Chapter 10 - Cell respiration Flashcards
(118 cards)
1
Q
What does photosynthesis generate?
A
Oxygen as well as organic molecules used by the mitochondria of eukaryotes as fuel for cellular respiration
2
Q
What are the key pathways of respiration?
A
Glycolysis, pyruvate oxidation and the citric acid cycle, and oxidative phosphorylation.
3
Q
What is fermentation?
A
Fermentation is an anaerobic process in which energy can be released from glucose even though oxygen is not available. It is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen
4
Q
What is aerobic respiration?
A
Aerobic respiration requires oxygen (O2) in order to create ATP.
5
Q
What is anaerobic respiration?
A
Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2)
6
Q
What is cellular respiration?
A
Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert chemical energy from oxygen molecules or nutrients into adenosine triphosphate, and then release waste products
7
Q
What types of respiration does cellular respiration involve?
A
both aerobic and anaerobic processes.
8
Q
What is the simple equation for respiration?
A
Organic compounds + Oxygen > Carbon dioxide + Water + Energy
9
Q
Is cellular respiration an endergonic or exergonic reaction?
A
Exergonic
10
Q
What are oxidation reactions?
A
The loss of electrons from one substance is called oxidation
11
Q
What are reduction reactions?
A
The addition of electrons to another substance is known as reduction
12
Q
What are oxidation-reduction reactions?
A
A transfer of one or more electrons (e-) from one reactant to another in a chemical reaction.
13
Q
What is the reducing agent?
A
Reducing agent is an element or compound that loses an electron to an electron recipient in a redox chemical reaction
14
Q
What is the oxidising agent?
A
an oxidizing agent (oxidant, oxidizer) is a substance that has the ability to oxidize other substances — in other words to accept their electrons
15
Q
An electron loses potential energy when it what?
A
it shifts from a less electronegative atom toward a more electronegative one
16
Q
What is respiration?
A
In physiology, respiration is the movement of oxygen from the outside environment to the cells within tissues, and the transport of carbon dioxide in the opposite direction.
17
Q
In respiration, the oxidation of glucose transfers electrons to a lower energy state, which does what? .
A
It liberates energy that becomes available for ATP synthesis. So, in general, we see fuels with multiple C—H bonds oxidised into products with multiple C—O bonds.
18
Q
Why is it important that enzymes in your cells lower the barrier of activation energy when you eat glucose?
A
Because without this to break the C-H bonds, a food substance like glucose would combine almost instantaneously with O
19
Q
Does cellular respiration oxidise glucose in one step or multiple steps and why?
A
Multiple steps because if energy is released from a fuel all at once, it cannot be harnessed efficiently for constructive work.
20
Q
What is the basic thing that happens at each step of glucose oxidation?
A
At key steps, electrons are stripped from the glucose. As is often the case in oxidation reactions, each electron travels with a proton—thus, as a hydrogen atom.
21
Q
What is nicotinamide adenine dinucleotide?
A
In metabolism, nicotinamide adenine dinucleotide is involved in redox reactions, carrying electrons from one reaction to another.
22
Q
What is NAD+?
A
The oxidised form of NADH which can accept electrons and hydrogens
23
Q
What is NADH?
A
The reduced form of NAD+ that has accepted electrons or hydrogens
24
Q
How does NAD+ trap electrons from glucose and the other organic molecules in food?
A
Enzymes called dehydrogenases remove a pair of hydrogen atoms (2 electrons and 2 protons) from the substrate (glucose), thereby oxidising it. The enzyme delivers the 2 electrons along with 1 proton to its coenzyme, NAD+, forming NADH
25
Do electrons lose a-lot of their potential energy when they are transferred from glucose to NAD+.?
No! They lose very little
26
What does each NADH molecule formed during respiration represent?
Stored energy
27
How do electrons that are extracted from glucose and stored as potential energy in NADH finally reach oxygen?
