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Biochemistry > Carbohydrate Metabolism II: Aerobic Respiration > Flashcards

Carbohydrate Metabolism II: Aerobic Respiration Flashcards

1
Q

Acetyl-CoA

A
  • Starting substrate for the citric acid cycle
  • Produced by metabolism of:
    1. carbohydrates
    2. amino acids
    3. fatty acids
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2
Q

Citric Acid Cycle

A

AKA Kreb Cycle or TCA [Tricarboxylic Acid]
—takes place in the mitochondria
—produces:
I. NADH & FADH2
II. CO2 & H2O & Acetyl-CoA

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3
Q

Pyruvate Dehydrogenase

A

Complex of 5 enzymes that oxidize pyruvate to Acetyl-CoA in the mitochondria through an exergonic process if not inhibited by accumulation of acetyl-CoA & NADH

Constituent enzymes:

  1. PDH [Pyruvate dehydrogenase] ]
  2. Dihydrolipoyl Transacetylase ]
  3. Dihydrolipoyl dehydrogenase ]
  4. Pyruvate Dehydrogenase Kinase }
  5. Pyruvate Dehydrogenase phosphatase }
  • ***First 3 convert pyruvate to acetyl-CoA
  • ***Last 2 regulate actions of PDH
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4
Q

Action of Pyruvate Dehydrogenase Complex’s 3 Enzymes that Convert Pyruvate to Acetyl CoA

A
  1. PDH
    I. Oxdizes pyruvate to CO2 & 2 other carbons
    II. Attaches the 2 other carbons to TPP with
    help of Mg2+
    III. TPP oxidizes the 2 other carbons and transfers
    them to lipoic acid
  2. Dihydrolipoyl Transacetylase
    I. Lipoic Acid’s disulfide group oxidizes the 2
    carbons to an acetyl group
    being reduced itself*
    II. The lipoic acid bonds to the acetyl group through
    a thioester linkage
    III. Dihyrolipoyl Transacetylase transfers the acetyl-
    group to CoA-SH to form Acetyl-CoA
  3. Dihydrolipoyl Dehydrogenase
    I. catalyzes reoxidation of lipoic acid through
    reduction of FAD to FADH2
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5
Q

TPP

A

—–Thiamine Pyrophosphate [aka Vitamin B1]
—–a coenzyme held to PDH through noncovalent
interactions

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6
Q

Lipoic Acid

A

A coenzyme with a disulfide group, covalently bonded to dihydrolipoyl transacetylase, that reduces the 2 carbons transferred from TPP to an acetyl group

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7
Q

FAD

A

Flavin Adenine Dinucleotide

Coenzyme that reoxidizes Lipoic acid after acetyl coa has been formed

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8
Q

Pathways that Contribute to Acetyl-CoA Formation

A
  1. Fatty Acid Oxidation/Beta-Oxidation
    I. Thioester linkage forms b/w carboxylic
    acids of fatty acids and CoA-SH
    2. Fatty Acyl-CoA forms & gets transported to
    the transmembrane space of mitochondria
    3. Fatty Acyl group gets transferred to the
    carnitine via a transesterification rxn
    **B/c fatty acyl-CoA cannot cross the
    mitochondrial inner membrane
    4. Acyl-Carnitine crosses the inner membrane
    5. Acyl-Carnitine transfers its fatty acyl group to
    a mitochondrial CoA-SH group via another
    transesterification rxn to form acyl-CoA
    6. Beta-oxidation removes the carboxylic ends of
    Acyl-CoA to form acetyl-CoA
  2. Amino-Acid Catabolism & Ketones
    1. Amino acids lose their amine group through
    transamination
    2. Their remaining carbon cytoskeletons get
    converted to ketone bodies
    3. Ketones convert to acetyl-CoAs
    **Acetyl-CoAs can also convert to
    Ketone bodies when pyruvate
    dehydrogenase complex is
    inhibited    *
  3. Alcohol
    1. Alcohol consumption in moderate amounts
    produces Acetyl-CoA & NADH via activities of
    I. Acetaldehyde dehodrogenase &
    II. Alcohol dehyrogenase
    **NADH accumulation inhibits the kreb
    cycle, leading to fatty acid synthesis instead*****
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9
Q

Carnitine

A

Molecule that contributes to fatty acids’ oxidation to acetyl-CoA by carrying the acyl group from the cytosolic CoA-SH to a mitochondrial CoA-SH

