Respiration Flashcards
(94 cards)
1
Q
Where does respiration occur?
A
Respiration occurs in living cells to release the energy stored in organic molecules such as glucose.
2
Q
What is the energy produced by respiration used for?
A
The energy is used to synthesise molecules of ATP, from ADP and inorganic phosphate (Pᵢ), which can be hydrolysed in cells to release the energy needed to drive biological processes.
3
Q
What respires to gain energy?
A
Protoctists, fungi, plants and animals all respire to obtain energy.
4
Q
Draw a cycle to represent the energy transfer between and within living organisms.
A
5
Q
The potential chemical energy stored in complex organic molecules such as proteins, carbohydrates and fats is released via respiration in order to make ATP to drive which biological processes?
A
Energy is the capacity to do work;
- Transport of molecules
- Synthesis of molecules
- Cell division
- Activation of chemicals.
6
Q
What are all the chemical reactions that take place within living cells are known collectively as?
A
All the chemical reactions that take place within living cells are known collectively as metabolism or metabolic reactions:
7
Q
What are two types of metabolic reaction?
A
Anabolic reactions are metabolic reactions where large molecules are synthesised from smaller molecules
Catabolic reactions are metabolic reactions where large molecules are hydrolysed into smaller molecules
8
Q
Draw a molecule of ATP.
A
9
Q
What is ATP?
A
ATP is a phosphorylated nucleotide consisting of:
- Adenosine
- Three phosphate groups.
10
Q
Why is ATP the standard intermediary between energy-releasing and energy-consuming metabolic reactions?
A
ATP is the standard intermediary between energy-releasing and energy-consuming metabolic reactions in both eukaryotic and prokaryotic cells as it is relatively stable is solution in cells, but is readily hydrolysed by enzyme catalysis.
11
Q
The energy-releasing hydrolysis of ATP is coupled with an energy-consuming metabolic reaction, what is released at this stage?
A
ATP is the immediate energy source for this metabolic reaction.
When ATP is hydrolysed to ADP and Pᵢ, a small quantity of energy is released for use in the cells so they can obtain the energy they need in small manageable amounts that will not cause damage or be wasteful.
12
Q
What other forms of energy is released from the hydolysis of ATP?
A
Some of the energy released from the hydrolysis of ATP is as thermal energy: this may seem inefficient but the heat actually helps the organism keep warm so their enzyme-catalysed reactions can proceed around their optimum rate.
13
Q
How much ATP do you have in your body at any one time?
A
In your body you have, at any one time, around 5 g of ATP: however, you may use 36 – 50 kg each day. This is possible because the ATP molecules are continually being hydrolysed then resynthesised.
At rest, a person consumes and continually regenerates ATP at the rate of 1.5 kg per hour.
14
Q
What are the four stages of respiration?
A
Respiration of glucose has four stages:
- Glycolysis
- The link reaction
- The Krebs cycle
- Oxidative phosphorylation.
15
Q
What stages of respiration require areobic conditions?
A
The last three stages only take place under aerobic conditions where the pyruvate molecules from glycolysis are actively transported into the mitochondria for the link reaction.
16
Q
How does the process of respiration change for anerobic conditions?
A
In anaerobic conditions, pyruvate is converted to lactate or ethanol, in the cytoplasm, where reduced NAD molecules are reoxidised so that glycolysis can continue generating two molecules of ATP for every glucose molecule metabolised.
17
Q
What is glycolysis?
A
- Glycolysis is a biochemical pathway that occurs in the cytoplasm of all living organisms that respire, including many prokaryotes.
- The pathway involves a sequence of 10 reactions, each catalysed by a different enzyme, some with the help of coenzyme, NAD.
18
Q
What are the three main stages of glycolysis?
A
The three main stages are:
- Phosphorylation of glucose to hexose bisphosphate
- Cleavage of each hexose bisphosphate into two triose phosphate molecules
- Oxidation of triose phosphate to pyruvate.
