Respiration✅ Flashcards
Describe glycolysis
Occurs in cytoplasm of cell
1.glucose is phosphorylated to hexose bisphodphate by two ATP molecules, this destabilises glucose molecule so they can’t leave and easier to breakdown
- Hexose bisphodphate splits into 2 molecules of triose phosphate
- TP is phosphorylated (by free inorganic phosphate rather then ATP)
- The 2 TP molecules lose H atoms (dehydrogenation, forming reduced NAD) and phosphate (enabling ATP formation) to produce two molecules of pyruvate
What is the overall net gain of ATP in glycolysis
+2
1 glucose, 2 pyruvate, 4 ATP, 2 reduced NAD, 2 ATP used
Explain why one glucose molecule yields two molecules of ATP from glycolysis (3 marks)
2 ATP used to convert glucose to hexose 1,6-bisphodphate
4 ATP produced in converting TP to pyruvate
Net of 2 ATP produced
Describe the role of phosphorylation in glycolysis (4 marks)
ATP phosphorylates glucose
To prepare it for subsequent reactions/ to be broken down
TP is phosphorylated
By inorganic phosphate
ADP is phosphorylated when TP is converted to pyruvate
Describe the link reaction
Occurs in matrix of mitochondria, requires pyruvate to move from cytoplasm into mitochondria through active transport
Pyruvate loses hydrogen (degydrogenation), which produces reduced NAD
Pyruvate loses carbon (decarboxylation), which produces CO2 and a 2-C group called acetyl
Acetyl group binds to coenzyme A, which produces Acetyl coenzyme A (Acetyl coA)
What is the role of coenzyme A in the link reaction
Deliver the Acetyl group to the Krebs cycle
Pyruvate + coenzyme A——-> Acetyl coenzyme A + CO2
(NAD—-> reduced NAD)
What is used and produced in the link reaction
Used: 2 pyruvate molecules
Produced: 2CO2, 2 reduced NAD, 2 Acetyl coA
Describe the structure of a mitochondrion
Outer mitochondrial membrane (separates contents of mitochondrion from rest of the cell)
Inner mitochondrial membrane (contains ETC chains and ATP synthase)
Cristae (projections of inner membrane which increase SA available for oxidative phosphorylation)
Matrix (contains enzymes for Krebs cycle and link reaction and mitochondrial DNA)
Inter membrane space (proteins pumped into space by ETC, the space is small so concentration builds up quickly)
Describe what happens to pyruvate after it has been produced in glycolysis (4 marks)
Enters mitochondria
(Through) active transport
Converted to Acetyl groups
Decarboxylated
Dehydrogenated
Explain what happens to CO2 produced by link reaction in plant species (2 marks)
Leaves the plant through stomata
Used in photosynthesis
Suggest why pyruvate is transported into mitochondria after it is produced in glycolysis (2 marks)
Subsequent stages of aerobic respiration take place in mitochondria
Enzymes in Krebs cycle are located in mitochondrial matrix
ETC are located on inner mitochondrial membrane
Describe the Krebs cycle
- Acetyl CoA delivers an acetyl group
- Acetyl (2C) reacts with oxaloacetate (4C) to produce citrate (6C)
- Citrate undergoes dehydrogenation forming reduced NAD and decarboxylation forming CO2. This results in a 5C being produced
- The 5C compound is decarboxylated and dehydrogenated further, regenerating oxaloacetate, which is free to react with another Acetyl CoA
What is being used and produced in the Krebs cycle
Used: 2 Acetyl-CoA
Produced:
4CO2,
6 reduced NAD (which are used in ETC)
2 reduced FAD (which are used in ETC)
2 ATP (through substrate level phosphorylation)
How many original 6C atoms in a glucose molecule are released as CO2 during the Krebs cycle (1 mark)
4
Suggest why oxaloacetate is present in cells at very low concentrations (2 marks)
/idea/ of rapid turnover/ constantly reacting
Reacts with Acetyl CoA to form citrate
What is the purpose of the electron transport chain
Located in inner mitochondrial membrane
