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Ch 9
3

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

Cell Respiration = catabolic, makes ATP, exergonic (ΔG -686 kcal/mol)
C
6
H
12
O
6
+ 6 O
2
→ 6 CO
2
+ 6 H
2
O + energy
 ATP is made and used for energy, recycled, ATP ↔ ADP

ADP + P = phosphorylation (common)

P-bond is very energetic
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 Redox reaction = transfer of electrons from reactants to products, energy released
 oxidation = loss of e , reduction = gain of e -
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Figure 9.UN01
becomes oxidized
(loses electron) becomes reduced
(gains electron)

Figure 9.UN03
becomes oxidized becomes reduced


Electrons are passed “downhill” from: glucose  NADH  electron transport chain
 oxygen

In a series of redox reactions

Releases energy, therefore is exergonic

 In resp., transfer of e uses NAD + and electron transport chain
 NAD + = an electron shuttle, is coenzyme and e- acceptor, converts to NADH, gains 2 eand 1 p+, p165
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WHAT IS ROLE OF OXYGEN IN THESE EXAMPLES?
12

 Video
 Made of e- carrier molecules in the mitochondrial membrane
 electrons slowly get passed down to oxygen
(final electron acceptor) and energy is given off, p165
 Why slow?
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 Oxygen is HIGHLY electronegative

(6 valence electrons)
 Final electron acceptor in respiration

Ultimately results as water, also picking up H+ ions
 Once a molecule has been oxidized, it has very little free energy

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(what does the word mean?)

 catabolic, glucose is broken into two 3carbon parts, which are converted into two pyruvate molecules, easy, video
Where: cytosol



 anaerobic uses 2 ATP to start, 4 are released by substrate level
phosphorylation
: 2 ATP
NET
2 NAD + converted (reduced) to 2 NADH
Exergonic: ΔG = -140 kcal/mol
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 Options → If O
2 is available – pyruvate moves to a mitochondrion and the citric acid cycle (a.k.a. the
Krebs cycle) to complete oxidation, if not then fermentation occurs (we’ll do later)
In Mitochondria


Pyruvate is converted into acetyl CoA, (3-C into a 2-
C molecule), makes it reactive, p170
2 NADH’s made (1 per pyruvate)
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During part 1 of phase 2 (pyruvate oxidation) pyruvate is oxidized and becomes acetyl coenzyme A, or acetyl CoA
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 (citric acid, TCA cycle) – catabolic, in mitochondrial matrix



The CoA on acetyl CoA is removed and the acetyl group is added to oxaloacetate to create citrate energy released, 8 step cycle
For every acetyl CoA (2 per glucose) 


3 NADH, 1 FADH
2
, 2 CO
2
, 1 ATP made (SLP) most energy is hidden in the electron carriers
 ? GTP and GDP
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

Where: inner mitochondria
Problem – we have many e- carriers
 electronegativity increases down the chain so e are pulled
“downhill” towards oxygen, the final acceptor
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What is the ultimate purpose of the electron transport chain? Of the electrons?
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 most carriers are metals or cytochromes
 ATP production powered by [H + ] gradient, p174

ATP Synthase 
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
Flow of H+ (osmos = “pushing” H+)
 = coupling of rxns to make ATP, p173,
(diffusion & pumps)
 e- move down ETC, H + pumped out into intermembrane space creating a protonmotive force, H + diffuse into matrix through ATP synthase to make ATP
 process is enhanced by cristae (folds) in mitochondria
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Process
Glycolysis
ATP by SLP CoEnzyme ATP by ETC Total
Net 2
2 NADH 4-6 6-8
Oxidation of pyruvates
2 NADH 6 6 krebs 2 6 NADH
2 FADH
2
18
4
TOTAL =
24
36-38
- range 36-38 because of rounding p176-177
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 Resp. is very efficient – 40%
7.3 kcal/mol ATP x 38 ATP/mol
686 kcal/mol glucose
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
 anaerobic, makes only 2 ATP, starts after glycolysis if no oxygen, 2 types
1) alcoholic- 2 pyruvates broken down into 2 CO
2 and ethanol, 2 NADH oxidized to 2 NAD + , replenishes NAD +
 many yeast, and bacteria, do
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 2) lactic acid – 2 pyruvates broken down into lactate
 occurs in muscles when O
2 is low
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