Instead of occurring in one explosive reaction, respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy-releasing steps
28
The combination of H2 and O2 is used to as an explosion to boost rockets into space, how come when cellular respiration occurs in our cells there is no explosion?
Instead of occurring in one explosive reaction, respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy-releasing steps.
29
What is an electron transport chain?
An electron transport chain is a series of complexes that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons across a membrane. The electron transport chain is built up of peptides, enzymes, and other molecules.
30
How do electron carriers (NADH) get the electrons to O2 using an electron transport chain (To prevent explosion and loss of energy)?
Electrons removed from glucose are shuttled by NADH to the “top,” higher-energy end of the chain. At the “bottom,” lower-energy end, O2 captures these electrons along with hydrogen nuclei (H+), forming water.
31
Is the electron transfer from NADH to oxygen an endogonic or exergonic reaction?
Exergonic with a free energy change of -53 cal/mol.
32
What is the difference between exergonic and exothermic?
an exergonic reaction means that a reaction is spontaneous, an exothermic reaction has nothing to do with spontaneity, but that an energy is released to the surrounding.
33
In the electron transport chain is each downhill carrier more or less electronegative?
More electronegative, thus capable of oxidising its uphill neighbour.
34
During cellular respiration what travel route do most electrons take?
The "downhill" route: glucose-NADH-electron transport chain-oxygen
35
What are the 3 stages for the harvesting of energy from glucose by cellular respiration?
Glycolysis, pyruvate, and oxidative phosphorylation
36
Where does glycolysis occur?
In the cytosol
37
What does glycolysis do in cellular respiration?
Begins the degradation process by breaking glucose into two molecules of a compounds called pyruvate. In eukaryotes pyruvate enters the mitochondrion and is oxidised to a compound called acetyl CoA which enters the Citric acid cycle.
38
What occurs in the citric acid cycle of cellular respiration?
In the mitochondrion, a series of chemical reactions that are used by all aerobic organisms, generate energy through the oxidation of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide.
39
What occurs in the third stage of respiration (oxidative phosphorylation)?
The electron transport chain accepts electrons from NADH or FADH2, generated during the first two stages and passes these electrons down the chain. At the end of the chain the electrons are combined with molecular oxygen and hydrogen ions forming water. The energy released at each step of the chain is stores in a form the mitochondrion can use to make ATP from ADP. This mode of ATP synthesis is called oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain.
40
What part of the mitochondrion is the site of electron transport and other processes like chemiosmosis that together make up oxidative phosphorylation?
The inner membrane
41
Oxidative phosphorylation accounts for what percentage of the ATP generated by respiration?
90% A smaller amount is formed directly in a few reactions of glycolysis and the citric acid-cycle by a mechanism called "substrate-level phosphorylation"
42
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.
43
For each molecules of glucose degraded to carbon dioxide and water how many molecules of ATP does the cell make?
32 molecules of ATP each with 7.3 cal/mol of free energy. Having so many molecules of ATP is more practical for the cell to spend on work.
44
What does the word glycolysis mean?
Sugar splitting
45
What is split during glycolysis?
Glucose a 6 carbon sugar is split into 2 three carbon sugars. these smaller sugars are then oxidised and their remaining atoms rearranged to form two molecules of pyruvate.
46
What are the two phases of glycolysis?
The energy investment phase and the energy payoff phase.
47
During the energy investment phase what happens to ATP?
The cell 'spends' ATP, but this investment in repaid with interest during the energy payoff phase.
48
What happens during the energy payoff phase?
ATP is produced by substrate level phosphorylation and NAD+ is reduced to NADH by the electrons being released from the oxidation of glucose
49
How many steps of glycolysis are there?
10 Steps
50
Is any carbon from glucose released as CO2 during glycolysis?
No all the carbons are used in the pyvurates.
51
Does glycolysis have to occur when O2 is present?
No, however if O2 is present the chemical energy stored in pyruvate and NADH can be extracted by pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.
