8.2 Cell Respiration Flashcards
1
Q
What is ATP?
A
Adenosine triphosphate (ATP) is a high energy molecule that functions as an immediate power source for cells
2
Q
Where is the energy for ATP stored?
A
One molecule of ATP contains three covalently bonded phosphate groups – which store potential energy in their bonds
3
Q
Why is ATP a readily reactive molecule?
A
Phosphorylation makes molecules less stable and hence ATP is a readily reactive molecule that contains high energy bonds
4
Q
What happens during ATP hydrolysis?
A
When ATP is hydrolysed (to form ADP + Pi), the energy stored in the terminal phosphate bond is released for use by the cell
5
Q
What are the two key functions of ATP?
A
It functions as the energy currency of the cell by releasing energy when hydrolysed to ADP (powers cell metabolism)
It may transfer the released phosphate group to other organic molecules, rendering them less stable and more reactive
6
Q
How is ATP synthesised with solar energy?
A
Solar energy – photosynthesis converts light energy into chemical energy that is stored as ATP
7
Q
How is ATP synthesised with oxidative processes?
A
cell respiration breaks down organic molecules to release chemical energy that is stored as ATP
8
Q
What is cell respiration?
A
Cell respiration is the controlled release of energy from organic compounds to produce ATP
9
Q
What does anaerobic respiration involve?
A
Anaerobic respiration involves the incomplete breakdown of organic molecules for a small yield of ATP (no oxygen required)
10
Q
What does aerobic respiration involve?
A
Aerobic respiration involves the complete breakdown of organic molecules for a larger yield of ATP (oxygen is required)
11
Q
Why is the breakdown of organic molecules done in steps?
A
By staggering the breakdown, the energy requirements are reduced (activation energy can be divided across several steps)
The released energy is not lost – it is transferred to activated carrier molecules via redox reactions (oxidation / reduction)
12
Q
how is chemical energy transferred when organic molecules are broken down?
A
When organic molecules are broken down by cell respiration, the chemical energy is transferred by means of redox reactions
13
Q
What is redox?
A
Redox reactions involved the reduction of one chemical species and the oxidation of another (redox = reduction / oxidation)
14
Q
what do most redox reactions typically involve the transfer of?
A
Most redox reactions typically involve the transfer of electrons, hydrogen or oxygen
15
Q
what is reduction?
A
Reduction is the gain of electrons / hydrogen or the loss of oxygen
16
Q
what is oxidation?
A
Oxidation is the loss of electrons / hydrogen or the gain of oxygen
17
Q
What does cell respiration transfer?
A
Cell respiration breaks down organic molecules and transfers hydrogen atoms and electrons to carrier molecules
18
Q
In respiration, does the organic molecule undergo reduction or oxidation?
A
As the organic molecule is losing hydrogen atoms and electrons, this is an oxidation reaction
19
Q
Where is energy stored in the organic molecule transferred to?
A
Energy stored in the organic molecule is transferred with the protons and electrons to the carrier molecules
20
Q
What are the carrier molecules called?
A
The carrier molecules are called hydrogen carriers or electron carriers, as they gain electrons and protons (H+ ions)
21
Q
What is the most common hydrogen carrier? What happens to it?
A
The most common hydrogen carrier is NAD+ which is reduced to form NADH
(NAD+ + 2H+ + 2e– → NADH + H+)
22
Q
What is a less common hydrogen carrier? What happens to it?
A
A less common hydrogen carrier is FAD which is reduced to form FADH2 (FAD + 2H+ + 2e– → FADH2)
23
Q
What is the function of hydrogen carriers?
A
The hydrogen carriers function like taxis, transporting the electrons (and hydrogen ions) to the cristae of the mitochondria
24
Q
What are the cristae the site of?
A
The cristae is the site of the electron transport chain, which uses the energy transferred by the carriers to synthesize ATP
25
What does the ETC need, which makes it only occur in certain conditions?
This process requires oxygen to function, and hence only aerobic respiration can generate ATP from hydrogen carriers
This is why aerobic respiration unlocks more of the energy stored in the organic molecules and produces more ATP
26
What organic compounds can be used for respiration?
The main organic compound used in cell respiration is carbohydrates (glucose) – although lipids and proteins can be used
27
WHy are carbohydrates more commonly used in respiration than lipids?
Lipids are not preferentially used as they are harder to transport and digest (although will yield more energy per gram)
28
WHy are carbohydrates more commonly used in respiration than proteins?
