Test 3 Flashcards
1
Q
Explain the difference in efficiency (ATP yield) of aerobic and anaerobic pathways.
A
The theoretical yields for 1 molecule of glucose is of 36 to 38 ATP for aerobic respiration and of 2 to 36 ATP for anaerobic respiration.
2
Q
What are the 3 reasons for the difference between the actual yield and the theoretical yields in respiratory pathways?
A
1) NADH transport costs 1 ATP/NADH (1 glucose = 2 ATP)
2) IMM is leaking = loss of protons
3) Pyruvate transport = secondary active transport (proton pumps use H+ so those are not available for chemiosmosis)
IMM : Inner mitochondrial membrane
3
Q
For each NADH that is oxidized (for each pair of electrons that travels down the ETC) what is pumped in the inter membrane space?
A
10 protons (H+)
4
Q
How many protons are needed to flow back through the ATP syntase for the synthesis of 1 ATP?
A
Somewhere between 3 and 4 H+
5
Q
Overall, what is the NADH:ATP ratio for every NADH oxidized by the ETC?
A
Between 2.5 and 3.3 molecules of ATP (1:2.5-3.3)
6
Q
Why are there only 2 ATP synthesized for each FADH2 oxidized?
A
Because the oxidation of FADH2 skips the proton-pumping complex I.
7
Q
What is the FADH2:ATP for each FADH2 oxidized?
A
1:2
8
Q
What happens to the pyruvate if oxygen is absent or in short supply?
A
It remains in the cytosol, where it is reduced, consuming the NADH generated by glycolysis in a metabolic process called fermentation.
9
Q
In what types of organisms does alcohol fermentation occur?
A
Microorganisms such as yeasts (single-celled fungi)
10
Q
In what types of organisms does lactate fermentation occur?
A
In many bacteria and some plant and animal tissues.
11
Q
In photosynthesis, light energy is used to extract electrons frome water. What happens to the electrons then?
redox
A
The electrons combine with hudrogen to reduce carbon dioxide into glucose, a carbohydrate.
12
Q
In cellular respiration, glucose is reduced or oxidized?
A
It is oxidized into CO2.
13
Q
In cellular respiration, is O2 reduced or ozidized?
A
It is reduced into water.
14
Q
How do you know if a molecule is oxidized?
A
It looses It loses electrons (hydrogens)
15
Q
How do you know if a molecule is reduced?
A
It gains electrons (hydrogens)
16
Q
Explain how redox processes lead to ATP production?
A
Because redox reactions involve electron transfer which are the foundation of ATP production in cellular respiratio through oxidative phosphorylation.
Involve the redox reactions of NADH and FADH2
17
Q
ha
What are the 2 parts of oxidative phosphorylation?
A
Electron transport system and chemiosmosis.
18
Q
What happens to electrons in the electron transport system?
A
High-energy ectrons (carried by NADH and FADH2) move spontaneously down a potential energy gradient from one complex to the next. The release of energy is used to pump protons into the intermembrane space.
19
Q
What happens during chemiosmosis?
A
ATP synthase catalyzes ATP synthesis using energy from the H+ gradient across the membrane.
The proton gradient provides the driving force for ATP synthase
20
Q
Illustrate how NAD+ and NADH serve as a transport for electrons in cellular respiration.
A
NAD+ + H+ + 2e- –> NADH –> (cycle)
21
Q
Explain how the redox processes leading to ATP production involve the redox reactions of NADH and FADH2.
2 steps
A
- The electron transport chain converts the potential energy in NADH and FADH2 into a proton-motive force (that leads to a concentration gradient)
- The electron transport chain facilitates the transfer of electrons from NADH and FADH2 to oxygen.
22
Q
How is the rate at which food molecules are oxidized by cellular respiration regulated?
A
It is tightly controlled such that the rate of ATP generation matches the requirements of the cell for chemical energy.
23
Q
What is the key enzyme of glycolysis that is tightly regulated? What type of enzyme is it? What does it catalyze?
A
Phosphofructokinase, an allosteric enzyme. It catalyzes the conversion of fructose 6-phosphate to fructose 1,6-biphosphate.
24
Q
Why is it relevant that phosphofructokinase is an allosteric enzyme?