19
Q
What is the respiritory pathway in anerobic and areobic conditions?
A
20
Q
What is the purpose of NAD?
A
Enzymes that catalyse redox reactions need the help of coenzymes as they accept the hydrogen atoms removed during oxidation.
NAD (nicotinamide adenine dinucleotide) is a non-protein molecule that helps dehydrogenase enzymes to carry out oxidation reactions as it oxidises substrate molecules by accepting two hydrogen atoms in the nicotinamide ring during glycolysis, the link reaction and the Krebs cycle.
21
Q
How is NAD synthesised?
A
NAD is synthesised in living cells from nicotinamide (vitamin B₃), ribose, adenine and two phosphate groups.
22
Q
How does NADH complete its cycle and be reused?
A
- Reduce NAD (NADH) carries the protons and electrons to the cristae of the mitochrondria to be used in oxidative phosphorylation for the generation of ATP from ADP and Pᵢ.
- When NADH donates the protons and electrons that accepted during glycolysis, link or Krebs, its oxidised to be reused to oxidise more substrate.
23
Q
Draw the molecular structure of NAD.
A
24
Q
What are the three main stages of glycolysis?
A
- Phosphorylation
- Cleavage
- Oxidation
25
Describe the process of phosphorylation in glycolysis.
Glucose molecules are stable so they need to be activated before they can be split into two three-carbon compounds.
1. One molecule of ATP is hydrolysed where the released Pᵢ group is added to glucose making **hexose monophosphate**.
2. Another molecule of ATP is hydrolysed where the released Pᵢ group is added to the hexose monophosphate making **hexose bisphosphate**.
3. The energy from the hydrolysed ATP molecules activates the hexose sugar and prevents it from being transported out of the cell.
26
Describe the process of cleavage in glycolysis.
The hexose bisphosphate is split into two three-carbon molecules called **triose phosphate** which each have a phosphate group attached.
27
Describe the process of oxidation in glycolysis.
1. Dehydrogenase enzymes, aided by NAD, remove two hydrogen atoms from each triose phosphate to become **pyruvate**.
2. The two NAD molecules accept the two hydrogen atom each to become reduced.
3. Four molecules of ATP are made for every molecule of glucose (two molecules of triose phosphate).
28
What are the products of glycolysis?
**_Net gain_**
* ATP = 2
* NADH = 2
* Pyruvate = 2
29
What deficiency disease is related to NAD?
Pellagra is a dietary deficiency disease that has symptoms of diarrhoea, dermatitis and dementia, caused by the lack of nicotinamide.
Humans can synthesis nicotinamide from the amino acid tryptophan.
30
Describe the discovery of the mitrochondrion.
Mitochondria are organelles that are present in all types of eukaryotic cells which were first identified in animal cells in 1840 and in plant cells in 1900. However, their ultrastructure was not worked out until the 1950s after extensive studies using electron microscopes.
31
What shape are mitrochondria?
Mitochondria can be rod-shaped, threadlike or spherical with diameters of 0.5–1.0 µm and lengths of 2–5 µm, but occasionally up to 10 µm.
32
What features does the mitrochondria which enable it to function?
1. A nuclear **envelope** made of an inner and an outer phospholipid membrane
2. An **intermembrane** space between the membranes
3. The outer membrane is smooth and the inner membrane is folded into **cristae** giving it a large surface area
4. Proteins that transport electrons embedded in the inner membrane are proteins that transport electrons and protein channels associated with **ATP synthase** enzyme that allows protons to diffuse through them
5. A **matrix**, enclosed by the inner membrane, which is semi-rigid and gel-like; it contains mitochondrial ribosomes, lopped mitochondrial DNA, enzymes for the link reaction and Krebs cycle.
33
How does the mitrochondrial marix allow it to carry out its function?
