3.3 respiration releases chemical energy in biological processes Flashcards
(98 cards)
1
Q
what is the overall equation for aerobic respiration?
A
C6H12O6 + 6O2 —> 6CO2 + 6H2O + 38 ATP
2
Q
aerobic respiration definition
A
release of large amounts of energy as ATP from the breakdown of molecules where oxygen acts as the terminal electron acceptor
3
Q
anaerobic respiration definition
A
release of relatively little energy as ATP from the breakdown of molecules in the absence of oxygen by substrate level phosphorylation
4
Q
aerobic respiration yields a relatively (small/large) amount of energy?
A
large
- theoretically up to 38 ATP (although a range of 32-38 ATP is often accepted)
5
Q
- what is aerobic respiration performed by?
- what are microorganisms (bacteria and yeast) that can respire with or without the presence of oxygen termed?
- what are bacteria that cant grow in the presence of oxygen so can only undergo anaerobic respiration termed?
A
- obligate aerobes
- facultative anaerobes
- obligate anaerobes
6
Q
dehydrogenation definition
A
the removal of hydrogen atoms, performed by dehydrogenase enzymes
7
Q
what are the 4 stages of aerobic respiration?
A
- glycolysis
- link reaction
- krebs cycle
- the electron transport chain
8
Q
where does glycolysis occur?
A
in the cytoplasm
9
Q
does glycolysis require oxygen?
A
no
10
Q
what are the steps in glycolysis?
A
- glucose is phosphorylated to produce hexose bisphosphate
- this makes glucose more reactive (by lowering the activation energy of the reactions involved) making it easier to split into triose phosphate
- 2NADs are reduced to NADH when triose phosphate is dehydrogenated
- 4 ATP are produced by substrate-level phosphorylation, and pyruvate is produced
- as 2 ATP are used to phosphorylate glucose, the net gain is +2 ATP
- if oxygen is available, the pyruvate moves to the link reaction, and its products move onto the Krebs cycle, where more NAD is reduced and some ATP is produced directly
11
Q
what is the net yield of glycolysis?
A
2 ATP
in total 4 ATP are produces in glycolysis, but as 2 are used to phosphorylate glucose, the net yield is only 2 ATP
12
Q
decarboxylation definition
A
the removal of carbon dioxide, performed by decarboxylase enzymes
13
Q
where does the link reaction occur?
A
in the mitochondrial matrix
(so pyruvate has to diffuse into the mitochondria)
14
Q
does the link reaction require oxygen?
A
yes
- it only happens in the presence of oxygen
15
Q
the link reaction happens x___ per glucose molecule?
A
x2 / twice per glucose molecule
- because there are 2 molecules of pyruvate
16
Q
why does glucose have to be broken down into pyruvate before it enters the mitochondrion?
A
- as glucose is too big to diffuse into the mitochondrion
- and the mitochondrion doesn’t possess the enzymes needed for glycolysis
17
Q
what are the steps in the link reaction?
A
(happens x2 per glucose)
- pyruvate diffuses into the mitochondrial matrix where it is dehydrogenated and the hydrogen released reduced NAD
- pyruvate is decarboxylated, producing acetate
- coenzyme A (CoA) is added to form acetyl CoA which enters the Krebs cycle
18
Q
where does the Krebs cycle occur?
A
in the mitochondrial matrix
19
Q
does the Krebs cycle require the presence of oxygen?
A
yes
- it only occurs in the presence of oxygen
20
Q
the Krebs cycle happens x____ per glucose molecule?
A
x2 / twice per glucose molecule
because there are 2 molecules of acetyl CoA
21
Q
what are the steps in the Krebs cycle?
A
- acetyl CoA joins to [4C] acid to produce [6C] acid
- [6C] acid is decarboxylated, releasing 1 molecule of CO2, and dehydrogenated, reducing 1 NAD molecule
- the resulting [5C] acid is decarboxylated, releasing 1 molecule of CO2, and dehydrogenated, reducing 2 NAD and 1 FAD molecules
- ATP is produced directly by substrate level phosphorylation
- the resulting [4C] acid combines with acetyl CoA and the cycle repeats
22
Q
without oxygen, why can’t the electron transport chain happen?
