respiration

Question 1

where does glycolysis occur?and does it require oxygen

Answer 1

Occurs in the cytosol. Glycolysis occurs in anaerobic and aerobic respiration (doesn’t need O2).

Question 2

describe how glycolysis occur

Answer 2

1. Phosphorylation of glucose to hexose bisphosphate:
   - 2 molecules of ATP are hydrolysed (used), and the
   released phosphoryl groups are added to glucose to form
   hexose bisphosphate. This molecule has phosphate
   groups at C1 an C6.
   - The energy from hydrolysed ATP activates the hexose
   sugar and prevents it being transported out the cell.
2. Splitting each hexose bisphosphate molecule into 2 triose
   phosphate molecules:
   - Each molecule of hexose bisphosphate is split into 2
   triose-phosphate molecules (3C – TP), each with a
   phosphate group attached.
3. Oxidation of triose phosphate to pyruvate.
   This process is anaerobic but is oxidation as it involved removal of
   H atoms from substrate molecules.
   - Dehydrogenase enzymes, aided by 2 NAD coenzymes, remove hydrogen from triose phosphate.
   - The 2 molecules of NAD accept the hydrogen atoms and become reduced NAD.
   - The triose phosphate is converted to pyruvate by a series of enzyme-controlled reactions, this
   releases energy used to produce 4 ATP by substrate-level phosphorylation.

Question 3

whats the net gain in glycolysis

Answer 3

Per molecule of glucose: net gain of 2 ATP (4 made but 2 used to phosphorylate glucose), 2 red NAD, 2
pyruvates produced. The 2 reduced NAD go to the cristae of mitochondria for oxidative phosphorylation.
The 2 pyruvate molecules are actively transported into the mitochondrial matrix for the link reaction (in
aerobic)

Question 4

what and where does the link reaction occur

Answer 4

Occurs in the mitochondrial matrix. Pyruvate produced in glycolysis is actively transported across outer and
inner mitochondrial membranes into the mitochondrial matrix via specific pyruvate-proton symporter – a
transport protein that transports pyruvate and H in same direction

Question 4

what and where does the link reaction occur

Answer 4

Occurs in the mitochondrial matrix. Pyruvate produced in glycolysis is actively transported across outer and
inner mitochondrial membranes into the mitochondrial matrix via specific pyruvate-proton symporter – a
transport protein that transports pyruvate and H in same direction

Question 5

what is pyruvate converted to in the link reaction

Answer 5

Pyruvate is converted to 2C acetyl group (combined with CoA) in link reaction, which reacts in Krebs cycle.
1 Acetyl CoA, 1 red NAD and 1 CO2 produced in reaction. No ATP is produced. Red NAD go to oxidative
phosphorylation.
2 pyruvate produced per glucose in glycolysis, so link reaction happens 2 times per glucose molecule.
2 pyruvate + 2NAD + 2CoA -> 2CO2 + 2 reduced NAD + 2 acetyl CoA

Question 6

describe what happend in the link reaction

Answer 6

1. Pyruvate is decarboxylated (carboxyl group removed) producing CO2 (1C)
   – catalysed by pyruvate dehydrogenase complex
2. Product is dehydrogenated, forming reduced NAD (from NAD), this
   produces acetate (2C) – catalysed by pyruvate dehydrogenase complex.
3. Acetate combines with coenzyme A to form acetyl coenzyme A (CoA).

Question 7

where does the krebs cycle occurs and what does it produce

Answer 7

Also occurs in mitochondrial matrix. It is a series of enzymecatalysed reactions that oxidise the acetate from the link reaction.
Produces 2 CO2, 1 ATP, 3 red NAD and 1 red FAD. Krebs cycle
happens 2 times per glucose molecule.

Question 8

describe what happends in the krebs cycle

Answer 8

1. The acetate from Acetyl CoA from the link reaction combines
   with oxaloacetate (4C) to form citrate – a 6C compound.
   - This is catalysed by citrate synthase.
   - Coenzyme A released and is reused in the link
   reaction.
2. 6C Citrate is decarboxylated and dehydrogenated, producing
   a 5C compound,
   - Decarboxylation produces 1 molecule of CO2
   - Dehydrogenation removes hydrogen producing 1 molecule of reduced NAD.
3. This 5C compound is further decarboxylated and dehydrogenated, producing a 4C compound.
   - A series of decarboxylation and dehydrogenation reactions produce 1 red FAD and 2 red NAD
   and 1 more CO2.
   - Substrate-level phosphorylation takes place, a phosphate ion group combines with ADP,
   forming 1 molecule of ATP.
4. Rearrangement of atoms in a 4C intermediate, followed by a final dehydrogenation reaction,
   regenerates oxaloacetate, so the cycle can continue.