A
Because its activity can thus be adjusted by the binding of certain metabolic activators and inhibitors.
25
What are the two key regulators of phophofructokinase?
ATP and ADP
26
Is ATP an allosteric inhibitor or activator? What doess it do?
Inhibitor. If excess ATP is present in the cytosol, it binds to phosphofructokinase, inhibiting its activity. The resulting decrease in the concentration of fructose 1,6-biphosphate slows or stops the subsequent reactions of glycolysis.
27
Is the increase in phosphofructokinase activity due solely to the release of ATP inhibition?
No. However, ADP, which accumulates when ATP is hydrolyzed during metabolism, is an allosteric activator of the enzyme.
28
It ADP an allosteric inhibitor or activator for phosphofructokinase?
Activator
| It stimulates the molecule.
29
What is another allosteric regulator of phosphofructokinase that inhibits it?
Citrate which is a product of the citric acid cycle. When its levels increase, it slows down glycolysis through the inhibition of phosphofructokinase.
30
What enters the citric acide cycle as acetyl-CoA?
The fatty acids and many other types of lipids which are split into two-carbon fragments.
31
What happens to proteins before the oxidation process of cellular respiration?
Proteins are first hydrolyzed to amino acids. The amino group NH2 is thus removed and the remainder of the molecule enters the respiratory pathway as pyruvate, acetyl units carried by the coenzyme A, or intermediates of the citric acid cycle.
| By intermediates we mean any pieces of larger macromolecules.
32
What amino acid is converted to pyruvate before it enters the respiratory pathway?
Alanine
33
What amino acid is converted to acetylene units before in enters the respiratory pathway?
Leucine
34
What amino acid is converted to fumarate before it enters the citric acid cycle?
Phenylalanine
35
Provide an explanation for the difference between the energy-requiring phase and the energy-releasing phase of glycolysis.
The energy-requiring phase consumes ATP (2)to prepare glucose for splitting while the energy-releasing phase generates ATP (4) and NADH (2) from G3P.
| G3P: Glyceraldehyde-3-phosphate
36
Compare chemiosmosis (oxidative phosphorylation) to substrate level phsphorylation.
Substrate-level phosphorylation occurs during glycolysis and the citric acid cycle. It directly transfers a phosphate group from ADP to ATP. Oxidative phosphorylation relies on the action of large multiprotein complex that spans the inner mitochondrial membrane called ATP synthase. Chemiosmosis uses a proton gradient to drive ATP synthesis through ATP synthase.
37
What is chemiosmosis?
The ability of cells to use the proton-motive force to do work. It is the final astep of oxidative phosphorylation.
38
What is oxidative phosphorylation?
Tye kode of ATP synthesis that is linked to the oxidation of energy-rich molecules by an ETC.
39
Describe the structure of ATP synthase.
This enzyme has a nasal unit which is embedded in the inner mitochondrial membrane and connected to a headpiece by a stalk, with the stator bridgeng the basal unit and headpiece.
40
How do protons move in ATP synthase?
They move through a channel between the basal unit and the stator, making the stalk and headpiece spin. This results in ATP synthesis.
41
What happens during substrate-level phosphorylation?
A phosphate group is transferred from a high-energy donnor directly to ADP, forming ATP
42
Is substrate-level phosphorylation mediateds by a specific enzyme?
Yes, although the enzyme depends on the step we are reffering to.
43
What is the role of the type of enzyme kinase in glycolysis?
It transfers a phosphate between ATP and another molecule.
44
What is the role of the type of enzyme mutase in glycolysis?
It transfers functionnal groups from one position to another within the same molecule.
45
What is the role of the type of enzyme isomerase in glycolysis?
It changes a molecule's conformation.
46
What is the role of the type of enzyme dehydrogenase in glycolysis?
It removes an hydrogen from the substrate.
47
What is the role of the type of enzyme enolase in glycolysis?
It removes water from the substrate.
48
Im the electron transport system, what are ubiquinone and cytochrome c? What is their role?
UQ and cyt c are two small electron carriers that act as shuttles between the major complexes .
49
What are the four complexes of the electron transport chain?
