Transcript Cellular Respiration

Cellular Respiration
Extracting energy from Organic
compounds (food)
California Science Standards #1f, 1g,
1i, 6d, 9a
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What do we know?

Photosynthesis
– Occurs in autotrophs
– Stores ENERGY
– Produces glucose
– CO2 + H2O

C6H12O6 + O2
Cellular respiration
– Occurs in autotrophs and heterotrophs
– Releases ENERGY
– Uses glucose
– C6H12O6 + O2
CO2 + H20
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Respiration is a combustion reaction

Like the burning snack
foods, the “burning” of
food molecules (glucose)
in cells produces CO2
and H20, and it is an
exothermic process.
•In exothermic reactions, the reactants
contain more energy before the reaction
than the products contain at the end of the
reaction. (i.e: energy is released.)
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Some key differences

In the lab, the combustion
released energy as heat
(which increased the temp
of the water in the test
tube). This reaction
occurred very quickly.
– A cell cannot use heat to
do cellular work, not to
mention the fact that
this large increase in
temp would be
dangerous!
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Respiration “slows down” the
combustion of glucose

The energy from
glucose is released
slowly by many
enzyme-catalyzed
reactions during cell
respiration. This
released energy is
used to make ATP.
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Respiration uses energy stored in
glucose to make ATP



ATP is adenosine triphosphate
and is the main stored form of
energy in all cells
ATP contains three phosphate
groups (see pic: the negative
charges repel one another so the
ATP is “unstable”). When one
is removed, energy is released.
The released energy from ATP
is used for cellular work.
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ATP: The energy “currency” of a
cell.

All cellular work comes at the “expense” of
ATP.
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Cellular Respiration
 An
Overview (“Map”)
ATP
ATP
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Glycolysis

First step of cellular respiration; occurs in
the cytoplasm.
 Breaks apart 1 glucose molecule (6-C) into
2 pyruvic acid molecules (3-C each)
 Requires glucose and 2 ATP
 Produces pyruvic acid /pyruvate, NADH,
and 2 ATP (net yield)
– Pyruvic acid used later in Krebs cycle
– NADH (transports electrons) used in electron
transport chain (ETC)
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STEP 3
Glucose
2 NADH
C C C C C C
STEP 1
-2 ATP
6-carbon
compound
P C C C C C C P
STEP 2
2 molecules
of PGAL
P C C C
C C C P
2 molecules of
3-C compound
P C C C P
P C C C P
STEP 4
2 molecules
of pyruvic acid
C C C
C C C
4 ATP
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Cellular Respiration
 Check
the Map…
ATP
ATP
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Aerobic Respiration (one branch
of cellular respiration)

Requires oxygen
Produces nearly 20x more ATP than is produced
by glycolysis alone
 2 major stages:

– Krebs cycle
– Electron transport chain

Location: Mitochondria
 Begins with pyruvic acid that is modified to
become acetyl-CoA
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Krebs Cycle

Occurs in the mitochondrial matrix
 Acetyl CoA binds to oxaloacetic acid
producing citric acid.
 In reactions, the hydrogens are “stripped”
off the organic compounds, releasing
carbons as CO2 (waste).
 Produces CO2, NADH, FADH2, and 2
ATP
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C
Citric acid
C C
C C C C C C
Oxaloacetic
acid
C C C C
NADH
Krebs Cycle
5-C
compound
C C C C C
C
NADH
4-C
compound
4-C
compound
C C C C
C C C C
FADH2
NADH
ATP
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Electron Transport Chain

Last stage of aerobic respiration
 Located on inner membrane folds (cristae)
of mitochondrion
cristae
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(Mitochondrial MatrixLocation of R&P of Krebs Cycle)
Electron transport chain is here
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(ETS)
a.k.a ATP synthase
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Electron Transport, continued

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NADH and FADH2 contain high energy
electrons.
When NADH and FADH2 reach the ETC they
lose H+ and e-. Their high-energy e- are
passed along the ETC, and energy from the eis used to pump H+ (protons) to the outer
compartment of the mitochondrion.
Energy from diffusion of H+ back into the
matrix is used to generate 34 ATP molecules
(chemiosmosis)
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ATP
Synthase
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Let’s Review the Summary
Equation

C6H12O6 + O2
CO2 + H20
– Glucose used in glycolysis
– CO2 produced in Krebs cycle (completing the breakdown of
glucose)

What is the importance of Oxygen?
– There must be a “final acceptor” of e- at the end of the
ETC. If the last protein in the chain holds onto the ethere will be a “traffic jam” and no other e- will flow
down the chain.
– Result: H+ pumping stops, so H+ gradient disappears
and there is no energy to drive the synthesis of ATP.
– Oxygen is the final e- acceptor of the ETC, so it keeps
the ETC “running”.
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
So oxygen is used in the ETC and this is
where water is formed.
– When oxygen accepts the e-, it also bonds with
H+ to form H2O.
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Total ATP From Cellular
Respiration
34
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Cellular Respiration
 Check
the Map…
ATP
ATP
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Fermentation
(Anaerobic Respiration)
No oxygen? No problem…(kind of)
2 types: lactic acid fermentation,
alcoholic fermentation
 Pros: can regenerate NAD+ when short on O2

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– Keeps glycolysis going (small net gain of ATP)

Cons: Cannot produce additional ATP
– Only unicellular organisms, like bacteria or yeast, can
survive with the ATP made by glycolysis alone.
– Some cells in multicellular organisms can switch to
anaerobic respiration, but only for a short time.
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Lactic Acid Fermentation

Manufacture of yogurt, cheese
 Muscle cells
– “Anaerobic exercise” (sprints)
– Lactic acid build-up (muscle burn, fatigue, cramps)
Glucose
Pyruvic acid
C C C C C C
C C C
NAD+
NADH + H+
Lactic acid
C C C
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Alcoholic Fermentation

Basis of wine and beer industries
– Yeast + fruit juice = alcohol

Takes place when making bread
– CO2 makes bread rise; alcohol evaporates
Glucose
Pyruvic acid
C C C C C C
C C C
NAD+
CO2
C
NADH + H+
Ethyl alcohol
2-C compound
C C
C C
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