Key area 2 – Cellular respiration The Role of ATP

You should already know that: the chemical energy stored in glucose must be released by all cells through a series of enzyme-controlled reactions called respiration; the energy released from the breakdown of glucose is used to generate ATP from ADP and phosphate; the chemical energy stored in ATP can be released by breaking it down to ADP and phosphate; ATP can be regenerated during respiration; each glucose molecule is broken down via pyruvate to carbon dioxide and water in the presence of oxygen, and yields 38 molecules of ATP; the breakdown of each glucose molecule via the fermentation pathway yields two molecules of ATP when oxygen is not present; in the absence of oxygen in animal cells, glucose is broken down into lactate via pyruvate; in the absence of oxygen in plant and yeast cells, glucose is broken down into alcohol/ethanol and carbon dioxide via pyruvate; fermentation occurs in the cytoplasm; aerobic respiration starts in the cytoplasm and is completed in the mitochondria.

Learning Objectives By the end of this topic you should be able to: Describe how glucose is broken down to ultimately deliver ATP Explain that ATP is used to transfer energy to carry out cell processes. Explain the reversible nature of ATP production Describe how ATP is synthesised

ATP (Adenosine triphosphate) ATP is essential to biological systems as it is the link between reactions that release energy (catabolic) and those that use energy (anabolic).

Think back to the beginning of the unit Write down an example of anabolic reaction and a catabolic reaction

ATP = Energy Currency ATP is ‘spent’ during cellular work such as muscular contraction or the formation of proteins, and is 'banked' or stored when glucose is broken down during cellular respiration. Coupling of reactions

ATP – crash course video http://www.youtube.com/watch?v=00jbG_cfGuQ Watch the first 4 minutes

How is ATP made? ATP comes from the breakdown of food – usually glucose Remember the equation Glucose + Oxygen ---- > ATP + carbon dioxide + water In the presence of oxygen glucose is broken down in to energy (ATP), carbon dioxide and water.

ATP When glucose is broken down in a cell, it releases energy which is used to produce ATP. ATP is made from joining a phosphate to ADP The end phosphate bond contains a lot of energy which is released when broken off. This is used by cells to do work and carry out anabolic reactions

ATP’s other role ATP also has the role of carrying out phosphorylation reactions in cells (adding phosphates to things). This is an enzyme controlled process. E.g during glycolysis ATP is broken down to ADP + Pi and the phosphate group is used to phosphorylate the substrate of glycolysis.

ATP cycling ATP breakdown and production is reversible. Think back to the reaction coupling diagram!

How much do you know? Define the terms anabolic and catabolic. Label this diagram How is ATP produced? What other role does ATP have?

The chemistry of respiration By the end of this topic you should be able to: Describe glycolysis Describe the progression of respiration pathways, in the presence and absence of oxygen

The chemistry of respiration There are 3 sets of reactions in cellular respiration that release the energy contained in food, by oxidation. Glycolysis The citric acid cycle The electron transport chain

Respiration During respiration, glucose is gradually broken down and hydrogen released at various stages along the pathway. Each of these stages is controlled by an enzyme called a dehydrogenase.

Glycolysis (revision from N5) It is a series of reactions (enzyme-controlled) that break down the sugar glucose in to pyruvate. Glycolysis takes place in the _________ of the cell and _____ require oxygen.

To start the process off, energy from two ATP molecules is needed. This can be thought of as an energy investment phase where ATP is used to phosphorylate intermediates in glycolysis. The series of reactions eventually produces four ATP molecules, so there is a net gain of two ATP from glycolysis (energy pay-off stage). GLYCOLYSIS

Dehydrogenase enzymes remove hydrogen ions and high energy electrons that are passed to a co-enzyme called NAD which is reduced to form NADH.. Later on the NADH will be used to produce ATP GLYCOLYSIS

How much do you know? Where does glycolysis take place in the cell? What is the net gain in ATP from one glucose molecule during glycolysis? Is glycolysis anabolic or catabolic? Why?

Respiration continues… If Oxygen is present pyruvate gets passed on to the CITRIC ACID CYCLE..

Learning objectives By the end of this topic you should be able to: Describe the citric acid cycle. Understand that respiration is a series of enzyme mediated reactions Explain the importance of the products of the citric acid cycle

Citric acid cycle From N5 you should know that in the presence of oxygen, pyruvate can continue to be broken down in the MITOCHONDRIA of the cell

Mitochondria Has a double membrane The inner membrane is folded in to many cristae which provide a large surface area. On the inner membrane the reactions of the ETC occur (electron transport chain)

Citric acid cycle The fluid filled matrix contains the enzymes involved in the CAC reactions.

Citric acid cycle Pyruvate preparation! Pyruvate diffuses from the cytoplasm to the mitochondria. Once inside the mitochondria, a carbon and two oxygen atoms are removed, forming carbon dioxide as a waste. The molecule that remains is a 2-carbon acetate molecule.