52
How much of the chemical energy in glucose does glycolysis release?
Only 1/4, most of the energy remains stockpiled in the two molecules of pyruvate.
53
After glycolysis where is the oxidation of glucose completed?
If O2 is present, In the mitochondrion (eukaryotic cells)
54
When the pyruvate enters the mitochondrion what is the first thing that happens?
Pyruvate is first converted into a compound called acetyl coenzyme A, or acetyl CoA.
55
How is pyruvate converted into acetyl CoA?
This step is carried out by a multi enzyme complex that catalyses 3 reactions
1. Pyruvate's carboxyl group (-coo-) already somewhat oxidised and thus carrying little chemical energy is now fully oxidised and given off as a molecule of CO2
2. The remaining two carbon fragments are oxidised and the electrons are transferred to NAD+, storing energy in the form of NADH.
3. Coenzyme A is attached via its sulfur atom to the two carbon intermediate, forming acetyl CoA.
56
Does acetyl CoA have high or low potential energy?
High potential energy which is used to transfer the acetyl group to a molecule in the citric acid cycle, a reaction that is therefore highly exergonic.
57
What happens during the citric acid cycle specifically?
Pyruvate oxidation occurs first and pyruvate is broken down into 3 CO2 molecules including CO2 molecule released during the conversion of pyruvate to acetyl CoA. The citric acid cycle generates 1 ATP per turn by substrate level phosphorylation but most of the energy is transfered to NAD+ and FAD during the redox reactions. During this the reduced coenzymes NADH and FADH2 shuttle their cargo of high-energy electrons to the electron transport chain.
58
How many steps does the citric acid cycle have?
8 steps each catalysed by a specific enzyme.
59
What is step 1 of the citric acid cycle?
Acetyl CoA adds its two-carbon acetyl group to oxaloacetate, producing citrate.
60
What is step 2 of the citric acid cycle?
Citrate is converted to its isomer, isocitrate, by removal of one water molecule and addition of another.
61
What is step 3 of the citric acid cycle?
Isocitrate is oxidized, reducing NAD+ to NADH. Then the resulting compound loses a CO2 molecule.
62
What is step 4 of the citric acid cycle?
Another CO2 is lost, and the resulting compound is oxidized, + reducing NAD to NADH.
The remaining molecule is then attached to coenzyme A by an unstable bond.
63
What is step 5 of the citric acid cycle?
CoA is displaced by a phosphate group, which is transferred to GDP, forming GTP, a molecule with functions similar to ATP. GTP can also be used, as shown, to generate ATP. Step 5 forms an ATP molecule directly by substrate level phosphorylation. Step 5 represents the only ATP generated during the citric acid cycle
64
What is step 6 of the citric acid cycle?
Two hydrogens are transferred to FAD, forming FADH2 and oxidising succinate.
65
What is step 7 of the citric acid cycle?
Addition of a water molecule rearranges bonds in the substrate.
66
What is step 8 of the citric acid cycle?
The substrate is oxidized, reducing NAD+ to NADH and regenerating oxaloacetate (The starting substrate)
67
What is the total yield per glucose from the citric acid cycle?
6 NADH, 2 FADH2, and the equivalent of 2ATP
68
What is chemiosmosis?
Chemiosmosis is the movement of ions across a semipermeable membrane, down their electrochemical gradient.
69
How many ATP are produced via the first 2 steps of respiration glycolysis and the citric acid cycle
Only 4 ATP molecules per glucose molecule, all by substrate-level phosphorylation: 2 net ATP from glycolysis and 2 ATP from the citric acid cycle.
70
Which molecules link glycolysis and the citric acid cycle to the last stage of respiration, oxidative phosphorylation?
The molecules of NADH (and FADH2) as they account for most of the energy extracted from each glucose molecule.
71
What is the electron transport chain?
