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Fuel Metabolism > Enzymes and Bioenergetics > Flashcards

Enzymes and Bioenergetics Flashcards

1
Q

Km

A
  • Km= 1/2 Vmax
    • Lower Km …high affinity of enzyme for substrate (need less conc of substrate to saturate)
    • Higher Km…lower affinity of enzyme for substrate (need inc conc of substance to saturate)
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2
Q

Vmax

A

Vmax = velocity at which enzyme is saturated w/ substrate so adding additional enzyme does not inc velocity anymore

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3
Q

Km and Vmax on Lineweaver-Burke Plot

A

Dbl Reciprocal of M-M —> Lineweaver-Burke Plot (linear)

- Slope = Km/Vmax
- Y-int = 1/Vmax
- X-int = -1/Km
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4
Q

How do competitive inhibitors affect Lineweaver-Burke plot?

A

Vmax unchanged but inc Km

So inc/steeper slope and dec x-int (more negative)

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5
Q

How do non-competitive inhibitors affect Lineweaver-Burke plot?

A

Km unchanged but Vmax dec

So inc/steeper slope and inc y-int (higher)

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6
Q

Competitive Enzyme v Noncompetitive Enzyme

A

Comp- - Resembles substrate; competes w/ substrate @ ACTIVE SITE; overcome by inc conc of substrate

Non-Comp- Does not resemble substrate; binds to enzyme NOT NEC @ ACTIVE SITE; cannot be overcome by inc conc of substrate

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7
Q

Suicide Substrate (+4 clinical examples)

A

Irreversible enzyme inhibitor- reacts COVALENTLY on some functional group of enzyme —> poison/inactivate enzyme

Ex) Viagra, Aspirin (modifies cycloxygenase in prostaglandin formation), Flurouracil (inhibits thymidylate synthase in chemo), allopurinol (inhibits xanthine oxidase to treat gout)

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8
Q

3 Characteristics of Reg Enzymes

A
  • Catalyze Irreversible rxns (non-equilibrium)
  • Catalyze the rate-limiting step in a pathway (slowest step)
  • Catalyze the committed step in a pathway (first step committed solely to formation particular product)
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9
Q

3 Mechanisms of Enzyme Regulation

A

1- Change amount of enzyme (inc enzyme amount)
**Alt transcription
2-Change catalytic properties of enzyme (inc activity- change kinetics)
**Alt substrate conc, covalent mod, allosterics
3-Multienzyme complexes (inc efficiency)
**Mult enzymes so rxn cont 1 after other w/o mixing product w/ solvent (efficiency)

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10
Q

What is the most important type of reversible covalent modification and what enzymes does it use?

A

Phosphorylation!

  • P added by kinases (transfer from ATP —> hydroxyl on serine/threonine/tyrosine—> phosphate ester linkage)
  • P removed by phosphatases (use water to hydrolyze phosphate ester)
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11
Q

How do you know if phosphorylation activates or inactivates?

A
  • If enzyme in CATABOLIC path —> P activates it

- If enzyme in ANABOLIC path —> P deactivates it

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12
Q

Allostery (+ example)

A

-Allosteric Effector- pos/act or neg/inact effect on enzyme activity by binding to site DISTINCT FROM ACTIVE SITE

  • Allosteric act- dec Km, inc Vmax or both
  • Allosteric inhib- inc Km, dec Vmax or both
  • Usually either end products of pathway or metabolites that reflect energy status of cell
  • Acts by changing conformation of enzyme
  • Ex) phosphofructokinase-1
    • rate limiting step in glycolysis - commits glucose to glycolysis
    • allosteric effectors for this enzyme - AMP, ADP, ATP, fructose-2,6-P2 and citrate
    • ATP inhibits while ADP and AMP relieve the ATP inhibition
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13
Q

Limited Proteolysis (what is it an example of?)

A

Irreversible Covalent Modification!

  • Cleave peptide bonds at limited # sites
  • Remove conformational restraints
  • New conformation —> new function —> cascade act

Ex) blood clotting, complement act, etc

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14
Q

Free Energy Change

A
  • Value shows the energy diff b/n substrate and products
  • Sign (+/-) shows if the rxn requires/yields energy
    + delta G requires energy (endergonic)
    - delta G yields energy (exergonic)
    deltaG=0 at equilibrium
  • *Indep of path by which rxn occurs
  • *Rxn goes toward neg deltaG
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15
Q

What is required for coupled enzymatic reactions?

A

Reactions must share a common intermediate

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16
Q

What is the function of adenine nucleotides?