The matrix is where the link reaction and the Krebs cycle take place so it contains:
* Enzymes that catalyse the stages of these reactions
* Molecules of the coenzymes NAD and FAD
* The four-carbon compound, oxaloacetate, that accepts the acetyl group from the link reaction
Mitochondrial DNA which closes for mitochondrial enzymes and other proteins
34
How does the outer membrane enable the mitrocondria to correctly carry out its function?
* Phospholipid bilayer
* Contains protein channels and carries that allow the passage of molecules such as pyruvate into the mitochondria
35
How does the inner membrane enable the mitrocondria to correctly carry out its function?
* Phospholipid bilayer
* Less permeable to small ions such as hydrogen ions than the outer membrane
* The cristae gives it a large surface area for the electron carriers and ATP synthase enzymes embedded in them
The electron carriers are arranged in electron transport chains
36
How does the intermembrane space enable the mitrocondria to correctly carry out its function?
The inner membrane is in close contact with the matrix so the molecules of NADH and FADH₂ can easily deliver hydrogens to the electron transport chain
37
In the electron transport chain what are electron carrier proteins?
Electron carrier proteins are **oxido-reductase** enzymes which contain a cofactor, a non-protein haem group, which contains an iron ion, Fe³ᐩ.
38
In the electron transport chain how do the oxido-reductase enzymes pass on electrons?
The iron ion can accept and donate electrons because it can be reduced to Fe²ᐩ, by accepting an electron; and reoxidised to Fe³ᐩ, by donating the electron to the next electron carrier.
39
How does the passing of charge along an electron transport chain electron create a proton gradient?
* The enzymes also have a coenzyme that, using energy released from the electrons, pumps protons from the matrix to the intermembrane space.
* The protons accumulate in the intermembrane space causing a proton gradient to form across the inner membrane.
40
How does a proton gradient across the inner membrane cause the synthesis of ATP?
The proton gradient causes a flow of protons through the channels in the ATP synthase enzymes to make ATP.
41
Describe ATP synthase enzymes.
ATP synthase enzymes are large proteins, which protons can pass through, that protrude from the inner membrane into the matrix.
42
What is interesting about the genetic make up of mitrochondrial cells?
_NOTE:_ all mitochondria in your cells come from your mother because, although sperm have mitochondria just above the tail, only the nucleus of the sperm enters the egg cell. The egg cell contains mitochondria that divide each time the zygote, and subsequent embryo cells, divide. This means mitochondrial DNA (mtDNA) can be used for ancestry tracing along the maternal line. In 1987, an article published in Nature showed that all people on Earth today are descended from an African population of humans, supporting the theory that modern humans evolved in Africa around 200,000 years ago and then spread to other regions of the world.
43
Describe the transition of pyruvate from glycolysis to the link reaction.
Pyruvate produced during glycolysis is transported across the outer and inner mitochondrial membranes via a specific **pyruvate-H**ᐩ **symport**, a transport protein that transports two ions or molecules in the same direction, into the matrix.
44
Where does the link reaction occur?
The link reaction occurs in the matrix.
45
What is the link reaction cataylsed by?
It is catalysed by a large multi-enzyme complex called **pyruvate dehydrogenase**.
46
State the stages of the link reaction.
1. Pyruvate is carboxylate and dehydrogenated to produce an **acetyl** group
2. The acetyl group combines with coenzyme A (CoA) to become **acetyl CoA** to carry the acetyl group onto the Krebs cycle
3. The coenzyme NAD becomes reduced.
**(2pyruvate + 2NAD + 2CoA** → **2C)**
47
What is the net gain of molecules in the link reaction?
ATP = 0, NADH =2, CO2 = 2
48
What is the decarboxylation of pyruvate is the origin of?
NOTE: the decarboxylation of pyruvate is the origin of some of the carbon dioxide produced in respiration.
49
Define decarboxylation.
DECARBOXYLATION is the removal of a carboxyl group from a substrate molecule.