A
as there is no terminal electron acceptor
23
Q
does the electron transport chain require oxygen?
A
yes
(its the terminal electron acceptor)
24
Q
where does the electron transport chain occur?
A
on the inner membrane of mitochondrion
(cristae)
25
what are the steps in the electron transport chain?
- NADH joins the first proton pump, and is dehydrogenated, releasing the hydrogen atoms which split into protons and electrons
- the protons are pumped across the membrane using energy from the high energy electrons as the electrons pass to the next proton pump
- as the electrons pass the second proton pump they provide energy to pump a further pair of protons from the matrix to the inter membrane space
- the electrons pass the third proton pump; a further two protons are pumped across, which creates a proton gradient
- as the electrons pass to the terminal electron acceptor (oxygen), 2 protons pass back into the matrix through the stalked particle (ATP synthetase) down the proton gradient phosphylating ADP into ATP
- proton movement here is referred to as chemiosmosis
- water is formed from 2H+, 2e- and 1/2 O2
- NADH uses three proton pumps so generates 3 ATP
- FADH joins at the second proton pump so only utilises 2 pumps so only generates 2 ATP
26
how does cyanide act as a non-competitive inhibitor in the electron transport chain
- it is a non competitive inhibitor of the final carrier in the electron transport chain
- and so electrons cant pass to the terminal electron acceptor
- this results in the electrons no longer moving, which prevents the proton pumps from functioning
- ATP synthesis soon stops
27
the products of respiration (per molecule of glucose): glycolysis produces how many:
ATP
NADH
FADH
CO2
H2O
ATP: 2
NADH: 2
FADH: 0
CO2: 0
H2O: 0
28
the products of respiration (per molecule of glucose): the link reaction produces how many:
ATP
NADH
FADH
CO2
H2O
ATP: 0
NADH: 2
FADH: 0
CO2: 2
H2O: 0
29
the products of respiration (per molecule of glucose): the Krebs cycle produces how many:
ATP
NADH
FADH
CO2
H2O
ATP: 2
NADH: 6
FADH: 2
CO2: 4
H2O: 0
30
the products of respiration (per molecule of glucose): the electron transport chain produces how many:
ATP
NADH
FADH
CO2
H2O
ATP: 34 *
NADH: 0
FADH: 0
CO2: 0
H2O: 6
* from 10 NADH x3 = 30 ATP and 2 FADH x2 = 4 ATP
31
in anaerobic respiration, what stage still occurs?
glycolysis still occurs
(but the lack of oxygen prevents link reaction, krebs cycle and the electron transport chain from occurring)
32
what is a major consequence of a lack of oxygen meaning the link reaction, krebs cycle and electron transport chain cant occur?
- that NADH is not oxidised in the electron transport chain, so NAD is not regenerated
- as dehydrogenation occurs before production of the final 4 ATPs in glycolysis, the lack of NAD would stop ATP production
33
how do animals overcome the problems that arise due to a lack of oxygen?
for a short time,
- animals can reduce pyruvate to lactate using hydrogen from NADH, which regenerates NAD, allowing glycolysis to continue
34
how do plants and yeast overcome the problems that arise due to a lack of oxygen?
- the pyruvate is first decarboxylated to ethanal
- then reduced to ethanol using the hydrogen from NADH
35
why cant anaerobic respiration be sustained indefinitely?
- because lactate and ethanol build up
36
- in animals, anaerobic respiration creates an ‘oxygen debt’ which requires lactate to be oxidised later, releasing further energy
- in plants, ethanol cant be broken down later, so it can accumulate to reach toxic concentrations
(a build up of lactate in the muscles is toxic and causes cramp. it results in an oxygen debt as it has to be oxidises in the liver later)
37
in both plants and animals, only ___ ATP are produced during anaerobic respiration?
2 ATP
38
1 mole of glucose contains ____kJ of energy
2880kJ
39
what is the energy liberated from the hydrolysis of ATP?
