Q

key concepts for PDH- Regulation

A

• Regulation
– Inhibition by products (NADH and Acetyl CoA)
– Phosphorylation of Pyruvate Dehydrogenase
– Regulation of PDH Kinase
– Regulation of expression
– Mechanism by which HIF senses Oxygen

37
Q

When glucose is converted to ethanol by yeast (as in the production of beer) how much of the chemical energy that was originally stored in glucose still remains in the end product, ethanol, that is produced?

A

92%

38
Q

Which one of the following molecules has the highest molecular weight?

A

Acetyl CoA

39
Q

When Acetyl CoA reacts with oxaloacetate in the Citrate Synthase reaction how many carbons are in the product, citrate that is formed?

A

5

40
Q

Which ONE of the following is NOT a coenzyme or substrate involved in the pyruvate dehydrogenase complex reaction?

A

ATP`

41
Q

Which ONE of the following provides a long arm that can swing a substrate from one site to another in the PDH complex?

A

Lipoamide

42
Q

To get you to look carefully at these structures – answer this - which ONE has the highest molecular weight?

A

FAD

43
Q

Which part of the PDH complex is affected most directly by Arsenite?

A

FAD

BIOCHEM 405 (25 decks)

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