Module 5: Respiration Flashcards
Define respiration
The release of chemical potential energy from organic molecules inside mitochondria.
What does ATP stand for?
Adenosine triphosphate
Name 4 uses of ATP
> Active Transport > Endocytosis > Exocytosis > Synthesis of large molecules (collagen, enzymes, antibodies) > DNA replication > Cell division > Movement > Activation of chemicals
Describe the structure of ATP
- ATP is a phosphorylated nucleotide (similar to the structure of DNA and RNA).
- ATP can’t leave the cell where it is made.
- When 1 phosphate group is removed from each molecule in one mole of ATP, 30.5 kJ of energy is released.
- This is a hydrolysis reaction (requires water), and is catalysed by enzymes called ATPases.
Describe ATP role as an energy currency
• ATP is useful as an energy carrier (currency) because it cycles.
• Respiration provides the energy required for the condensation reaction that converts ADP ‐‐> ATP
• i.e. For each 30.5 kJ mol‐1 of energy that is released by
hydrolysis of ATP, the same energy must also be input from respiration to reform the ATP.
• The energy for condensation reaction comes from the
chemical energy stored in glucose.
Describe the role of a coenzyme in respiration
• Enzymes needed to assist other enzymes in a reduction or oxidation reactions (because they can pick up and lose hydrogen atoms)
• Co‐enzymes used in respiration:
- NAD Nicotinamide
- Adenine Dinucleotide
- CoA Coenzyme A
- FAD Flavine Adenine Dinucleotide
• Co‐enzymes that have been reduced are used in the final stage of respiration (oxidative phosphorylation) which produces a lot of ATP.
What are the 4 stages of respiration?
1) Glycolysis
2) Link reaction
3) Krebs cycle
4) Oxidative phosphorylation
What is glycolysis?
The first stage in respiration in which pyruvate is produced.
Where does glycolysis take place?
Cytoplasm
How many stages are in glycolysis?
There are 3 main stages that involve a sequence of 10 chemical reactions
Describe the 3 main stages of glycolysis
1) Glucose is phosphorylated to hexose bisphosphate.
2) Hexose bisphosphate is split into 2 x triose phosphate.
3) Oxidation of TP to pyruvate.
Describe what happens when glucose is phosphorylated to hexose bisphosphate
- Glucose is a stable compound.
- Two molecules of ATP are hydrolysed ‐ what will this produce?
- Each phosphate group is added to glucose (on 1C and 6C) to form hexose bisphosphate.
- What is it called with only one phosphate group added?
- The energy released from the hydrolysed ATP activates the hexose sugar to prevent it being transported out of the cell.
Describe what happens when hexose bisphosphate is split into triose phosphate
Each molecule of hexose bisphosphate is split into 2x 3C molecules called triose phosphate.
Describe what happens when TP is oxidised to Pyruvate
- Dehydrogenase enzymes (aided by NAD) remove hydrogens from triose phosphate (oxidation, but still an anerarobic process)
- This produces two molecules of pyruvate
- 2x NAD accept the hydrogen atoms and are reduced to NADH
- Two molecules of NAD are reduced for every molecule of glucose
- 4 ATP produced for every 2 triose phosphate molecules ‐ what is the net gain?
Describe the possible fate of the pyruvate molecules at the end of glycolysis
- actively transported into mitochondria for link reaction
(aerobic conditions) - converted into lactate (anaerobic conditions)
- converted into ethanol (anaerobic conditions)
Describe the key structural features of a mitochondria
Outer membrane:
• It contains protein channels or carriers to allow pyruvate to pass through.
Inner membrane:
• Has a different membrane structure and is much less
permeable to small ions (e.g. hydrogen ions).
• Folded into cristae to give a large surface area.
• Contains electron carriers and ATP synthase enzymes.
Mitochondrial matrix: • This is where the link reaction and the Krebs cycle take place • It contains; > Enzymes > Molecules of coenzyme NAD > Oxaloacetate (4C compound in the link reaction) > Mitochondrial DNA > Mitochondrial ribosomes
Describe the steps in the link reaction
Pyruvate is transported across the mitochondrial envelope using a transport protein called the pyruvate‐H+ symport.
