C16 - Cellular Respiration

Question 1

What do all living organisms require a supply of energy from respiration for?

Answer 1

Metabolic reactions

Movement

Homeostasis

Anabolic reactions

Active transport

Chemical activation

Bioluminescence

Secretion

Question 2

How do cells use energy from respiration for movement?

Answer 2

Many ways e.g. Movement of cilia, movement of flagella, movement of chromosomes and muscle contractions.

Question 3

How do cells use energy from respiration for anabolic reactions?

Answer 3

For the synthesis of large, complex molecules from smaller, simpler molecules e.g. Synthesis of polypeptides, complex carbohydrates and nucleic acids.

Question 4

What’s the equation for aerobic respiration?

Answer 4

Glucose + oxygen -> carbon dioxide + water (+ ATP)

Question 5

What are the products of aerobic respiration ?

Answer 5

Carbon dioxide, water and ATP.

Question 6

What is produced during anaerobic respiration?

Answer 6

Lactate (Lactic acid)

Question 7

What are the four stages of respiration?

Answer 7

Glycolysis

Link reaction

Kerbs cycle

Oxidative phosphorylation and Electron transport chain (ETC)

Question 8

What do decarboxylase enzymes do?

Answer 8

They hydrolyse the carboxyl group of a molecule, commonly producing carbon dioxide.

Question 9

What do dehydrogenase enzymes do?

Answer 9

They remove hydrogen atoms from certain molecules and pass them to other molecules e.g. the coenzymes NAD and FAD.

Question 10

What do coenzymes NAD and FAD do?

Answer 10

Transfer hydrogen atoms from one molecule to the next.

By doing so, the coenzymes become reduced the re-oxidised, transferring chemical potential energy in the process.

Question 11

How is ATP used?

Answer 11

Adenosine triphosphate can be hydrolysed to ADP (adenosine diphosphate) and inorganic phosphate (Pi).

It’s hydrolysis is catalysed by the enzyme ATPase.

Energy released from its hydrolysis is used by the cell to drive metabolic reactions in the cell. (And ADP and AMP can be converted back to ATP using the inorganic phosphate groups.

Question 12

What occurs during glycolysis?

Answer 12

Glucose is split into 2 triose pyruvate molecules. ATP is also formed from ADP.
2 ATP molecules are hydrolysed but 4 are formed so there’s a net gain of two.

The first reaction involves the phosphorylation of glucose to form glucose-6-phosphate. This is endergonic meanwhile the hydrolysis of ATP is exergonic.

The reactions are coupled and the combined reaction proceeds spontaneously. Phosphorylation of glucose both prevents it from being able to diffuse out of the cell and also reduces the Ea that will be needed for the next reaction in the pathway.

Question 13

What are the stages of glycolysis?

Answer 13

Stage 1: ATP is converted into ADP, producing a phosphate molecule. This causes a glucose molecule to become phosphorylated, forming glucose phosphate from glucose.

Stage 2: The glucose phosphate molecule is reorganised into its isomer, fructose phosphate.

Stage 3: Another ATP molecule is converted into ADP to produce another phosphate molecule. This causes further phosphorylation of the fructose phosphate to form fructose bisphosphate.

Stage 4: The 6C sugar (fructose bisphosphate) is split into 2 3C sugars (glyceraldehyde 3-phosphate).

Stage 5: More phosphorylation occurs however, this time, the source is inorganic and not ATP. This produces 2 molecules of glycerate 1,3-bisphosphate and 2 pairs of hydrogen atoms are removed.

Stage 6: A phosphate molecule is lost from each of the glycerate 1,3-bisphosphate molecules, producing 2 molecules of ATP from 2 molecules of ADP.
This produces 2 molecules of glycerate 3-phosphate.

Stage 7: A further pair of phosphates are removed, forming two more ATPs (from 2 ADPs). This forms 2 molecules of pyruvate plus 2 H2O molecules.

Question 14

What happens during the link reaction?

Answer 14

The 2 pyruvate molecules formed in glycolysis are passed across the outer and inner mitochondrial membrane via active transport.

