C. Cellular Energetics . . . . . . . 8% of the course
Coupled reactions
Fermentation and cellular respiration
Photosynthesis
Big Idea 2: Biological systems utilize free energy
and molecular building blocks to grow, to
reproduce and to maintain dynamic homeostasis.
Essential knowledge:
2.a.1 All living systems require constant input of free
energy.
2.a.2 Organisms capture and store free energy for use in
biological processes.
Chapter 9 - Cellular Energetics (Coupled Reactions)
Fermentation and Cellular Respiration
Cellular Energetics (Coupled Reactions) (Fermentation and Cellular Respiration)
(Chapter 9 and Lab5)
 Relate the laws of thermodynamics to the biochemical processes that provide energy to living
systems
 Explain the role of ATP in coupling the cell’s anabolic and catabolic processes
 Explain how chemiosmosis functions in bioenergetics
 Explain how organic molecules are broken down by catabolic pathways
 Describe the role of oxygen in energy-yielding pathways
 Explain how cells generate ATP in the absence of oxygen
 Use the Gas Laws to explain how a respirometer works
 Discuss the general processes of metabolism in living organisms
 Calculate the rate of cell respiration from experimental data
 Relate gas production to respiration rate
 Test the effect of temperature on the rate of cell respiration in ungerminated versus germinated
seeds in a controlled experiment
View: BioFlix: Cellular Respiration chapter 9 on website
AP Biology Cellular Respiration
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1.
Relate the laws of thermodynamics to the biochemical processes that provide
energy to living systems.
Label the diagram.
• Energy flows into an ecosystem as sunlight and leaves as heat
• Photosynthesis generates O and organic molecules, which are used in
2
cellular respiration
• Cells use chemical energy stored in organic molecules to regenerate ATP,
which powers work
Respiration is a catabolic pathway. Organic compounds such as glucose are broken down
releasing the energy stored in the chemical bonds.
AP Biology Cellular Respiration
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2. Explain the role of ATP in coupling the cell’s anabolic and catabolic pathways
Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
• Several processes are central to cellular respiration and related pathways
Catabolic Pathways and Production of ATP
•
The breakdown of organic molecules is _______gonic
•
_______________ is a partial degradation of sugars that occurs without O
•
____________ respiration consumes organic molecules and O and yields ATP
•
_______________ respiration is similar to aerobic respiration but consumes
compounds other than O
2
2
2
•
Cellular respiration includes both aerobic and anaerobic respiration but is often
used to refer to aerobic respiration
•
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful
to trace cellular respiration with the sugar glucose.
Write out the balanced equation
for cellular respiration:
AP Biology Cellular Respiration
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The importance of ATP
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Cells need energy to perform cellular work:

