Week 12 FINAL SLIDES for Sections 202 (MWF 2pm) and 203 (TTh 11am)

8/12/2019 Week 12 FINAL SLIDES for Sections 202 (MWF 2pm) and 203 (TTh 11am)

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Week 12 - Biology 112


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Most of the energy captured from glucose oxidation is in

the form of reduced electron carriers (NADH and FADH2)


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Three mechanisms of ATP synthesis

Light-independent synthesis - catabolism

1. Substrate-level phosphorylation

2. Oxidative phosphorylation

Light-dependent synthesis - photosynthesis

3. Photophosphorylation


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Oxidative phosphorylation

Depends on the function of the electron transport chain

(ETC)and theATP synthase enzyme

Eukaryotic mitochondrion Bacterial cell

Outer

membrane Intermembranespace

Matrix

Innermembrane

Cell wall

Cytoplasmicmembrane

PeriplasmCytoplasm

Eukaryotes

Inner mitochondrial membrane

Bacteria

Cytoplasmic membrane

Location


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Mitochondria: the sites of oxidative phosphorylation in

eukaryotic cells.

Remember, plant cells have mitochondria, too!

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Modes of catabolism

Respiration

Aerobic Anaerobic

Fermentation

Cell makingALL of its

ATP by substrate levelphosphorylation

Some bacteria use other

TEAs

eg. NO3-, SO4

-2

Cell making MOSTof

its ATP by oxidativephosphorylation

TEA = O2TEA = O2


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Electron transport chain

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Mostly large membrane protein complexes

One lipid component Q


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Protein complexes have bound electron

carrying groups that undergo oxidation-

reduction.

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Example: Cytochrome c

has a bound Fe-atom


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Goes through a redox cycle = 2 redox reactions

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Oxidative phosphorylation is an oxidation-reduction (redox)-

based process

Electron donors (carriers) are oxidized: NADH, FADH2

(Terminal) electron acceptor O2is reduced


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As electrons from the carriers pass through the chain, some

of the protein complexes capture the energy from their redox

cycles and use it to actively transport H+across the

membrane The transported H+ comes from matrix or cytoplasmic water.

Remember water= H2O + HO-+ H+


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Transport of H+creates a H+concentration difference (=

gradient) across the membrane.

Transport of H+without transport of HO- (= separating

charge) creates an electrical difference (= potential, gradient)across the membrane

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Final step: Synthesis of ATP form membrane localized

ATP synthase


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The picture shows transport of H

+

through the ATP synthase.

What sort of transport would this be?

A. Passive diffusion

B. Facilitated diffusionC. Active transport

D. Cant tell without more information


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If the flow of protons were reversed,

from the direction shown, what sortof transport would it be?

A. Passive diffusion

B. Facilitated diffusion

C. Active transportD. Cant tell without more information


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Membrane localized

ATP synthasepassivelytransports

H+downtheelectrochemical

gradient.

Electrochemical gradient also called theProton Motive Force

Captures energy that becomes available to phosphorylate ADP.

?


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Membrane fragments

showing the ATP

synthase stalk and F1

heads


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2

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2:

22

ETC is a series of

spontaneous redox

reactions

Last redox reaction:

O2is e-acceptor =terminal electron

acceptor (TEA)

Reduced to H2O

Energy captured from the

decrease in free energy

over the series of reactions

is used to transport H+


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Bigger picture: a cells metabolic grid

Glycolysis and Krebs cycle


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MetabolismCatabolism

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A,


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$(?&6: BCDB

Fats, fatty acids, amino acids, can also be oxidized

via the Krebs cycle (acetyl-CoA intermediate)


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Week 12 - Biology 112

Short lecture followed by

activity


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2

222

2:

22

ETC is a series of

spontaneous redox

reactions

Last redox reaction:

O2is e-acceptor =terminal electron

acceptor (TEA)

Reduced to H2O

Energy captured from thedecrease in free energy

over the series of reactions

is used to transport H+


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Fermentation


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Modes of catabolism

Respiration

Aerobic Anaerobic

Fermentation

Cell makingALL of its

ATP by substrate levelphosphorylation

Some bacteria use otherTEAs

eg. NO3-, SO4

-2

Cell making MOSTof

its ATP by oxidativephosphorylation

TEA = O2TEA = O2


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Some cells mustferment because they are geneticallyincapableof respiration, i.e. no genes for ETCcomponents. Ferment even in presence of O2.

Bacterial cells

Some cells ferment when O2(or other TEAs, anaerobic

respiration) are in short supply.

Some cells mustferment because they lack mitochondriaand thus have no ETC and no way of using O2as a TEA.

Eukaryotic cells (cont)

eg. red blood cells, some eukaryotic microbes.

( )


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Fermentation (of glucose)

NADH cannot be used to make ATP by oxidative

phosphorylation: either no ETC or no TEA

In the absence of O2 as a TEA, NAD+cannot be

regenerated again to carry electrons - needs to be

alternative way to oxidize NADH2

TEA

Regenerated


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In fermentation NAD+is regenerated because NADHdonates e-to pyruvate or a derivative of pyruvate

Allows glycolysis to continue producing ATP via substrate-

level phosphorylation in the absence of a TEA e.g., O2

Fermentation yields a fermentation by-product = waste product

Fermentations often named for their waste products


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Skeletal muscle cellsRed blood cells

and

Some bacteria

Root cells of someplants

Waste

Lactic acid fermentation


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Comparing Glucose Respiration and Fermentation

Glucose respiration yields far more free energy and thus ATP

synthesized than fermentation ( ~ 10X more ATP)

Fundamental reason

Compared to fermentation, products of respiration are

more oxidized and much more stable than reactants.

Mostly due to enthalpy not entropy, i.e products much more

strongly bonded than reactants.


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Fermentation (example lactic acid fermentation, 25oC)

G =TS =

H =

100%

H = -46 kcal/mol

Compared to

respiration,collection of

bonds in products

not much stronger

than collection of

bonds bonded in

reactants

-47 kcal/mol

-46 kcal/mol

-1 kcal/mol 2%

98%


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Now its time for an activity.

Documents

Week 12 FINAL SLIDES for Sections 202 (MWF 2pm) and 203 (TTh 11am)