30.6kJ per mole
40
- one mole of glucose contains 2880kJ of energy
- the energy liberated from the hydrolysis of ATP = 30.6kJ per mole
- if we assume a theoretical maximum yield of 38 molecules of ATP from a mole of glucose then:
efficiency of aerobic respiration:
= energy from ATP / energy in glucose
= ((30.6 x 38) / 2880 ) x 100
= 40.4%
41
can you make energy?
no
- it can only be converted from one form to another, or transfer it
42
when can lipids be respired?
when carbohydrate supplies are low
43
what are the steps for the alternative respiratory pathway for lipids?
- lipids are hydrolysed into glycerol
- which is phosphorylated, and dehydrogenated to form triose phosphate which can enter glycolysis
- the fatty acids are split into two carbon molecules that enter krebs as acetyl CoA
- bc fatty acids have large numbers of carbon and hydrogen atoms, respiring them yields more carbon dioxide, water and ATP (due to more hydrogen being utilised in the electron transport chain)
44
when can proteins be metabolised?
when fats and carbohydrates are unavailable, or when diets contain a high proportion of protein
45
what are the steps for the alternative respiratory pathway for proteins?
- the excess amino acids are deaminated in the liver
- the amine group NH2, is converted to urea in the liver and the urea is then excreted via the kidneys as urine
- the carboxyl group that remains can be converted into a number of different krebs cycle intermediates
46
what are the experiments with artificial hydrogen acceptors?
- a number of artificial hydrogen acceptors e.g methylene blue (which turns colourless when reduced) or TTC (which turns red when reduced), can be used with yeast to measure the rate of respiration
- the time taken for the colour change to occur can be measures under a number of different independent variables e.g temperature or glucose concentration
47
what are the problems associated with the experiments with artificial hydrogen acceptors? and how can you improve them?
- its difficult to determine the end point, as the time taken for the colour change to occur is subjective
- it produces a reciprocal graph i.e a short tome represents a high rate of respiration
- using a colorimeter to measure how dark the solution is (% transmission) is a good improvement to determine the endpoint of the reaction
48
the oxidation of each of the triose phosphates to pyruvate through the loss of hydrogen is catalysed by what enzyme?
dehydrogenase
49
what does glycolysis produce?
- net yield of 2 ATP produced by substrate level phosphorylation
- 2 molecules of reduced NAD
- 2 pyruvates
50
name the type of enzyme that catalyses the production of carbon dioxide in the link reaction/krebs cycle etc
decarboxylase
51
how many carbon atoms are found in pyruvate?
3
52
how many carbon atoms are found in the acetyl group in acetyl CoA?
2
53
what is the source of hydrogen ions in ATP synthesis by the electron transport chain?
- reduced NAD
- reduced FAD
54
where does a high concentration of H+ build up in ATP synthesis by the electron transport chain?
in the inter-membrane space
55
what is the final electron acceptor in ATP synthesis by the electron transport chain?
- oxygen
(electrons from the electron transport system and protons (H+ from the matrix) combined with an oxygen atom to form water)
56
under anaerobic conditions, why can’t the link reaction and the Krebs cycle take place?
without oxygen, the reduced NAD (and reduced FAD) cannot be reoxidised and therefore made available to pick up more hydrogen atoms
57
each molecule of reduced NAD and reduced FAD transport how many hydrogens to the electron transport chain?
2
58
the electrons that are released as the H+ is passed across the membrane provide energy for the second and third proton pump to pass more H+ across the membrane.
how many H+ are required to synthesise one ATP molecule?
2 H+
59
are more H+ pumped into the inter-membrane space due to reduced NAD or reduced FAD?
reduced NAD
60
why are more H+ pumped into the inter-membrane space due to reduced NAD than reduced FAD?
because reduced NAD delivers the hydrogens to the first proton pump and reduced FAD delivers hydrogen to the second pump
61
what is the yield of ATP from 1 reduced NAD?
3 ATP
62
what is the yield of ATP from 1 reduced FAD?
2 ATP
63
why is the maximum yield of ATP in aerobic respiration never achieved?
- as there is a loss of energy as heat energy
- ATP is needed to pump pyruvate into the mitochondrial matrix
- and some H+ may leak through the inner mitochondrial membrane rather than diffusing through ATP synthetase
64
what is the oxygen debt?
the amount of oxygen needed to remove the lactic acid produced during anaerobic respiration
65
is lactic acid production reversible?
yes - if oxygen becomes available
66
is alcoholic fermentation reversible?
no - ethanol is toxic and will eventually kill the cells
67
what is the yield of ATP in anaerobic conditions?