Proteins are not preferentially used as they release potentially toxic nitrogenous compounds when broken down
29
What is the first stage of respiration?
The first step in the controlled breakdown of carbohydrates is glycolysis, which occurs in the cytosol of the cell
30
What is the general overview of glycolysis?
In glycolysis, a hexose sugar (6C) is broken down into two molecules of pyruvate (3C)
31
What are the 4 key events of glycolysis?
1. phosphorylation
2. lysis
3. oxidation
4. atp formation
32
1. what is phosphorylated in glycolysis?
A hexose sugar (typically glucose) is phosphorylated by two molecules of ATP (to form a hexose bisphosphate)
33
2. What is the role of phosphorylation in glycolysis?
This phosphorylation makes the molecule less stable and more reactive, and also prevents diffusion out of the cell
34
3. What happens in lysis?
glycolysis
The hexose biphosphate (6C sugar) is split into two triose phosphates (3C sugars)
35
4. What is oxidised in glycolysis? What is in term reduced?
Hydrogen atoms are removed from each of the 3C sugars (via oxidation) to reduce NAD+ to NADH (+ H+)
36
5. what is formed in oxidation?
glycolysis
Two molecules of NADH are produced in total (one from each 3C sugar)
37
6. What type of phosphorylation is in glycolysis?
Some of the energy released from the sugar intermediates is used to directly synthesise ATP
This direct synthesis of ATP is called substrate level phosphorylation
38
7. How many ATP molecules are produced by glycolysis?
In total, 4 molecules of ATP are generated during glycolysis by substrate level phosphorylation (2 ATP per 3C sugar)
39
What has glucose been broken down into via glycolysis?
Glucose (6C) has been broken down into two molecules of pyruvate (3C)
40
What has been reduced in glycolysis?
Two hydrogen carriers have been reduced via oxidation (2 × NADH + H+)
41
What is the net total of ATP molecules produced?
A net total of two ATP molecules have been produced (4 molecules were generated, but 2 were used)
42
Where does glycolysis occur? Is it anaerobic or aerobic?
Glycolysis occurs in the cytosol and does not require oxygen (it is an anaerobic process)
43
What may cause the products fo glycolysis to differ?
Depending on the availability of oxygen, the pyruvate may be subjected to one of two alternative processes:
44
What does aerobic respirationrespiration produce?
Aerobic respiration occurs in the presence of oxygen and results in the further production of ATP (~ 34 molecules)
45
What does anaerobic glycolysis produce?
Anaerobic respiration (fermentation) occurs in the absence of oxygen and no further ATP is produced
46
What happens to pyruvate in aerobic conditions?
If oxygen is present, the pyruvate is transported to the mitochondria for further breakdown (complete oxidation)
47
What does the oxidtaon of pyruvate form?
This further oxidation generates large numbers of reduced hydrogen carriers (NADH + H+ and FADH2)
48
What is the role of the reduced hydrogen carriers in the presence of oxygen?
In the presence of oxygen, the reduced hydrogen carriers can release their stored energy to synthesise more ATP
49
What 3 stages does aerobic respiration involve
Aerobic respiration involves three additional processes – the link reaction, krebs cycle and the electron transport chain
50
1. What is pyruvate broken down into in anaerobic conditions?
If oxygen is not present, pyruvate is not broken down further and no more ATP is produced (incomplete oxidation)
51
2. Where does pyruvate remain in anaerobic conditions and what happens to it?
The pyruvate remains in the cytosol and is converted into lactic acid (animals) or ethanol and CO2 (plants and yeast)
52
3. Is the conversion of pyruvate into lactic acid or ethanol irreversible?
This conversion is reversible and is necessary to ensure that glycolysis can continue to produce small quantities of ATP
53
4. What does glycolysis involve in terms of redox?
Glycolysis involves oxidation reactions that cause hydrogen carriers (NAD+) to be reduced (becomes NADH + H+)
54
5. What happens to reduced hydrogen carriers?
Typically, the reduced hydrogen carriers are oxidised via aerobic respiration to restore available stocks of NAD+
55
6. What will glycolysis do to hydrogen carriers in anaerboic conditions?
In the absence of oxygen, glycolysis will quickly deplete available stocks of NAD+, preventing further glycolysis
56
7. What does fermentation of pyruvate involve?
Fermentation of pyruvate involves a reduction reaction that oxidises NADH (releasing NAD+ to restore available stocks)
57
8. What does the fermentation of pyruvate allow for?
Hence, anaerobic respiration allows small amounts of ATP to be produced (via glycolysis) in the absence of oxygen
58
What is the link reaction?
