3.1 Respiration

Question 1

Define respiration

Answer 1

The process by which chemical energy in organic molecules is released by oxidation

Question 2

What is the difference between aerobic and anaerobic respiration?

Answer 2

Aerobic: Presence of O2
Anaerobic: Absence of O2

Question 3

Functions of respiration

Answer 3

Muscular contraction, beating of cilia/ flagella
Synthesis of substances
Bioluminescence
Active transport of substances into or out of cells
Electrical transmission of nerve impulses

Question 4

What makes ATP the universal energy currency?

Answer 4

Highly soluble and mobile energy carrier that is transported easily to point of need
Easy interconversion; ADP + Pi form ATP and ATP can be easily hydrolysed to ADP + Pi to release energy

Question 5

What are the stages in aerobic respiration and where does each take place?

Answer 5

Glycolysis in cytosol
Link reaction in mitochondrial matrix
Krebs cycle in mitochondrial matrix
Oxidative phosphorylation involving ETC on cristae

Question 6

Write the equation for the reaction in Glycolysis

Answer 6

Glucose + 2ADP + 2Pi + 2NAD+ > 2Pyruvate + 2ATP + 2NADH`

Question 7

Aerobic respiration: Glycolysis: 1. Phosphorylation of glucose

Answer 7

Initial investment of 2 ATP
1 Pi from each ATP used to phosphorylate glucose to from fructose 1,6-bisphosphate
Hexokinase catalyses the addition of the 1st Pi
Phosphofructokinase (PFK) catalyses the addition of the 2nd Pi (end product inhibition: ATP and citrate act as inhibitors; ADP and AMP act as allosteric activators)
Activates sugar, making it more reactive, commiting it to the glycolytic pathway
Confers negative charge on glucose, making it impermeable and unable to diffuse through cell membrane, trapping it inside the cytosol

Question 8

Aerobic respiration: Glycolysis: 2. Lysis

Answer 8

Fructose 1,6-bisphosphate (6C) splits to form 2 3C sugar phosphates
G3P: Glyceraldehyde 3-phosphate/ triose phosphate/ PGAL: Phosphoglyceraldehyde
Dihydroxyacetone phosphate (can be converted to G3P by isomerase)

Question 9

Aerobic respiration: Glycolysis: 3. Oxidation by dehydrogenation

Answer 9

G3P is oxidised by dehydrogenation
Coenzyme NAD+ is reduced to NADH
highly exergonic redox reaction: energy released used to add 2nd Pi to G3P to form 1,3-bisphosphoglycerate

Question 10

Aerobic respiration: Glycolysis: 4. Substrate-level phosphorylation

Answer 10

1,3-bisphosphoglycerate dephosphorylated to form pyruvate
2 Pi transferred by enzymes to 2 ADP
2 G3P yield: 4ATP + 2 NADH (net 2 ATP)

Question 11

Aerobic respiration: Link reaction/ Oxidative decarboxylation

Answer 11

Pyruvate 3C decarboxylated via removal of C through loss of CO2
Oxidation by dehydrogenation yields 2 NADH and a 2C compound
2C + coenzyme A = acetyl coA

Question 12

Aerobic respiration: Krebs cycle

Answer 12

Acetyl CoA [2C] combines with Oxaloacetate [4C] to form citrate [6C]

Citrate undergoes oxidative decarboxylation; loss of 1C through loss of CO2 in decarboxylation to form Alpha ketoglutarate [5C] and NADH (dehydrogenation)

Oxaloacetate [4C] regenerated:
1 decarboxylation to form 1CO2
3 dehydrogenation to from 2NADH and 1FADH2
1 substrate-level phosphorylation to form 1ATP

Question 13

What is the location of oxidative phosphorylation and what makes it suitable?