 both break down pyruvate and use NADH in ferm. – final electron acceptor is pyruvate, in resp. it is O
2 more energy from respiration, 18 x more ATP
 respiration needs O
2
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

 some organisms are facultative anaerobes= they can switch back and forth from aerobic to anaerobic
What evolved first, aerobes or anaerobes?
other energy molecules
(ex. fats) can be broken into parts to go into glycolysis, p180
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 Control of cell respiration is done by feedback inhibition – too much product inhibits rxn
 control at certain enzymes in glycolysis and krebs
 key control enzyme for citric acid cycle (in glycolysis) is phosphofructokinase
 sensitive to ratios of ATP:ADP:AMP
 citrate and ATP are allosteric inhibitors of pfk

ADP and AMP are allosteric activators of pfk
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How can sunlight, seen here as a spectrum of colors in a rainbow, power the synthesis of organic substances?

 Photosynthesis creates 160 billion metric tons of carbohydrates per year (or 17 stacks of our AP text reaching all the way to the sun)

4/12/2020
Ch 10
Start with BioFlix on Masteringbiology.com
41

Figure 10.2
(a) Plants
(b) Multicellular alga
(c) Unicellular protists
10
 m
(e) Purple sulfur bacteria
1
 m
(d) Cyanobacteria
40
 m




 = converts light energy trapped by chloroplasts into chemical energy stored as sugar uses CO
2 to as carbon source
Endergonic
Anabolic
WAYS OF ENERGY AQUISITION
 Autotroph = organism that makes its own food for energy



Photoautotroph= uses light, ex. algae
Chemoautotroph= uses chemicals, ex. bacteria
Heterotroph = organism that acquires (eats) its food for energy, ex. us
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
where photosynthesis occurs



 contains chlorophyll = green pigment, absorbs light mostly in mesophyll of leaves gas exchange through pores (stomata)
Anatomy of chloroplast:
1) intermembrane space- separates double membrane
2) thylakoid space- inside the thylakoid membrane
- thylakoids (sacs in the chloroplast) and stacks called grana
3) Stroma = fluid-filled space outside the thylakoids, where sugar is made, only in eukaryotes
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2


2
Van Neil: gave bacteria H
2
S instead of water the rxn gave sulfur as a byproduct, so…


 splits H
2
O to give O
2
, later done with radioactivity water is split and the electrons are transferred from water to carbon dioxide, reducing it to sugar resp. was exergonic, photosynthesis is endergonic, energy required is light
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6 CO
2
+ 6 H
2
O + light energy → C
6
H
12
O
6
+ 6 O
2
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(including the Electron Transport Chain)
 1 st stage in photosynthesis, convert light energy to chemical energy as ATP &
NADPH, p188
 Light = electromagnetic energy
 distance it travels = wavelength, ranges from 380 to 750 nm (visible spectrum)
 plants absorb blue and red light best, reflect green
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What is water’s chief purpose?
50

 Pigments = substances that absorb light,
 each has a specific wavelength it can absorb = absorption spectrum
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 measured with a spectrophotometer
 graph wavelength vs. rate of photosynthesis
= action spectrum, p192
 main pigments are chlorophyll a,b, carotenoids (yellow)
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Structure of chlorphyll
53

RESEARCH METHOD: Determining an Absorption Spectrum
TECHNIQUE
Chlorophyll solution
White light
Refracting prism
Photoelectric tube
Galvanometer
Slit moves to pass light of selected wavelength.
Green light
High transmittance
(low absorption):
Chlorophyll absorbs very little green light.
Blue light
Low transmittance
(high absorption):
Chlorophyll absorbs most blue light.

