5.6 RESPIRATION

Question 1

What is the role of ATP in cells?

Answer 1

Role of ATP in cells:
- ATP can release its energy quickly by hydrolysis of the terminal phosphate. this is catalysed by the enzyme ATPase
- once ATP has released its energy, it becomes ADP. ADP is a low energy molecule that can be recharged by adding a phosphate

Question 2

What is respiration?

Answer 2

Respiration is the transfer of chemical potential energy from nutrient molecules (carbohydrates) into a usable energy form through the synthesis of ATP that can be used for work within an organism.

Question 3

What metabolic processes require energy?

Answer 3

Metabolic processes that require energy:
- maintaining body temperature
- movement
- transporting substances across membranes

Question 4

What is decarboxylation?

Answer 4

Decarboxylation is the removal of carbon dioxide from a molecule.

Question 5

What is dehydrogenation?

Answer 5

Dehydrogenation is the removal of hydrogen atoms from a molecule.

Question 6

What is phosphorylation?

Answer 6

Phosphorylation is the addition of phosphate to a molecule.

Question 7

What is chemiosmosis?

Answer 7

Chemiosmosis is the diffusion of protons from a high to a low concentration across a semi-permeable membrane

Question 8

What is a coenzyme?

Answer 8

A coenzyme is a non-protein organic molecule that is required for an enzyme to function.

Question 9

Summary of aerobic respiration.

Answer 9

Summary of aerobic respiration:
- glycolysis = occurs in cytoplasm, where glucose is broken down into two molecules of pyruvate
- link reaction = occurs in mitochondrial matrix, pyruvate is converted to accurate
- krebs cycle = occurs in mitochondrial matrix, a series of reactions producing co2, ATP and hydrogens
- ETC = occurs in mitochondrial cristae, energy is released as ATP (oxidative phosphorylation)

Question 10

What is glycolysis?

Answer 10

Glycolysis is an anaerobic process that doesn’t require oxygen (so is part of aerobic and anaerobic respiration) and takes place in the cytoplasm = splitting glucose
yields:
- 2 molecules of pyruvate
- 2 ATP
- 2 reduced NAD

• pyruvate is transported into the mitochondrial matrix for respiration

Question 11

What are the purposes of glycolysis?

Answer 11

Purposes of glycolysis:
1. production of cellular energy sources (ATP and reduced NAD) for anaerobic and aerobic respiration
2. production of pyruvate for use in the krebs cycle
3. production of intermediate carbon compounds, which can be removed
for other cellular purposes

Question 12

What is the process of glycolysis?

Answer 12

Glycolysis process:
1. phosphorylation- glucose is phosphorylated using the phosphate groups from 2 ATP molecules to form
hexose biphosphate (which is less stable than glucose)
2. lysis- the unstable molecule splits to form two triode phosphate molecules
glucose (6c) - (ATP) - glucose 6-phosphate - (isomerism to another 6c molecule) - fructose 1-phosphate- (ATP) - hexose biphosphate
3. phosphorylation- another phosphate group is added to each triode phosphate, forming two triose biphosphate molecules (from free inorganic molecules in the cytoplasm, not ATP)
4. dehydrogenation and formation of ATP- 2 hydrogen atoms are removed from each 3 carbon compounds (oxidation) using dehydrogenase enzyme. coenzyme NAD accepts these hydrogens becoming reduced NAD. ATP molecules are formed from substrate-level phosphorylation where the phosphates from triose biphosphate are transferred to ADP. substrate level phosphorylation is where there is no electron transport chain (ETC)

Question 13

What is the matrix of mitochondria?

Answer 13

The matrix of mitochondria is basically the cytoplasm of the mitochondria. It is involved in the krebs cycle and link reactions. It is an aqueous solution, contains enzymes (coenzyme NAD and other enzymes for krebs cycle and link reaction), contains ribosomes and mitochondrial DNA.

Question 14

What is the outer membrane of the mitochondria?

Answer 14

The outer membrane is not involved in respiration. It is smooth, permeable to several small molecules (e.g pyruvate due to protein carriers), separates contents of mitochondrion from cytoplasm.

Question 15

What is the inner membrane of the mitochondria?

Answer 15

The inner membrane is involved during oxidative phosphorylation in respiration. It is folded into cristae, impermeable to most small ions, and has proteins involved in the ETC and ATP synthase enzymes embedded within it.

Question 16

What is the inter membrane space of the mitochondria?

