Chapter 4 Flashcards
1
Q
Metabolic pathways harvest energy from high- energy molecules, such as
A
Glucose
2
Q
The energy released is used to add a phosphate group to ADP to make
A
ATP
3
Q
Cells generally contain enough ATP to sustain
A
from 30 seconds to a few minutes of activity
– ATP is unstable
– Most cells are making it all the time
4
Q
Cells obtain glucose to make
A
ATP
– Plants produce glucose during photosynthesis
– Other organisms obtain glucose from food
5
Q
Organisms store glucose as
A
glycogen or starch
6
Q
When glucose is oxidized to carbon dioxide by burning
A
some energy is released as heat and light
7
Q
Glucose + 6 oxygen –>
A
6Carbon dioxide+ 6 water+ heat and light
8
Q
Oxygen atoms are reduced to form
A
water
– Oxygen acts as electron acceptor
9
Q
In cells, glucose is oxidized through
A
a long series of carefully controlled redox reactions
– The released free energy is used to synthesize ATP
– These reactions comprise cellular respiration
10
Q
Fermentation
A
also oxidizes glucose
– Does not oxidize it fully
– Small, reduced organic molecules are produced as waste
11
Q
Does cellular respiration or fermentation produce more energy?
A
Cellular respiration
12
Q
Cellular respiration is a set of four processes, they are
A
Glycolysis, pyruvate processing, citric acid cycle, electron transport & oxidative phosphorylation
13
Q
Glycolysis is when
A
A six-carbon glucose is broken down into two three-carbon pyruvate
14
Q
Pyruvate processing involves
A
Each pyruvate is oxidized to form acetyl CoA
15
Q
The citric acid cycle is
A
Each acetyl CoA is oxidized to CO2
16
Q
Electron transport and oxidative phosphorylation involve
A
Electrons move through a transport chain and their energy is used to set up a proton gradient, which is used to make ATP
17
Q
Each of the four processes of cellular respiration produce
A
High-energy molecules in the form of nucleotides (ATP) and/or electron carriers (NADH or FADH2). Because the four processes are connected, cellular respiration is an integrated metabolic pathway. The first three processes oxidize glucose to produce NADH and FADH2, which then feed the electron transport chain.
18
Q
cellular respiration is
A
Cellular respiration is any set of reactions that uses electrons from high-energy molecules to make ATP
19
Q
Two fundamental requirements of cells are :
A
- Energy to generate ATP
- A source of carbon to use as raw materials for synthesizing macromolecules
20
Q
Catabolic pathways
A
– Involve the breakdown of molecules
– Often harvest stored chemical energy to produce ATP
21
Q
Anabolic pathways
A
– Result in the synthesis of larger molecules from smaller
components
– Often use energy in the form of ATP
22
Q
Cellular respiration interacts with
A
other catabolic and anabolic pathways
23
Q
For ATP production, cells use
A
– First use carbohydrates
– Then fats
– And finally proteins
24
Q
Proteins, carbohydrates, and fats can all furnish what for cellular respiration
A
substrates
25
A variety of high-energy compounds from carbohydrates, fats, or proteins can be broken down in catabolic reactions and
used by cellular respiration for ATP production.
26
Several of the intermediates in cellular respiration serve as precursor molecules in anabolic reactions leading to
the synthesis of carbohydrates, nucleotides, lipids, and amino acids
27
Fats are broken down into
– Glycerol, which enters glycolysis
– Fatty acids, which are converted to acetyl CoA, which enters the citric acid cycle
28
Proteins are broken down into amino acids
– Amino groups are removed and excreted as waste
– The remaining carbon compounds are converted to
pyruvate, acetyl CoA, or other intermediates
– Used in glycolysis and the citric acid cycle
29
Molecules found in carbohydrate metabolism are used to synthesize
macromolecules
30
About half the required amino acids can be synthesized from
citric acid cycle molecules
31
Acetyl CoA is the starting point in
fatty acid synthesis
Can be used to build phospholipids or fats
32
Glycolysis intermediates can be used to make
nucleotides for DNA and RNA synthesis
33
Pyruvate and lactate can be used to make
glucose
34
Metabolism comprises thousands of different
chemical reactions.