50
Define dehydrogenation.
DEHYDROGENATION is the removal of hydrogen atoms from a substrate molecule.
51
Define substrate level phosphorylation.
SUBSTRATE-LEVEL PHOSPHORYLATION is the production of ATP from ADP and Pᵢ during glycolysis and the Krebs Cycle.
52
Where does the krebs cycle occur?
The Krebs cycle is a series of enzyme-catalysed reactions that occur in the **matrix**.
53
What is the purpose of NAD and FAD in the krebs cycle?
The coenzymes NAD and FAD aid in the conservation of energy by being reduced to carry hydrogen atoms to the electron transport chain on the cristae in the final stage of respiration.
54
What is the first stage of the krebs cycle?
1. The acetyl group released from acetyl CoA combines with a four-carbon compound, oxaloacetate, to form a six-carbon compound, citrate.
55
What is the second stage of the krebs cycle?
Citrate is decarboxylated and dehydrogenated, producing a five-carbon compound, one molecule of carbon dioxide and one molecule of NADH.
56
What is the third stage of the krebs cycle, producing a four carbon compound?
The five-carbon compound is further decarboxylated and dehydrogenated, producing a four-carbon compound, one molecule of carbon dioxide and one molecule of NADH.
57
Describe the 4th and 5th steps of the krebs cycle, where substrate-level phosphorylation is used.
4. The four-carbon compound combines temporarily with CoA to produce one molecule of ATP in **substrate-level phosphorylation**.
5. The four-carbon compound is dehydrogenated, producing a different four-carbon compound and one molecule of FADH₂.
58
In the krebs cycle how does the four carbon compound regenerate?
The atoms of the four-carbon compound are rearranged, catalysed by an **isomerase** enzyme, following by further dehydrogenation producing one molecule of NADH and regeneration of oxaloacetate so the cycle can continue.
59
What is the net gain of molecules during the krebs cycle?
* NADH = 6
* FADH2 = 2
* CO2 = 4
* ATP = 2
60
How many turns of the Krebs cycle occur for each molecule of glucose?
For every molecule of glucose there are two turns of the Krebs cycle.
61
How can other substrates besides glucose can be respired aerobically?
1. Fatty acids are broken down to many molecule of acetate that enter the Krebs cycle via acetyl CoA.
2. Glycerol may be converted to pyruvate and enter the Krebs cycle via the link reaction.
3. Amino acids may be deaminated (NH₂ removed) and the rest of the molecule can enter Krebs directly or be changed into pyruvate or acetyl CoA.
62
State the requirements for oxygen and the production of carbon dioxide during the krebs cycle?
63
Describe the process of the electron transport chain.
1. The electrons from the hydrogen atoms pass along the chain of electron carrier protein, the iron ions, Fe³ᐩ in the proteins cores gain an electron to become reduced Fe²ᐩ.
2. The reduced iron ion can then donate the electron to the iron ion in the next electron carrier in the chain to be reoxidised to Fe³ᐩ.
3. As the electrons pass along the chain, some of their energy is used to pump protons across the inner mitochondrial membrane, into the intermembrane space.
64
Where does oxidative phosphorylation take place?
Oxidative phosphorylation takes place in the mitochondria.
65
How does oxidative phosporylation begin?
1. NADH and FADH₂ are reoxidised by delivering their hydrogen atoms to the electron transport chain.
2. The hydrogen atoms released from the reduced coenzymes split into protons and electrons.
3. The protons go into solution in the mitochondrial matrix.
66
What are the stages of oxidative phosphorylation?
Electron transport chain and then chemiosmosis.
67
Describe the process of chemiosmosis.
1. As the protons accumulate in the intermembrane space, a proton gradient forms across the membrane generating a **chemiosmotic potential**.
2. Protons diffuse, down their concentration gradient by **chemiosmosis**, through the protein channels associated with ATP synthase enzymes that are in the inner membrane, causing a proton motive force which is a source of potential energy to generate ATP molecules.