Answer 16

The inter membrane space is involved in oxidative phosphorylation of photosynthesis. It has a low pH due to a high concentration of protons and the small space allows high concentration to build up quickly. The concentration gradient across the inner membrane is formed during oxidative phosphorylation and is essential for ATP synthesis.

Question 17

What is the mitochondrial DNA used for?

Answer 17

Mitochondrial DNA has coded for enzymes required in respiration.

Question 18

How do mitochondria achieve a larger surface area?

Answer 18

Mitochondria achieve a large surface area due to presence of cristae which enables the membrane to hold many ETCs and ATP synthase enzymes. More active cells have larger mitochondria and more tightly packed cristae.

Question 19

What impact does the metabolic activity of a cell have on the number of mitochondria within it?

Answer 19

Depending on cell activity, the number of mitochondria varies. More active cells have larger and more mitochondria. e.g muscle cells have more mitochondria than fat cells.

Question 20

What is the link reaction?

Answer 20

The link reaction links the anaerobic process of glycolysis in the cytoplasm to the aerobic processes inside mitochondria. Pyruvate is actively transporter into the mitochondrial matrix before the link reaction begins.

Question 21

What is oxidative decarboxylation (link reaction)?

Answer 21

Oxidative decarboxylation:
- co2 removed
- hydrogen removed

Question 22

What does coenzyme A do in the link traction?

Answer 22

Coenzyme A bounds the 2 carbon acetyl group forming acetylcoenzyme A (acetylcoA) which delivers the acetyl to the next stage called the krebs cycle.

Question 23

What happens during the link reaction?

Answer 23

During the link reaction, co2 diffuses away to be removed as metabolic waste (or used for photosynthesis if autotrophic). All of the reduced NAD produced from glycolysis and the link reaction is transported to the inner mitochondrial membrane.
Pyruvate (3C) is converted to co2 (1C) and acetylcoenzyme A (2C)

Question 24

What are the coenzymes used during respiration?

Answer 24

Coenzymes:
NAD - works with dehydrogenase enzymes which catalyse the removal of H atoms from substrates. NAD accepts H atoms and passes them to the best hydrogen carrier. exists as NAD+ (NAD)
coenzyme A - used in the link traction. carries ethanoate (acetate) groups made from pyruvate during the link reaction to the krebs cycle
FAD - also works with dehydrogenase enzymes to remove H atoms from substrates during the krebs cycle. each FAD accepts 2 hydrogens to form FADH2

Question 25

What is the krebs cycle?

Answer 25

Krebs cycle:
- takes place in the mitochondrial matrix
- each step is enzyme controlled
- each turn of the krebs cycl uses one acetyl group (acetate) so the cycle must turn twice for every glucose molecule

Question 26

Other than glucose, what other respiratory substrates can enter the krebs cycle?

Answer 26

Other respiratory substrates:
fatty acids = broken down to acetates enter via coA
amino acids = deaminated and changed to pyruvate or acetate

Question 27

What happens during the krebs cycle?

Answer 27

Krebs cycle:
1. acetyl coA delivers an acetyl group to the cycle. the 2c acetyl group combines with 4c oxaloacetate to form 6c citrate
2. the citrate molecule under decarboxylation and dehydrogenation producing one NAD and CO2. a 5c compound is formed
3. the 5c compound undergoes further decarboxylation and dehydrogenation reactions, eventually regenerating oxaloacetate and so the cycle continues. more CO2, two more reduced NADs, and one reduced FAD are produced. ATP is also produced by substrate level phosphorylation

Question 28

What is oxidative phosphorylation?

Answer 28

Oxidative phosphorylation is the last stage of aerobic respiration and occurs in the inner mitochondrial membrane.

Question 29

What does oxidative phosphorylation produce?

Answer 29

Oxidative phosphorylation produces many molecules of ATP and water from oxygen.

Question 30

In the chemiosmotic theory where does energy come from to pump protons across the membrane? (Oxidative phosphorylation)

Answer 30

In the chemiosmotic theory, energy comes from electrons to pump protons across the membrane against their concentration gradient.

Question 31

How to protons re-enter the mitochondrial matrix?

Answer 31

Protons re-enter the matrix by facilitated diffusion in ATP synthase. The energy of protons flowing down their concentration gradient is harnessed, resulting in the phosphorylation of ADP into ATP by ATP synthase.

Question 32

Where do hydrogen atoms come from for oxidative phosphorylation?