Question 9

where does all the reduce FAD and FAD go

Answer 9

All red NAD and FAD produced in glycolysis, Link
reaction and Krebs cycle go to oxidative
phosphorylation. They carry H atoms to the ETC
on the cristae, where they will be involved in
producing many more ATP molecules.

Question 10

where does the oxidative phosphorylation takes place

Answer 10

Takes place in the inner mitochondrial membrane (cristae). It involves electron carrier proteins, arranged in
ETCs, embedded in the cristae, and chemiosmosis.

Question 11

describe what happends in the oxidative phosphorylation

Answer 11

Hydrogen atoms are released from reduced NAD and reduced FAD (coenzymes oxidised to NAD and
FAD). The H atoms split into protons (H+
) and electrons. The protons go into solution in the matrix.
- The electrons pass along the electron transport chain (in the inner mitochondrial membrane)
between electron carriers.
- Electron carriers get reduced as they accept electrons and oxidised as electron pass to the
next carrier).
- Electrons lose energy at each carrier as they pass along the ETC.
- This energy released by electrons is used by electron carriers to actively pump protons from the
mitochondrial matrix across the inner mitochondrial membrane into the intermembrane space.
Product per 1
glucose
Glycolysis Link reaction
(x2)
Krebs
cycle (x2)
Reduced NAD 2 2 6
Reduced FAD 0 0 2
CO2 0 2 4
ATP 2 (4-2) 0 2
- As protons accumulate in the
intermembrane space, H+ conc in the
intermembrane space increases, forming a
proton gradient (electrochemical gradient).
- This generates a chemiosmotic
potential (/proton motive force).
- Protons cannot easily diffuse through the
lipid bilayer of the mitochondrial
membranes; the inner membrane is
impermeable to protons.
- Protons flow into the matrix (by facilitated diffusion) through channel proteins associated with ATP
synthase enzymes in the inner membrane.
- The flow of protons causes a conformational change in the ATP synthase enzyme allowing
ADP and Pi to combine to form ATP.
- This process is called chemiosmosis. The formation of ATP in this way, in the presence of O2 is
called oxidative phosphorylation.
- In the mitochondrial matrix, oxygen (the final electron acceptor), combines with electrons coming off
the end of the ETC and with protons diffusing through the ATP synthase channel proteins, forming
water:
- 4H+ + 4e- + O2 -> 2H2O

Question 12

why is that the Theoretical yield is rarely achieved, (28 ATP) but the actual yield is closer to 30 or less because

Answer 12

Some ATP is used to actively transport pyruvate into the mitochondrial matrix (between glycolysis
and link reaction).
- Some ATP is used to transport red NAD (made in glycolysis) into mitochondrial matrix.
- Some protons may leak out through outer mitochondrial membrane in oxidative phosphorylation

Question 13

describe what happens to the eukaryotesif anaerobic respiration takes place (oxygen is not present)

Answer 13

If oxygen is absent:
1. O2 cannot act as final electron acceptor at the end of oxidative phosphorylation. Protons diffusing
through channels associated with ATP synthase can’t combine with electrons and O2 to form water.
2. Proton conc increases in matrix and reducing proton gradient across inner mitochondrial membrane.
3. Protons stop diffusing through channels associated with ATP synthase enzymes.
4. Oxidative phosphorylation stops.
5. Reduced NAD and reduced FAD cannot release their H atoms and cannot be reoxidised.
6. Krebs cycle stops, as does the link reaction (as no source of (oxidised) NAD and FAD).
Product per 1
glucose
Glycolysis Link reaction
(x2)
Krebs
cycle (x2)
Reduced NAD 2 2 6
Reduced FAD 0 0 2
CO2 0 2 4
ATP 2 (4-2) 0 2
Glycolysis can take place, but the red NAD generated in the oxidation of TP to pyruvate has to be reoxidised
so glycolysis can continue. Another metabolic pathway must run to reoxidise them as the ETC has stopped.
These processes occur in the cytoplasm.
- Anaerobic respiration consists of glycolysis and one of these pathways

