Chapter 5 Flashcards
1
Q
What is cellular respiration?
A
- Breaks down carbohydrates, lipids, and proteins
- Converts energy that is liberated into ATP
- Allows the cell to do work
2
Q
What does cellular respiration use to produce ATP? What type of reaction occurs
A
Cellular respiration uses chemical energy stored in molecules such as carbohydrates and lipids to produce ATP
Cellular respiration is a series of catabolic reactions
Collection of metabolic reactions within cells that breaks down
food molecules (catabolic reactions) to produce ATP
Catabolism: the breakdown of molecules into smaller units, in the process, these reactions release chemical energy that can be stored in molecules of ATP
3
Q
What is ATP required for?
A
ATP is the form of chemical energy required for thousands of
biosynthetic reactions (anabolic reactions) taking place within
the cell
- Recall: anabolic reactions build molecules from smaller units,
requiring an input of energy
4
Q
Where is energy coming from?
A
The Sun
* Ultimate source of energy for most organisms
Photosynthesis
* Captures energy of sunlight
* Converts it to the chemical energy of complex organic molecules
5
Q
What are the two fuel molecules?
A
Gasoline and glucose
6
Q
What are Oxidation-Reduction (Redox)
Reactions?
A
Chemical reactions in which electrons are transferred from one atom or molecule to another
LEO the lion says GER
Loss of Electrons = Oxidation
Gain of Electrons = Reduction
7
Q
What is electron sharing?
A
The gains or loss of an electron in a redox reaction is not always complete. Sometimes only the degree of electron sharing in covalent bonds changes (a relative loss or gain of electrons)
Example: When methane burns, carbon loses a relative share of electrons, and oxygen gains a relatively larger share
Glucose is oxidized to carbon dioxide and oxygen is reduced to water.
The carbon atoms of glucose are bonded to other carbon atoms, hydrogen atoms, and oxygen atoms. Electrons are shared equally with hydrogen, but in CO2, they are not shared equally. The oxygen atom is more electronegative than the carbon atoms, therefore the electrons that are shared between them spend more time near the oxygen.
* As a result, carbon atoms have partially lost electrons to oxygen atoms. The carbon atoms have been oxidized.
8
Q
What is oxidation?
A
The partial or full loss of electrons from a substance
The substance from which the electrons are lost (the e- donor) is oxidized
9
Q
Is glucose a good electron donor?
A
Yes
10
Q
What is reduction?
A
The partial or full gain of electrons to a substance
The substance that gains the electrons (the e- acceptor) is
reduced
11
Q
Is oxygen a good electron acceptor?
A
Yes
12
Q
What happens between O2 and water?
A
- In O2, the electrons are shared equally between the two oxygen atoms.
- In water, the oxygen atom is more electronegative than the hydrogen atoms, therefore the electrons spend more time near the oxygen atom.
- The electron density around the oxygen atom has increased—that is, the oxygen atom has gained electrons.
- The oxygen atom is thus reduced.
- Because it gains electrons, the oxygen atom is the electron acceptor, and because it oxidizes glucose, it can be called the oxidizing agent.
- Glucose is the electron donor and is considered the reducing agent.
13
Q
What are redox reactions?
A
Redox reactions are coupled reactions: The oxidation reaction and the reduction reaction occur simultaneously
Oxidation-reduction (redox) reactions result in the partial or complete transfer of electrons from one substance to another. (a) Basic redox reaction where there is a complete transfer of an electron. (b) The breakdown of glucose during cellular respiration is a redox reaction that results in the partial transfer of electrons.
14
Q
Is Cellular respiration a controlled combustion?
A
Yes
A comparison of the oxidation of glucose by combustion and cellular respiration
15
Q
What is NAD+
A
an electron carrier
As the carrier is reduced to NADH, an electron is added at each of the two positions marked by a red arrow; a proton is also added at the position boxed in red. The nitrogenous base (blue) that adds and releases electrons and protons is nicotinamide, which is derived from the vitamin niacin (nicotinic acid).
16
Q
Oxidation-Reduction Reactions examples
A
· Reduction reactions:
NAD+ + 2e- + H+ NADH
FAD + 2e- + 2H+ FADH2
· Oxidation reactions:
NADH NAD+ + 2e- + H+
FADH2 FAD + 2 e- + 2H+
17
Q
Cellular respiration formula and what occurs?
A
-cellular respiration uses chemical energy stored in reduced molecules such as carbohydrates and lipids to produce ATP
- Carbohydrates and lipids have high potential energy because the electrons shared in bonds are far from the nuclei of the atoms in the bond.
