5.2.2 Respiration Flashcards
Where does glycolysis occur in the cell?
- in the cytoplasm
Which stages of respiration occur in the mitochondria?
- link reaction
- krebs cycle
- oxidative phosphorylation
Is glycolysis an aerobic or anaerobic process?
- anaerobic
- doesn’t need oxygen to take place and it is the first stage
Explain the two stages in glycolysis
Stage 1 Phosphorylation:
- glucose is phosphorylated by adding two phosphates from 2 molecules of ATP
- this creates 1 molecule of hexose bisphosphate and 2 molecules of ADP
- then hexose bisphosphate is split up into 2 molecules of triose phosphate
Stage 2 Oxidation:
- triose phosphate is oxidised, forming 2 molecules of pyruvate
- NAD collects the hydrogen ions, forming 2 reduced NAD
- 4 ATP are produced by 4 ADP and 4 inorganic phosphate molecules
- 2 ATP molecules were used in stage one, so there is a net gain of 2 ATP
Describe the link reaction
- takes place in the mitochondrial matrix
- pyruvate is decarboxylated: one carbon atom is removed from pyruvate in the form of CO2
- NAD is reduced: it collects hydrogen from pyruvate into acetate
- acetate is combined with coenzyme A to form acetyl coenzyme A
- no ATP is produced in this reaction
How many pyruvate molecules are made for every glucose molecule that enter glycolysis
- two pyruvate molecules meaning link reaction and krebs cycle happen twice for every glucose molecule
- two molecules of acetyl CoA go into Krebs cycle
- two molecules of CO2 are released as a waste product of respiration
- two molecules of reduced NAD are formed and go to oxidative phosphorylation
Describe the Krebs Cycle
- involves a series of oxidation-reduction reactions
- takes place in the matrix
- acetyl CoA combines with oxaloacetate to form citrate catalysed by citrate synthase
- coenzyme A goes back to the link reaction to be used again
- the 6C citrate molecule is converted to a 5C molecule
- decarboxylation occurs, where CO2 is removed
- dehydrogenation also occurs, where hydrogen is removed
- the hydrogen is used to produced reduced NAD from NAD
- the 5C molecule is then converted to a 4C molecule
- decarboxylation and dehydrogenation occur, producing one molecule of reduced FAD and two reduced NAD
- ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ADP
- when a phosphate group is directly transferred from one molecule to another it’s called substrate-level phosphorylation
- citrate is now converted to oxaloacetate
where do 1 CoA, oxaloacetate, 2 CO2, 1ATP, 3 reduced NAD, 1 reduced FAD go after the Krebs cycle
- 1 CoA: reused in the next link reaction
- 2 CO2: released as a waste product
- oxaloacetate: regenerated for use in the next Krebs cycle
- 1 ATP: used for energy
- 3 reduced NAD: to oxidative phosphorylation
- 1 reduced FAD: to oxidative phosphorylation
Briefly explain oxidative phosphorylation
- oxidative phosphorylation is the process where energy carried by electrons, from reduced coenzymes (reduced FAD and NAD) is used to make ATP
- oxidative phosphorylation takes place in the inner mitochondrial membrane
Fully describe oxidative phosphorylation
- H atoms are released from reduced NAD and reduced FAD as they’re oxidised to NAD and FAD
- the H atoms split into protons (H+) and electrons
- the electrons move along the electron transport chain (made up of three electron carriers), losing energy at each carrier
- the electron transport chain occurs in the inner mitochondrial membrane
- this energy is used by electron carriers to pump protons from the mitochondrial matrix into the inter membrane space
- the concentration of photons is now higher in the inter membrane space then in the mitochondrial matrix, forming an electrochemical gradient
- protons move down the electrochemical gradient, by chemiosmosis, back into the mitochondrial matrix, via ATP synthesis
- this movement drives the synthesis of ATP from ADP and inorganic phosphate
- in the matrix at the end of the electron transport chain, the protons, electrons and O2 (from blood) combine to form water
- oxygen is said to be the final electron acceptor
How many ATP molecules can be made from one glucose molecule and why?
- 32 molecules
- glycolysis: 2 ATP produced
- glycolysis: 2 reduced NAD = 2 x 2.5 = 5 ATP molecules
- link reaction (x2): 2 reduced NAD = 2x 2.5
- Krebs cycle (x2): 2 ATP = 2
- Krebs cycle (x2): 6 reduced NAD= 6 x 2.5 = 15
- Krebs cycle: 2 reduced FAD = 2 x 1.5 = 3
= 32
Which processes are not used in anaerobic respiration?
- link reaction
- Krebs cycle
- oxidative phosphorylation
What are the two types of anaerobic respiration?
- alcoholic fermentation
- lactate fermentation
Describe lactate fermentation
- occurs in mammals to produce lactate
- reduced NAD (from glycolysis) transfers hydrogen to pyruvate to form lactate and NAD
- NAD can then be reused in glycolysis
Why is glycolysis able to continue without oxygen in anaerobic respiration>
- NAD is regenerated, which glycolysis needs
- so a small amount of ATP is still produced to keep other processes going
How much can the body tolerate lactate?
- our cells can tolerate high lactate for short periods of time
- however, too much lactate is toxic and is removed into the bloodstream
- liver takes up lactate from bloodstream and converts it back into glucose in gluconeogenesis
Describe alcoholic fermentation
- CO2 is removed from pyruvate to form ethanal using the enzyme pyruvate decarboxylase with coenzyme thiamine diphosphate
- reduced NAD from glycolysis transfers hydrogen to ethanal to form ethanol and NAD
- NAD can then be reused in glycolysis
Why does anaerobic respiration release less energy than aerobic respiration?
- anaerobic respiration only include one energy-releasing stage, glycolysis, which only produce 2 ATP per glucose molecule
- other energy-releasing reaction, Krebs and oxidative phosphorylation require oxygen
What is a respiratory substrate?
- any biological molecule that can be broken down in respiration to release energy is a respiratory substrate
What is the order of energy value in different respiratory substrate?
- lipids: 39.4 kJ/g
- proteins: 17
- carbs: 15.8
Why are there different energy values for different respiratory substrate?
- most ATP is made in oxidative phosphorylation, requiring hydrogen atoms from reduced NAD and reduced FAD
- respiratory substrate that contain more H atoms per unit of mass caused more ATP to be produced
What is the respiratory quotient and its classifications
- RQ = volume of CO2 released / volume of O2 consumed
- triglycerides: 0.7
- proteins or amino acids: 0.9
- carbs: 1.0
Why is the RQ helpful?
- 0.7-1.0 is usual RQ for humans, showing fats and carbs are used
- High RQ, means that organism is short of oxygen, and is respiring anaerobically
- plants may have low RQ because CO2 released in respiration is used for photosynthesis so is not measured
Describe a respirometer experiment
- each tube contains potassium hydroxide which absorbs CO2
- control tube has no woodlice
- syringe is used to set fluid to known level
- left for a period of time
- there will be a decrease in the volume of air in test tube due to oxygen consumption by woodlice and CO2 is absorbed
- decrease in volume of air will reduce the pressure in the tube and cause coloured liquid in manometer to move towards test tube
- distance moved by liquid in a given time is measure
- the volume of oxygen can be calculated