3. The flow of protons causes a conformation change in the ATP synthase enzyme to allow ADP and Pᵢ to combine, forming ATP.
4. Oxygen is the final electron acceptor as it combines the electrons coming of the electron transport chain with the protons diffusing down the ATP synthase channels, forming water.
**4H**ᐩ **+ 4e**ᐨ **+ O₂** → **2H₂O**
68
Why do protons pass through the ATP synthase enzymes rather than the membrane?
Protons diffuse through the ATP synthase channels as the outer membrane has a low degree of permeability to protons and the inner membrane is impermeable to protons.
69
Why is the transport of electrons into the intermembrane space described as pumping protons?
The transport of protons across the cristae into the intermembrane space is an active process, but the energy comes from electrons, not ATP, so it is described as 'pumping' the protons.
70
How much ATP can be produced from each molecule in oxidative phosphorylation?
I. The protons and electrons from one molecule of NADH can theoretically produce 2.5 molecules of ATP.
II. The protons and electrons from one molecule of FADH₂ can theoretically produce 1.5 molecules of ATP.
III. So, oxidative phosphorylation may theoretically produce 28 molecules of ATP per molecule of glucose.
NADH: (2+2+6) x 2.5 = 25
FADH₂: 2 x 1.5 = 3
Total: 25 + 3 = 28
71
How much ATP can be produced from aerobic respiration, per molecule of glucose?
* Glycolysis = 2
* The link reaction = 0
* The Krebs cycle = 2
* Oxidative phosphorylation = 28
* Total = 32
72
Why is 32 ATP being produced in respiration just a theoretical yield?
This is a theoretical yield so it is rarely ever achieved, the actual yield is closer to 30 molecules or less because:
* Some ATP is used to actively transport pyruvate into the mitochondria
* Some ATP is used in a shuttle system that transports NADH, made during glycolysis, into the mitochondria
* Some protons leak out through the outer mitochondrial membrane
73
What is the chemiosmotic theory?
Peter Mitchell proposed the chemiosmotic theory in 1961 as he realised that the accumulation of protons on one side of a membrane and the movement of protons across the membrane, down the electrochemical gradient, could provide energy to form ATP from ADP and Pᵢ.
74
Why was the chemiosmotic theory not accepted at first?
Previously, scientists thought a high-energy intermediate compound provided the mechanism behind oxidative phosphorylation so Mitchell's theory was not readily accepted.
75
When was the chemiosmotic theory accepted?
However, by 1978, so much experimental evidence supported the idea of chemiosmosis that Mitchell's theory became widely accepted and consequently, he won the Nobel Prize for Chemistry.
76
What is chemiosmosis responsible for in plants?
NOTE: chemiosmosis is also responsible for the formation of ATP during photophosphorylation during the light-dependent stage of photosynthesis in chloroplasts.
77
Where is ATP synthase used in bacteria?
Some bacteria use ATP synthase, but 'in reverse', to power the movement of their flagella: ATP is used to produce a proton gradient where pmf causes a flow of protons that rotates it.
78
Why does aerobic respiration not take place with a lack of oxygen?
* Oxygen cannot act as the final electron acceptor at the end of oxidative phosphorylation so protons diffusing through ATP synthase channels will not be able to combine with the electrons to form water
* So, the concentration of protons increases in the matrix and reduces the proton gradient across the inner mitochondrial membrane
* Oxidative phosphorylation stops
* NADH and FADH₂ are not able to unload their hydrogen atoms and cannot be reoxidised
* The Krebs cycle stops and so does the link reaction.
79
How do organisms survive in a lack of oxygen?
I. For organisms to survive in these conditions, glycolysis can take place, but the NADH generated during the oxidation of triose phosphate to pyruvate has to be reoxidised so glycolysis can contain.