The pyruvate becomes decarboxylated (losing a molecule of carbon) and dehydrogenated (losing a pair of hydrogen atoms which are picked up by NAD to form NADH), and the 2 carbon remainder of the pyruvate molecule combines with CoA to form acetyl CoA.

Question 15

What happens to the 2 pyruvate molecules (formed in glycolysis) during the link reaction?

Answer 15

The pyruvate becomes:

Decarboxylated (losing a molecule of carbon)

Dehydrogenated (losing a pair of hydrogen atoms which are picked up by NAD to form NADH)

The 2 carbon remainder of the pyruvate molecule combines with CoA to form acetyl CoA.

Question 16

What happens during the Krebs Cycle

Answer 16

Acetyl CoA (formed in the link reaction) remains in the matrix for the Krebs Cycle.

Acetyl CoA (2C) combines with oxaloacetate (4C) to produce citrate (6C) and reform the CoA.

Decarboxylation and dehydrogenation occur to form a 5C compound (as well as a molecule of CO2 and NADH from NAD)

Further decarboxylation and dehydrogenation forms another molecule of NADH and CO2 plus a 4C compound.

Dehydrogenation then froms another 4C compound and FADH2.

Dehydrogenation then reforms the oxaloacetate molecule and NADH.

Question 17

What does ETC stand for?

Where does it occur?

Answer 17

Electron transfer chain.

Inner membrane (cristae)

Question 18

What occurs during ETC?

Answer 18

NADH (produced in the matrix during Krebs cycle) is oxidised by the first protein, ‘NADH dehydrogenase’ (an electron carrier).
This forms a proton, NAD and 2 electrons (which bind to the protein).

The e- are then passed between ETC proteins via redox reactions. (As they move they lose energy).
Some energy is used to pump H+ ions from the matrix into the intermembrane space. The rest is lost as heat.

Since the membrane is impermeable to H+ ions, a concentration gradient forms.

H+ ions move down their conc’ gradient into the matrix using protein channels. These are associated with the enzyme ATP Synthase, which phosphorylates 1 ADP for each H+ ion passing through it.

The final protein, ‘cytochrome oxidase’ donates an electron pair to an oxygen atom. This is the final proton and electron acceptor as it binds with the H+ ions in the matrix to form water.

Question 19

What’s chemiosmosis?

Answer 19

The movement of ions across a semipermeable membrane, down their electrochemical gradient.

An example of this would be the generation of adenosine triphosphate (ATP) by the movement of hydrogen ions across a membrane during cellular respiration or photosynthesis.

Question 20

What occurs during chemiosmosis?

Answer 20

Proton pumping builds up a high concentration of protons in the space between inner and outer membranes.

This produces a concentration gradient and electrical gradient (due to the charge of protons).

Therefore, protons flow down an electrochemical gradient through ATP synthase molecules.

This releases energy that’s used by ATP synthase to phosphorylate ADP.

Question 21

What occurs to aerobic respiration in the absence of oxygen?

Answer 21

ETC cannot occur as there’s no final electron acceptor.

This causes a build up of NADH. NAD isn’t recycled so Krebs cannot continue. This then means no CoA is recycled for the link reaction so there’s a build up of pyruvate.

Question 22

What occurs during anaerobic respiration in muscle cells?

Answer 22

Cells use pyruvate as an alternative hydrogen acceptor. This allows NADH to be reoxidised to NAD so glycolysis can continue.

This allows a small amount of ATP to be produced via substrate level phosphorylation.

Pyruvate is converted to lactate.

Question 23

What type of phosphorylation occurs in anaerobic respiration?

Answer 23

Substrate level phosphorylation.

Question 24

What occurs during anaerobic respiration due to lactate build up?

Answer 24

Build up of lactate can cause inhibition of glycolysis as (being acid) it can cause a change in pH so enzymes denature.

It can also cause cramp and fatigue (lactic acidosis).

Once O2 is available again, its oxidised back to pyruvate and NADH

Question 25

What is anaerobic respiration in yeast called?