Answer 32

For oxidative phosphorylation, hydrogen atoms are donated by reduced NAD and reduced FAD. The hydrogen atoms are then split into protons and electrons.

Question 33

During oxidative phosphorylation, where does the energy come from to move protons across the membrane?

Answer 33

During oxidative phosphorylation, high energy electrons provide energy to move protons across the membrane into the intermembrane space.

Question 34

Why is oxygen needed in oxidative phosphorylation?

Answer 34

Oxidative phosphorylation needs oxygen as oxygen acts as the final electron acceptor and combines with protons and electrons at the end of the ETC to form water.

Question 35

What are the steps of oxidative phosphorylation?

Answer 35

Oxidative phosphorylation:
1. hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD (FADH2) from the krebs cycle
2. hydrogen atoms split into protons (H+ ions) and electrons
3. the high energy electrons enter the electron transport chain and release energy as they move through the ETC
4. the released energy is used to transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space
5. a concentration gradient of protons is established between the intermembrane space and the matrix
6. the protons return to the matrix via facilitated diffusion through the channel protein ATP synthase
7. the movement of protons down their concentration gradient provides energy for ATP synthesis
8. oxygen acts as the final electron acceptor and combines with protons and electrons at the end of the ETC to form water

Question 36

What is the electron transport chain in respiration?

Answer 36

ETC:
- the ETC is made up of a series of membrane proteins/electron carriers - most are organised into large complexes containing cytochromes - the complexes are labelled I-IV across the chain
- they are positioned close together which allows the electrons to pass from carrier to carrier
- reduced NAD donates hydrogen at complex I and reduced FAD donated hydrogen at complex II
- the inner membrane of the mitochondria is impermeable to hydrogen ions so these electron carriers are required to pump the protons across the membrane to establish the concentration gradient

Question 37

What are obligate anaerobes?

Answer 37

Obligate anaerobes cannot survive in the presence of oxygen. e.g clostidium bacteria

Question 38

What are facultative anaerobes?

Answer 38

Facultative anaerobes can use anaerobic or aerobic respiration as needed. e.g yeast

Question 39

What are obligate aerobes?

Answer 39

Obligate aerobes need oxygen to synthesise ATP. individual cells may be able to respire without oxygen at times (e.g muscle) but they need oxygen eventually so the whole organism is considered dependent on oxygen. e.g mammals

Question 40

What happens if there is no oxygen as the final electron acceptor?

Answer 40

If there is no oxygen as the final electron acceptor, electron carriers cannot pass on electrons. So electrons cannot be donated by reduced NAD so reduced NAD cannot be converted back into NAD. So there is no NAD to pick up hydrogen from the krebs cycle and link reaction. Therefore the link reaction, krebs cycle and ETC cannot occur.

Question 41

What are the anaerobic pathways?

Answer 41

Anaerobic pathways:
- all organisms can metabolise glucose anaerobically (without O2) using glycolysis in the cytoplasm
- each pathway needs an electron acceptor (as no O2) to reoxidise the reduced NAD, or glycolysis will stop
= in alcoholic fermentation the electron acceptor is ethanal
= during lactic acid fermentation the electron acceptor is pyruvate itself and the end product is lactic acid

Question 42

What is lactic acid fermentation?

Answer 42

Lactic acid fermentation (fermentation):
- pryruvate is converted into lactate
- pyruvate + reduced NAD = NAD + lactate
- the enzyme involved is lactate dehydrogenase
- lactic acid is toxic and this pathway cannot continue indefinitely
- excess lactic acid lowers pH and causes proteins to denature

Question 43

What is the fate of lactate?

Answer 43

Fate of lactate:
- lactate is eventually taken to the liver, where it is regenerated into pyruvate, then into glucose
- it can then re-enter glycolysis
- this regeneration requires lots of ATP (which is produced by aerobic respiration)
- this regeneration therefore leads to an oxygen debt, where the athletes oxygen consumption continues at high level post-exercise

Question 44

What is alcoholic fermentation?

Answer 44

Alcoholic fermentation:
- yeast is a facultative anaerobe as it can live without oxygen but growth is faster aerobically
- at ethanol levels above 12-15% fermentation is toxic to the yeast cells so alcoholic fermentation cannot be used indefinitely. it needs to be converted to respiratory intermediates and respired aerobically
- the root cells of plants also use fermentation as a pathway when oxygen is unavailable

Question 45

What happens during during alcoholic fermentation?