 Linear electron flow- passes electrons from water to
NADP + to make NADPH, uses P680 and P700
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
Photons bump electrons’ to orbital of higher energy level
(photoexcitation). This is unstable and the electrons want to drop back down, immediately


When e- drops back down releases heat (think of your car’s hood)
Some pigments delay in their giving off photons as electrons settle back down…this is fluorescence.
 What color of light would a fluorescing flask of chlorophyll give off?

 Redorange… why ?
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• photosystem I (P700), and II(P680), video
58

 Alternate means of generating ATP:

Cyclic electron flow – simpler, only involves P 700, makes ATP but no NADPH, nor oxygen

More common in primitive bacteria groups * p195
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vs.
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 e- source is organic molecules (sugar) vs. water
 H+ reservoir in intermembrane space vs. into the thylakoid space

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


electrons from water go to NADP + , NADPH is made to reduce CO
2 to sugar
ATP made, O
2 is byproduct pH gradient of 5 inside to 8 in stroma
(1000x H+ inside)
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



2 nd stage of photosynthesis, also called dark rxns., light not directly used here
Where: stroma carbon source is CO
2 sugar and is ultimately reduced to
 produces 3-C sugar G3P (1/2 a sucrose) powered by ATP made from light reaction, uses
NADPH as reducing agent to add electrons to Ccpds, which ultimately become sugar
 p 198*
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(Like citric acid cycle in reverse)

JUST LIKE
RESPIRATION
65


 a) Carbon fixation = CO
2 is attached to a 5-C molecule (RuBP), catalyzed by rubisco (fun fact: most abundant protein on earth ), later the new 6-C molecule is broken in two b) Reduction –coupled rxns: 6 ATP to 6 ADP, used to convert 3PG to G3P, 6 NADPH to 6
NADP +
 c) Regeneration of RuBP - uses ATP to make
RuBP
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QUICK
REVIEW
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 a) both use ETC via a membrane
 b) both make ATP by diffusion of H + over a gradient
 c) similar electron carriers
 d) both are involved in energy conversion

 for mitochondria → chemical energy from food to ATP for chloroplast → light energy into chemical energy
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1) Photorespiration - uses O
2
, makes no ATP, so it reduces photosynthetic output by wasting C


 occurs when O
2 is higher in leaf than CO
2 evolutionary relic?
favored on hot, dry days
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2) C
4 plants - 4 carbon intermediate formed at
Calvin cycle
 C
3 plants make 3 carbon intermediate, ex. rice, wheat


C
4 ex. corn, sugarcane enhances carbon fixation by minimizing photorespiration
 PEP carboxylase can fix carbon efficiently when
Rubisco cannot
 important in hot regions
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 3) CAM plants - only open stomata during the night, opposite of usual

 reduces water loss in hot areas, also keeps
CO
2 out during the day ex. cacti, pineapple
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outline only in 12 min.
A controlled experiment was conducted to analyze the effects of darkness and boiling on the photosynthetic rate of incubated chloroplast suspensions. The dye reduction technique was used.
Each chloroplast suspension was mixed with DPIP, an electron acceptor that changes from blue to clear when it is reduced. Each sample was placed individually in a spectrophotometer and the percent transmittance was recorded. The three samples used were prepared as follows.
• Sample 1 – chloroplast suspension + DPIP
• Sample 2 – chloroplast suspension surrounded by foil wrap to provide a dark environment +
DPIP
• Sample 3 – chloroplast suspension that has been boiled + DPIP a) On the graph provided, construct and label a graph showing the results for the three samples.
b) Identify and explain the control or controls for this experiment.
c) The differences in the curves of the graphed data indicate that there were differences in the number of electrons produced in the three samples during the experiment. Discuss how electrons are generated in photosynthesis and why the three samples gave different transmittance results.
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