- The energy in these molecules is released gradually in a series of reactions.
-glucose is the most common fuel molecule in animals, plants, and microbes
- Because glucose is oxidized slowly in a controlled manner, the chemical energy stored in glucose can be harnessed in the chemical bonds of other molecules such as ATP and electron carriers.
Glucose is a good electron donor because its oxidation to carbon dioxide releases a lot of energy
18
Q
What are the three stages of cellular respiration?
A
- Glycolysis (cytosol)
- Pyruvate oxidation and the citric acid cycle (mitochondria)
- Oxidative phosphorylation (mitochondria)
Stages 1-2: Glucose is oxidized through a series of chemical reactions, releasing energy in the form of ATP and reduced electron carriers.
Stage 3:
Electron carriers donate electrons to the electron transport chain, leading to the synthesis of ATP and a large amount of ATP is
produced.
19
Q
What is the site of cellular respiration in eukaryotes?
A
the mitochondrion
20
Q
Where do most reaction of cellular respiration take place?
A
mitochondria
21
Q
What reactions occur in glycolysis?
A
Because two molecules of G3P are produced in reaction 5, all the reactions from 6 to 10 are doubled (not shown). The name of the enzyme that catalyzes each reaction is in red.
22
Q
What is the summary of glycolysis?
A
Glycolysis, which occurs in the cytosol of all cells, splits glucose (six carbons) into pyruvate (three carbons) and yields ATP and NADH
23
Q
Glycolysis?
A
24
Q
What is ATP?
A
· ATP molecules
· Produced in glycolysis
Result from substrate-level phosphorylation
25
What is Substrate-level phosphorylation?
* Enzyme-catalyzed reaction
* Transfers phosphate group from a substrate to ADP
· Mechanism that synthesizes ATP by substrate-level phosphorylation. A phosphate group is transferred from a high-energy donor directly to ADP, forming ATP.
26
Cellular respiration diagram
Substrate-level phosphorylation produces only a small amount of the ATP generated in cellular respiration
12% of ATP is generated here
27
What are the several mechanisms ATP is generated using?
1. Substrate level phosphorylation: An enzyme-substrate complex is used in a hydrolysis reaction.
· Only a small amount of ATP is generated this way.
2. Energy is transferred to electron carriers, transport electrons to the respiratory electron transport chain, transfers the electrons along a series of membrane-associated proteins to a final electron acceptor, while harnessing the energy released to produce ATP.
3. This is called oxidative phosphorylation.
The majority of ATP is produced using this mechanism.
28
How much ATP is produced by electron carriers?
88%
Electron carriers transfer electrons (and energy) from one set of reactions to another
29
What is pyruvate oxidation?
· Takes place in mitochondria
· Pyruvate (3C) is oxidized to an acetyl group (2C)
- CO2 is produced
· Electrons removed are accepted by (or used to reduce) NAD+ to form NADH
· Acetyl group linked to Co-Enzyme A (CoA)
30
pyruvate oxidation diagram
Pyruvate (three carbons) is oxidized to an acetyl group (two carbons), which is carried to the citric acid cycle by CoA. The third carbon is released as CO2 . NAD+ accepts two electrons and one proton removed in the oxidation. The acetyl group carried from the reaction by CoA is the fuel for the citric acid cycle.
31
What does each pyruvate produce?
- 1 acetyl group
- 1 NADH
- 1 CO2
· Acetyl groups attached to coenzyme A
· Delivered to citric acid cycle
· Pyruvate oxidation links glycolysis and the citric acid cycle
· At the end of pyruvate oxidation, acetyl-CoA carries the acetyl group to the citric acid cycle
TWO OF EVERYTHING SINCE 2 PYRUVATE
32
At the end of glycolysis, glucose produced 2 pyruvate molecules 2 acetyl-CoA
2 CO2 and 2 NADH, what occurs after?
1. First, the pyruvate is oxidized to form CO2 and an acetyl group.
- the electrons lost in this process are donated to NAD+, which is reduced to NADH
- the remaining acetyl group still contains a large amount of potential energy that can be harnessed
2. The acetyl group is then transferred to coenzyme A, which carries the acetyl group to the citric acid cycle.
3. These reactions are catalyzed by a group of enzymes called the pyruvate dehydrogenase complex.
4. One molecule of pyruvate produces one CO2 molecule, one molecule of NADH, and one molecule of acetyl-CoA.
Remember that at the end of glycolysis, we had two molecules of pyruvate, therefore at the end of this process, we have two molecules of CO2, two molecules of NADH, and two molecules of acetyl-CoA for each glucose molecule.
pyruvate + CoA + NAD+ → acetyl-CoA + NADH + H+ + CO2
33
What is the citric acid cycle?