Answer 25

Fermentation

Question 26

What occurs during fermentation? (Anaerobic respiration in yeast)

Answer 26

Pyruvate is decarboxylates in the cytoplasm and converted into ethanal and CO2.

The ethanal is then used as the hydrogen acceptor to form ethanol, allowing NADH to convert back to NAD.

If ethanol builds up, it can become toxic to yeast and can’t be broken down by yeast cells.

Question 27

How much ATP is produced in aerobic and anaerobic respiration?

Answer 27

Aerobic: 32

Anaerobic: 2

Question 28

What happens during respiration of lipids?

Answer 28

They’re hydrolysed to glycerol and fatty acids.

The glycerol molecules are then phosphorylated into glyceraldehyde phosphate and broken down in glycolysis.

3 fatty acids are released from the hydrolysis of each triglyceride are broken down in the matrix of the mitochondria into 2 carbon fragments via beta oxidation, while NAD and FAD are reduced.
They then combine with CoA forming acetyl CoA, which can enter the Krebs cycle.

Question 29

What happens with the respiration of proteins? (amino acids)

Answer 29

Proteins are hydrolysed into constituent amino acids.

They’re then deaminated in the liver (lose an amine group).

The remaining part of the amino acid enters the respiratory pathway based on the number of C atoms.

Question 30

What’s gluconeogenesis?

Answer 30

Amino acids that will convert into pyruvate or components of the Krebs cycle are known as glycogen in amino acids and can be converted into glucose.

This is called gluconeogenesis.

Question 31

What does RQ stand for and how is it calculated?

Answer 31

Respiratory quotient

RQ = CO2 / O2
CO2 and O2 measured in volume or moles

Question 32

What is the respiratory quotient?

Answer 32

The ratio of CO2 given off to oxygen used up during respiration in a given time period.

RQ = CO2 / O2
(CO2 and O2 measured in volume or moles)

Question 33

What do the values of RQ mean about the type of respiration?

Answer 33

Above 1 - anaerobic respiration

1 - respiration by carbohydrates/glucose

0. 8 - proteins
1. 7 - lipids

Question 34

What device is used to measure the rate of respiration of a living organism by measuring the rate of exchange of oxygen and CO2?

Answer 34

A respirometer.

Question 35

What does a respirometer consist of?

Answer 35

Simple: a graduated pipette is attached via a bung to the respirometer chamber. A small amount of coloured fluid is inserted into the tip of the pipette.
The starting point of the meniscus and its position every few monitors is then recorded to identify O2 uptake.

OR

Double chamber respirometer: In tube A, the organism being tested is placed with soda lime (which absorbs excess CO2). A bung is placed on top which is attached to a screw-clip and manometer.

Test tube B is filled with water and a bung is placed on top which is connected to a manometer and three-way clip attached to a syringe.

The manometer links between both test tubes and contains (index) fluid.
The distance the fluid moves in a time period shows rate of O2 consumption.

Question 36

Outline the role of coenzymes in aerobic respiration:

Answer 36

NAD / FAD receive electrons (H+) and are reduced.

They’re then reoxidised during ETC to produce ATP via oxidative phosphorylation.

Question 37

Give a brief outline of ETC / oxidative phosphorylation:

Answer 37

The hydrogen from the respiratory reactions is split to release electrons.
These pass through carriers and generate ATP. The hydrogen then reforms and is combined with oxygen to release water.

Question 38

Why does the Krebs cycle continue even if glycolysis stops?

Answer 38

Acetyl CoA can still be formed from other substances and respiration of lipids and amino acids can also occur.

Question 39

What happens to pyruvic acid under anaerobic conditions?

Answer 39

NADH is oxidised to form NAD and H.

Pyruvate is converted into ethanal and CO2 which becomes reduced to form ethanol.

Question 40

Why does lactate accumulate in the body of a person after vigorous exercise?

Answer 40

Oxygen demand is greater than oxygen supply so ETC is inhibited. This means NADH cannot be reoxidised to lactate is produced which changes NADH to NAD.