2 ATP per molecule of glucose
68
carbon dioxide is released during anaerobic respiration in (yeast/animal) cells?
yeast cells
69
why is respiration described as a catabolic process?
complex molecules (respiratory substrates) are broken down into smaller, simpler molecules
70
why do organisms need to respire?
- releases chemical energy in ATP
- releases heat energy for thermoregulation
71
how does pyruvate from glycolysis enter the mitochondria?
via active transport
72
describe the role of reduced NAD and reduced FAD in the electron transport chain
they are a source of electrons and protons
73
how does chemiosmosis produce ATP during aerobic respiration?
- protons flow down their concentration gradient from the intermembrane space into the mitochondrial matrix via ATP synthase
- ATP synthase phosphorylates ADP to form ATP as protons flow through it
74
state the product of anaerobic respiration in animals
lactic acid
75
state the products of anaerobic respiration in plants and microorganisms
ethanol and carbon dioxide
76
name the 2 types of molecules that can be used as alternative respiratory substrates
- (amino acids from) proteins
- (glycerol and fatty acids from) lipids
77
briefly describe how reduced FAD and reduced NAD are used to create an electrochemical gradient [4]
- reduced NAD and reduced FAD pass electrons to the Electron Transport Chain
- the HIGH ENERGY electrons / electrons provide energy
- (used to power) proton pumps
- on the inner mitochondrial membrane / cristae
- which pump H+ into the inter-membrane space
- reduced NAD powers all 3 pumps / reduced FAD passes to 2nd pump
78
suggest a suitable tissue to examine mitochondrial function and explain why you have chosen this tissue with respect to patient safety [2]
- (skeletal) muscle
- high numbers of mitochondria and easy to access
79
what could be deduced if the oxygen consumption was low with pyruvate as a substrate but high with a 5 carbon compound as a substrate? [2]
LOW WITH PYRUVATE:
- {the pathway leading to acetyl CoA/ link reaction} is not working / {enzymes/dehydrogenase/decarboxylase} are not active / there is no reduced NAD for the electron transport chain (so no O2 needed)
HIGH WITH 5 CARBON COMPOUND:
- the pathway between it and the rest of the cycle is working correctly / there is enough reduced NAD/FAD to drive the ETC (which needs oxygen)
80
what could be deduced if there was a build up of any one of the krebs cycle intermediates? [1]
- enzymes catalysing the conversion of the molecule to the next in the cycle are not functional / build up of reduced NAD and FAD
81
explain why there is a raised blood lactate level in many patients with mitochondrial disease [2]
- the {krebs cycle / link reaction / electron transport chain} is not working (as well)
- pyruvate levels (build up/increase/higher)
- (excess) (pyruvate/reduced NAD) is converted to lactate
82
name the process by which carbon dioxide is removed [1]
decarboxylation
83
describe briefly what happens to a molecule of carbon dioxide removed by decarboxylation in a human [3]
- diffuses out of mitochondria
- into blood/tissue fluid/plasma
- carried as hydrogen carbonate ions
- breathed out
84
reduced NAD is also produced during glycolysis.
explain what happens to the reduced NAD under anaerobic conditions and why this is essential for glycolysis to continue [2]
- pyruvate is used to form lactic acid
- regenerated NAD
85
the proton gradient can be maintained as long as reduced NAD is available in the mitochondrion.
explain the reasons for reduced NAD being required to maintain a proton gradient [2]
- reduced NAD supplied protons
- and brings high energy electrons
- electrons (supply energy for proton pumping / fuels proton pumps)
86
outline the pathway for the production of triose phosphate in glycolysis [3]
- glucose is phosphorylated by ATP
- two phosphorylations / production of hexose bisphosphate
- hexose bisphosphate is SPLIT (from 6C to two 3C)
87
the reaction from pyruvate to lactate occurs in humans when there are anaerobic conditions in a tissue.