· Acetyl groups completely oxidized to CO2
· Electrons removed in a series of oxidations
- Accepted by NAD+ or FAD (which get reduced to NADH and FADH2)
Some ATP made by substrate-level phosphorylation
The reactions of pyruvate oxidation and the citric acid cycle. Each turn of the cycle oxidizes an acetyl group of acetyl–CoA to 2 CO2. Acetyl-CoA, NAD+, FAD, and ADP enter the cycle; CoA, NADH, FADH2, ATP, and CO2 are released as products.
34
Summary of the citric acid cycle?
· The eight reactions of the citric acid cycle (tricarboxylic acid cycle or Krebs cycle) oxidize acetyl groups completely to CO2, generate 3 NADH and 1 FADH2, and synthesize 1 ATP by substrate-level phosphorylation (cycle because starting molecule oxaloacetate is regenerated at the end.)
· 1 acetyl-CoA + 3 NAD+ + 1 FAD + 1 ADP + 1 Pi + 2 H2O *arrow* 2 CO2 + 3 NADH + 1 FADH2 + 1 ATP + 3 H+ + 1 CoA
- During this stage of cellular respiration, the fuel molecules are completely oxidized.
- The chemical energy in the bonds of acetyl-CoA is transferred to ATP by substrate-level phosphorylation and to the electron carriers NADH and FADH2.
- This process also takes place in the mitochondrial matrix.
Acetyl-CoA, NAD+, FAD, and ADP enter the cycle; CoA, NADH, FADH2 , ATP, and CO2 are released as products.
The CoA released in reaction 1 can cycle back for another turn of pyruvate oxidation.
35
What is produced at the end of the citric acid cycle?
2 molecule of acetyl-CoA yields:
* 2 ATP
* 6 NADH
* 2 FADH2
- 2 CO2
- 1 ATP
- 3 NADH
- 1 FADH2
The chemical energy in the bonds of acetyl-CoA is transferred to ATP and to the electron carriers NADH and FADH2
36
How do the Electron Transfer System and
Oxidative Phosphorylation correlate?
· Oxidative phosphorylation: the mitochondrial ETC and ATP synthase complex. The electron transport system includes three major complexes, I, III, and IV. Two smaller electron carriers, ubiquinone (UQ) and cytochrome c (cyt c), act as shuttles between the major complexes; and succinate dehydrogenase (complex II) passes electrons to ubiquinone, bypassing complex I. Blue arrows indicate electron flow; red arrows indicate H+ movement. H+ is pumped from the matrix into the intermembrane space as electrons pass through complexes I and IV. H+ is also moved into the intermembrane space by the cyclic reduction/oxidation of ubiquinone. Chemiosmotic synthesis of ATP involves the ATP synthase complex, which uses the energy of the proton gradient to catalyze the synthesis of ATP.
37
What are the two important electrons carriers?
The oxidized forms of these carriers are NAD+ and FAD and the reduced forms are NADH and FADH2.
3. In the course of glycolysis, pyruvate oxidation, and the citric acid cycle, the oxidized form accepts electrons and becomes reduced.
4. The reduced form has high potential energy, used to synthesize ATP in the final stage of cellular respiration.
-Changes in free energy is much greater for the steps that generate electron carriers compared to those that produce ATP directly
38
What is the electron transfer system?
The electron transport chain converts the potential energy in NADH and FADH2 into a proton-motive force, which is used to drive ATP synthesis.
Located in the mitochondrial inner membrane
Electrons enter the ETC via either complex I or II depending on whether they enter as NADH or FADH2.
Electrons are passed from electron donors to acceptors until they reach the final electron acceptor, oxygen.
When oxygen accepts the electron, it is reduced to water.
Electron Transport Chain includes
- 4 protein complexes
- 2 smaller shuttle carriers
· Electrons move spontaneously along the electron transport chain
39
What is the Respiratory Electron Transport Chain?
· 3 major protein complexes (I, III, and IV)
- Pump H+ from Matrix to IMS
Contain prosthetic groups that cycle between reduced and oxidized states
40
What happens to electrons during the respiratory Electron Transport Chain?
* Depleted of energy
* Delivered to oxygen as final
electron acceptor
41
Respiratory Electron Transport Chain Diagram
· Redox components of the ETC are organized from high to low potential energy. Electron flow is spontaneous from high to low potential energy as electrons are passed from one redox molecule to the next.
