respiration

Question 1

stages of aerobic respiration

Answer 1

• glycolysis (glucose –> pyruvate)
• link reaction (acetyl CoA)
• Krebs cycle
• ETC

Question 2

stages of glycolysis (can draw out)

Answer 2

1. phosphorylation
2. lysis
3. phosphorylation
4. dehydrogenation and formation of ATP

Question 3

stage 1 of glycolysis (can draw out)

Answer 3

phosphorylation:
- requires 2 molecules of ATP
- 2 phosphates released from the 2 ATP molecules are attached to a glucose molecule - forming hexose bisphosphate

Question 4

stage 2 of glycolysis (can draw out)

Answer 4

lysis:
- this destabilises the molecule, causing it to split into 2 triose phosphate molecules

Question 5

stage 3 of glycolysis (can draw out)

Answer 5

phosphorylation:
- another phosphate group is added to each triose phosphate - forming 2 triose bisphosphate molecules
- (these phosphate groups come from free inorganic phosphate (Pi) ions present in the cytoplasm)

Question 6

stage 4 of glycolysis (can draw out)

Answer 6

dehydrogenation and formation of ATP:
- the 2 triose bisphosphate molecules are oxidised by the removal of hydrogen atoms (dehydrogenation) to form 2 pyruvate molecules
- NAD coenzymes accept the removed hydrogens - they are reduced, forming 2 reduced NAD molecules (NADH)
- at the same time, 4 ATP molecules are produced using phosphates from the triose bisphosphate molecules

Question 7

why is glycolysis an example of substrate level phosphorylation

Answer 7

• the formation of ATP without the involvement of an ETC
• ATP is formed by the transfer of a phosphate group from a phosphorylated intermediate (triose bisphosphate - in this case) to ADP

Question 8

link reaction (can draw out)

Answer 8

1. pyruvate (3C) is decarboxylated (CO2 removed) to give a 2C product - one C lost
2. CO2 diffuses out of cell as waste product
3. H removed from pyruvate is picked up by NAD, making NADH (reduced NAD) and acetate (acetyl group) (2C)
4. acetate/acetyl group combines with coenzyme A - forming acetyl CoA

• no ATP is produced in this part of the reaction
• this link reaction will happen to each of the pyruvates (occurs twice for every glucose)
• takes place in the mitochondrial matrix

Question 9

krebs cycle (can draw out)

Answer 9

1. acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C) - CoA goes back to link reaction
2. enzyme linked reaction occurs, CO2 is decarboxylated (decarboxylation), 6C –> 5C
3. enzyme linked reaction occurs, CO2 is decarboxylated, 5C –> 4C, NAD dehydronated (dehydrogenation) to NADH - accepts H atom
4. enzyme linked reaction occurs, ADP + Pi –> ATP (substrate level phosphorylation)
5. enzyme linked reaction occurs, FAD dehydronated (dehydrogenation) to FADH2 - accepts 2 H atoms
6. enzyme linked reaction occurs, NAD dehydronated (dehydrogenation) to NADH - accepts H atom
7. enzyme linked reaction occurs, NAD dehydronated (dehydrogenation) to NADH - accepts H atom (citrate has been gradually converted back to oxaloacetate - back to start of cycle)

• cycle happens for every acetyl CoA molecule - occurs twice for every glucose - 2 ATP produced
• takes place in mitochondrial matrix

Question 10

oxidative phosphorylation

Answer 10

2 processes
- ETC (electron transport chain)
- chemiosmosis

• happens across inner mitochondrial membrane

Question 11

ETC (can draw out)

Answer 11

1. NADH and FADH2 get oxidised (into NAD and FAD) and release H atoms
2. H atoms split into protons (H+) and electrons (e-)
3. electrons are passed between 3 electron carries - losing energy at each carrier

Question 12

Chemiosmosis (can draw out)

Answer 12

1. the energy gained from passing the electron between carries is used to pump protons (H+) from the mitochondrial matrix into the intermembranal space
2. this forms an electrochemical gradient

Question 13

oxidative phosphorylation (can draw out)

Answer 13

1. protons (H+) diffuse down the electrochemical gradient back into the matrix via ATPase (ATP synthase
2. this movement drives the synthesis of ATP (ADP + Pi –> ATP)
3. in the mitochondrial matrix at the end of the ETC, the protons (H+) and electrons (e-) and O2 (from breathing in) combine to form H2O

• oxygen is the final electron acceptor + the ETC cannot operate unless oxygen is present
• Total ATP = 38 (32 - 38)

Question 14

how is the matrix of the mitochondria adapted for (aerobic) respiration

Answer 14

• link reaction + krebs cycle occurs here
  contains:
• the required enzymes for these reactions
• Coenzyme NAD molecules
• Oxaloacetate

Question 15

how is the outer membrane of the mitochondria adapted for (aerobic) respiration

Answer 15

• phospholipid composition with protein channels and carries
• allows the passage of molecules into the mitochondrion e.g. pyruvate