II. As the electron transport chain cannot reoxidise them, another metabolic pathway must.
III. Eukaryotic cells have two metabolic pathways to reoxidise NADH:
80
What are the two pathways of anaerobic respiration?
The ethanol fermentation pathway and the lactate fermentation Pathway.
Both take place in the cytoplasm of the cell.
81
Where does the ethanol fermentation pathway occur?
Ethanol (alcohol) fermentation occurs in fungi, such as yeast, or plants.
82
What is the first stage of the ethanol fermentation pathway?
Each molecule of pyruvate produced during glycolysis is decarboxylated, producing one molecule of carbon dioxide, to be converted to ethanal, catalysed by pyruvate decarboxylase, which has a coenzyme, thiamine diphosphate, bound to it.
83
How is ethanol produced from ethanal in the ethanol respiration pathway?
1. The ethanal accepts hydrogen atoms from NADH, becoming reduced to ethanol, catalysed by the enzyme ethanol dehydrogenase.
2. In the process, NADH is reoxidised becoming available to accept more hydrogen atoms from glycolysis, thus allowing glycolysis to continue.
84
Why does yeast only produce a certain concentration of alcohol?
Yeast is a facultative anaerobe. It can live without oxygen, but if oxygen is present it will respire aerobically. However, under anaerobic condition, 15% accumulation of ethanol will kill the yeast cells.
85
What is the lactate fermentation pathway?
Lactate fermentation occurs in mammalian muscle tissue during vigorous activity when the demand for ATP for muscle contraction is high and there is an oxygen deficit
86
State the stages of lactate fermentation.
1. Pyruvate, produced during glycolysis, accepts hydrogen atoms from the NADH, also made during glycolysis, catalysed by the enzyme lactate dehydrogenase.
2. Pyruvate is reduced to lactate and NAD is reoxidised.
3. The reoxidised NAD can now accept more hydrogen atoms from triose phosphate during glycolysis, and glycolysis can continue to produce ATP to sustain muscle contraction for a short period of time.
87
What happens to the lactate after the lactate fermentation pathway?
The lactate produced in the muscle tissue is carried away from the muscles, in the blood, to the liver when more oxygen is available to:
* Convert it to pyruvate, which may enter the Krebs cycle via the link reaction
* Recycle it to glucose and glycogen
88
Why does lactate need to be removed from the muscle tissue?
If lactate was not removed from the muscle tissues, the pH would be lowered which would inhibit the action of many enzymes involved in glycolysis and muscle contraction.
89
How does anaerobic respiration produce ATP?
Neither ethanol fermentation nor lactate fermentation produces ATP, however, because these processes allow glycolysis to continue, the net gain of two molecules of ATP per molecule of glucose is still obtained.
90
How is enough ATP produced in respiration?
Because the glucose is only partly broken down, many more molecules can undergo glycolysis per minute, therefore the overall ATP yield is large.
91
How does the amount of ATP produced in anaerobic respiration compare to that of aerobic respiration?
For each molecule of glucose, the yield of ATP via anaerobic respiration is about 1/15 of that produced during aerobic respiration.
92
How do the mitochondria present in slow and fast twitch muscles compare?
Fast-twitch muscle fibres have very few, if any, mitochondria as they use glycolysis to power their short-duration contractions. They fatigue easily and appear pale in colour due to the lack of electron transport proteins and myoglobin (a protein that stores oxygen in some muscles).
Slow-twitch muscle fibres contain many mitochondria as they aerobically respire to power endurance exercise. They do not fatigue easily and appear darker in colour.
93
Not important - give an example of the difference between slow and fast twitch muscles that we can see.
The breast meat of chickens is pale because they have mainly fast-twitching muscle fibres as they only fly occasionally to escape from a predator; however, the breast meat of ducks and geese is very dark because they have mainly slow-twitching muscle fibres as they fly long distances to migrate.
94
The end :)
Good work.
