Unit 4: Chapter 18 Flashcards
Is Digestive System Catabolic or Anabolic process?
Ctabolic: break down to smaller molecules
Stages of Digestive System
- Polymers broken down into smaller subunits in digestive system
- Simple subunits are further broken down to activated carrier, Acetyl CoA
- Acetyl CoA is oxidized to CO2, coupled to production of large amounts of ATP
Pyruvate Dehydrogenase Complex
Forming acetyl coenzyme A from pyruvate
How is pyruvate dehydrogenase complex regulated?
phosphorylation and dephosphorylation
Acetyl CoA (Coenzyme A)
- active carrier carrying acetyl groups
- fuel for citric acid cycle
- 2 carbon acetyl unit
Under aerboic conditions (O2), ______ enters ________ where it is converted to acetyl CoA
pyruvate; mitochondria
Where is acetyl CoA formed?
Mitochondrial matrix via pyruvate dehydrogenase complex
Acetyl CoA cannot enter two membrane of mitochondria
Structure of Acetyl CoA
ADP, hydrocarbon tail, acetyl group (acetyl group contains thioester bond which is very high energy rich bond)
SH group forms ____ bond with acetyl CoA
thioester
Thioester bonds
Have high standard free energy of hydrolysis so will release energy and can donate their acyl group to a variety of acceptors
Pyruvate dehydrogenas complex
Preparing citric acid cycle with product of acetyl CoA
5 enzymes in mitochondrial matrix enzyme
Links glycolysis to citric acid cycle
What are E1, E2, E3 involved in pyruvate dehydrogenase complex?
Involved in converting pyruvate to acetyl CoA (catalytic, break down)
Regulation of pyruvate dehydrogenase complex
- Pyruvate dehydrogenase kinase: add phosphate to inactivate
- Pyruvate dehydrogenase phosphatase: removes phosphate to activate
- Energy charge
Overall reaction equation of pyruvate dehydrogenase complex
pyruvate + CoA + NAD+ –> acetyl CoA + CO2 + NADH + H+
Is pyruvate dehydrogenase complex reversible or irreversible reaction?
Irreversible reaction
Acetyl CoA cannot be made into pyruvate and glucose
Pyruvate dehydrogenase complex (E1)
Prosthetic group:
Reaction catalyzed:
Prosthetic group: TPP
Reaction catalyzed: Oxidative decarboxylation of pyruvate
Dihydrolipoyl tranacetylase (E2)
Prosthetic group:
Reaction catalyzed:
Prosthetic group: Lipoamide
Reaction catalyzed: Transfer of acetyl group of CoA
Dihydrolipoyl dehydrogenase (E3)
Prosthetic group:
Reaction catalyzed:
Prosthetic group: FAD
Reaction catalyzed: Regeneration of oxidized form of lipoamide
Prosthetic group
Tightly attached to enzyme and help catalyst
Do not undergo changes and must be returned back to original state
Synthesis of acetyl coenzyme A from pyruvate requires
5 enzymes and 3 coenzymes
Synthesis of acetyl conenzyme A consists of 3 steps
- decarboxylation
- oxidation
- transfer to CoA
Step 1 of synthesis of acetyl coenzyme A: Decarboxylation
- slowest step, rate limiting step
- E1 catalyzes
- E1 combines with ionized form of coenzyme TPP
- Pyruvate combines with TPP and is then decarboxylated to yield hydroxyethyl group
- C1 of pyruvate released as CO2
- Productis hydroxyethyl TPP
Thiamine Pyrophosphate (TPP)
Conezyme derived from vitamin thiamine and plays a role in decarboxylation of pyruvate
Protesthetic group of E1
Step 2 of synthesis of acetyl coenzyme A: Oxidation
- Hydroxyethyl group attached to TPP is oxidized to form acetyl group while being simutaneously transferred to a sulfur atom of the reduced form of lipoamide
- E2 inserts lipamide arm of lipoamide to E1
- E1 catalyzes transfer of acetyl group to lipoamide
- Acetylated arm leaves E1 and enters E2
- Disulfide group of lipoamide is reduced to its disulfhydryl form
- Reaction is catalyzed by E1 and yields acetyl lipoamide
Step 3 of synthesis of acetyl coenzyme A: Formation of Acetyl CoA
- E2 catalyzes the transfer of acetyl group from acetyl lipoamide to conezyme A to form acetyl CoA
- E3 catalyzes for lipoamide to return back to disulfide (oxidized) form since prosthetic groups must return back to original state
- 2 electrons are transfered to an FAD and reduced to FADH2
- 2 electrons are transfered from FADH2 to NAD+ and then reduced to NADH
Hihg concentration of NADH and acetyl CoA inform the enzyme that
- energy needs of the cell have been met or that enough acetyl CoA and NADH have been produced from fatty acid degradation
- No need to metabolize pyruvate to acetyl CoA
During your exercise the concentration of ____ and ____ will increase
ADP; pyruvate
During you exercise, muscle contraction consumes _____ and _____ is converted to _____ to meet energy demands
ATP; Glucose; pyruvate
Both ___ and ____ activate dehydrogenase by inhibiting pyruvate dehydrogenase kinase
ADP; pyruvate
Phosphotate is stimulated by ____
Ca2+
Ca2+
- A signal that initiates muscle contraction
- Rise in Ca2+ activates the phosphatase, enhancing pyruvate dehydrogenase activity
What enzyme is this: transfers a 2 carbon unit to TPP and releases CO2 and forms acetyl lipoamide?
Pyruvate dehydrogenase (E1)
What enzyme is this: transfers the 2 carbon acetyl unit to lipoic acid and then to enzyme A (formation fo acetyl Coa)?
Dihydrolipoyl transacetylase (E2)
What enzyme is this: reoxidizes lipoic acid and reduces NAD+ to NADH?
Dihydrolipoyl dehydrogenase (E3)
Pyruvate dehydrogenase kinase
For regulation of pyruvate dehydrogenase complex
Phosphorylates E1 for complex to be inhibited
Pyruvate dehydrogenase phosphatase
For regulation of pyruvate dehydrogenase complex
Removes phosphate from E1 so complex activated
Coenzymes involved in Pyruvate dehydrogenase complex
TPP, lipoamide, FAD, NAD+, conenzyme A
____ impairs activity of pyruvate dehydrogenase componet of pyruvate dehydrogenase complex
Lack of TPP
__ and ___ are toxic because of these chemicals bind to lipoci acid coenzyme of dihydrolipoyl dehydrogenase, inhibiting activity of this enzyme
Arsenite and Mercury
Advantages of Multienzyme Complex
- The various stages of the reaction can take place more efficiently because reactants and enzymes are so close to each other; higher rate of rxn
- Coordinated control; regulatory controls can apply more efficiently
- Minumum side reaction
2 Fates of Acetyl CoA
- Metabolism of citric acid cycle
- Incorporation into fatty acids
The synthesis of _____ by the pyruvate dehydrogenase complex is key irreversible step in metabolism of glucose
acetyl CoA
Which enzyme is key site of regulation for pyruvate dehydrogenase complex?
E1
What can inhibit the pyruvate dehydrogenase complex?
ATP, acetyl CoA, NADH
What can stimulate the pyruvate dehydrogenase complex?
ADP and pyruvate