explain the biochemical reasons for carrying out the reaction, despite the fact that lactate is toxic in high concentrations [3]
- allows reduced NAD to be converted back to NAD/ regenerate reduced NAD / without oxygen reduced NAD not converted to NAD by {electron transport chain/krebs/link reaction}
- allowing ATP production / without oxygen no ATP production by oxidative phosphorylation
- allows {glycolysis/substrate level phosphorylation} to continue
- no O2 to act as the final {hydrogen/electron} acceptor/ reduced NAD {must find an alternative hydrogen acceptor/must use pyruvate}
88
the reaction from pyruvate to lactate occurs in muscle fibres when a short burst of very rapid ATP production is needed. suggest a reason for this [1]
- only glycolysis required / shorter metabolic pathways
- oxygen supply too slow / no need for oxygen {supply/diffusion}
- no need to carry out krebs cycle / electron transport / oxidative phosphorylation
- no need to build up a proton gradient
- no need to transport pyruvate into the mitochondrion
89
out of glycolysis, link reaction, krebs cycle and oxidative phosphorylation, where does substrate level phosphorylation take place?
glycolysis and krebs cycle
90
out of glycolysis, link reaction, krebs cycle and oxidative phosphorylation, when is coenzyme A used as an acceptor?
link reaction
91
out of glycolysis, link reaction, krebs cycle and oxidative phosphorylation, when is oxygen used?
oxidative phosphorylation
92
more than 1 billion years ago, aerobic bacteria colonised primordial eukaryotic cells that lacked the ability to use oxygen metabolically. a symbiotic relationship developed and became permanent. the bacteria evolved into mitochondria, thus enabling the host cells to carry out aerobic metabolism, a much more efficient way to release energy than anaerobic glycolysis.
describe the role of mitochondria in eukaryotic cells using your knowledge of respiratory pathways.
explain how the original aerobic bacteria and primordial eukaryotic cells benefited from this relationship [9QER]
LINK REACTION AND KREBS CYCLE:
- pyruvate transported in from cytoplasm
- correct description of link reaction
- decarboxylation and dehydrogenation to produce 2C Acetyl Coenzyme A
- correct description of krebs cycle
- correct description of 4C + acetyl coenzyme A giving 6C molecule
- progressive removal of C as CO2 to reform 4C molecule
- removal of H / use of dehydrogenase/ use of decarboxylase
- formation of reduced NAD and reduced FAD
ELECTRON TRANSPORT CHAIN:
- correct description of ETC
- use of oxygen as final electron acceptor
- use of reduced NAD and reduced FAD as source of high energy electrons for ETC
- formation of an EC gradient / chemiosmosis
- subsequent synthesis of ATP by the use of ATP synthase in stalked particles
BENEFITS
- bacteria have a source of pyruvate/oxygen
- constant environment e.g pH/water potential
- protection from predation
- eukaryote - increased ATP availability - increased metabolic rate / increased cell division / increased active transport / able to metabolise other respiratory substrates / e.g fatty acids
- compartmentalisation
- increase in size/complexity
93
describe the reactions that link glycolysis to the krebs cycle [3]
- pyruvic acid / puruvate is converted to two carbon acetate
- two molecules of reduced NAD formed
- loss of two molecules of carbon dioxide
- acetate combines with coenzyme A (to form acetyl coenzyme A)
94
explain why the two hydrogen acceptors NAD and FAD lead to the production of different numbers of ATP molecules [1]
NAD has three pumps FAD has two pumps
95
what does ATP stand for?
adenosine triphosphate
96
state the net gain of ATP when one molecule of glucose is broken down to pyruvate in glycolysis [1]
2
97
describe what would happen to the pyruvate molecules formed under anaerobic conditions in human muscle [3]
- accept hydrogen / reduced by
- reduced NAD
- lactic acid
98
the chemical formula for the fat tripalmitin is C15H98O6 and for the sugar glucose C6H12O6
use your knowledge and the information above to explain what happens to tripalmitin under aerobic conditions and why it has a higher energy value per molecule than glucose [3]
- fats to fatty acids and glycerol
- glycerol into glycolysis
- fatty acids to 2C fragments
- acetyl group into krebs
- oxidative phosphorylation
- more hydrogen in a substrate more for oxidative phosphorylation
- ref. chemiosmosis