A collection of molecules embedded in the inner membrane of the mitochondrion in eukaryotic cells. The folding of the inner membrane to form cristae increases its surface area, providing space
for thousands of copies of each component of the electron transport chain in a mitochondrion. The in-folded membrane with its concentration of electron carrier molecules is well-suited for the series of sequential redox reactions that take place along the electron transport chain.
72
What are most components of the electron transport chain?
Proteins and tightly bound to these are prosthetic groups (non-protein groups such as cofactors and coenzymes)
73
True or False? During electron transport, electron carriers alternate between reduced and oxidised states as they accept and then donate electrons.
True. Each component of the chain becomes reduced when it accepts electrons from its 'uphill' neighbour which has a lower affinity for electrons and then it returns to its oxidised form as it passes electrons downhill to its more electronegative neighbour.
74
What are cytochromes?
The remaining electron carriers between ubiquinone and oxygen. Their prosthetic group, called a heme group, has an iron atom that accepts and donates electrons. . The last cytochrome of the chain, Cyt a3, passes its electrons to oxygen, which is very electronegative
75
At the end of the electron transport chain what happens?
The last cytochrome of the chain, Cyt a3, passes its electrons to oxygen, which is very electronegative. Each oxygen atom also picks up a pair of hydrogen ions (protons) from the aqueous solution, neutralising the -2 charge of the added electrons and forming water
76
What are the two sources of electrons for the electron transport chain?
FADH2 and NADH
77
True or False? FADH2 adds electrons to a lower energy level in the electron transport chain than NADH.
True although they both still donate an equivalent number of electrons (2) for oxygen reduction,
78
True or False? the electron transport chain provides about one-third less energy for ATP synthesis when the electron donor is FADH2 rather than NADH.
True
79
Does the electron transport chain make ATP directly?
No, Instead, it eases the fall of electrons from food to oxygen, breaking a large free-energy drop into a series of smaller steps that release energy in manageable amounts, step by step.
80
How does the mitochondrion couple the electron transport and energy release to ATP synthesis?
Through chemiosmosis
81
What is ATP synthase?
The enzyme that makes ATP from ADP and inorganic phosphate
82
How does ATP synthase work?
ATP synthase works like an ion pump running in reverse. Ion pumps usually use ATP as an energy source to transport ions against their gradients. Rather than hydrolysing ATP to pump protons against their concentration gradient, ATP synthase uses the energy of an existing ion gradient to power ATP synthesis. The power source for ATP synthase is a difference in the concentration of H+ on opposite sides of the inner mitochondrial membrane. This process is used to drive cellular work such as the synthesis of ATP, is called chemiosmosis
83
True or False? Chemiosmosis couples the electron transport chain to Atp synthesis.
True
84
What are the two steps of oxidative phosphorylation?
1: The electron transport chain, 2. Chemiosmosis (ATP synthesis)
85
How do the two steps of oxidative phosphorylation work?
Firstly, in the electron transport chain, the electron transport and pumping of protons (H+), creates an H+ gradient across the membrane. Secondly, then ATP synthesis is powered by the flow of H+ back across the membrane.
86
How does the inner mitochondrial membrane or the prokaryotic plasma membrane generate and maintain the H+ gradient that drives ATP synthesis by the ATP synthase protein complex?
Establishing the H+ gradient is a major function of the electron transport chain, The chain is an energy converter that uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across the membrane, from the mitochondrial matrix into the inter-membrane space. The H+ has a tendency to move back across the membrane, diffusing down its gradient. And the ATP syntheses are the only sites that provide a route through the membrane for H+ the passage of H+ through ATP synthase uses the exergonic flow of H+
to drive the phosphorylation of ADP. Thus, the energy stored in an H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis.
87
How does the electron transport chain pumps hydrogen ions?
Certain members of the electron transport chain accept and release protons (H+) along with electrons. At certain steps along the chain, electron transfers cause H+ to be taken up and released into the surrounding solution. In eukaryotic cells, the electron carriers are spatially arranged in the inner mitochondrial membrane in such a way that H+ is accepted from the mitochondrial matrix and deposited in the inter-membrane space
88
What is a proton-motive force?