42
Electron transport chain diagram
Electrons donated by NADH and FADH2 is transported along the series of ETC complexes
43
What are the steps of the electron transport chain?
1. Complexes I and II harvest electrons from NADH and FADH2
2. Coenzyme Q or ubiquinone accepts electrons from both complexes I and II.
3. In doing so, it is reduced to CoQH2, which diffuses in the inner membrane, docks, and transfers electrons to complex III.
4. Complex III transfers electrons to cytochrome c.
5. When cytochrome c accepts an electron, diffuses in the membrane, and moves to complex IV where oxygen is reduced to form water.
6. These electron transfer steps are each associated with the release of energy as electrons are passed from the reduced electron carriers NADH and FADH2 to the final electron acceptor, oxygen.
7. Protons in the intermembrane space are able to diffuse down their electrical and concentration gradients through a transmembrane protein channel into the mitochondrial matrix
ATP synthase uses the electrochemical proton gradient to drive the synthesis of ATP.
44
What occurs to protons due to proton pumping of the ETC?
Due to the proton pumping of the ETC, protons have a
high concentration in the intermembrane space and a low
concentration in the mitochondrial matrix. The proton concentration gradient contains high-potential energy
45
What is ATP synthase?
· ATP synthase catalyzes ATP synthesis using energy from the H+ gradient across the membrane (chemiosmosis)
· ATP synthase
- Molecular motor
- Embedded in inner mitochondrial membrane with electron transfer system
The enzyme consists of a basal unit that is embedded in the inner mitochondrial membrane and connected to a headpiece by a stalk; a stator bridges the basal unit and the headpiece. Protons move through a channel between the basal unit and the stator, making the stalk and headpiece spin. This results in ATP synthesis.
46
Understanding the difference between:
* Electron Transport Chain
* Proton-motive force
* Chemiosmosis
* ATP Synthase
* Oxidative Phosphorylation
Some ATP at the end of the process are needed outside of the cell and transported outside of the cell using transporters. Used by other enzymes that need energy and when this happens, ATP gets turned back into ADP and Pi and then come back to the mitochondria to create more substrate. NOT ALL.
47
What is the Uncoupling of Electron Transport and ATP Synthesis
· Electron transport and chemiosmotic generation of ATP
are separate and distinct processes, BUT ACTIVITY IS COUPLED by PMF.
Uncoupling proteins do not use energy in to the gradient to make ATP but generate heat (hibernating animals)
Uncoupling of electron transport and ATP synthesis. Respiratory electron transport results in the formation of a proton gradient across the membrane. Usually, this gradient is dissipated by protons flowing back to the matrix through the ATP synthase. Uncouplers, which may be specific chemicals or proteins, provide an alternative route for protons to flow back across the membrane. By circumventing the ATP synthase, no ATP is generated.
48
What is ATP Yield from the Oxidation of Glucose?
· ATP yield from the oxidation of glucose. The maximum possible ATP yield from the oxidation of 1 molecule of glucose is 38. However, this yield is rarely achieved. (OXPHOS = oxidative phosphorylation)
1. The complete oxidation of glucose forms 32 molecules of ATP.
2. The energy of glucose is released slowly in a series of reactions and captured in chemical form.
3. Some energy is released by substrate-level phosphorylation, and some is generated through redox reactions that transfer energy to electron carriers NADH and FADH2.
4. These carriers donate electrons to the electron transport chain. That energy is used to pump protons across the inner membrane of the mitochondria.
· Majority of energy from ETC
- The cell now has a form of energy that it can use in many ways to perform work
1. The energy of the electron carriers is thus transformed into energy stored in a proton electrochemical gradient.
2. ATP synthase then converts the energy of the proton gradient to rotational energy, which drives the synthesis of ATP.
49
What are the Major Pathways Oxidizing
Carbohydrates, Fats, and Proteins?
Reactions that occur in the cytosol are shown against a tan background; reactions that occur in mitochondria are shown inside the organelle. CoA funnels the products of many oxidative pathways into the citric acid cycle.
Besides simple sugars, energy can be extracted from fats, proteins, and carbohydrates that enter the respiratory chain at different points
50
What is the relationship between cellular respiration and oxygen?
· In eukaryotes, oxygen is the terminal electron acceptor (aerobic organisms)
- Aerobic cellular respiration
· Some aerobic organisms (or tissues) can survive in the absence of oxygen (facultative aerobes)
- Fermentation
· Some organisms (bacteria and archaea) can't grow at all in the presence of oxygen (strict anaerobes)
- Anae4robic cellular respiration
51
What are Respiratory Intermediates?