Complex I: NADH dehydrogenase
Complex II: succinate dehydrogenase
Complex III: cytochrome
Complex IV: cytochrome oxidase
50
In the ETC, what is the structure charged with the transfer of electrons?
Electron transport is facillated by nonprotein molecules called prosthetic groups.
| Prosthetic groups are like coenzymes that are permenantly attatched.
51
What do protein subunits of complexes I, III and IV do to allow for electron transport to happen?
They bind a number of prosthetic groups very precisely.
52
What are prosthetic groups?
They are redox-active cofactors that alternate between reduced and oxidized states as they accept electrons from upstream molecules and subsequently donate electrons to downstream molecules.
53
During electron transport, what happens to one of the prosthetic group of complex I (FMN)?
| 2 steps.
1. Flavin mononucleotide is reduced by electron donation from NADH on the matrix side of the inner membrane.
2. It then donates the electron to the Fe/S prosthetic group, which, in turn, donates the electron to ubiquinone.
Remark: This process of reduction followed by oxidation of each carrier continues along the entire chain until, finally, the electrons are donated to oxygen, reducing it to water.
54
Give a characteristic of the electron flow as electrons are passed from one redox molecule to the next in the ETC.
The electron flow is spontaneous and the movement is done from high to low potential energy.
55
How are the prosthetic groups and other electron carriers organized in the ETC?
They are organized in a very specific way; from high to low free energy.
56
What is the consequence that follows from the organization of thw prosthetic groups and other electron carriers being organized from high to low free energy?
Electron movement is thus thermodynamically spontaneous, down a free energy gradient.
57
Are all prothetic groups inside the electron transport system working to take O2 and reduce it?
All except for ubiquinone and cytochrome c.
58
Where, in cellular respiration, are the carbon atoms of a glucose molecule released?
There are in total 6 CO2s to release in cellular respiration.
2 CO2s are released after pyruvate oxidation.
4 CO2s are released during the citric acid process.
59
Where is the first carbon of glucose released in cellular respiration?
| Be precise
2 pyruvates are obtained from the spliting of glucose. 1 pyruvate is made of 3 carbons. When the pyruvate is oxidized to an acetyl group ( 2 carbons) and carried to the citric acid cycle by CoA, the third carbon is released as CO2.
60
How are the remaining carbons from glucose released in the citric acid cycle?
| For 2 turns
The energy required to synthesize the 2 ATP, the 6 NADH, and the 2 FADH2 is obtained from the complete oxidation of 2 acetyl units, resulting in the release of 4 molecules of carbon dioxide.
61
After the citric acid cycle, where is contained the initial potential energy contained inside glucose (besides in the ATP formed)?
In the NADH (10) and FADH2 (2) molecules.
62
What is the role of the electron transport chain coupled with the process of chemiosmosis?
The goal is to synthesize additional ATP. It is done by extracting the potential energy contained in the NADH and FADH2 molecules.
63
How can carbohydrates such as glucose and other dissacharides enter cellular respiration to be converted to energy?
Because they are easily broken down into monosaccharides such as glucose and fructose which then enter glycolysis at early steps.
64
How can starch, a carbohydrate enter cellular respiration to be converted to energy?
Starch is hydrolyzed by digestive enzymes into individual glucose molecules.
65
How can glycogen, a complex carbohydrate enter cellular respiration to be converted to energy?
Glycogen is broken down and converted by enzymes into glucose-6-phosphate, an early substrate molecule in glycolysis.
66
How can fatty acids and many other types of lipids enter cellular respiration to be converted to energy?
Fatty acids and some lipids are split into two-carbon fragments, which enter the citric acid cycle as acetyl-CoA.
67
How can proteins enter cellular respiration to be converted to energy?
Proteins are hydrolyzed to amino acids before oxidation. The amino group NH2 is removed, and the remainder of the molecule enters the respiratory pathway as pyruvate, acetyl units carried by coenzyme A, or intermediates of the citric acid cycle.
68
What are the theoretical and realistical yields for the ATP production of prokaryotes and eukaryotes in cellular respiration?
Eukaryotes: 36 (th), 30 (real)
Prokaryotes: 38 (th), 32 (real)
69
What do light reactions involve?
The involve the capture of light energy by pigment molecules and the utilization of that energy to synthesize both NADPH and ATP.
