1. 3.5 Energy transfer in and between organisms 3.5.2 Respiration
Tuesday, 18 September 2018
3.5 Energy transfer in and between organisms Respiration
• explain the main reactions which occur during glycolysis, the link reaction and the Krebs cycle • explain the roles of FAD and NAD in respiration

2. Glycolysis: True or False
Glycolysis produces a net gain of 4 ATP molecules
The co-enzyme NADH is oxidised during glycolysis
When coenzymes become reduced, they carry hydrogen molecules
Glycolysis takes place in the matrix of the mitochondrion
In glycolysis, glucose is converted in this order: glucose, triose phosphate, hexose bisphosphate then pyruvate
Hydrolysis occurs when triose phosphate is converted to pyruvate
If you think they are false, you must write the correct version- and there are false ones!!!

3. Glycolysis: True or False
Glycolysis produces a net gain of 4 ATP molecules- False: the net gain is 2 ATPs as 2 are used up
The co-enzyme NADH is oxidised during glycolysis- False: NAD is reduced during glycolysis to form NADH
When coenzymes become reduced, they carry hydrogen molecules- False: they carry hydrogen atoms, not molecules or ions
Glycolysis takes place in the matrix of the mitochondrion- False: it takes place in the cytoplasm
In glycolysis, glucose is converted in this order: glucose, triose phosphate, hexose bisphosphate then pyruvate- False: the correct order is glucose, hexose bisphosphate, triose phosphate, pyruvate
Hydrolysis occurs when triose phosphate is converted to pyruvate- False: hydrolysis occurs when hexose bisphosphate is converted to triose phosphate

4. Questions Outline the role of co-enzymes in the glycolysis pathway
Explain why the net gain of ATP during glycolyisis is two and not four
Explain how oxidation occurs during glycolysis, although no oxygen is involved
the coenzyme NAD accepts hydrogen atoms from the substrate molecules as triose phosphate is oxidised
because two molecules of ATP are used to activate hexose sugar at the beginning of the process, four ATP are made so the net gain is two
hydrogen atoms are removed from triose phosphate and combine with NAD which is an oxidation reaction

5. What Happens Where? Glycolysis = Cytoplasm of the cell.
Link reaction = Matrix of the mitochondria.
Krebs cycle = Also in the matrix.
Electron transfer chain Utilises proteins found in the membrane of the christa.

6. Products of Glycolysis
2 reduced NAD (NADH + H+)
2 Pyruvate
2 ATP
The Fate of Pyruvate?
THIS DEPENDS ON THE AVAILABILITY OF OXYGEN!!!

7. Aerobic Respiration
If O2 is present 3C pyruvate passes into mitochondria.
Here it is completely oxidised forming CO2 and H2O.
The second stage of aerobic respiration is the link reaction.

8. What now?
The pyruvate (pyruvic acid) is now moved by active transport from the cell cytoplasm into the mitochondrial matrix for the next stage of aerobic respiration

9. The Link Reaction Links Glycolysis to the Krebs Cycle.
Cytoplasm
Mitochondria
The Link reaction
The Krebs Cycle
Glycolysis
Links Glycolysis to the Krebs Cycle.
The end product of the link reaction can enter the Krebs Cycle.

10. Coenzyme A now combines with the Acetate to form
NAD+
NADH + H+
Coenzyme A
Acetyl coenzyme A
(2C)
Pyruvate
(3C)
Acetate
(2C)
CO2
Coenzyme A now combines with the Acetate to form
Acetyl coenzyme A
Start with Pyruvate produced in Glycolysis
The Pyruvate is decarboxylated (CO2)
It is also dehydrogenated (H+ removed)
This produces Acetate
The Acetyl coenzyme A now enters Krebs cycle

11. Link Reaction Pyruvate(3C) CO2 (1C) NAD+ NADH + H+ Coenzyme (CoA)
One carbon atom is removed from pyruvate in the form of CO2.
The remaining 2-carbon molecule combines with coenzyme A to produce Acetyl Coenzyme A (acetyl CoA).
Another oxidation reaction occurs when NAD+ collects more hydrogen ions. This forms reduced NAD (NADH + H+)
No ATP is produced in this reaction.
Pyruvate(3C)
Decarboxylation
CO2 (1C)
NAD+
Oxidation
Reduction
NADH + H+
Coenzyme (CoA)
Acetyl CoA (2C)

