1. ATP use, synthesis and structure
A2 Human Biology
Miss Tagore

2. Learning Outcomes
Outline the need for ATP in living organisms, as illustrated by anabolic reactions, active transport, movement, and the maintenance of body temperature;
Describe, with the aid of diagrams, the structure of ATP;
State that ATP provides the immediate source of energy for biological processes.

3. Uses for ATP
Adenosine triphosphate is the body’s most common energy source. It is used in every cell in the body for activities such as:
Active transport
Maintaining body temperature
Anabolic reactions (synthesis of smaller molecules into larger ones)

4. The Structure of ATP
The structure of ATP is similar to that of a nucleotide. What two features are similar?
ATP is water soluble and so is easily transported across membranes within a cell.
Free electrons surround the phophate groups – these give the molecule its high energetic potential.
Nitrogenous base
3 phosphate groups
5-carbon Ribose sugar

5. The Structure of ATP Adenosine Adenosine monophosphate (AMP)
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)

6. ATP as a source of energy
The phosphate “tail” of an ATP molecule is where the main source of energy is.
Removal of a phosphate group by the process of hydrolysis (the addition of water) releases energy.
When ATP is hydrolysed to ADP, 30.5KJ of energy is released.
ADP can be further broken down into AMP, which also releases a small amount of energy.
Pi + ADP

7. ATP as a source of energy
The energy released as a result of hydrolysis can be channelled into other molecules and used directly by cells. Some energy is lost as heat.
ATP is continually being brown down and reformed at a rate of 8000 cycles per day.
30.5KJ released

8. How is ATP synthesised?
All living organisms use and synthesis ATP in different ways:
Plants - photophosphorylation
Yeast - glycolysis and fermentation
Animals – glycolysis and respiration
Varying amounts of ATP are produced in different reactions, as are the locations and requirements for oxygen.
Plant and animal ATP synthesis both require the enzyme ATP snythase (ATPase).

9. Questions (from page 135)
Explain how an ATP molecule is similar to that of DNA or RNA
Describe how the hydrolysis of ATP helps maintain the core body temperature
Explain why it is an advantage for an organism to hydrolyse ATP to meet its energy requirements rather than hydrolyse glucose directly

10. For next time… Read pages 136 – 139
(do on one day and on another)
Write down the key points under each heading – try to put this in your own words!
Bring this to class – we will discuss it at the start of the lesson

11. First stages of respiration

12. Learning Outcomes
(d) state the locations of glycolysis, the link reaction and the Krebs cycle;
(e) outline glycolysis, with reference to the production of pyruvate and NAD;
(f) outline the link reaction, with reference to the decarboxylation of pyruvate (3C) to acetyl (2C) coenzyme A and the reduction of NAD;

13. First stages of respiration
Cellular respiration has many stages.
It occurs in the cytoplasm of a cell, the matrix and the cristae of the mitochondria.
Glucose cannot be broken down directly to produce ATP – a series of metabolic reactions must take place that leads the the synthesis of ATP.
Three stages that you should know are glycolysis, Kreb’s cycle and oxidative phosphorylation.

14. The role of enzymes and coenzymes in respiration
Respiration is an enzyme-controlled process. It relies on different enzymes and coenzymes.
Dehydrogenase enzymes remove hydrogen from other molecules and make this hydrogen available to be passed on to coenzymes (this is important later).
Decarboxylase enzymes hydrolyse the carboxyl group (COOH) from a molecule, usually producing CO2
FAD and NAD are coenzymes that act as hydrogen acceptors for the dehydrogenase enzymes.

15. FAD and NAD
FAD and NAD enable potential energy to be transferred from one molecule to another.
Coenzymes are important because they can be oxidised and reduced (lose and gain electrons)

16. Glycolysis Occurs in the cytoplasm (cystol) of a cell.
Glucose is split in this stage
ATP, pyruvate and reduced NAD are produced (reduction is gain of electrons!)

17. Glycolysis Glucose enters cells by active transport or diffusion.
To make sure that the glucose does not leave the cell, it is chemically altered.
The glucose molecule becomes phosphorylated. 2 ATP molecules do this.
Phosphorylation is when phosphate groups are added to a molecule. This changes the chemical conformation.