1. Pyruvate is decarboxylated (carboxyl group removed)
This is the cause of some CO2 production.
2. It is also dehydrogenated (H atoms removed) to produce an acetyl group.
3. These reactions are catalysed by a multi‐enzyme complex called pyruvate dehydrogenase.
4. The acetyl group combines with coenzyme A to become acetyl CoA.
5. The coenzyme NAD becomes reduced.
How would you summarise the link reaction?
2 pyruvate + 2 NAD + 2 CoA –> 2 Acetyl CoA + 2 NADH + 2 CO2
What is the Krebs cycle?
The Krebs Cycle takes place in the mitochondrial matrix, this is the same as the link reaction.
The Krebs cycle is a series of enzyme controlled reactions that produces 6x reduced NAD, 2x Reduced FAD, 4x Carbon Dioxide, 2x ATP 2x CoA’s.
FAD & NAD are responsible for carrying H atoms to the electron transport chain on the cristae of the mitochondria where oxidative phosphorylation takes place, the final stage of aerobic respiration.
For every molecule of glucose there are 2 turns of the Krebs Cycle.
What are the stages of the Krebs cycle?
1) Acetyl combines with oxaloacetate to form a citrate molecule (6C) recycling CoA back to the link reaction.
2) Citrate (6C) is decarboxylated (C Removed) and dehydrogenated (H removed) to form a 5C compound. CO2 and reduced NAD are produced.
3) The 5C compound is decarboxylated (C Removed) and
Dehydrogenated (H Removed) to produce a 4C compound. CO2 and reduced NAD are produced.
4) Substrate level phosphorylation occurs between the 4C compound and Coenzyme A producing 1x ATP.
5) The 4C compound is dehydrogenated (H removed) producing a new 4C compound and reducing FAD.
6) The new 4C compound is rearranged by an isomerase, further dehydrogenation occurs reducing NAD to regenerate a molecule of oxaloacetate.
Describe the process of oxidative phosphorylation
Oxidative phosphorylation takes place in the mitochondria across the inner membrane. The cristae provides a large surface area for electron carrier proteins and ATP synthase.
summary:
- NADH & FADH are reoxidised.
- H atoms split into H+ & e-.
- H+ released into matrix.
- NADH binds to complex I
- Releases H atom as H+ & e-
- NADH oxidsed to NAD
- A total of 10H+ can be pumped from matrix to intermembrane space using energy from e- passing along the electron transport chain.
- FADH binds to complex II
- Releases H atom as H+ & e-
- FADH oxidsed to FAD
- A total of 6H+ can be pumped from matrix to intermembrane space using energy from e- passing along the electron transport chain.
Electrons from H atoms pass along the electron carriers. As the electrons pass along the chain some of their energy is used to pump protons into the intermembrane space. Oxygen is the final electron acceptor.
4H+ + 4e- + O2 –> 2H2O
- Protons build up in the intermembrane space creating a proton gradient this is due to the outer membrane low permeability to H+.
- This generates a chemiosmotic potential also known as a proton motive force (pmf).
What is chemiosmosis?
The flow of protons down their concentration gradient across a membrane through a channel associated with ATP synthase.
How much ATP is produced from 1 glucose molecule in aerobic respiration?
During aerobic respiration:
2 x FADH
10 x NADH are produced.
1 Molecule of NADH produces 2.5 ATP.
1 Molecule of FADH produces 1.5 ATP.
Therefore, 32 ATP’s per glucose is a theoretical yield.
- Some ATP is used to transport pyruvate into the mitochondria as it is produced in the cytoplasm during glycolysis.
- Some ATP is used to transport NADH into the mitochondria.
- Some protons may leak out from the outer membrane of the mitochondria reducing the amount of H+ which can move through ATP synthase.
What stage of respiration occurs under anaerobic conditions?
Glycolysis
Why can’t oxidative phosphorylation, krebs cycle and link reaction not occur without oxygen?
If no Oxygen is present it cannot act as the final electron acceptor in oxidative phosphorylation.