Question 14

how does fungi and plants produce ethanol

Answer 14

1. Each molecule of pyruvate produced in glycolysis is
   decarboxylated (CO2 produced) forming ethanal –
   catalysed by pyruvate decarboxylase.
2. Ethanal accepts hydrogen atoms from reduced NAD
   (from glycolysis), forming ethanol – catalysed by ethanol dehydrogenase.
   - This reoxidises the reduced NAD to NAD so it can be used in glycolysis (to accept H atoms from TP).
   Produces ethanol & CO2 (2 NAD, 2ATP – from glycolysis).

Question 15

how do mammals lactate fermentation

Answer 15

. Pyruvate from glycolysis accepts hydrogen atoms from reduced NAD forming lactate and (reoxidised)
NAD – catalysed by lactate dehydrogenase.
- The reoxidised NAD can accept hydrogen from TP during glycolysis, so glycolysis can continue to
produce enough ATP to sustain muscle contraction for a short period.
Produces lactate (2 NAD, 2ATP – from glycolysis) NO CO2 produced.. Pyruvate from glycolysis accepts hydrogen atoms from reduced NAD forming lactate and (reoxidised)
NAD – catalysed by lactate dehydrogenase.
- The reoxidised NAD can accept hydrogen from TP during glycolysis, so glycolysis can continue to
produce enough ATP to sustain muscle contraction for a short period.
Produces lactate (2 NAD, 2ATP – from glycolysis) NO CO2 produced.

Question 16

name and explain the 3 respiratory substrate

Answer 16

Carbohydrates:
The monosaccharide glucose is the main respiratory substrate. Some mammalian cells (brain/red blood) can
only use glucose. Animals and some bacteria store carbs as glycogen, plants as starch.
Lipids:
Important for many tissues, including muscle tissue. Triglycerides are hydrolysed by lipase to fatty acids and
glycerol. Glycerol is then converted to pyruvate and enter the Krebs cycle via the link reaction.
Fatty acids are long-chain hydrocarbons (carboxylic acids). So, each molecule has many carbons, many
hydrogens and few oxygen atoms. Hydrogen is the source of protons for chemiosmosis in oxidative
phosphorylation, so fats produce more ATP than equivalent mass of carbohydrate.
1. Using the energy from hydrolysis of ATP, each fatty acid is combines with CoA.
2. The fatty acid-CoA complex is transported to the mitochondrial matrix, where it is broken down into
2C acetyl CoA groups which can enter the Krebs cycle. This is called the beta-oxidation pathway

Question 17

whats deamination

Answer 17

Excess amino acids, released after digestion of proteins, are deaminated in the liver. Deamination of an
amino acids involves removal of the amino (-NH2) group forming a keto acid that enters Krebs cycle or Link
reaction as pyruvate or acetyl CoA.

Question 18

what happends when we start having insufficient amount of glucose or lipid

Answer 18

During fasting, starvation or prolonged exercise, when insufficient glucose or lipid are available for
respiration, protein from muscle can be hydrolysed to amino acids which are then respirated.

Question 19

why does the number of hydrogen affects the reactions during chemiosmosis

Answer 19

The greater availability of protons (H+
) for chemiosmosis (oxidative phosphorylation), the more ATP can be
produced. As most ATP is produced by chemiosmosis in oxidative phosphorylation, the greater proportion of
H atoms (most H atoms per unit mass) there are in the respiratory substrate, the more ATP is produced.
- As protons eventually combine with O2 to form water, the more H atoms a substrate has, the more
O2 will be needed for its respiration.

Question 20

which out of the 3 contains the most hydrogen number

Answer 20

Lipids contain the most H atoms per unit mass, followed by proteins then carbs. Lipids produce most
ATP per unit mass, then protein, then carbs.

Question 21

Respiratory quotient:

Answer 21

RQ = volume of CO2 produced/volume of O2 consumed

• (no units)

Question 22

why are lipids and proteins less than one in the RQ values

Answer 22

Lipids and proteins are less than 1 because more O2 is needed to oxidise them.