Organizing them into pathways allows them to be regulated
35
Maintaining a stable internal environment even under different environmental conditions is
Homeostasis
36
Glycolysis is
Oxidizing Glucose to Pyruvate
37
The enzymes responsible for glycolysis have been observed in
nearly every prokaryote and
eukaryotes
– Glycolysis is an ancient method to make ATP
– Process discovered by accident
38
How many chemical reactions occur in the cytosol during glycolysis
10
39
Three key points regarding glycolysis
1. Glycolysis starts by using two ATP in the energy investment phase (reactions 1–5)
2. During the energy payoff phase (reactions 6–10), NADH is made and ATP is produced by substrate- level phosphorylation
3. The net yield is two NADH, two ATP, and two pyruvate
40
Substrate-level phosphorylation involves
An enzyme and a phosphorylated substrate. Substrate-level phosphorylation occurs when an enzyme catalyzes the transfer of a phosphate group from a phosphorylated substrate to ADP, forming ATP
41
Reaction 1 of glycolysis
Hexokinase uses ATP to phosphorylate glucose, increasing its potential energy
42
reaction 2 of glycolysis
Phosphoglucose isomerase: converts glucose-6-phosphate to fructose-6-phosphate; referred to as an isomer of glucose-6-phosphate
43
reaction 3 of glycolysis
Phosphofructokinase uses ATP to phosphorylate the opposite end of fructose-6-phosphate, increasing its potential energy
44
reaction 4 of glycolysis
Fructose-biphosphate aldolase: cleaves fructose-1,6-biphosphate into two different 3-carbon sugars
45
reaction 5 of glycolysis
Triose phosphate isomerase converts dihydrogen phosphate (daP) to glyceraldehyde-3-phosphate (G3P). Although the reaction is fully reversible, the DAP-to-GDP reaction is favoured because G3P is immediately used as a substrate for step 6
46
reaction 6 of glycolysis
Glyceraldehyde-3-phosphate dehydrogenase: a two-step reaction that first oxidizes G3P using the NAD+ coenzyme to produce NADH. Energy from this reaction is used to attach a Pi to the oxidized product to form 1,3-biphosphoglycerate
47
reaction 7 of glycolysis
Phosphoglycerate kinase transfers a phosphate from 1,3-biphosphoglycerate to ADP to make 3-phosphoglycerate and ATP
48
reaction 8 of glycolysis
Phosphoglycerate mutase: rearranges the phosphate in 3-phosphoglycerate to make 2-phosphoglycerate
49
reaction 9 of glycolysis
Enolase: removes a water molecule from 2-phosphoglycerate to form a C=C double bond and produce phosphoenolpyruvate
50
reaction 10 of glycolysis
Pyruvate kinase: transfers a phosphate from phosphoenolpyruvate to ADP to make pyruvate and ATP
51
Glycolysis is regulated by
feedback inhibition
High levels of ATP (a product of glycolysis) inhibit the third enzyme: phosphofructokinase
52
Phosphofructokinase has two binding sites for ATP
1. When ATP binds to the active site, the enzyme catalyzes the third step in glycolysis. In the active site, ATP is used as a substrate to transfer one of its phosphate groups to fructose-6-phosphate
2. When ATP levels are high, it binds to a regulatory site and inhibits the enzyme. In the regulatory site, ATP binding inhibits the reaction by changing the shape of the enzyme
53
Pyruvate produced during glycolysis is transported into
Mitochondria
54
Mitochondria have both inner and outer
Membranes that define the inter-membrane space and matrix
55
Cristae are extensions of the
inner membrane
– Layers of sac-like structures
– Fill the interior of the mitochondria
– Are connected to the inner membrane by short tubes
56
The mitochondrial matrix
is inside the inner membrane
57
Pyruvate processing occurs in the
mitochondrial matrix
58
Pyruvate processing takes place inside an enormous enzyme complex called
pyruvate dehydrogenase
– Located in the mitochondrial matrix in eukaryotes
– Located in the cytosol in prokaryotes
59
Pyruvate undergoes a series of reactions
– One of its carbons is oxidized to CO2
– NADH is produced
– The remaining two-carbon unit is attached to coenzyme A, producing acetyl CoA
60
During the reactions of pyruvate what goes in and comes out
– Pyruvate, NAD+, and CoA go in
– CO2, NADH, and acetyl CoA come out
61
Pyruvate processing is also regulated by feedback inhibition
– When products of glycolysis and pyruvate processing are abundant
– Pyruvate dehydrogenase is phosphorylated
– Changes shape and is inhibited
62
The Citric Acid Cycle
Oxidizes Acetyl CoA to CO2
63
In the citric acid cycle, each acetyl CoA from pyruvate processing is oxidized into
two CO2
64
The citric acid cycle is located in the
– Mitochondrial matrix in eukaryotes
– Cytosol in prokaryotes
65
The reactions of citric acid cycle