Therefore electrons do not pass don’t pass down the ETC so H+ build up in the matrix of the mitochondria reducing the H+ gradient.
Therefore NADH & FADH cannot release their H atoms so do not get reoxidised back to NAD and FAD so cannot return to the Krebs cycle. This causes the link reaction to also stop.
What are the two pathways pyruvate can take
1) The ethanol fermentation pathway (fungi, plants)
2) The lactate fermentation pathway (animals)
Desrcibe the ethanol fermentation pathway
1) Decarboxylation of pyruvate (pyruvate decarboxylase)
2) Reduction of ethanal to ethanol (ethanol dehydrogenase)
3) Reduced NAD reoxidised to NAD (accepts 2 hydrogens)
Describe the lactate fermentation pathway
1) pyruvate is reduced to lactate (lactate dehydrogenase)
2) Reduced NAD is reoxidised to NAD (accepts 2 hydrogens)
When does the lactate fermentation pathway occur?
Occurs in animals during strenuous activity, when ATP demand is high and there is an oxygen deficit.
Where does ethanol and lactate fermentation occur?
Cytoplasm
Explain why ATP yield is lower in anaerobic conditions than in aerobic conditions.
Although alcohol or lactate fermentation produce no ATP they do allow the process of glycolysis to continue by reoxidising NADH.
Glycolysis produces 2 molecules of ATP per glucose.
Whereas aerobic respiration produces 32 molecules of ATP per glucose.
If glucose is not present, what other respiratory substances can be respired to produce ATP?
Other carbohydrates - Glycogen, Starch, Fructose, Galactose
If glucose is not present, what other respiratory substances can be respired to produce ATP?
1) Other carbohydrates - Glycogen, Starch, Fructose, Galactose
2) Lipids
3) Protein
Describe how each respiratory substrate enters the respiration pathway
Carbohydrates:
Glycogen can be easily hydrolysed to produce molecules of glucose.
Lipids:
Lipids can be hydrolysed to fatty acids and glycerol.
Glycerol can be converted into TP (glycolysis).
Fatty acids contain many H atoms so are a good source of H+ & e- for oxidative phosphorylation.
Protein:
Amino Acids in excess following digestion are deaminated in the liver. (Removal of the amine group).
The rest of the amino acid enters respiration as either pyruvate, acetyl CoA, or as oxaloacetate in the Krebs cycle. During starvation protein from muscles can be hydrolysed to AA for respiration.
• Below are 3 respiratory substrates and their energy value
> Glucose 15.8kJg-1
> Lipid 39.4kJg-1
> Protein 17.0kJg -1
The more hydrogen atoms there are in the structure of a molecule, the greater the energy value.
Describe beta oxidation
Fatty acids combine with CoA, this requires ATP. The combined fatty acid and CoA can then enter the matrix from the cytoplasm.
Fatty acids, such as Palmitic Acid is broken down into 2C Acetyl CoA molecules this produces 1x NADH & 1x FADH.
CoA is released and acetyl group can enter the Krebs cycle.
8 turns of the krebs cycle will happen using Palmitic Acid
8 turns = 8 x 3 NADH + 8 x 1 FADH
= 24 NADH + 8 FADH
= 60 ATP + 12 ATP + 8 ATP (8 turns of krebs cycle)
= 80 ATP
+28 1ATP = 27
80+27 = 107 ATP
Explain the purpose of the respiratory quotient
The respiratory quotient (RQ) is the ratio of the volumes of oxygen absorbed and carbon dioxide given off in respiration, it can indicate which respiratory substrate is being respired.
RQ = Volume of carbon dioxide given off
Volume of oxygen taken in
If the RQ value is greater than 1 it indicates anaerobic respiration must be taking place as more CO2 is produced than O2 used.
Describe how to use a respirometer
1) Place equal volumes of KOH in two boiling tubes.
2) Place a gauze basket above the solution in each test tube.
3) Place woodlice in one tube and glass beads in another.
4) Connect a manometer into both tubes.
5) Close the screw clip
6) Use a syringe to make the fluid in the manometer level.
7) Note the manometer fluid level and start a stop clock.
8) Read off the manometer fluid level at regular intervals.