The H+ gradient that results from the electron transport chain is referred to as a proton-motive force, emphasizing the capacity of the gradient to perform work. The force drives H+ back across the membrane through the H+ channels provided by ATP synthases.
89
In general terms what is chemiosmosis?
Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of an H + gradient across a membrane to drive cellular work.
90
How do chloroplasts use chemiosmosis to generate ATP during photosynthesis?
In these organelles, light (rather than chemical energy) drives both electron flow down an electron transport chain and the resulting H+ gradient formation.
91
Who was awarded the Nobel Prize in 1978 for originally proposing the chemiosmotic model?
Peter Mitchell
92
Per glucose how many ATP molecules are made during the first stage of respiration: Glycolysis?
2 ATP molecules
93
Per glucose how many ATP molecules are made during the first stage of respiration: Citric acid cycle?
2 ATP molecules
94
Per glucose how many ATP molecules are made overall during respiration?
About 30 or 32 ATP molecules
95
What is the first reason for why the amount of ATP molecules produced during respiration is inexact?
Phosphorylation and the redox reactions are not directly coupled to each other, so the ratio of the number of NADH molecules to the number of ATP molecules is not a whole number. 1 NADH results in 10 H+ being transported, but the exact number of H+ that must reenter the mitochondrial matrix via ATP synthase to generate 1 ATP has long been debated. biochemists now agree that the most accurate number is 4 H+. Therefore, a single molecule of NADH generates enough proton-motive force for the synthesis of 2.5 ATP. The citric acid cycle also supplies electrons to the electron transport chain via FADH2, but since its electrons enter later in the chain, each molecule of this electron carrier is responsible for transport of only enough H+ for the synthesis of 1.5 ATP.
96
What is the second reason for why the amount of ATP molecules produced during respiration is inexact?
The ATP yield varies slightly depending on the type of shuttle used to transport electrons from the cytosol into the mitochondrion. The mitochondrial inner membrane is impermeable (waterproof) to NADH, so NADH is segregated from the machinery of oxidative phosphorylation. The 2 electrons of NADH captured in glycolysis must be conveyed into the mitochondrion by one of several electron shuttle systems. The electrons are passed either to NAD+ or to FAD in the mitochondrial matrix. If the electrons are passed to FAD, as in brain cells, only about 1.5 ATP can result from each NADH that was originally generated in the cytosol. If the electrons are passed to mitochondrial NAD+, as in liver cells and heart cells, the yield is about 2.5 ATP per NADH.
97
What is the third reason for why the amount of ATP molecules produced during respiration is inexact?
The use of the proton-motive force generated by the redox reactions of respiration to drive other kinds of work. If all the proton-motive force generated by the electron transport chain were used to drive ATP synthesis, one glucose molecule could generate a maximum of 28 ATP produced by oxidative phosphorylation plus 4 ATP (net) from substrate-level phosphorylation to give a total yield of about 32 ATP (or only about 30 ATP if the less efficient shuttle were functioning).
98
The inner mitochondrial membrane contains a channel protein called the uncoupling protein which allows for what?
that allows protons to flow back down their concentration gradient without generating ATP. Activation of these proteins in hibernating mammals results in ongoing oxidation of stored fuel (fats), generating heat without any ATP production.
99
Can the cells produce ATP without O2?
Yes through fermentation and anaerobic respiration
100
What is the difference between fermentation and anaerobic respiration?
An electron transport chain is used in anaerobic respiration and not in fermentation
101
Can other less electronegative substances besides oxygen serve as the final electron acceptors in the electron transport chain?
Yes but not as efficient.
102
How can food be oxidized without cellular respiration? aka in fermentation.