Answer 13

Inner mitochondrial matrix (cristae);

Many ETC and ATP synthases

Question 14

Describe the function of NAD+ and FAD

Answer 14

NAD+: Nicotinamide adenine dinucleotide
FAD: Flavin adenine dinucleotide
Serve as mobile electron carriers

Through glycolysis, Link reaction and Krebs cycle, organic molecules are oxidised to yield high energy electrons
These electrons (together with protons) are transferred to NAD+ and FAD to form NADH and FADH2
NADH and FADH2 transport high energy electrons from organic molecules to the ETC in the mitochondria
As electrons are passed down the ETC, energy released is coupled to the formation of ATP
By passing electrons to the ETC, NADH is oxidised to NAD+ and FADH2 is oxidised to FAD
Coenzymes NAD+ and FAD regenerated to take up electrons from glycolysis, link reaction and krebs cycle

Question 15

Define proton motive force

Answer 15

Potential energy
stored in the form of a 
proton chemical gradient
generated by the pumping of H+
across a biological membrane
during chemiosmosis

Question 16

Define chemiosmosis

Answer 16

Energy stored in the form of a
proton gradient
across a membrane
used to drive cellular work

Question 17

Describe the process of oxidative phosphorylation

Answer 17

NADH donates its electrons to the 1st electron carrier of the ETC which then passes the electrons to the next electron carrier etc.

As high energy electrons travel down the ETC, energy released is coupled to the pumping of H+ from the mitochondrial matrix into the intermembrane space via electron carriers of the ETC

As H+ diffuses down conc gradient via ATP synthase, ADP phosphorylated to form ATP

O2 is the final electron acceptor and combines with e and H+ to form H2O

Question 18

Describe the importance of oxygen

Answer 18

O2 allows oxidative phosphorylation to continue to produce ATP via chemiosmosis
O2 acts as the final electron acceptor that allows electron carriers NADH and FADH2 to continue donating their electrons to the ETC, generating ATP
in addition, reduction of O2 to H2O removes H+ from the matrix and further maintains proton gradient across the mitochondrial matrix

Question 19

Where does Anaerobic respiration take place?

Answer 19

Cytosol

Question 20

What are the two forms of fermentation?

Answer 20

Alcohol fermentation (yeast)
Lactic acid fermentation (mammals)

Question 21

Briefly describe what fermentation does/ how it allows anaerobic respiration to occur

Answer 21

fermentation processes are pathways to regenerate NAD+ from NADH thereby allowing 2ATP to be produced per glucose

Question 22

What is the final electron acceptor in Anaerobic respiration?

Answer 22

Pyruvate/ ethanal (via lactate/ alcohol fermentation respectively)

Question 23

What are the functions of Anaerobic respiration?

Answer 23

1. To generate a small yield of energy
   2ATP per glucose molecule through glycolysis
   1/19 that of aerobic respiration
2. To regenerate NAD+ from NADH

Question 24

Anaerobic respiration: Alcohol fermentation

Answer 24

During glycolysis, glucose is oxidised to form 2 Pyruvate [3C]; 2ATP and 2NADH produced
Following glycolysis, pyruvate decarboxylase converts pyruvate [3C] to ethanal/ acetaldehyde [2C] through decarboxylation via loss of CO2
Alcohol dehydrogenase reduces ethanal/ acetaldehyde to ethanol, removing H+ from NADH to regenerate NAD+

Question 25

Anaerobic respiration: Lactic acid fermentation: What are the end products?

Answer 25

2 ATP and 2 lactate per glucose molecule

[NO CO2 PRODUCED since no decarboxylase involved]

Question 26

Anaerobic respiration: Lactic acid fermentation

Answer 26

During glycolysis, glucose is oxidised to form 2 Pyruvate [3C]; 2ATP and 2NADH produced
Following glycolysis, lactate dehydrogenase reduces pyruvate to 2 lactate, removing H+ from NADH to regenerate NAD+

Question 27

Fate of lactate

Answer 27

Lactate contains a large part of energy orginally contained in glucose: lactate is eventually carried from muscle cells via blood to the liver where it can be converted back to pyruvate by liver cells and can enter link reaction and krebs cycle during aerobic respiration to produce more ATP​