Respiration

Aerobic Respiration

Aerobic Respiration

The release of energy, made available by ATP, from the breakdown of molecules (which oxygen as the terminal electron acceptor)

Anaerobic Respiration

The breakdown of molecules in the absence of oxygen, releasing small amounts of energy

What are the types of phosphorylation?

• Oxidative phosphorylation

• Photophosphorylation

• Substrate-level phosphorylation

What are the stages of aerobic respiration?

1. Glycolysis \n 2. Link reaction \n 3. Krebs cycle \n 4. Electron Transport Chain (oxidative phosphorylation)

Where does glycolysis occur?

In the cytoplasm of a cell

Where in the cell does the link reaction take place?

Mitochondrial Matrix

Where does the Kreb cycle occur?

Mitochondrial Matrix

Where does oxidative phosphorylation occur?

Inner mitochondrial membrane

Why does glycolysis occur in the cytoplasm?

Glucose cannot pass through the membranes of mitochondria, and the necessary enzymes are located in the cytoplasm

Dehydrogenation

The removal of hydrogen from a molecule

Decarboxylation

The removal of CO2 from a molecule

What are the reactants of glycolysis?

Glucose, 2 ATP, 2 ADP, 2 Pi + 2 NAD

What are the products of glycolysis?

2 ATP, 2 NADH, 2 Pyruvate molecules

What is the net production of ATP during glycolysis? Why?

2 ATP

2 ATP are put into the system, and 4 ATP are synthesised

How is glucose converted to fructose biphosphate?

The glucose molecule is phosphorylated by the addition of two phosphate groups from two molecules of ATP

How many triose phosphate molecules are made for each glucose molecule?

2 triose phosphate molecules

How many pyruvates are produced from one glucose molecule in glycolysis?

2 pyruvates

Draw a labelled flow diagram of glycolysis

Write a summary word equation for glycolysis

Glucose + 2ADP + 2Pi + 2NAD → Pyruvate + 2NADH + 2ATP

Write a summary word equation for the link reaction

Pyruvate + NAD + CoA → Acetyl CoA + NADH + CO₂

Each turn of the Krebs cycle produces:

• 1 ATP

• 3 NADH

• 1 FADH

• 2 CO2 Molecules

How many times does the Krebs cycle occur for each glucose molecule?

Twice

What is a coenzyme?

An enzyme required by an enzyme in order to function

How many ATP molecules are synthesised from 1 NADH molecule?

3 ATP

How many ATP molecules are synthesised from 1 FADH molecule?

2 ATP

Where does the electron transport chain occur?

On the inner membrane of the mitochondria

For each glucose molecule entering the Krebs cycle, the electron transport chain receives how many NADH?

10 NADH

For each glucose molecule entering the Krebs cycle, the electron transport chain receives how many FADH?

2 FADH

Describe the electron transport chain

• Reduced NAD donates electrons from the hydrogen atoms to the first of the 3 proton pumps

• The electrons move from the first pump to the second, providing energy to the proton pumps on the inner mitichondrial matrix

• H+ is pumped into the inter-membrane space

• The movement of of protons into the inter-membrane creates a proton gradient

• The protons flow down their concentration gradient through ATP Synthetase

• The flow of protons causes ATP Synthetase to synthesise ATP from ADP + Pi

• The protons combine with electrons and oxygen to form water

What maintains the proton concentration gradient across the inner mitochondrial membrane?

The proton pumps pumping protons across the inner membrane

What is the final electron acceptor in respiration?

Oxygen

How many ATP are produced from oxidative phosphorylation by just glycolysis for each molecule of glucose?

6 ATP (2 NADH molecules are made)

How many ATP are produced from oxidative phosphorylation by just the link reaction for each molecule of glucose?

6 ATP (2 NADH molecules are made)

How many ATP are produced from oxidative phosphorylation by just the Krebs cycle for each molecule of glucose?

22 ATP (6 NADH molecules are made, and 2 FADH molecules are made)

How many ATP are produced by substrate-level phosphorylation by just glycolysis for each molecule of glucose?

2 ATP

How many ATP are produced by substrate-level phosphorylation by just the link reaction for each molecule of glucose?

None

How many ATP are produced by substrate-level phosphorylation by just the Krebs cycle for each molecule of glucose?