70
Draw the connection between cellular respiration and photosynthesis.
They are the reverse process of one another. Photosynthesis uses the energy that comes from sunlight , water and carbon dioxide to produce glucose and oxygen.
71
In light reactions, what is needed to reduce NADPH?
Electrons are needed to reduce NADPH. They come from the oxidation of H2O, resulting in the release of O2.
72
What are the light reactions?
Photosystem I and photosystem II are the two light-trapping components involved in photosynthetic electron transport (ETC).
73
What are the dark reactions?
The dark reactions include the Calvin cycle, the Hatch Slack cycle, photorespiration and CAM photosynthesis.
74
In photosynthetic prokaryotes, where do the light reactions and the Calvin cycle take place?
Both those reactions take place within the chloroplast, an organelle that is comprised of three membranes that define three distinct compartments.
75
What is the role of chloroplasts?
They synthesize carbohydrates.
76
What is the role of mitochondria?
They convert carbohydrates into ATP.
77
What does the fact that plants cells also possess mitochondria allows them to do?
It allows for them to produce their own oxygen and use it to generate ATP for themselves.
78
What is useds for anabolic reactions?
Respiratory intermediates.
79
For what are the intermediates of glycolysis and the citric acid cycle used for the purpose of anabolic reactions?
Those intermediates are routinely diverted and used as the starting substrates required to synthesize amino acids, fats, and the purine bases needed for nucleic acid synthesis.
80
What do the respiratory intermediates supply in anabolic processes?
They supply the carbon backbones for the array of hormones, growth factors, prosthetic groups, and cofactors that are essential to cell function.
81
What does the metabolic flexibility of cellular respiration allows for?
It allows for reactions to be adjusted rapidly.
82
How can fatty acids be used in anabolic reactions?
They can be used as a source of energy by being oxidized to acety-CoA.
83
What happens to excess acetyl-CoA in anabolic reactions?
Excess acetyl-CoA can be removed from the respiration and used to synthesize the fatty acids needed for a range of cellular processes.
84
What happens when glucose levels are low in the body?
New glucose can be synthesized through a process called glyconeogenesis.
85
What does glyconeogenesis has many of?
Substrates which include glucogenic amino acids (from the breakdown of lipids such as triglycerides) and glycerol. They also include pyruvate and lactate which are from other steps in metabolism.
86
When started with pyruvate, what is glucogenesis?
The reverse process of glycolysis.
87
How do photons have to be to be used as a source of energy?
The photons of light must be absorbed/captured.
88
When does the absorbtion of a photon occur?
It occurs when the energy of a photon is transferred to an electron within a molecule, moving the electron from the ground state to an excited state.
89
What happens to the electron when it is in its excited state?
The electron is farther away from the nucleus and thus it contains more energy.
90
What are pigments?
A major class of molecules that are very efficient at absorbing visible light because their structure results in a number of excitable electrons.
91
What are photoautotrophic organisms known as and why?
Earth's primary producers because they represent the major group of organisms that generate the organic compounds that are used by other organisms: the consumers, the organisms that live by eaing plants or other animals.
92
What is the chloroplast?
It is an organelle that is comprised of three membranes that define three distinct compartments.
93
What is evidence that indicates that chloroplasts are descended from free-living cyanobacteria?
In most ways, photosynthesis carried out in cyanobacteria is biochemically identical to that found in the chloroplasts of plant leaves.
| It is more evidence for endosymbiosis.
94
Describe the outer membrane of chloroplasts.
It covers the entire surface of the organelle.
95
Describe the inner membrane of the chloroplasts.
It lies just inside the outer membrane. The aqueous environment within the inner membrane is the stroma of the chloroplast.
96
What is found within the stroma of the chloroplasts?
The third membrane system, the tylakoid membranes (or thylakoids) which often form flattened, closed sacs.
97
What is the space embedded within the thylakoid membrane?
The components that carry out the light reactions of photosynthesis: proteins, pigments, electron transport carriers, and ATP synthase.
98
99
Where are the enzymes that catalyze the reactions of the Calvin cycle found?
In the stroma of the chloroplast.
100
What are the three fates of a pigment molecule?
| Light and Atomic Excitation
1. The electron returns to its ground state by emitting a less energetic photon (fluorescence) or releasing energy as heat.