18. Glycolysis
Phosphorylated glucose is eventually broken down through enzyme controlled steps.
The following are produced in glycolysis:
4 x ATP are released
2 x NADH2 (reduced NAD)
2 x 3-carbon pyruvate molecules

19. Glycolysis This stage of respiration is the “setting up” stage
Glucose is prepared for further breakdown to produce more ATP
Reduced NAD created here has the potential to make ATP in later stages

21. Link reaction
Pyruvate produced in glycolysis contains lots of potential energy that can be channelled into ATP synthesis.
This will not happen without the presence of oxygen.
Only when oxygen is present is pyruvate actively transported to the mitochondria.
Here it undergoes a link reaction to become acetyl coenzyme A

22. Link reaction Pyruvate loses a hydrogen (becomes dehydrogenated)
Pyruvate also loses carbon as carbon dioxide (becomes decarboxylated)
This results in the formation of a substance called acetyl coenzyme A
Acetyl co-A is fixed in the matrix of the mitochondria. From here it can enter the next stage of aerobic respiration, the Kreb’s cycle.
The hydrogen acceptor molecule is NAD.

24. Questions Read over pages 136-137 of your textbook.
Write down the key definitions
Answer questions 1-4

25. Question 1 - answer
Glycolysis can be described as a metabolic pathway because it is a biochemical reaction that involves a series of enzymes to control processes that are linked together.

26. Question 2 - answer
Glycolysis means to split glucose into two lots of pyruvate

27. Question 3 - answer
Substrate level phosphorylation changes the confirmation of a glucose molecule by adding a phosphate group to it (from ATP). This allows glucose to be broken down in glycolysis to pyruvate.

28. Acetyl co-A, CO2 and reduced NAD
Question 4 - answer
Starting molecules
Products of reactions
Site of reactions
Oxygen required
Glycolysis
Glucose, ATP, NAD
2 x pyruvate
Cytoplasm / cystol no
Link reactions
Pyruvate
Acetyl co-A, CO2 and reduced NAD
Mitochondria
yes

29. The Krebs Cycle

30. Learning Outcomes
(g) outline the Krebs cycle, with reference to the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate (names of intermediate compounds are not required);
(h) explain that during the Krebs cycle, decarboxylation and dehydrogenation occur, NAD and FAD are reduced and substrate level phosphorylation occurs.

31. The Krebs Cycle
A series of chemical reactions that occur in the matrix of the mitochondrion
Acetyl is completely broken down into carbon dioxide
Hydrogen is removed to form reduced coenzymes
More ATP is synthesised directly

32. The Krebs Cycle
2C acetyl coenzyme A combines with a 4C compound called oxcaloacetate.
This forms a 6C compound called citrate

33. The Krebs Cycle
6-carbon citrate is an intermediate compound that is rapidly decarboxylated in a series of enzyme-linked reactions
This compound is also dehydrogenated
The carrier molecules NAD and FAD combine with the liberated hydrogen
Carbon is released as carbon dioxide
It is eventually broken down to 4C oxaloacetate again.

34. Dehydrogenation
Decarboxylation

35. Importance of Krebs Cycle
The Krebs cycle breaks down acetyl co-A to CO2
Decarboxylase and dehydrogenase enzymes also release hydrogen atoms.
Coenzyme hydrogen carriers become reduced (NADH/FADH). This is really important for later stages of ATP synthesis.
Acetyl co-enzyme A can be produced from fatty acids and amino acids. The body will metabolise any substrate available to produce ATP.

36. The Outcome of the Krebs Cycle
Three molecules of reduced NAD
One molecule of reduced FAD
One molecule of ATP produced by substrate-level phosphorylation
Two molecules of CO2
One molecule of regenerated oxaloacetate

37. Control of the Krebs cycle
Allosteric feedback mechanisms:
High levels of ATP inhibit first three stages of Krebs cycle
Following enzymes then become inhibited by high levels of reduced coenzyme (NADH/FADH) to stop the cycle from continuing
This means substrates are only broken down as and when needed
High concentration of citrate inhibits continual glycolysis of glucose, therefore regulating the amount of substrate going through the pathways

38. What is allosteric inhibition?
Enzymes involved in respiration pathways can be inhibited by an inhibitor binding temporarily to somewhere other than the active site, changing the active site.

39. What to do… Answer questions on page 139.
Mark your answers and add to them if you are missing information in a different colour pen.

40. Lesson starter Answer these three questions:
What is the name of the 4C molecule that combines with acetyl CoA to form a 6C acid?
What is the name of the 6C acid?
What stage in respiration do the above questions refer to?