Growth

Metabolism

Movement

Contraction

Cell division

transport
http://www.slideshare.net/guest970cb3/chapter-9-presentation-647121 slide share for cellular
respiration
AP Biology Cellular Respiration
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Redox Reactions: Oxidation and Reduction
What are oxidation and reduction and how are redox reactions related to energy transfer in cells?
•
•
•
The transfer of electrons during chemical reactions releases energy stored in organic
molecules
This released energy is ultimately used to synthesize ATP
•
•
Chemical reactions that transfer electrons between reactants are called
oxidation-reduction reactions, or redox reactions
In oxidation, a substance loses electrons, or is oxidized
In reduction, a substance gains electrons, or is reduced (the amount of positive
charge is reduced)
•
•
The electron donor is called the ____________________ agent
The electron receptor is called the ____________________ agent
AP Biology Cellular Respiration
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•
•
Some redox reactions do not transfer electrons but change the electron sharing in covalent
bonds
An example is the reaction between methane and O
2
AP Biology Cellular Respiration
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During cellular respiration, the fuel (such as glucose) is oxidized, and O is reduced
2
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4.
What is the role of the coenzyme NAD+ in oxidation-reduction reactions?
Nicotiamide adenine dinucleotide.
•
In cellular respiration, glucose and other organic molecules are broken down in a
series of steps
•
Electrons from organic compounds are usually first transferred to NAD , a
coenzyme. ie. NAD+ removes electrons from food via a series of reactions.
•
As an electron acceptor, NAD functions as an oxidizing agent during cellular
respiration
+
+
+
•
Each NADH (the reduced form of NAD ) represents stored energy that is tapped
to synthesize ATP
AP Biology Cellular Respiration
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5. (S5) Describe the role of oxygen in energy-yielding pathways
• NADH passes the electrons to the electron transport chain
• Unlike an uncontrolled reaction, the electron transport chain passes
electrons in a series of steps instead of one explosive reaction
• O pulls electrons down the chain in an energy-yielding tumble
2
• The energy yielded is used to regenerate ATP
http://academicearth.org/lectures/cellular-respiration very helpful website
AP Biology Cellular Respiration
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• Cellular respiration has three (four) stages:
– Glycolysis – anaerobic and takes place in the
cytoplasm (breaks down glucose into two molecules of
pyruvate 2 three C molecules)
– Formation of acetyl CoA (When oxygen is present
pyruvic acid enters the mitochondria and each pyruvic
acid is converted to acetyl coenzyme A – a 2 carbon
molecule- and carbon dioxide is released.)
– The citric acid cycle = Krebs Cycle (completes the
breakdown of glucose)
– Oxidative phosphorylation – requires oxygen
(accounts for most of the ATP synthesis)
Cellular respiration helpful videos.
http://youtu.be/rVXHYx8zYeI good overview
http://youtu.be/3aZrkdzrd04 Black eyed peas song accompaniment
AP Biology Cellular Respiration
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6. (S4) Explain how organic molecules are broken down by catabolic pathways.
Activity: Overview of Cellular Respiration
Here is a good summary diagram of the major steps in cellular respiration:
The first major step is glycolysis:
______Glycolysis occurs in the cytoplasm; degrades glucose into pyruvate. ___________
_______One glucose C6 is broken down into 2 pyruvic acid molecules, C3 each.
AP Biology Cellular Respiration
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Glycolysis is followed by the Citric Acid
Cycle:
___Occurs in the mitochondrial matrix;
converts pyruvate into carbon dioxide.
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Finally, hydrogen atoms are transferred to the electron transport chain:
Occurs in the inner membrane of the mitochondrion; electrons passed to oxygen.
• Oxidative phosphorylation accounts for almost 90% of the ATP
generated by cellular respiration
• A smaller amount of ATP is formed in glycolysis and the citric acid
cycle by substrate-level phosphorylation
AP Biology Cellular Respiration
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7.What is ‘substrate-level phosphorylation’?
This occurs when an enzyme transfers a phosphate group from a substrate
molecule to ADP, rather than adding an inorganic phosphate to ADP as in
oxidative phosphorylation. The substrate molecule in a cell is commonly an
intermediate molecule generated in catabolism of glucose.
• Glycolysis (“splitting of sugar”) breaks down glucose into two
molecules of pyruvate
• Glycolysis occurs in the cytoplasm and has two major phases:
– Energy investment phase: cell uses ATP to phosphorylate fuel
– Energy payoff phase: ATP is produced by substrate level
phosphorylation and NAD+ is reduced to NADH by food
oxidation.
8.
What is the overall yield of glycolysis?
Net energy yield per glucose molecule is
2ATP plus 2NADH; no CO2 is released.
AP Biology Cellular Respiration
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9. Glycolyis in detail: You do not need to reproduce these steps; they are shown here just so
that you can understand better what is happening in the series of steps from one glucose to
two pyruvate molecules. These are CATABOLIC reactions, including a number of
oxidation-reduction reactions. Also, note that each step requires a specific enzyme.
http://www.johnkyrk.com/glycolysis.html
_use Campbell ppt. (note to self ) (draw a
summary gel sheet)
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10.



What happens as pyruvate is transported into the mitochondrion where the next stages of
cellular respiration will occur?
The pyruvate enters the
mitochondrion by active transport,
in the presence of O2.
Before the citric acid cycle can
begin, pyruvate must be converted
to Acetyle CoA which links the
cycle to glycolysis.
CO2 will diffuse out of the cell.
AP Biology Cellular Respiration
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11.Here is an overview of the major events that occur once pyruvate enters the mitochondrion and
the Citric Acid Cycle:
•
The citric acid cycle, also called the Krebs cycle, takes place within the
mitochondrial matrix
•
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3
NADH, and 1 FADH per turn
2
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AP Biology Cellular Respiration
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12.
What happens to the
acetyl CoA molecule as it
passes through the Citric Acid
Cycle?
http://www.johnkyrk.com/kreb
s.html
(note to self use ppt)
•
The citric acid cycle
has eight steps,
each catalyzed by a
specific enzyme
•
The acetyl group of
acetyl CoA joins the
cycle by combining
with oxaloacetate,
forming citrate
•
The next seven
steps decompose
the citrate back to
oxaloacetate,
making the process
a cycle
•
The NADH and
FADH produced by
2
the cycle relay electrons extracted from food to the electron transport chain
AP Biology Cellular Respiration
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13.
How do the hydrogens (electrons) that have been transferred to NAD+ and FAD
finally get to oxygen (the low energy position)?