2. The electron returns to the ground state as its energy is transferred to an electron in a neighbouring pigment.
3. The high-eergy electron is transferred to another molecule, an electron acceptor.
101
How do chlorophyll a and b differ by?
a has a methyl group (CH3) while b has an aldehyde group (CHO)
102
What do the unsaturated bonds in pigments allow for them to receive?
A photon of light which will get them excited.
103
What wavelenghts does chlorophyll a strongly absorb and does not absorb?
It absorbs blue and red light but not green or yellow light.
104
What is a photosystem?
A group of pigment proteins that form an antenna complex that surrounds a reaction center.
| The antenna complex is made up of 500 pigment molecules.
105
In a photosystem, what is the absorbed light converted to?
It is converted to chemical energy when an excited electron from the chlorophyll a is transferred to a primary acceptor, also in the reaction center.
106
Where are the photosystems in the chloroplasts?
They are embedded in the thylakoid membrane.
107
What happens to high-energy electrons in relation to the photosystem?
Those electrons are passed out of the photosystem to the electron transport system.
108
In what way does the photosynthetic electron transport operates just like the respiratory electron transport?
| In non-cyclic photophosphorylation
It operates with electrons flowing spontaneously from molecules that are easily oxidized to molecules taht are progressively more easily reduced.
| In non-cyclic photophosphorylation.
109
What are the two different types of photosystems?
Photosystem I and II
110
What is the specialized chlorophyll in the reaction centre of photosystem I?
It is a specialized chlorophyll a which is called P700 because its absorbtion maximum is at a wavelenght of 700 nm.
111
What is the specialized chlorophyll in the reaction centre of photosystem II?
It is a specialized chlorophyll a which is called P680 because it absorbs light maximally at 680 nm.
112
How many photosystems are there within a single leaf chloroplast?
There are thousands of photosystems (both I and II) each containing about 500 chlorophyll molecules.
113
What are the three ways to produce a proton gradient in non-cyclic photophosphorylation?
- The first is to use the plastoquinone pool after photosystem II to increase proton concentration within the thylakoid lumen.
- The second is the oxidation of water to oxygen which increases the proton concentration withing the thylakoid lumen.
- The third is to decrease the proton concentration within the stroma by the help of ferredoxin for the reduction of NADP+ to NADPH with the help of the enzyme NADP+ reductase.
114
In non-cyclic phosphorylation, why do we normally transport electrons?
For a proton gradient to be created?
115
In the light reactions, how is ATP generated?
By chemiosmosis
116
What is the process in three steps of protons in non-cyclic photophosphorylation?
1. Protons are translocated into the lumen by the cyclic reduction and oxidation of plastoquinone as it migrates from photosystem II to the cytochrome complex and back again.
2. The gradient is enhanced by the addition of two protons to the lumen from the oxidation of water, which occurs on the luminal side of photosystem II.
3. The removal of one proton from the stroma for each NADPH molecule synthesized futher decreases the H+ concentration in the stroma, thereby enhancing the gradient across the thylakoid membrane.
117
What is the pathway of electron flow in cyclic photophosphorylation?
Electrons flow from photosystem II through photosystem I to synthesize NADPH. This pathway is called the linear electron transport.
118
What is the pathway of electron flow that occurs most often?
Linear electron transport of cyclic photophosphorylation.
119
Can photosystem I function independently of photosystem II in cyclic photophosphorylation?
Yes.
120
What is different from the non-cyclic process in electron flow for the cyclic process?
Electron flow from photosystem I to ferrodoxin is not followed by electron donation to the NADP+ reductase complex. Instead, reduced ferredoxin donates electrons back to the plastoquinone pool.
121
What particular thing is happening with the plastoquinone pool in cyclic phosphorylation?
The plastoquinone pool gets continually reduced and oxidized and keeps moving protons across the thylakoid membrane without the involvement of electrons coming from photosystem II.
122
True or false? Overall, cyclic electron transport only involves light absorption by photosystem I.
True. In fact, the energy is being used to establish a proton-motive force and generate ATP.
123
Thinking about NADPH formation, what is different in linear electron transport?
NADPH is not formed during cyclic electron transport.