The first stage of aerobic respiration is the link reaction, which transports pyruvate into the mitochondria
59
What does aerobic respiration use more oxygen to do?
Aerobic respiration uses available oxygen to further oxidise the sugar molecule for a greater yield of ATP
60
Why is it called the link reaction?
The link reaction is named thus because it links the products of glycolysis with the aerobic processes of the mitochondria
61
1. How and where is pyruvate transported into the mitochondrion?
link
Pyruvate is transported from the cytosol into the mitochondrial matrix by carrier proteins on the mitochondrial membrane
62
2. What does the pyruvate lose?
link
The pyruvate loses a carbon atom (decarboxylation), which forms a carbon dioxide molecule
63
3. What does the decarboxylated pyruvate form?
link
The 2C compound then forms an acetyl group when it loses hydrogen atoms via oxidation (NAD+ is reduced to NADH + H+)
64
4. What does the acetyl compound join with?
The acetyl compound then combines with coenzyme A to form acetyl coenzyme A (acetyl CoA)
65
How many times does the link reaction occur?
As glycolysis splits glucose into two pyruvate molecules, the link reaction occurs twice per molecule of glucose
66
What does one molecule of glucose form in the link reaction?
Per glucose molecule, the link reaction produces acetyl CoA (×2), NADH + H+ (×2) and CO2 (×2)
67
What is the second stage of aerobic respiration?
The second stage of aerobic respiration is the Krebs cycle, which occurs within the matrix of the mitochondria
68
1. What is the first step of krebs?
n the Krebs cycle, acetyl CoA transfers its acetyl group to a 4C compound (oxaloacetate) to make a 6C compound (citrate)
69
2. What is recycled in Krebs?
Coenzyme A is released and can return to the link reaction to form another molecule of acetyl CoA
70
3. What is the overall breakdown of krebs?
Over a series of reactions, the 6C compound is broken down to reform the original 4C compound (hence, a cycle)
71
4. What two atoms are released and what do they form?
krebs
Two carbon atoms are released via decarboxylation to form two molecules of carbon dioxide (CO2)
72
5. What type of redox reactions occur in krebs?
Multiple oxidation reactions result in the reduction of hydrogen carriers (3 × NADH + H+ ; 1 × FADH2)
73
5. How many molecules of ATP are produced by krebs?
One molecule of ATP is produced directly via substrate level phosphorylation
74
6. How many times does krebs occur?
As the link reaction produces two molecules of acetyl CoA (one per each pyruvate), the Krebs cycle occurs twice
75
7. What are the products of Krebs per glucose molecule?
Per glucose molecule, the Krebs cycle produces:
4 × CO2 ;
2 × ATP ;
6 × NADH + H+ ;
2 × FADH2
76
What is the final stage of aerobic respiration?
The final stage of aerobic respiration is the electron transport chain, which is located on the inner mitochondrial membrane
77
How is the inner membrane of the mitochondria adapted?
The inner membrane is arranged into folds (cristae), which increases the surface area available for the transport chain
78
What is the role of the ETC?
The electron transport chain releases the energy stored within the reduced hydrogen carriers in order to synthesise ATP
79
What is oxidative level phosphorylation?
This is called oxidative phosphorylation, as the energy to synthesise ATP is derived from the oxidation of hydrogen carriers
80
What are the 3 main stages of oxidative level phosphorylation?
Proton pumps create an electrochemical gradient (proton motive force)
ATP synthase uses the subsequent diffusion of protons (chemiosmosis) to synthesise ATP
Oxygen accepts electrons and protons to form water
81
1. What redox reaction occurs to start ETC?
The hydrogen carriers (NADH and FADH2) are oxidised and release high energy electrons and protons
82
2. Where are the e- transferred ? ETC
The electrons are transferred to the electron transport chain, which consists of several transmembrane carrier proteins
