ATP use, synthesis and structure

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 http://www.bbc.co.uk/schools/gcsebitesize/science/videos/aerobic_video1.shtml • 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 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. The Structure of ATP 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. 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. ATP as a source 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 136-137 on one day and 138-139 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

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. Question 4 - answer

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 • Acetylis completely broken down into carbon dioxide • Hydrogenis removed to form reduced coenzymes • MoreATPis 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 reducedNAD • 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

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