– Starts by moving the acetyl group from acetyl CoA to
oxaloacetate to form citrate
– At the end, oxaloacetate is regenerated
66
Some of the potential energy released in citric acid cycle is used to
1. Reduce three NAD+ to NADH
2. Reduce one FAD to FADH2
3. Phosphorylate ADP (or GDP) to form ATP (or GTP)
67
The cycle turns twice for each
glucose molecule,
since two pyruvate are produced by glycolysis
68
What goes in and comes out of the citric acid cycle
Acetyle CoA goes into the citric acid cycle and carbon dioxide, NADH, FADH, and ATP or GTP come out. ATP or GTP is produced by substrate-level phosphorylation. If you follow individual carbon atoms around the cycle several times, you'll come to an important conclusion. Each of the carbons in the cycle is eventually a “red carbon” that is released as CO2
69
The citric acid cycle can be turned off at multiple points via several mechanisms of
feedback inhibition
70
Reaction rates are high in citric acid cycle when
ATP and NADH are
scarce
71
reaction rates are low in citric acid cycle when
ATP or NADH are
abundant
72
How many reactions are there in the citric acid cycle
8
73
reaction 1 of citric acid cycle
Citrate synthase: transfers the 2-carbon acetyl group from acetyl CoA to the 4-carbon oxaloacetate to produce the 6-carbon citrate
74
reaction 2 of citric acid cycle
Aconitase: convert citrate to isocitrate by the removal of one water molecule and the addition of another water molecule
75
reaction 3 of citric acid cycle
Isocitrate dehydrogenase: oxidizes isocitrate using the NAD+ coenzyme to produce NADH and releases one CO2, resulting in the formation of the 5-carbon molecule alpha-ketoglutarate
76
reaction 4 of citric acid cycle
Alpha-ketoglutarate: oxidizes alpha-ketoglutarate using the NAD+ coenzyme to produce NADH and releases one CO2. the remaining 4-carbon molecules are added to coenzyme A (CoA) to form succinyl CoA
77
reaction 5 of citric acid cycle
Succinyl CoA synthetase: CoA is removed, converting succinyl CoA to succinate., the energy released is used to transfer Pi to ADP to form ATP, or to GDP to form GTP, depending on the enzyme used
78
reaction 6 of citric acid cycle
Succinate dehydrogenase: oxidizes succinate by transferring two hydrogens to the coenzyme FAD to produce FADH2, resulting in the formation of fumarate
79
reaction 7 of citric acid cycle
Fumarase converts fumarate to malate by the addition of one water molecule
80
reaction 8 of citric acid cycle
Malate dehydrogenase: oxidizes malate by using the NAD+ coenzyme to produce NADH, resulting in the regeneration of the oxaloacetate that will be used in step 1 of the cycle
81
For each molecule of glucose that is oxidized, the cell produces
– 6 CO2—disposed of when you exhale
– 4 ATP—directly used as fuel
– 10 NADH
– 2 FADH2
82
Free energy changes as
glucose is oxidized
About 2680 kj/mol of free energy is released from the oxidation of glucose
Much of the energy is harnessed in the form of ATP, NADH, and FADH2
83
Most of glycose's original energy is contained in the electrons transferred to
NADH and FADH2
84
The electrons (and protons) are ultimately transferred to oxygen to form
water
85
Researchers determined that NADH is oxidized when combined with
the inner membrane of
mitochondria
86
In prokaryotes,NADH is oxidized by
The plasma
membrane
87
Molecules in the inner mitochondrial membrane could cycle between
oxidized and reduced states
88
The molecules that oxidize NADH and FADH2 are called the
electron transport chain (ETC)
– Most are proteins that are easily oxidized
– One is a lipid-soluble, non-protein called ubiquinone or coenzyme Q or “Q”
– They have different ability to accept electrons, called their redox potential
– Some accept only electrons; others accept electrons plus protons
89
As electrons move from one molecule to another in the ETC
– They are held more and more tightly
– A small amount of energy is released in each reaction
– Each successive bond holds less potential energy
90
The ETC is organized into four protein complexes
– Called complexes I–IV
– Cytochrome c transfers electrons between complexes
91
At the end of the ETC
– Low-energy electrons are passed to oxygen, along with protons
– Water is formed
92
Which reactions occur in the electron transport chain
oxidation and reduction reactions
- The potential energy in shared electrons steps down from the electron carriers NADH and FADH2 through an electron transport chian to a final electron acceptor
- In this electron transport chain, oxygen is the final electron acceptor and it forms water as a by-product
- The overall free-energy change of 222 KJ/mol (from NADH to oxygen) is borken into small steps