83
3. What happens to the e- as they move through the ETC? What is the purpose of this?
As electrons pass through the chain, they lose energy – which is used by the chain to pump protons (H+ ions) from the matrix
84
4. What does the accumulation of H+ within the intermembrane space cause? ETC
The accumulation of H+ ions within the intermembrane space creates an electrochemical gradient (or a proton motive force)
85
5. What will the proton motive force cause? ETC
The proton motive force will cause H+ ions to move down their electrochemical gradient and diffuse back into matrix
86
6. What is chemiosmosis? What facilitates it? ETC
This diffusion of protons is called chemiosmosis and is facilitated by the transmembrane enzyme ATP synthase
87
7. What does the movement of H+ trigger? ETC
As the H+ ions move through ATP synthase they trigger the molecular rotation of the enzyme, synthesising ATP
88
8. What must be removed for ETC to continue?
In order for the electron transport chain to continue functioning, the de-energised electrons must be removed
89
9. What acts as the final electron acceptor?
ETC
Oxygen acts as the final electron acceptor, removing the de-energised electrons to prevent the chain from becoming blocked
90
10. What does the final electron acceptor bind with?
ETC
Oxygen also binds with free protons in the matrix to form water – removing matrix protons maintains the hydrogen gradient
91
11. What happens to the final stage of ETC if no oxygen is present?
In the absence of oxygen, hydrogen carriers cannot transfer energised electrons to the chain and ATP production is halted
92
What does aerobic respiration involve?
Aerobic respiration involves the breakdown of glucose in the presence of oxygen to produce water and carbon dioxide
93
What is the yield of aerobic respiration?
It requires the involvement of mitochondria and generates a large yield of ATP (typically 36 ATP per glucose consumed)
94
What are the 3 main reactions in aerobic respiration?
Aerobic respiration involves three main types of reactions – decarboxylation, oxidation and phosphorylation
95
What is decarboxylation in aerobic respiration?
Carbon atoms are removed from the organic molecule (glucose) to form carbon dioxide
96
How many CO2 are produced in aerobic respiration and why?
Aerobic respiration involves the complete combustion of glucose (6C) – so six CO2 molecules are produced
97
What are the 3 main oxidation reactions in aerobic respiration?
Electrons and hydrogen ions are removed from glucose and taken up by hydrogen carriers (NADH and FADH2)
The hydrogen carriers are in turn oxidised at the electron transport chain (where the energy is used to make ATP)
The electrons and hydrogen ions are then taken up by oxygen (reduction) to form water molecules
98
What are the products of the oxidation reactions in aerobic respiration?
Twelve hydrogen carriers are produced and so six oxygen molecules are required (12 × O = 6 × O2)
99
What is the energy released from glucose used to do?
Energy released from the breakdown of glucose is used to phosphorylate ADP to make ATP
100
How many molecules of ATP are produced by substrate level phosphorylation?
A net total of four ATP molecules are produced directly via substrate level phosphorylation
101
Where are the ATP molecules produced, that are not produced by substrate level phosphorylation?
The remaining ATP is produced indirectly via the electron transport chain (oxidative phosphorylation)
102
What is the net total of ATP formed in glycolysis?
A net total of 2 ATP are produced in glycolysis via substrate level phosphorylation (four are produced, but two are consumed)
103
What is the net total of ATP formed in krebs?
further 2 ATP are similarly produced in the Krebs cycle (one ATP per cycle – two cycles occur per glucose molecule)
104
What is the net total of ATP formed in ETC?
Lastly, 32 ATP are produced in the electron transport chain using energy from hydrogen carriers (oxidative phosphorylation)
105
What can cause ATP yield to differ?
Hydrogen carriers produce different amounts of ATP depending on where they donate electrons to the transport chain
106
How many ATP molecules do NADH carriers "produce"?
NADH molecules located in the matrix donate electrons to the start of the chain and produce 3 ATP per hydrogen carrier
107
Q
How many ATP molecules does cytosolic NADH "produce"?
Cytosolic NADH (from glycolysis) donate electrons later in the chain and only produce 2 ATP per hydrogen carrier
108
How many ATP molecules does cytosolic FADH2 "produce"?
FADH2 also donates electrons later in the chain and so only produce 2 ATP per hydrogen carrier
109
DO prokaryotes have mitochondria?
All eukaryotic cells possess mitochondria – aerobic prokaryotes use the cell membrane to perform oxidative phosphorylation
110
What are the 5 key structures of the mitochondria?
outer membrane
inner membrane
cristae
intermembrane space
matrix
111
How is the outer membrane adapted to its function?
Outer membrane – the outer membrane contains transport proteins that enable the shuttling of pyruvate from the cytosol
112
How is the inner membrane adapted to its function?