12. The Link Reaction occurs Twice for every Glucose Molecule
For each glucose molecule used in glycolysis, two pyruvate molecules are made.
But the link reaction uses only one pyruvate molecule, so the link reaction and the Krebs cycle happen twice for every glucose molecule which goes through glycolysis.
Overall equation for one link reaction and Kreb cycle:
Pyruvate + NAD + CoA acetyl CoA +
reduced NAD + CO2

13. The Products of the Link Reaction go to the Krebs Cycle and the ETC
So for each glucose molecule:
2 acetyl coenzyme A (go into the Krebs cycle)
2 Carbon dioxide (released as a waste products)
2 Reduced NAD (go to the electron transport chain)

14. Krebs Cycle Sir Hans Krebs in 1937
AKA Citric acid cycle or the Tricarboxylic acid cycle (TCA cycle)
Takes place in the matrix.

15. Krebs Cycle
From one glucose molecules you get 2 pyruvate molecules. (GLYCOLYSIS)
So Krebs cycle goes around twice per glucose molecule.

17. The Krebs Cycle Acetyl Coenzyme A (2C) NAD Coenzyme A 2C Reduced NAD
Oxaloacetate (4C)
Citrate (6C)
(6C)
(4C)
NAD
(4C)
CO2
FAD
Reduced
NAD
Reduced
FAD
CO2
(5C)
(4C)
NAD
ADP + Pi
ATP
(4C)
Reduced
NAD

18. DeNa DeNa A Fa... Na
This little tune will help you to remember the Krebs Cycle.
Remember, respiration is all about releasing energy from your food.
Oxidation releases energy.
When a carbon compound is oxidised, coenzymes are reduced.
The coenzymes involved are: NAD and FAD.
Decarboxylation is the removal of CO2.
Remember this: 665 and five 4’s.

19. DENA DENA A FA... NA
DENA: Decarboxylation and production of reduced NAD
A: Production of ATP
FA... : Production of reduced FAD (The ‘...’ means a gap)
NA: Production of reduced NAD

20. The Krebs Cycle: DENA DENA A FA... NA
Acetyl Coenzyme A (2C)
NAD
Coenzyme A 2C NA
Reduced
NAD
Oxaloacetate (4C)
Citrate (6C)
(6C)
(4C)
NAD
(4C)
DENA
CO2
FAD
Reduced
NAD FA
Reduced
FAD
CO2
(5C)
(4C)
DENA
NAD
ADP + Pi
ATP A
(4C)
Reduced
NAD

21. Krebs Cycle Summary 2 CO2 molecules 1 ATP molecules (S.L.P)
Each Acetyl CoA entering the cycle results in:
2 CO2 molecules
1 ATP molecules (S.L.P)
4 pairs of H atoms (Later used in the E.T.C to produce ATP)
Used to reduce NAD and FAD. Three reduced NAD are produced and 1 reduced FAD per cycle.
NAD = Nicotinamide adenine dinucleotide
FAD = Flavine adenine dinucleotide

22. Coenzymes in Respiration
Coenzymes are complex organic molecules that are used by enzymes to accept or donate molecules involved in a reaction.
They are often referred to as ‘Helper’ molecules as they carry chemical groups or ions about, e.g. NAD removes H+ and carries it to other molecules.

23. Krebs Questions
Why do living organisms only have a small amount of oxaloacetate in their cells?
Explain why each stage of the Krebs cycle needs to be catalysed by its own specific enzyme
State the role of pyruvate dehydrogenase

24. Krebs Questions
Why do living organisms only have a small amount of oxaloacetate in their cells? It is constantly being regenerated
Explain why each stage of the Krebs cycle needs to be catalysed by its own specific enzyme each substrate needs it’s own enzyme with a specifically shaped active site that is complementary to the substrate
State the role of pyruvate dehydrogenase it removes hydrogen from pyruvate

25. Respiration
The process of aerobic respiration can be split into 4 stages:
Glycolysis (splitting of the 6-carbon glucose molecule into two 3-carbon pyruvate molecules)
Link reaction (the 3-carbon pyruvate molecules enter a series of reactions which lead to acetylcoenzyme A – a 2-carbon molecule)
Krebs Cycle (acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD
Oxidative phosphorylation (electrons from NAD and FAD are released from the Krebs cycle to synthesis ATP with water produced as a by-product

26. http://highered. mheducation
Respiration Song