93
What is the reaction of complex I in ETC
Complex I (NADH dehydrogenase): oxidizes NADH and transfers two electrons through proteins containing FMN prosthetic groups and Fe.S cofactors to reduce and oxidized from of the ubiquinone (Q). Four H+ are pumped out of the matrix to the inter-membrane space
94
What is the reaction of complex II in ETC
Complex II (succinate dehydrogenase): oxidized FADH2 and transfers the two electrons through proteins containing Fe.S cofactors to reduce an oxidized form of Q. this complex is also used in step 6 of the citric acid cycle
95
What is the reaction of Q in ETC
Q (ubiquinone): reduced by complexes I and II and moves throughout the hydrophobic interior of the ETC membrane, where it is oxidized by complex III
96
what is the reaction of complex III in ETC
Complex III (cytochrome c reductase): oxidizes Q and transfers one electron at a time through proteins containing heme prosthetic groups and Fe.S cofactors to reduce an oxidized form of cytochrome c (cyt c). A total of four H+ for each pair of electrons is transported from the matrix to the intermembrane space
97
What is the reaction of cyt c in the ETC
Cyt c (cytochrome c): reduced by accepting a single electron from complex III and moves along the surface of the ETC membrane, where it is oxidized by complex IV
98
What is the reaction of complex IV in ETC
Complex IV ( cytochrome c oxidase): oxidizes cyt c and transfers each electron through protein containing heme prosthetic groups to reduce oxygen gas (O2) which picks up two H+ from the matrix to produce water. Two additional H+ are pumped out of the matrix to the inter-membrane space
99
The reactions of the ETC comprise the
fourth pathway of cellular respiration
100
The energy released as electrons moves through the ETC and
– Is used to pump protons across the mitochondrial inner membrane into the intermembrane space
– Forms a strong electrochemical gradient
101
Most of the chemical energy from glucose is now accounted for by
a proton electrochemical
gradient
102
How does the electron transport chain work
- The individual components of the electron transport chain are found in the inner membrane of the mitochondria
- Electrons are carried from one complex to another by Q and by cytochrome c; Q also shuttles protons across the membrane.
- The orange arrow indicates Q moving back and forth
- Complexes I and IV use the energy released by the redox reactions to pump protons from the mitochondrial matrix to the inter-membrane space
103
ATP synthase is
the enzyme that synthesizes
ATP – “complex V
104
Protons move through a proton channel in ATP synthase
– Driving the production of ATP from ADP and Pi
– Process is called chemiosmosis
– ATP production is dependent on a proton-motive force generated by the proton electrochemical gradient
105
What is the chemiosmotic hypothesis
The linkage between the electron transport chain and ATP production is indirect.
The ETC creates a protein gradient and ATP synthase uses the gradient to synthesize ATP
106
What is the alternate hypothesis to chemiosmotic hypothesis
Alternate hypothesis: the linkage is direct. Specific ETC proteins are required for ATP synthesis by ATP synthase
107
What is the experimental setup for chemiosmotic hypothesis
1. Produce venues from artificial membranes: add ATP synthase, an enzyme found in mitochondria
2. Add bacteriorhodopsin, a protein that acts as a light-activated proton pump
3. Illuminate the vesicle so that bacteriorhodopsin pumps protons out of the vesicle, creating a proton gradient
108
Prediction of chemiosmotic hypothesis:
ATP will be produced within the vesicle
109
Prediction of alternate hypothesis:
No ATP will be produced without the ETC
110
results of chemiosmotic experiment
Results: ATP is produced within the vesicle, in the absence of the electron transport chain
111
conclusion of chemiosmotic experiment
Conclusion: the linkage between electron transport and ATP production by ATP synthase is indirect, the synthesis of ATP only requires a proton gradient
112
Oxidative Phosphorylation Involves
the ATP Synthase Motor and a Proton Gradient
- ATP synthase has two major components, designated F0 and F1, connected by a shaft
- The F0 unit spins as protons pass-through
- The shaft transmits the rotation to the F1 unit, causing it to make ATP from ADP and Pi
113
The Proton-Motive Force Couples
Electron Transport to ATP Synthesis
114
ATP synthase can reverse direction by
Hydrolyze ATP to build a proton gradient
115
If the proton gradient dissipates
the spin is reversed and ATP is hydrolyzed to pump protons from the matrix to the inter-membrane space.