Chain uses energy from electrons to pump H+ ions into inter membrane space. A proton gradient is established, which enables chemiosmosis to occur through ATP synthase
Describe what happens in the electron transport chain
1.High energy electrons are passed from NADH and FADH2 to electron Carriers in ETC
- Electrons are passed between carriers in a series of redox reactions
- Energy is released from each reaction
- The energy is used to pump H+ ions from matrix into inter membrane space
- H+ ions diffuse through ATP synthase (chemiosmosis) back into matrix, which produce ATP
- H+ ions and electrons react with O2 to produce water
What many ATP are produced per molecule for each stage of respiration
Glycolysis:
Substrate level phosphorylation-2
2 NADH- 3-5
Link reaction:
2NADH-5
Krebs cycle:
Substrate level phosphorylation-2
6NADH-15
2FADH2-3
Total-32
Explain how structure of mitochondrial Cristae maintains a high rate of oxidative phosphorylation (2 marks)
Cristae are folds of inner membrane
Which increase SA available for oxidative phosphorylation
Explain why oxygen is called the final
Electron acceptor in respiration (3 marks)
Oxygen accepts electrons that have passed through the ETC
Forming water
When combined with H+ ions
The theoretical max yield of ATP from aerobic respiration may not always be achieved, suggest why (2 marks)
Some ATP is used for active transport of pyruvate (from the cytoplasm)
ETC is inefficient/ some energy is released as heat (and is not used to transport H+ ions)
Some reduced coenzymes may be used in other processes (not the ETC)
How does anaerobic generate ATP
Generates small amounts of ATP through substrate-level phosphorylation in glycolysis.
Link reaction, Krebs cycle and ETC stop working in absence of oxygen
Define fermentation and what is its function
Breakdown of pyruvate into lactate or ethanol
To oxidize NADH, thereby generating NAD. This enables glycolysis to continue, glycolysis stops without fermentation because supplies of NAD would run out and TP would no longer be converted to pyruvate
State the equation of fermentation in animals
Pyruvate + reduced NAD—-> lactate + NAD
State the equation of fermentation in yeast and in plants
Pyruvat—-> ethanal + CO2
Explain why mammals use anaerobic respiration only for short periods of time (2 marks)
Relatively small amounts of ATP are generated
Insufficient chemical energy to sustain the functions of mammalian bodies
Suggest why the absence of oxygen stops
A) chemiosmosis and ETC (2 marks)
B) Krebs cycle (2 marks)
A: idea of no terminal electron acceptor to accept electrons from the final electron carrier protein complex
Proton gradient is disrupted because O2 is not present to remove H+ ions diffusing through ATP synthase
B: NAD is not regenerated because the ETC stops
Reactions needed to convert citrate back to oxaloacetate cannot occur
Which stage of respiration does amino acids enter and what molecules it It used to form
Link reaction or Krebs cycle
Depends on amino acid EG. Glycine—->pyruvate
Isoleucine—-> Acetyl CoA
Aspartate—-> oxaloacetate
What stage does triglycerides (glycerol and fatty acids) enter respiration and what molecule is it used to form
Glycerol: glycolysis, triose phosphate
Fatty acids: Krebs cycle, Acetyl CoA
What stage does lactate enter respiration and what molecules are formed from it
Link reaction
Pyruvate
What must be removed from all amino acids before they can be metabolized as respiratory substrates? State the name of this process (2 marks)
Amine group
Deamination
Some respiratory molecules are easier than others to form from an amino acid. Suggest the likely respiratory molecules formed from following amino acids. Explain your answer
A: asparagine (C4H8N2O3)
B: alanine (C3H7NO2)
A: oxaloacetate
Both have 4C
B: pyruvate
Both have 3C atoms