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10
Q

Key Rxns of Citric Acid Cycle

A
  1. Citrate Formation
    I. Acetyl-Coa & OAA couple to form Citryl-CoA
    II. Citrate Synthase hydrolyzes citryl-CoA to form
    1. Citrate
    &2. CoA-SH
  2. Citrate Isomerized to Isocitrate
    I. Citrate attaches to Aconitase at 3 points and
    loses water to form cis-aconitate
    II. Cis-Aconitate reacts with Fe2+ and gains water
    to form one of the four possible isocitrates
  3. Alpha-Ketoglutarate and CO2 Formation
    I. Isocitrate dehydrogenase oxidizes isocitrate to
    oxalosuccinate
    II. Oxalosuccinate then gets decarboxylized into
    1. CO2
    &2. alpha-ketoglutarate
    **Rate-Limiting Step of the cycle*
    1. produces NADH
    2. results in loss of the first CO2
  4. Succinyl-CoA and CO2 Formation
    I. Ketoglutarate and CoA-SH come together to
    form succinyl-CoA
    II. 2nd NADH gets produced, and 2nd CO2 gets
    lost
  5. Succinate Formation
    I. Succinyl-CoA Synthatase hydrolyzes the
    succinyl-CoA’s thioester to form
    1. Succinate and CoA-SH
    &2. Phosphorylated GTP [from GDP]
    II. Nucleosidediphosphate Kinase transfer GTP’s
    phosphate to ADP to produce ATP
    **Only step of Kreb cycle that
    produces ATP directly    *****
  6. Fumarate Formation
    I. Succinate dehydrogenase oxidizes succinate to
    fumarate in the inner mitochondrial membrane
    while also reducing FAD to FADH2
    **Only step that does not take place in the
    mitochondrial matrix b/c succinate
    dehydrogenase is a Flavoprotein (FAD) that
    is only found in the inner mitochondrial
    membrane    *
  7. Malate Formation
    I. Fumarase converts fumarate to malate by
    hydrolyzing its alkene bonds
  8. OAA Formation
    I. Malate Dehydrogenase oxidizes malate to OAA
    reducing the last NAD+ to NADH
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11
Q

Synthases

A

Enzymes that form new covalent interactions without the need for significant energy input

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12
Q

Synthatase

A

Enzyme that creates new covalent interactions with significant energy input

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13
Q

Kreb-Cycle’s Total Products

A 
3 NADH
1 FADH2
1 ATP
2 CO2
1 OAA
NADH= 2.5ATPs
FADH2= 1.5ATPs

**Conversion of pyruvate to Acetyl-CoA yields 1 NADH*

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14
Q

Glycolysis Total Product Yields

A

2 ATPs

2 NADH

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15
Q

Kreb Cycle Regulation Points

A
  1. PDH Regulation
    A. Phosphorylation of PDH by Pyruvate
    Dehydrogenase Kinase to prevent acetyl-
    CoA production when ATP levels are high
    B. Dephosphorylation of PDH by Pyruvate
    Dehydrogenase Phosphatase to restore CoA
    production when ADP levels are high
  2. Citrate Synthase Regulation
    I. ATP & NADH & Citrate & Succinyl-CoA inhibit
    Citrate Synthase allosterically
  3. Isocitrate Dehydrogenase Regulation
    I. ATP & NADH inhibit it
    II. ADP & NAD+ activate it
  4. Alpha-Ketoglutarate Dehydrogenase Complex
    I. ADP & Calcium activate it
    II. ATP, NADH & succinyl-CoA inhibit it
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16
Q

Electron Transport Chain

A

Exergonic Pathway that harvests electrons from electron carriers through an electron-motive force

17
Q

Proton Motive Force

A

An electrochemical gradient generated by proton-pumping of the ETC’s complexes that allows for ADP phosphorylation and ATP generation by the energy that it stores from proton pumping

18
Q

Steps of Aerobic Respiration

A
  1. Glycolysis
  2. Citric Acid Cycle
  3. Electron Transport
  4. Oxidative Phosphorylation
  • **Steps 3 & 4 in Detail**
    1. FADH2 & NADH, formed earlier in the process, transfer their electrons to carrier proteins localized in the inner mitochondrial membrane
    2. the carrier proteins in the inner mitochondrial membrane transfer the electrons as [H-] to oxygen and form H2O
    * O has a greater reduction potential, therefore NADH donates its electrons to it, reducing it in the process**
19
Q