Question 41

Why does anaerobic respiration produce much less ATP than aerobic respiration?

Answer 41

Oxygen is necessary within ETC as the final electron acceptor.

Without oxygen, there will be no regeneration of coenzymes, NAD and FAD.

Thus Krebs cycle stops however Krebs and ETC provide the most ATP within aerobic respiration.

Question 42

Why is it necessary to phosphorylate glucose using ATP? (2)

Answer 42

Glucose must be activated before it can be metabolised.

Using ATP gives glucose the energy necessary to do so.

Question 43

What is the importance of the dehydrogenation step in the (aerobic) respiration pathway? (2)

Answer 43

To produce NADH, which can be used in ETC so that ATP is synthesised.

Question 44

Why is deamination necessary within respiration pathways?

Answer 44

To remove amine groups as the amine groups are toxic.

Question 45

1) Identify a product of aerobic and anaerobic respiration in yeast cells:
2) Identify a product of anaerobic respiration in yeast cells that’s not produced in aerobic:

Answer 45

1) CO2

2) Ethanol

Question 46

Why can the anaerobic pathway be reversed in animal cells but not in yeast cells?

Answer 46

In animal cells, pyruvate is converted into lactate only. No atoms are lost therefore it can be reversed.

In yeast, pyruvate forms CO2 and ethanol. It can’t be reversed as the CO2 is lost.

Question 47

How does flow cytometry compare to haemocytometry when counting the number of yeast cells in a population?

Answer 47

A haemocytometer is:

Cheaper
Requires less training 
Easier to count 
Quicker
Mistakes are magnified 
Counting is manual
Can differentiate between dead and living cells (flow cytometry only detects dead)

Question 48

What are the advantages of using ATP to provide energy for biological processes?

Answer 48

Immediate energy source

Small molecule

Soluble

Easily regenerated

Question 49

What device is used to measure breathing rate and volume?

Answer 49

A Spirometer

Question 50

Why does the incomplete breakdown of glucose in anaerobic respiration produce less ATP than aerobic respiration?

Answer 50

Glucose is converted into pyruvate and 2 molecules of ATP are produced; by substrate level phosphorylation.

Oxygen is not available as a final electron acceptor, so pyruvate/ethanal regenerates NAD for glycolysis.

ETC / chemiosmosis doesn’t occur.

Question 51

How is ATP made in the cytoplasm of yeast and human cells from the metabolism of a 3C compound?

Answer 51

Triose phosphate is oxidised into pyruvate

ATP is produced by substrate level phosphorylation

Question 52

What’s the importance of the intermembrane space for mitochondrial function?

Answer 52

It establishes a proton gradient.

Question 53

Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum?

Answer 53

Some ATP is used to transport pyruvate (into mitochondria)

Some ATP is used to transport protons into mitochondria

Energy released in ETC may be lost as heat

Not all protons are used to generate ATP

Not all the NADH is used to feed into the ETC

Question 54

Where does glycolysis take place?

Answer 54

In the cell cytoplasm

Question 55

Where does the link reaction take place?

Answer 55

In the mitochondrial matrix

Question 56

Where does the Krebs cycle take place?

Answer 56

In the mitochondrial matrix

Question 57

Where does ETC / oxidative phosphorylation take place?

Answer 57

In the inner membrane

Question 58

How does the way ATP is produced in glycolysis differ to how ATP is produced using NADH and FADH in the inner mitochondrial membrane?

Answer 58

In glycolysis, ATP is produced by substrate level phosphorylation. ADP gains an inorganic Pi from a compound in glycolysis or Krebs cycle to form ATP.

At the inner mitochondrial membrane, ATP is produced by oxidative phosphorylation and chemiosmosis. Protons are pumped and pass through ATP synthase to produce ATP.

Question 59

In what (different) locations of yeast cells does the carboxylation of pyruvate take place?

Answer 59

Decarboxylation takes place in the cytoplasm, as part of anaerobic respiration (to produce ethanol).

It also occurs within the mitochondria, involved in formation of acetyl CoA in the link reaction.