Answer 45

Alcoholic fermentation:
- pyruvate is decarboxylated (pyruvate decarboxylase) to ethanal
- ethanal becomes ethanol with the addition of H from reduced NAD (ethanol dehydrogenase)
- ethanal is the H acceptor

Question 46

What are respiratory substrates?

Answer 46

Respiratory substrates:
- glucose is not the only respiratory substrate
- lipids and proteins can also be used in respiration
- lipids store and release around twice as much energy as carbohydrates
- proteins release around the same amount of energy as carbohydrates
- alcohol stores and releases more than carbohydrates but less than lipids

carbohydrate = 15.8 kJg-1 (energy value)
lipid = 39.4 kJg-1 (energy value)
protein = 17.0 kJg-1 (energy value)

Question 47

How can the differences in energy values of substrates be explained?

Answer 47

The differences in energy values of substrates can be explained by their molecular composition - specifically how many hydrogen atoms become available when the substrate molecules are broken down

Question 48

Why do lipids release the most energy?

Answer 48

Lipids release more energy than carbohydrates and proteins as they have a longer carbohydrate chain which means more hydrogen is available to be picked up by NAD and FAD and be transported into the membrane and form a chemiosmotic gradient to generate energy as ATP

Question 49

How are respiratory substrates used in respiration?

Answer 49

How are respiratory substrates used in respiration:
glycerol - converted to pyruvate - oxidative decarboxylation - produces an acetyl group - acetyl picked up by coA
fatty acids - beta oxidation cuts long chains into 2c units - this form several acetyl groups - acetyl combines with coA to form acetylcoA. = fatty acids can form up to 50 acetylcoA molecules. this in turn leads to the synthesis of up to 500 ATP
protein - hydrolysed into amino acids - deamination of amino acids - they can then enter the pathway at various points depending on the properties of the amino acid (normally via pyruvate)

Question 50

What is the respiratory quotient?

Answer 50

The respiratory quotient (RQ) is the ratio of CO2 molecules produced to the O2 molecules taken in during respiration.
- experimental data about O2 used and CO2 produced allows us to identify which respiratory substrate is being used based on RQs or different substrates

RQ = CO2 produced / O2 used

carbohydrate = RQ 1.0
lipid = RQ 0.7
protein = RQ 0.9

Question 51

RQ and anaerobic respiration.

Answer 51

RQ and anaerobic respiration:
- depending on the organism anaerobic respiration in cells can be done via lactate or ethanol fermentation
- the RQ cannot be calculated for anaerobic respiration in muscle cells because no oxygen is used and no CO2 is produced during lactate fermentation
- for yeast cells, the RQ tends towards infinity as no oxygen is used whilst CO2 is still being produced

Question 52

What is important when setting up a respirometer?

Answer 52

Important when setting up respirometer:
- once organisms have acclimatised the apparatus should be made airtight to ensure that only gas used within the respirometer is measured
- living organisms always compared to non-living/inert material of the same mass
- living organisms are placed on a metal mesh/cage within the tube

Question 53

In a respirometer, temperature and pressure will affect the volume of air in the apparatus, so how can temperature be controlled?

Answer 53

Temperature can be controlled via a water bath.

Question 54

What will happen to the gas pressure in the tube on the right as the seeds respire? And what effect will this have on the fluid in the U-tube

Answer 54

As seeds respire the pressure with decrease as oxygen is used in respiration and the soda lime will absorb the CO2. The fluid in the U-tube will move to the right.

Question 55

In a respirometer, how is rate of O2 consumption measured?

Answer 55

Rate of O2 consumption is measured by the distance moved by the fluid.

Question 56

How can the respirometer be reset?

Answer 56

The respirometer can be reset by pushing the syringe to add gas back in.

Question 57

In a respirometer why is potassium hydroxide/soda lime used?

Answer 57

Soda lime is used in a respirometer to absorb CO2.

Question 58

What are the importance of coenzymes in respiration?

Answer 58

Importance of coenzymes in respiration:
- NAD takes part in all stages of cellular respiration but FAD only accepts hydrogens in the Krebs Cycle
- NAD accepts one hydrogen and FAD accepts two hydrogens
- reduced NAD is oxidised at the start of the electron transport chain releasing protons and electrons while reduced FAD is oxidised further along the chain
- reduced NAD results in the synthesis of three ATP molecules but reduced FAD results the synthesis of only two ATP molecules