Electron Transport Flow-Order

A
  1. Complex I [NADH-CoQ Oxidoreductase]
    1. NADH—–e——FMN
    2. FMNH2—–e——Fe-S-Oxidized
    3. Fe-S-reduced——e——CoQ/Ubiquinone
    * Accompanied by pumping of 4 protons to mitochondria’s intermembrane space**
  2. Complex II [Succinate-CoQ Oxidoreductase]
    1. Succinate——e——-FAD
    2. FADH2———e——-Fe-Soxidized
    3. Fe-S reduced——e—–CoQ
    * **No protein Pumping *********
  3. Complex III [CoQH2-cytochrome Oxidoreductase]
    1. CoQH2 ——-e—-2 Cytochrome c [w/ Fe3+]
    * **Contributes to electron-Motive force through the Q cycle*****pg. 345
  4. Complex IV [Cytochrome c oxidase]
    1. Cytochrome c——-e——-O2
    * Accompanied by pumping of 2 protons**

pg. 345

20
Q

CoQ Complex

A

Complex with over 20 subunits used to oxidize NADH

Important Subunits

  1. Iron-sulfur Cluster
  2. flavoprotein with a FMN coenzyme
21
Q

FMN

A

Flavin Mononucleotide
A coenzyme binded to the flavoprotein of CoQ Complex important to NADH oxidation in electron transport chain and oxidative phosphorylation

22
Q

Cytochrome

A

Proteins with heme groups in which Fe gets reduced and oxidized to Fe2+ and Fe3+ respectively during electron transport

23
Q

Q Cycle

A

Cycle involved in Complex III of electron transport chain that contributes to electron-motive force

  • —Events of the cycle****
    1. 2 electrons get shuttled from a CoQH2 [ubiquinol] near the intermembrane space to a CoQ [ubiquinone] near the mitochondrial matrix
    2. another 2 electrons reduce cytochrome c by attaching to their heme moieties
    3. 4 protons displace to the intermembrane space in the process
  • **Assisted by a carrier containing Fe & S***

This cycle increases the gradient of the proton-motive force**

24
Q

NADH Shuttle

A

Energetically costing Mechanism that enables NADH to transfer its electrons to mitochondrial inner membrane;
Reason for which cells vary in the number of ATPs that they produce by metabolism of each glucose**

25
Q

NADH Shuttle Types

A
  1. Glycerol 3-Phosphate Shuttle
    I. FAD-dependent Glycerol 3-phosphate
    dehydrogenase transfers its e- to ETC via
    Complex II after being reduced to FADH2,
    yielding 1.5ATP for every molecule of
    cytosolic NADH that participates in this
    pathway
  2. Malate-Aspartate Shuttle
    I. OAA gets reduced to malate by oxidation of
    NADH to NAD+
    II. Malate crosses the inner mitochondrial
    membrane to the matrix
    III. Mitochondrial malate dehydrogenase reverses
    the rxn, restoring NADH
    IV. NADH transports its electrons to ECT through
    Complex I, generating 2.5 ATP per NADH
26
Q

Chemiosmotic Coupling Mechanism

A
  1. Proton motive force couples to F0 portion of ATP synthase
  2. Protons pumped into the mitochondrial intermembrane space flow through F0 in the direction of the gradient to the mitochondrial matrix
  3. F1 harnesses the energy of the electrochemical proton gradient in the process to phosphorylate ADP to ATP
27
Q

ATP synthase

A

Enzyme that drives ADP phosphorylation in oxidative phosphorylation after ECT

Has 2 portions:

  1. F0: is an ion channel
  2. F1: enzyme that harnesses energy of electrochemical gradient of the proton motive force to generate ATP from ADP
28
Q

Chemiosmotic Coupling

A

Mechanism that explains oxidative phosphorylation by describing a direction relationship b/w ATP synthase and proton gradient

29
Q

Oxidative Phosphorylation Debated Mechanisms

A
  1. Chemiosmotic coupling

2. Conformational Coupling

30
Q

Conformational Coupling

A

Oxidative phosphorylation mechanism that describes an indirect relationship b/w the ATP synthase and proton gradient , stating that F0 spins within a stationary compartment to harness ATP from the gradient

**Gradient causes conformational change; Synthase releases ATP*review 348

Biochemistry (12 decks)

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