2 ATP

How many ATP are produced by substrate-level phosphorylation in total for each molecule of glucose?

4 ATP

How many ATP are produced in total from all stages of respiration?

38 ATP

Why is 38 ATP only a theoretical amount of ATP generated by respiration?

• ATP is used to transport molecules such as pyruvate, NADH and FADH across the mitochondrial membrane

• Protons may leak out of the inter-membrane space, rather than through ATP synthetase, and compromise the proton gradient

• Molecules many also leak through membranes

What is the amount of energy required to make ATP?

30.6 kJ/mole

Can substrate-level phosphorylation occur in the absence of oxygen?

Yes

Can oxidative phosphorylation occur in the absence of oxygen?

No

What are the two different anaerobic pathways?

Lactate Fermentation: Glucose is converted into lactate (in animals) \n Ethanol Fermentation: Glucose is converted into ethanol (in various micro-organisms such as yeast)

What anaerobic pathway of respiration occurs in yeast?

Glucose is converted into ethanol

What anaerobic pathway of respiration occurs in animals?

Glucose is converted into lactate

Draw a flow diagram to show the conversion of glucose into lactate in anaerobic respiration

How many ATP are produced by anaerobic respiration of glucose into lactate?

2 ATP

How many ATP are produced by anaerobic respiration of glucose into ethanol?

2 ATP

What are the two alternate respiratory substrates?

Lipids and proteins

When glycogen stores and blood glucose are low, the alternate respiratory substrate used is…

Lipids

When dietary energy supplies are low, the alternate respiratory substrate used is…

Protein

Describe how lipids are used as a respiratory substrate

• Lipids are hydrolysed into their constituent molecules, glycerol and fatty acids

• The glycerol is phosphorylated with ATP, and dehydrogenated with NAD, converting it into triose phosphate

• Triose phosphate enters the glycolysis pathway

• The fatty acid chains are broken into 2-carbon fragments and fed into the Krebs cycle as Acetyl CoA

• Hydrogen released is picked up by NAD and used in the ETC

Longer fatty acids chains have more…

carbon atoms and hydrogen atoms

Longer fatty acid chains have more carbons. What effect does this have when long fatty acid chains are used in respiration?

More CO₂ is produced as a result. The body would produce more carbon dioxide than can be removed if lipids are respired

Longer fatty acid chains have more hydrogen atoms. What effect does this have when long fatty acid chains are used in respiration?

More NAD is reduced, so more ATP is produced. More water is also produced.

Describe how proteins are used as a respiratory substrate

• Amino acids are deaminated in the liver

• The amino group is converted into urea

Where in the cell do most of the aerobic respiration reactions take place?

Mitochondria

Outline Oxidative Phosphorylation

• Hydrogen atoms are donated by reduced NAD (NADH) and reduced FAD (FADH2) from the Krebs Cycle

• Hydrogen atoms split into protons (H+ ions) and electrons

• The high energy electrons enter the electron transport chain and release energy as they move through the electron transport chain

• The released energy is used to transport protons across the inner mitochondrial membrane from the matrix into the intermembrane space

• A concentration gradient of protons is established between the intermembrane space and the matrix

• The protons return to the matrix via facilitated diffusion through the channel protein ATP synthase

• The movement of protons down their concentration gradient provides energy for ATP synthesis

• Oxygen acts as the 'final electron acceptor' and combines with protons and electrons at the end of the electron transport chain to form water

Where in the cell do the anaerobic respiration reactions take place?

In the cytoplasm

What is the role of the coenzymes NAD and FAD in aerobic respiration?

To transport hydrogen from dehydrogenation reactions to the electron transport chain where they are used in chemiosmosis

- They pass electrons to the electron transport chain for ATP synthesis.

Which stage takes place on the cristae or inner membrane of the mitochondria?

The Electron Transport Chain

Describe the main difference between the way in which ATP is produced by oxidative phosphorylation and the way in which it is produced in photosynthesis

In photosynthesis the energy used to synthesise ATP is provided by light. In oxidative phosphorylation the energy is provided by chemical reactions

Describe precisely what happens to the pyruvate in the absence of oxygen in animals

Pyruvate is directly reduced to lactate by reduced NAD, during anaerobic respiration

Describe precisely what happens to the pyruvate in the absence of oxygen in yeast

Pyruvate is converted into ethanal by the removal of CO₂. Ethanol is then reduced to ethanol by reduced NADH

Without oxygen, what cannot happen to NADH?