Following glycolysis and the citric acid cycle, NADH and FADH
2
account for most of the energy extracted from food
•
These two electron carriers donate electrons to the electron transport chain,
which powers ATP synthesis via oxidative phosphorylation
 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP
synthesis ______________________________________________
AP Biology Cellular Respiration
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•
Electrons are transferred from NADH or FADH to the electron transport
•
chain
Electrons are passed through a number of proteins including cytochromes
(each with an iron atom) to O
•
•
The electron transport chain generates no ATP
The chain’s function is to break the large free-energy drop from food to O
2
2
2
into smaller steps that release energy in manageable amounts
+
•
Electron transfer in the electron transport chain causes proteins to pump H
from the mitochondrial matrix to the intermembrane space
•
H then moves back across the membrane, passing through channels in ATP
synthase
•
ATP synthase uses the exergonic flow of H to drive phosphorylation of ATP
•
This is an example of chemiosmosis, the use of energy in a H gradient to
drive cellular work
+
+
+
AP Biology Cellular Respiration
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14. (S3) Explain how chemiosmosis functions in cellular energetics. See ‘Energy Conversion’
in The Cell CD
http://www.youtube.com/watch?v=3y1dO4nNaKY chemical gradients and ATP synthase
_p.174
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AP Biology Cellular Respiration
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15.
How is the proton gradient required for chemiosmosis established?
http://www.johnkyrk.com/mitochondrion.html
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AP Biology Cellular Respiration
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16.
Here is an overview of all the stages of cellular respiration:
• During cellular respiration, most energy flows in this sequence:
glucose  NADH  electron transport chain  proton-motive
force  ATP
• About 40% of the energy in a glucose molecule is transferred to
ATP during cellular respiration, making about 38 ATP
Summary table
Glycolysis
Split to acetyl coA
Krebs cycle
Oxidative phosphorylation
Takes place in
Cytoplasm
Cytoplasm
Mitochondrial matrix
Inner mitochondrial membrane
Net result
2ATP (2NADH)
0ATP (2NADH)
2ATP (6NADH+2FADH2)
32 ATP
Net = 36ATP
AP Biology Cellular Respiration
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17. (S6) Explain how cells generate ATP in the absence of oxygen (ie. fermentation or
anaerobic respiration)
View fermentation overview animation.
•
Most cellular respiration
requires O to produce ATP
•
Glycolysis can produce ATP
with or without O (in aerobic or
2
2
•
•
anaerobic conditions)
In the absence of O , glycolysis
2
couples with fermentation or
anaerobic respiration to
produce ATP
Most cellular respiration
requires O to produce ATP
2
•
Glycolysis can produce ATP
with or without O (in aerobic or
2
•
•
anaerobic conditions)
In the absence of O , glycolysis
2
couples with fermentation or
anaerobic respiration to
produce ATP
Anaerobic respiration uses an
electron transport chain with an
electron acceptor other than O ,
2
•
for example sulfate
Fermentation uses
phosphorylation instead of an
electron transport chain to
generate ATP
+
•
•
•
Fermentation consists of glycolysis plus reactions that regenerate NAD ,
which can be reused by glycolysis
Two common types are alcohol fermentation and lactic acid fermentation
In alcohol fermentation, pyruvate is converted to ethanol in two steps, with
the first releasing CO
2
•
Alcohol fermentation by yeast is used in brewing, winemaking, and baking
AP Biology Cellular Respiration
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18. This diagram highlights the connection between aerobic (cellular) respiration and anaerobic
respiration (fermentation).
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AP Biology Cellular Respiration
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19.
How do our cells obtain energy from ALL major food groups, and not JUST from
carbohydrates?
AP Biology Cellular Respiration
•
Catabolic pathways
funnel electrons from
many kinds of organic
molecules into cellular
respiration
•
Glycolysis accepts a wide
range of carbohydrates
•
Proteins must be
digested to amino acids;
amino groups can feed
glycolysis or the citric
acid cycle
•
Fats are digested to
glycerol (used in
glycolysis) and fatty acids
(used in generating acetyl
CoA)
•
Fatty acids are broken
down by beta oxidation
and yield acetyl CoA
•
An oxidized gram of fat
produces more than twice
as much ATP as an
oxidized gram of
carbohydrate
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20.
How does the cell control the rate of ATP production. That is, what inhibits cellular
respiration and what stimulates cellular respiration? Note that the following three control
mechanisms all involve the same enzyme – phosphofructokinase.
•
•
•
Feedback inhibition is the most common mechanism for control
If ATP concentration begins to drop, respiration speeds up; when there is plenty of
ATP, respiration slows down
Control of catabolism is based mainly on regulating the activity of enzymes at
strategic points in the catabolic pathway
Allosteric enzymes at certain points in the pathway respond to inhibitors and
activators that set the pace of glycolysis and the citric acid cycle.
AP Biology Cellular Respiration
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Phosphofrutokinase, which catalyses an early step in glycolysis is one of
these enzymes. It is stimulated by AMP and inhibited by citrate.
_
AP Biology Cellular Respiration
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