116
Thus, the energy to produce ATP comes from a
proton gradient
117
Approximate yield of ATP from glucose is
29
– 25 ATP from ATP synthase
– This process is called oxidative phosphorylation
– As opposed to substrate-level phosphorylation that
occurs during glycolysis and the citric acid cycle
118
Most of the ATP made during cellular respiration is made by
oxidative phosphorylation
119
The actual yield of ATP per glucose (29 ATP) is lower than
the theoretical calculation (38 ATP) because the proton gradient is used to drive other mitochondrial activities, such as the active transport of Pi into the mitochondrial matrix
120
All eukaryotes and many prokaryotes
– Use oxygen as the final electron acceptor for the ETC
– This is called aerobic respiration
121
Some prokaryotes
– Especially those in oxygen-poor environments
– Use other electron acceptors
– This is called anaerobic respiration
122
Oxygen is the most effective electron acceptor because
– It is highly electronegative
– A large difference exists between the potential energy
of electrons in NADH and O2
– It allows the generation of a large proton-motive force
123
Aerobic organisms
grow and reproduce faster
124
What happens when there is no electron acceptor?
– The electrons have no place to go
– The ETC stops
125
NADH builds up and there is no NAD+ available to accept electrons causing
– Glycolysis, pyruvate processing, and the citric acid cycle stop
– The situation is life threatening
– NAD+ must be regenerated
126
Fermentation is
a metabolic pathway that
regenerates NAD+ from NADH
– Electrons from NADH are transferred to pyruvate
– Serves as an emergency backup in respiring cells
127
Glycolysis can continue to produce ATP by
substrate-level phosphorylation in the absence of oxygen
128
What are the alternative pathways for producing ATP
Cellular respiration and fermentation
- When oxygen or another final electron acceptor used by the ETC is present in a cell, the pyruvate produced by glycolysis enters the citric acid cycle and the electron transport system is active
- If no electron acceptor is available to keep the ETC running, then pyruvate undergoes reactions known as fermentation
129
When our muscle cells cannot get enough oxygen, they convert to
lactic acid fermentation
– Pyruvate produced by glycolysis accepts electrons
from NADH
– Lactate and NAD+ are produced
130
As muscle cells get more oxygen, lactate can be
converted back to pyruvate
131
Fermentation regenerates
NAD+ so that glycolysis can continue
- Lactic acid fermentation occurs in humans
- No intermediate; pyruvate accepts electrons from NADH
- Alcohol fermentation occurs in yeast (bubbles in beer and champagne)
132
Some yeast cells can perform
alcohol fermentation
– Pyruvate is converted to acetaldehyde and CO2
– Acetaldehyde accepts electrons from NADH
– Ethanol and NAD+ are produced
133
Cells that perform other types of fermentation are used to make
soy sauce, tofu, yogurt, cheese, etc
134
Prokaryotes that rely on fermentation are present in our
intestines
135
Fermentation is much less efficient than
cellular respiration
- It produces 2 ATP per glucose, compared with
about 29 ATP per glucose in cellular respiration
136
Some organisms can switch between fermentation and aerobic respiration called
facultative anaerobes
– They use fermentation only if an electron acceptor is
not available
137
Our transportations systems are run on
petroleum
– Mixture of organic material from long dead creatures
138
Biofuels can be produced
to power transportation
– Mixture of organic molecules produced by living organisms.
– Renewable
139
Gasoline in Canada must contain an average renewable fuel content of
5 percent
140
How to turn corn into the biofuel ethanol?
– remove the kernels from the cob.
– starch is broken down into glucose and then fermented into ethanol by the action of enzymes and yeast
– the water removed by distillation and dehydration.
– the pure ethanol is mixed with gasoline to serve as car fuel
141
Biofuels can be controversial because
– Growing corn uses
Fuel
Water
Land
Fertilizer
Less cropland for food
Increase food costs in developing nations
May not reduce greenhouse gas emissions
142
Brazil as an example
– Has produced bio-ethanol from sugar cane for more than 30 years
– Brazil’s automobile fuel has a minimum of 25% ethanol
Many vehicles use 100% ethanol
– Only 1% of Brazil’s land is used for growing this sugar cane.
143
Anaerobic respiration of waste material is another alternative
– methane is produced
– then used as a fuel to produce electricity