41. Answers
Oxaloacetate
Citric acid
Kreb’s cycle

42. Oxidative Phosphorylation

43. Learning Outcomes
(i) outline the process of oxidative phosphorylation, with reference to the roles of electron carriers, oxygen and the mitochondrial cristae;
(j) outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATPsynthase (HSW7a).

44. Recap… Krebs cycle occurs in matrix of mitochondrion.
Dehydrogenase enzymes remove hydrogen at various stages
NAD and FAD become reduced (accept hydrogen atoms)

45. Some products of Krebs cycle are used in oxidative phosphorylation
Product from Krebs cycle
Where it goes
1 coenzyme A
Reused in the next link reaction
Oxaloacetate
Regenerated for use in the next Krebs cycle
2CO2
Released as a waste product
1 ATP
Used for energy
3 Reduced NAD
To oxidative phosphorylation
1 Reduced FAD

47. Oxidative Phosphorylation
Reduced coenzymes from the Krebs cycle are now full of potential energy to make ATP through oxidative phosphorylation.
Oxidative phosphorylation occurs on the cristae of the mitochondrion and involves a series of enzyme controlled reactions.

48. What is oxidative phosphorylation?!
It’s a two part process.
First stage is electron transport chain
Second stage is the chemiosmosis
The entire process is called oxidative phosphorylation

49. The Stages of Oxidative Phosphorylation
There are cytochrome carriers on the cristae of the mitochondria. Reduced NAD and FAD become oxidised (lose their hydrogen atoms) when they come into contact with these carriers.
The hydrogen atoms split up into protons (H+) and electrons (e-)

50. The Stages of Oxidative Phosphorylation
Electrons pass along the cytochrome carriers and the energy released is used to pump protons (H+) into the intermembrane space.
H+ building up in the intermemebane space
e- passing through the membrane
Oxidation of NAD/FAD

51. Lots of hydrogen ions end up in the innermembrane space
Lots of hydrogen ions end up in the innermembrane space. This is the opposite side of where they started.

52. The Stages of Oxidative Phosphorylation
Protons create an electrochemical gradient as they cannot pass back through the membrane. (High concentration of H+) outside, low concentration inside
Protons which have built up in the intermembrane space end up diffusing through specialised protein channels back into the matrix.

53. The Stages of Oxidative Phosphorylation
These channels contain a structure on the matrix side which consists of the enzyme ATP synthease and is where ADP is phosphorylated to form ATP
(phosphorylated means that a phosphate group is added)

54. The Stages of Oxidative Phosphorylation
As the protons (H+) flow through these channels they “turn” this enzyme and fuel the process of ATP production. The “used” protons (H+) then combine with electrons (e-) and oxygen atoms to form water.
The electrons (e-) move along the membrane’s carriers until they reach the final carrier molecule, oxygen.
This process is referred to as chemiosmosis
e- passing through the membrane lose energy as they progress through each carrier (pink proteins above)
Some of the energy given off allows H+ to move across the membrane

58. Group Task That was A LOT of information to take in!
In groups (3/4), discuss what events took place in the cytochrome system.
Come up with a list of steps to explain this process to the other group.

59. What to do… Answer questions on page 141.
Mark your answers and add to them if you are missing information in a different colour pen.

60. Practice Questions
Carbon monoxide inhibits the final electron carrier in the electron transport chain.
Explain how this affects ATP production via the electron transport chain (2)
Explain how this affects ATP production via the Krebs cycle

61. Answers
(a) the transfer of electrons down the electron transport chain stops (1 mark). There is no energy released to phosphorylate ADP/produce ATP (1 mark)
(b) the Krebs cycle stops (1 mark) because there is no oxidised FAD/NAD coming from the electron transport chain (1 mark)
(remember that when the electron transport chain is inhibited, the reactions that depend on the products of the chain are also affected)

62. 32 ATP can be made from 1 glucose molecule
Stages of respiration
Molecules produced
Number of ATP molecules
Glycolysis
2 ATP 2
2 reduced NAD
2 x 2.5 = 5
Link reaction (x2)
Krebs cycle (x2)
6 reduced FAD
6 x 2.5 = 15
2 x 1.5 = 3
Total ATP = 32
2.5 ATP are made from each reduced NAD
1.5 ATP are made from each reduced FAD