Remember, oxidation simply refers to the loss of electrons to an electron acceptor, so it does not need to involve oxygen. Glycolysis oxidises glucose to two molecules of pyruvate. The oxidising agent of glycolysis is NAD+, and neither oxygen nor any electron transfer chain is involved. Overall, glycolysis is exergonic, and some of the energy made available is used to produce 2 ATP (net) by substrate-level phosphorylation.
103
True or False? Fermentation is completely different to Glycolysis.
False, Fermentation is an extension of glycolysis that allows continuous generation of ATP by the substrate-level phosphorylation of glycolysis. (at 2 net ATP molecules)
104
"Fermentation is an extension of glycolysis that allows continuous generation of ATP by the substrate-level phosphorylation of glycolysis" For this to occur what needs to happen?
For this to occur, there must be a sufficient supply of NAD+ to accept electrons during the oxidation step of glycolysis. Without some mechanism to recycle NAD+ from NADH, glycolysis would soon deplete the cell’s pool of NAD+ by reducing it all to NADH and would shut itself down for lack of an oxidising agent. Under aerobic conditions, NAD+ is recycled from NADH by the transfer of electrons to the electron transport chain. An anaerobic alter- native is to transfer electrons from NADH to pyruvate, the end product of glycolysis.
105
What are the two types of fermentation?
The two types are alcohol fermentation and lactic acid fermentation, and both are harnessed by humans for food and industrial production.
106
What occurs in alcohol fermentation?
Pyruvate is converted to ethanol (ethyl alcohol) in two steps. The first step releases carbon dioxide from the pyruvate, which is converted to the two-carbon compound acetaldehyde. In the second step, acetaldehyde is reduced by NADH to ethanol. This regenerates the supply of NAD+ needed for the continuation of glycolysis.
107
What occurs during lactic acid fermentation?
Pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of CO2. Human muscle cells make ATP by lactic acid fermentation when oxygen is scarce.
108
What are the three alternative pathways for producing ATP by harvesting the chemical energy of food?
Fermentation, aerobic respiration, and anaerobic respiration
109
What are the three alternative pathways for producing ATP by harvesting the chemical energy of food?
Fermentation, aerobic respiration, and anaerobic respiration
110
What is the difference between the three alternative pathways for producing ATP by harvesting the chemical energy of food?
In fermentation, the final electron acceptor is an organic molecule such as a pyruvate or acetaldehyde.
In cellular respiration, electrons are carried by NADH and transported to an electron transport chain which generates NAD+ required for the glycolysis. The other main difference is the amount of ATP produced. Fermentation yields 2 ATP
111
What is the difference between the three alternative pathways for producing ATP, in terms of the amount of ATP produced?
Fermentation yields 2 molecules of ATP produced by substrate level phosphorylation. In the absence of the electron transport chain the pyruvate stored energy is unavailable. In cellular respiration pyruvate is completely oxidised and most of this energy is shuttled by NADH and FADH2 in the forms of electrons to the electron transport chain. Here, the electrons move down a series of redox reactions to a final electron acceptor. These steps of cellular respiration can harvest up to 32 ATP molecules.
112
True or False? Some organisms can only exist under fermentation or anaerobic conditions
True
113
What are facultative anaerobes?
A facultative anaerobe is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent
114
What is the process of deamination?
Deamination is the removal of an amino group from a molecule. Enzymes that
115
What is beta oxidation?
Beta oxidation is a metabolic process involving multiple steps by which fatty acid molecules are broken down to produce energy. More specifically, beta oxidation consists in breaking down long fatty acids that have been converted to acyl-CoA chains into progressively smaller fatty acyl-CoA chains.
116
True or False? Fats make bad fuels
False, fats are great fuels for the body
117
How many more molecules of ATP does the oxidation of fat make compared to carbohydrates?
A gram of fat oxidized by respiration produces more than twice as much ATP as a gram of carbohydrate. Unfortunately, this also means that a person trying to lose weight must work hard to use up fat stored in the body because so many calories are stockpiled in each gram of fat
118
Is the energy that keeps us alive released or produces?
Released by cellular respiration