Question 23

what happens if the RQ value is more than 1

Answer 23

If the RQ value is greater
than 1, this indicates some
anaerobic respiration is
taking place, as more CO2
is being produced than O2
consumed. Plants have
very low RQ as CO2
released is used in
photosynthesis

Question 24

describe how yeast respires when O2 is available and when is not

Answer 24

Yeast is a eukaryotic, single-celled fungus, cells contain mitochondria, and it reproduces asexually by mitosis.
If O2 is available yeast respires aerobically, if O2 is lacking yeast cells respire anaerobically using glycolysis
and alcoholic fermentation.

Question 25

how can we deduce the respiration rate in yeast

Answer 25

Aerobic and anaerobic respiration in yeast produce CO2. Rate of CO2 production indicates respiration rate.

Question 26

describe how we set up an aerobic respiration in yeast

Answer 26

1. Put a known volume of substrate (glucose) and buffer (to keep pH constant) in test tube.
2. Place in water bath at 25 °C – ensure temp is constant, leave for 10mins to stabilise.
3. Add known mass of dried yeast and stir to dissolve in solution, put a bung and gas syringe on tube.
4. Start stopwatch and record gas syringe volume at regular time intervals (for 10mins)
5. Control: dead yeast/no yeast, repeat and calc mean CO2 production rate.

Question 27

how will the practical differ if we are finding the anaerobic respiration rate in yeast

Answer 27

For anaerobic:
Same apparatus, after yeast has dissolved add some liquid paraffin inside the test tube so that it covers the
surface of the solution – stops oxygen getting to the yeast, forces yeast to respire anaerobically.

Question 28

why is the buffer apparatus not suitable for this anaerobic and aerobic respiration in yeast

Answer 28

• This apparatus bad because in aerobic, O2 in tube is consumed, decreasing volume of gas over time.
  Also if all O2 used up in aerobic experiment, anaerobic respiration begins – inaccurate.
  Alternative: without buffer CO2 produced dissolves in medium changing pH – measure rate of change with
  pH meter.

Question 29

describe the Practical Investigating into the factors affecting rate of respiration

Answer 29

Setting up apparatus:
1. Control is same tube with glass beads instead of woodlice/soaked pea seeds.
1. Coloured liquid is placed in the manometer tube, the apparatus is connected with taps open.
2. Place apparatus in water bath for 10 mins.
3. The levels of liquid in manometer tube should be marked and then taps are closed to start
experiment.
4. The change in liquid level is the volume of O2 absorbed. The vol of O2 absorbed per min can be
calculated.
5. Repeat and mean.

Question 30

how does the O2 respirometer affect the respirometer

Answer 30

Organisms that are respiring aerobically absorb O2 and give
out CO2. The CO2 produced is absorbed by soda lime
(sodium hydroxide), so the volume change in the
respirometer is only due to O2 absorption by the
organisms.
If O2 is absorbed from the tube containing organism the air
exerts less pressure on the liquid, so the liquid in the
manometer tube rises up towards that tube. The volume of
O2 absorbed can be calculated by measuring distance liquid
moves (if bore radius known). Syringe depressed to reset
apparatus.

Question 31

how can we decrease chances in human error in the respiriometer

Answer 31

Respirometer can be set up with oxygen sensors to measure oxygen conc in chamber, and data loggers to
automatically record data – reduces chance of human error. Data analysis software can be used to analyse
data.

Question 32

what does the respirometer do

Answer 32

Respirometer used to investigate the effects of variables (temp, pH, substrate concentration or different
respiratory substrates) and aerobic respiration rate. For substrates use suspension of yeast (NaOH has to be
emitted but can measure CO2 evolution to indicate respiration rate).

Question 33

what enzyme can the yeast produce

Answer 33

All enzymes has specificity for a particular substrate. Yeast able to produce isomerase enzymes to hydrolyse
some disaccharides to monosaccharides and monosaccharides to glucose for glycolysis.

Question 34

how can we measure the effects on yeast with the respirometer

Answer 34

The respirometer, without sodium hydroxide can be used to measure evolution of CO2 (or gas syringe). If the
apparatus is set up with different monosaccharide substrates or disaccharides (e.g. maltose, sucrose,
lactose), distance liquid moves can be measured.
Measuring effect of temperature: Make sure organisms are given 10mins to adjust to new temperatures.
Animals should not be put in extreme temps.
Measuring effect of substrate conc: Suspension of yeast with differing concentrations of glucose solution
placed in tubes. Sodium hydroxide is emitted, evolution of CO2 in as specific time period can be measured