Citric acid cycle Pyruvate preparation When carbon dioxide is removed from pyruvate to make acetate, extra high energy electrons are produced. NAD+ captures these electrons and attracts H+ to balance the charge, forming a molecule of NADH. In addition to needing to regenerate NAD+, cells also have problems with controlling the movement of acetate molecules. Acetate molecules are small enough to diffuse away or evaporate (evaporating acetate molecules are what give vinegar its distinctive smell). To prevent this, cells covalently bond acetate molecules to a large carrier, called coenzyme A, making a complex is called acetyl-CoA.

Citric acid cycle Pyruvate preparation Because the acetate molecule produced from pyruvate is so small and can easily diffuse away, co-enzyme A is attached to it forming Acetyl CoA. This is now ready for the Citric acid cycle.

Citric acid cycle Each acetyl CoA (2C) combines with oxaloacetate (4C) to form a molecule called citrate (6C). Citrate then goes through a series of enzyme-catalysed reactions back to oxaloacetate. As each carbon is lost from the citrate molecule a carbon dioxide molecule and hydrogen ions are released

Citric acid cycle Hydrogen ions and high energy electrons become bound to to NAD to form NADH. Hydrogen and e- can also be bound to a different co-enzyme FAD which is reduced to form FADH2. NADH and FADH2 will be used in the next stage for ATP production

Citric acid cycle intermediate NAD+ Draw this in your jotter then fill in the boxes with the labels on the left CO2 NADH intermediate CO2 intermediate NAD+ ATP NADH ADP + Pi Oxaloacetate Acetyl CoA CO2 NADH NAD+ Pyruvate NAD+ NADH Citrate FADH2 FAD

How much do you know? What happens to the carbon dioxide that is produced in the citric acid cycle? What is the molecule produced when oxaloacetate combines with acetylCoA? Does the citric acid cycle require oxygen? Where does the CAC take place? What are NAD and FAD?

Watch this! From 4 minutes http://www.youtube.com/watch?v=00jbG_cfGuQ

Cool links to help learn! http://freevideolectures.com/Course/3160/Biology-I/36# http://www.wiley.com/college/boyer/0470003790/animations/tca/tca.htm https://www.youtube.com/watch?v=juM2ROSLWfw

The Electron Transport Chain (ETC) By the end of this topic you should be able to: Describe the electron transport chain as a membrane bound system. Explain the role of the dehydrogenase enzymes. Understand the key role of NAD and FAD and their reduced forms. Explain the role of oxygen in the ETC and the consequences of it’s absence.

The Electron Transport Chain The ETC is a series of proteins in the inner mitochondrial membrane All the Hydrogen ions and electrons that have been transferred to NAD or FAD are passed to the ETC.

The Electron Transport Chain Within the ETC the H ions and electrons now separate with the high energy electrons cascading down the ETC and releasing their energy

The Electron Transport Chain The electrons are used to pump Hydrogen ions across the mitochondrial membrane. The return flow of these H ions rotates part of the membrane protein ATP synthase. ATP synthase is an enzyme which catalyses the synthesis of ATP

The Electron Transport Chain Oxygen is the final electron acceptor, which combines with H ions and electrons forming water.

Why is oxygen needed? Without oxygen the CAC and ETC cannot function! Oxygen is needed to oxidise pyruvate to yield 36ATP With 2 ATP from glycolysis (doesn’t require O2) the yield from one glucose molecule oxidised is 38ATP

How much do you know? What enzyme is required to produce ATP? What is the final acceptor of hydrogen? What do the high energy electrons in the ETC do?

Anaerobic Respiration You should know from N5 that with no oxygen only glycolysis can take place and pyruvate follows a fermentation pathway. For both plants and animals complete the flow chart using the words; pyruvate, lactate, glucose and ethanol + CO2.

Anaerobic respiration – Animal cells oxygen debt builds up Glucose Pyruvate Lactate repaid

This should be revision…. In animal cells pyruvate is broken down in to lactate. This happens when doing vigorous exercise when O2 is used up. This is reversible! In plant and yeast cells pyruvate gets converted to ethanol and CO2. This is irreversible because CO2 is lost from the cell!

Which is more efficient? How many ATP are produced during aerobic respiration? How many ATP are produced during anaerobic respiration? Which is more efficient?

Measuring the rate of respiration You can measure respiration rate using a respirometer. If you’re lucky your teacher will show you how this works.

Measuring the rate of respiration As the creatures produce carbon dioxide through respiration this is absorbed by the sodium hydroxide beads As the creatures use up the oxygen in the tube, the level of liquid will rise. This can then be measured to see the volume of oxygen used.

Alternative Respiratory Substrates Other sugar molecules can be converted into glucose or intermediates of glycolysis; Proteins can be broken down to amino acids and converted into intermediates of glycolysis or the citric acid cycle; Fats can also be broken down to intermediates of glycolysis and the citric acid cycle.