Inner membrane – contains the electron transport chain and ATP synthase (used for oxidative phosphorylation)
113
How are the cristae adapted to its function?
the inner membrane is arranged into folds (cristae) that increase the SA:Vol ratio (more available surface)
114
How is the intermembrane space adapted to its function?
small space between membranes maximises hydrogen gradient upon proton accumulation
115
How is the matrix adapted to its function?
central cavity that contains appropriate enzymes and a suitable pH for the Krebs cycle to occur
116
When will the electron micrograph of a mitochondrion differ?
Electron micrographs of a mitochondrion may differ in appearance depending on where the cross-section occurs
117
What 4 features should a electron micrograph of a mitochondrion show?
Usually sausage-shaped in appearance (though will appear more rounded in perpendicular cross-sections)
Inner membrane contains many internal protrusions (cristae)
Intermembrane space is very small (allows for a more rapid generation of a proton motive force)
Ribosomes and mitochondrial DNA are usually not visible at standard resolutions and magnifications
118
What is electron tomography?
Electron tomography is a technique by which the 3-dimensional internal structure of a sample can be modelled
119
How are electron micrographs produced via electron tomography?
Samples are repeatedly imaged using a transmission electron microscope
Following each image, the sample is tilted to a different angle relative to the electron beam
The images are then compiled and used to computationally reconstruct a 3-D representation (called a tomogram)
120
How are samples prepared for electron tomography?
When dealing with biological materials, samples are first prepared by either fixing and dehydrating or freezing (cryogenics)
This stabilises the biological structures and prevents aqueous contents (i.e. water) from expanding and exploding
121
What 3 findings have electron tomography identified in features of active mitochondria?
The cristae are continuous with the internal mitochondrial membrane
The intermembrane space is of a consistent width thoughout the entire mitochondrion
The relative shape, position and volume of the cristae can change in active mitochondria
122
What is the purpose of anaerobic respiration?
The purpose of anaerobic respiration is to restore stocks of NAD+ – as this molecule is needed for glycolysis
123
Why is restoring NAD+ necessary?
By restoring stocks of NAD+ via anaerobic pathways, the organism can continue to produce ATP via glycolysis
124
What tissue requires large amounts of ATP and why?
Muscle contractions require the expenditure of high amounts of energy and thus require high levels of ATP
125
Why will muscles respire anaerobically during exercise?
When exercising at high intensity, the cells’ energy demands will exceed what the available levels of O2 can supply aerobically
Hence the body will begin breaking down glucose anaerobically to maximise ATP production
126
What will an increase in anaerobic respiration cause in muscle cells?
This will result in an increase in the production of lactic acid, which leads to muscle fatigue
127
What happens in the muscles when an individual stops exercising?
When the individual stops exercising, oxygen levels will increase and lactate will be converted back to pyruvate
128
What can the products of anaerobic respiration/fermentation in yeast be used for?
In yeasts, fermentation results in the production of ethanol and carbon dioxide – which can be used in food processing:
Bread – Carbon dioxide causes dough to rise (leavening), the ethanol evaporates during baking
Alcohol – Ethanol is the intoxicating agent in alcoholic beverages (concentrations above ~14% damage the yeast)
129
What can the fermentation of bacterial cultures be used for?
Bacterial cultures can also undergo fermentation to produce a variety of food products
Yogurt / Cheese – Bacteria produce lactic acid anaerobically, which modifies milk proteins to generate yogurts and cheeses
130
What is a respirometer?
A respirometer is a device that determines an organism’s respiration rate by measuring the rate of exchange of O2 and CO2
131
1. Where is the living specimen kept?
respirometer
The living specimen (e.g. germinating seeds or invertebrate organism) is enclosed in a sealed container
132
2. What can be used to measure CO2 production?
respirometer
Carbon dioxide production can be measured with a data logger or by pH changes if the specimen is immersed in water
133
3. How can O2 consumption be measured?
respirometer
When an alkali is included to absorb CO2, oxygen consumption can be measured as a change in pressure within the system
The pressure change can be detected with a data logger or via use of a U-tube manometer
134
What factors may affect respiration?
Factors which may affect respiration rates include temperature, hydration, light (plants), age and activity levels
135
What will an increase in CO2 indicate? respirometer
An increase in carbon dioxide levels will indicate an increase in respiration (CO2 is a product of aerobic respiration)
136
What will a decrease in oxygen indicate? respirometer
A decrease in oxygen levels will indicate an increase in respiration (O2 is a requirement for aerobic respiration)