It cannot be oxidised to regenerate NAD

Explain how ADP is involved in making energy available to the cells

• Energy is used to combine ADP with a phosphate group and make ATP

• Energy is released when ATP is broken down into ADP and a phosphate group \n Only one enzyme is required for this reaction

Explain why anaerobic respiration yields less ATP than aerobic respiration

• Anaerobic respiration only involves glycolysis, not the Krebs cycle or the ETC

• Most ATP produced is as a result of the Krebs cycle (absent in anaerobic)

• Glycolysis normally produces 8 ATP using NAD but can only produce 2 ATP in the absence of oxygen

• Ethanol and lactic acid still contain energy and are not broken down

Describe the role of oxygen in the electron transport chain

• Oxygen is the final electron acceptor of the ETC

• It accepts electrons and protons, forming water

• This maintains the flow of electrons, ensuring the pumps keep pumping protons

Explain how ATP production continues in humans in anaerobic conditions

Glycolysis continues, with glucose being converted into pyruvate. 2 ATP are produced by substrate-level phosphorylation. Pyruvate is then converted into lactate

A test tube containing a suspension of a unknown organelle is monitored for CO₂ production. Cyanide inhibits the enzyme cytochrome oxidase and prevents the regeneration of NAD. Explain why cyanide could be used to confirm that the sample in the test tube contains mitochondria

• The absence of NAD means that hydrogen atoms are not picked up and dehydrogenation does not take place

• Without dehydrogenation, many reactions do not take place, such as in the Krebs cycle

• Therefore, the mitochondria stops producing CO₂ is produced

• A sample containing mitochondria will show a sharp drop in CO₂ production

A chemical, Dinitophenol, causes holes to be produced in the inner membrane of mitochondria, through which protons can pass. Explain why this may affect oxidative phosphorylation and suggest why dinitrophenol causes a loss of weight and an increase in body temperature

• The leakage of protons from the inter-membrane space breaks the proton gradient

• Less protons will flow through ATP synthetase and so less ATP is produced as a result

• As less ATP is produced for each glucose molecule respired, more glucose will be used by the body

• As more glucose is used, the breakdown of glycerol and fat stores will occur, causing a loss of weight- As less energy is used to create ATP, more escapes as waste heat energy, which raises the body temperature

Describe how reduced FAD and reduced NAD are used to create an electrochemical gradient

• Reduced FAD and NAD pass electrons to the ETC

• The high energy electrons provide energy to power proton pumps

• On the inner mitochondrial membrane/cristae

• This pumps H+ into the inter-membrane space

• Reduced NAD powers all 3 pumps whereas Reduce FAD passes to the 2nd pump

What are the products of the electron transport chain per molecule of glucose?

34 ATP

Why is ATP known as the universal energy currency?

Can be used in all organisms for all reactions

Why is the ATP yield for FAD less than NAD ?

• Reduced FAD only uses two proton pumps

• Only 2 ATP produced per reduced FAD

Can you describe glycolysis?

• Phosphorylation of glucose into hexose bisphosphate

• Splitting of hexose bisphosphate into 2x triose phosphate

• Oxidation of TP into pyruvate

Describe the function of enzymes and coenzymes (carriers) in the process of respiration

• Coenzyme decarboxylase remove carbon dioxide in the link reaction

• Coenzyme dehydrogenase remove hydrogen atoms in the link reaction

• NAD is reduced in glycolysis

• FAD is reduced in Kreb’s cycle

• Reduced NAD carries protons to the electron transport chain

• ATP synthetase produces ATP from ADP+Pi

Describe briefly the process of decarboxylation

• CO2 diffuses out of the mitochondria into the blood/plasma

• It is then carried as hydrogen carbonate ions to which it is breathed out

Label the mitochondria with the process in each area

Label the mitochondria

-

How is Reduced NAD produced in the Krebs Cycle?

• Dehydrogenation of intermediate compounds

• Removal of hydrogen ions meand NAD is reduced to NADH2

Describe the position of the 'high energy bond of ATP’ in SLP

Bond between the last two phosphate bonds on ATP