A

ATP- major carrier of chemical energy in cell (high energy bonds)

Energy released by hydrolysis of 1 or 2 phosphate bonds —> supplies endergonic rxns

17
Q

Energy Charge

A

Index of metabolically available energy in the cell

=[ATP] + 1/2[ADP] /[ ATP] + [ADP] + [AMP]

    - If = 1 …all ATP
    - If = 0 …all AMP
18
Q

How does energy charge affect regulation of cell metabolism?

A

It is used to describe energy state of cell and energy state can regulate enzymes

ATP, ADP and AMP can act as allosteric regulators of many enzymes

19
Q

Oxidation v Reduction

A
  • Oxid- lose electrons …oxidizing agent accepts electrons

- Red- gain electrons …reducing agent donates electrons

20
Q

Relationship B/n Change in Free Energy (deltaG) and Diff in Redox Potential (deltaE’)

A

Pos deltaE’ = Neg deltaG = exergonic and vice versa

21
Q

2 Major Electron Carriers in Redox

A
  • 1- NADH (transfer hydride ion)
    • NAD+ + H+ + 2e- —> NADH
  • 2- FADH2 (transfer 2 hydrogen atoms to nitrogen atoms of rings)
    • FAD + 2H- + 2e- —> FADH2
22
Q

What enzymes are involved in detoxification of ROS?

A

Superoxide Dismutase (for superoxide O2-)

Peroxidase and Catalase (for hydroxide H2O2)

**None for hydroxyl radical b/c reacts so rapidly (*OH)

23
Q

What are the major components of the respiratory chain?

A
  • Complex I - NADH-linked dehydrogenase
  • Complex II - FADH-linked dehydrogenase (succinate dehydrogenase)
  • Coenzyme Q - mobile; transfers electrons to cytochromes of complex III
  • Complex III- cytochrome c reductase
    • Composed of 2 cytochromes (contain heme)
  • Cytochrome C - transfers electrons to complex IV
  • Complex IV- cytochrome oxidase; transfers electrons to molecular oxygen —> H2O
  • Iron sulfur proteins- non-heme iron proteins associated w/ complexes I II III)
  • ATP Synthase (Complex V)
24
Q

How does ETC turn dietary fuel into ATP?

A

-Fuels –> acetyl CoA –> TCA cycle to become NADH and FADH2 –> enter ETC and created proton gradient –> H+ travels back through ATP synthase and makes ATP

25
Q

Oxidative Phosphorylation v Substrate-Level Phosphorylation

A

Oxidative phosphorylation uses oxygen as ultimate electron acceptor and creates proton gradient that provides the energy to produce ATP (**energy comes from H+ gradient)

substrate level phosphorylation in which there is a direct transfer of PO3- from a reactive intermediate to produce ATP (**energy comes from another P bond)

26
Q

2 Shuttle Systems

A
  • 1- Malate-Aspartate
    • Reduce oxaloacetate —> malate in cytosol
    • Oxidize malate —> oxaloacetate in matrix
    • 2 NADH —> 2 NADH (no energy lost)
    • Uses isozymes of malate dehydrogenase
    • Mainly in liver and heart
  • 2- Glycerol Phosphate
    • Reduce DHAP —>glycerol-3-phospahte in cytosol
    • Oxidize glycerol-3-phosphate —> DHAP in matrix
    • NADH —> FADH2 (lose some energy)
    • Uses isozymes of alpha glycerol phosphate dehydrogenase
    • Mainly in brain and fast-contracting skeletal muscle
27
Q

ATP yield from pyruvate dehydrogenase v succinate dehydrogenase

A

Pyruvate dehydrogenase —> NADH (enters ETC at complex I —> more protons pumped so makes 3 ATP)

Succinate dehydrogenase —> FADH2 (enters ETC at complex II —> less protons pumped so makes only 2 ATP)

28
Q

Cyanide v dinitrophenol

A

Dinitrophenol - uncoupler; make the mito membrane more permeable to H+ so dec gradient - dec efficiency and inc heat lost in reaction

Cyanide - site specific inhibitor- bind to specific components of ETC blocking e- transfer (ex- cyanide binds to complex IV)

29
Q

How is mitochondria related to heat generation in newborns?

A

Uncoupling protein in brown fat (UCP1 thermogenic) —> 5% efficiency so lots of heat given off; more prevalent in infants (important in warming their blood especially)

30
Q

How does ATP synthase work?

A
  • H+ gradient/charge separation creates potential energy and H+ wants to go back into matrix but can only do so by entering F0 channel; H+ flow causes stalk to rotate which in turn causes F1 to synthesize ATP

**Protons are pumped out of complexes I II and III

Fuel Metabolism (6 decks)

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