· Intermediates of glycolysis and the citric acid cycle are routinely diverted and used as starting substrates to synthesize amino acids, fats, and the pyrimidine and purine bases needed for the nucleic acid synthesis
· Respiratory intermediates also supply the carbon backbones for hormones, growth factors, prosthetic groups, and cofactors essential to cell function
· Respiratory intermediates are utilized for anabolic reactions
52
What is the control (regulation) of cellular respiration?
A major mechanism is allosteric (active site and allosteric binding sites which means it slows down) control of the activity of the enzyme phosphofructokinase, which is found early in glycolysis.( which means the rest of the reactants will have less substrate to work with and will be slow. )
ADP is a allosteric activator of phosphofructokinase since it stimulates the activity phosphofructokinase
Higher citrate levels means the citric acid cycle will be slowing down which means the next intermediate of the process cannot be reached. (inhibitor of phosphofructokinase)
High levels of ATP and the citric acid cycle intermediate citrate allosterically inhibit phosphofructokinase. Alternatively, when ATP concentrations are low, the levels of ADP increase.
Supply and demand, ATP is the end product and a key regulator
53
Why is oxygen so important in pyruvate oxidation?
· The metabolic pathway of pyruvate oxidation depends upon the presence of oxygen.
· Pyruvate represents a metabolic branch point in Eukaryotic cells
54
What is fermentation?
· In eukaryotic cells, and some bacteria low oxygen levels result in fermentation
· Fermentation is the pathway of respiration that oxidizes fuel molecules in the absence of oxygen. STILL MAKES ATP
55
What are the two types of fermentation?
· Two types of fermentation exist: lactate fermentation (some eukaryotic cells, muscle cells and some bacteria) and alcohol fermentation (some eukaryotes like yeast for baking bread and beer)
56
Why is fermentation important to anaerobic organisms?
Fermentation pathways are important for anaerobic organisms that live without oxygen, as well as organisms such as yeast that favor fermentation over oxidative phosphorylation.
Fermentation is also sometimes used in aerobic organisms when oxygen cannot be delivered fast enough to meet the cell
S metabolic needs, as in exercising muscle.
57
fermentation diagram
58
What do fermentation reactions produce?
(a) lactate and (b) ethyl alcohol. The fermentations, which occur in the cytosol, convert NADH to NAD+, allowing the electron carrier to cycle back to glycolysis. This process keeps glycolysis running, with continued production of ATP.
59
What is alcohol fermentation?
1. Ethanol fermentation occurs in plants and fungi.
2. Here, pyruvate releases carbon dioxide to form acetaldehyde, and electrons from NADH are transferred to acetaldehyde to produce ethanol and NAD+.
3. In both types of fermentation, NADH is oxidized to NAD+, but because neither molecule is produced or lost in the process, they do not appear in the overall chemical reaction.
The breakdown of glucose by fermentation yields only 2 molecules of ATP, since lactic acid and ethanol are not fully oxidized and still contain a large amount of chemical energy in their bonds
60
What is lactate fermentation?
3. Lactic acid fermentation occurs in animals and bacteria.
4. Here, electrons from NADH are transferred to pyruvate to produce lactic acid and NAD+. Without NAD+, glycolysis cannot happen
61
What is aerobic respiration?
· Although they lack mitochondria, many bacteria and archaea (live in oxygen-less environments) have respiratory electron transport chains, located on internal membrane systems
· Some use a molecule other than O2 as terminal electron acceptor (strict anaerobes)
- Possess anaerobic respiration
Sulfate, nitrate, and ferric ion are common electron acceptors
62
What are some lifestyles dedicated to oxygen?
· Strict anaerobes: Cannot grow in presence of oxygen
· Strict aerobes: Require oxygen
· Facultative aerobes: Can grow in presence of oxygen and can grow using fermentative pathways
63
What is the Paradox of Aerobic Life?
· Although many organisms cannot exist without oxygen because it is required for electron transport, oxygen itself is inherently dangerous to all forms of life
· The paradox of aerobic life is that oxygen is both essential and toxic
· Reactive oxygen species (ROS)
- Include superoxide and hydrogen peroxide
- Strong oxidizing agents (remove electrons from any molecules)
64
Reduction of Oxygen to Water
· The conversion of O2 to water is a four-electron reduction. If this occurs stepwise, it results in the formation of the intermediate ROS, which are potentially harmful. Aerobic cells contain the enzymes superoxide dismutase (SOD) and catalase, which together quickly convert superoxide and hydrogen peroxide to water.