Question 16

how is the inner membrane of the mitochondria adapted for (aerobic) respiration

Answer 16

• different structure to the outer membrane
• impermeable to small ions e.g. H+, allowing build up of protons in the intermembrane space
• folded to give large SA
• has many electron carriers and ATP synthase molecules imbedded in it

Question 17

anaerobic respiration

Answer 17

• doesn’t use O2
• involves glycolysis, but not the link reaction, Kreb’s cycle or oxidative phosphorylation –> as oxidative phosphorylation involves oxygen being the final electron acceptor - if not present the electron transport chain ceases

two types:
- alcoholic fermentation
- lactate fermentation
- both happen in cytoplasm and start with glycolysis

Question 18

lactate fermentation (can draw out)

Answer 18

• happens in mammals, in the absence of o2
• takes place in cytoplasm
• 2 ATP produced - from glycolysis

1. glycolysis - pyruvate, NADH and 2 ATP molecules produced
2. NADH transfers hydrogen to pyruvate to make lactate and NAD (NADH oxidised to NAD) (enzyme = lactate dehydrogenase)
3. NAD is then recycled/reused in glycolysis - this is key for glycolysis to produce ATP and allows glycolysis to keep running

Question 19

what does lactate cause in muscles

Answer 19

• pain + fatigue e.g. cramp
• affects the sliding filament theory as it’s an acid and affects calcium –> could mean that vesicle don’t form well, or that we don’t have troponin to move tropomyosin

Question 20

what happens to the lactate

Answer 20

• it’s most likely in cells that are respiring rapidly e.g. muscle cells
• anaerobic respiration can run alongside aerobic respiration if o2 is limited
  1. lactate diffuses into plasma and is transported to the liver cells
  2. these cells convert it back to pyruvate to go into the rest of aerobic respiration later on. some is converted to glycogen to be stored
• this process requires o2 - oxygen debt

Question 21

alcoholic fermentation (can draw
out)

Answer 21

• happens in plant, bacteria and fungi cells e.g. yeast
• takes place in the cytoplasm
• anaerobic respiration in plants –> root tissues waterlogged - can’t get o2
• 2 ATP produced - from glycolysis

1. glycolysis - pyruvate, NADH and 2 ATP molecules produced
2. Co2 is removed from pyruvate to make ethanal (decarboxylation) (enzyme = ethanal dehydrogenase)
3. NADH transfers hydrogen to ethanal to make ethanol and NAD (NADH oxidised to NAD) (enzyme = ethanol dehydrogenase)
4. NAD is then recycled/reused in glycolysis - this is key for glycolysis to produce ATP and allows glycolysis to keep running

Question 22

respiratory substrates

Answer 22

• respiratory substrate = any biological molecule that can be broken down to release energy
• glucose, proteins and lipids can be used a respiratory substrates (some cells such as brain cells and RBCs can only use glucose)
• carbohydrates and protein result in similar energy yields, fats produce over twice as much energy

Question 23

glucose

Answer 23

• theoretical maximum energy yield = 2870 kJ/mol
• it takes 30.6 kJ to produce 1 mol of ATP
• theoretically 1 mol of glucose should produce nearly 94 mol of ATP
• the actual yield is approx 30 mol ATP –> because some is released as heat energy

Question 24

ATP and respiratory substrates

Answer 24

• the majority of ATP is formed during oxidative phosphorylation. this involves hydrogen ions flowing across the ATP synthase channels and combining with electrons and oxygen to form water
• therefore, the more hydrogen atoms there are in a molecule of respiratory substrate, the more ATP will be made
• it also follows that if there are more hydrogen atoms per mole of respiratory substrate, the more oxygen will be needed

Question 25

how are proteins respired

Answer 25

- excess proteins will be deaminated - amino groups removed to produce urea - some will be converted into glycogen or fat - depending on the particular amino acid - some can be converted to pyruvate or acetate, or some enter the Krebs cycle directly, at different stages - the number of hydrogen accepted by NAD per mole is slightly higher than for glucose --> so more ATP can be made per mole of protein

Question 26

how are lipids respired

Answer 26

- made of fatty acids and glycerol - glycerol is converted to glucose + respired - fatty acids are long hydrocarbon chains with carboxylic acid groups - so lots of C and H. these are a large source of hydrogen atoms for oxidative phosphorylation --> so lots of ATP made

Question 27

respiratory quotient

Answer 27

RQ = volume of carbon dioxide released/volume of oxygen consumed - look at the big number (the number they used to balance the equation) in front of the co2 and o2 - Glucose = 1 (6 in front of the o2 and co2 in the aerobic respiration balanced equation. 6/6 = 1) - Protein = 0.9 - Lipids = 0.7

Question 28

how does a respirometer work?

Answer 28

- two boiling tubes are connected by a capillary tube with an air bubble on a scale - one tube contains the object respiring (eg. bread mould) in a gauze basket above soda lime to absorb any CO2 produced from respiration - as O2 is used up and CO2 is absorbed, the air bubble moves towards this boiling tube - the other boiling tube contains a control substance that doesn’t respire - to calculate the rate of respiration, measure how far the air bubble moves in a certain time (eg. 25 min), repeat 3 times and calculate a mean