Title: The process of respiration

LO: To discover the stages of respiration

Keywords:

Mitochondria

Glycolysis

Citric Acid cycle

Electron transport

Starter:

What do you know about respiration?

What are the 3 stages of respiration?

An overview of respiration

Cellular respiration is a series of metabolic pathways that release energy from food and regenerates the high energy compound ATP

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There are 3 stages:

• Glycolysis
• Citric Acid Cycle
• Electron Transport Chain

What Happens Where?

Stage 1: Glycolysis

Glycolysis occurs in the cytoplasm

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This is the breakdown of glucose into pyruvate through a series of enzyme controlled reactions

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Oxygen is not required

Stage 1: Glycolysis

• Glucose is broken down into pyruvate in 2 phases.
• Glucose is first broken down into intermediate products
• This phase is the energy investment phase and requires energy in the form of 2 ATP

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• In the energy pay off stage, 4 molecules of ATP are formed.
• This results in the Net gain of 2 ATP

Energy investment phase: uses ATP

Energy payoff stage: generates ATP

Stage 1: Glycolysis

Dehydrogenase enzymes remove hydrogen ions and electrons from molecules

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They are passed to the coenzyme NAD

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This forms NADH

Glycolysis

Glucose

2 ATP

2 ADP

Glucose-6-

Phosphate

Pyruvate

4 ADP + 4Pi

4 ATP

NAD

Reduced NAD

2H x 2

Glycogen

• Why is Glycolysis termed anaerobic?
• What is the NET production of ATP?

NAD+ + 2H 🡪 NADH + H+�(oxidised form ) (reduced form) �

NB Rather then write NADH, examiners often simply refer to it as reduced NAD or reduced coenzyme

Dehydrogenase

Task: Describe the process of Glycolysis (5 marks)

Marker:

• Glycolysis is the process of splitting glucose into pyruvate.
• One glucose molecule is turned into two molecules of pyruvate.
• It occurs in the cytoplasm.
• This process requires energy to phosphorylate the glucose. Therefore this is known as the investment stage.
• It is an anaerobic process.
• Net gain of 2 ATP
• NADH is produced

What Happens Where?

Stage 2: Citric Acid Cycle

• The Citric Acid Cycle occurs in the matrix of the mitochondria

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• Only occurs if oxygen is present and is a series of dehydrogenase enzyme controlled reactions resulting in the generation of ATP and release of Carbon dioxide and Hydrogen

Stage 2: Citric Acid Cycle

Pyruvate is converted into Acetyl which combines with coenzyme A to form Acetyl coenzyme A

Acetyl co-A combines with a Oxaloacetate to form Citrate. This converts back into Oxaloacetate, releasing CO2

Dehydrogenase enzymes remove more hydrogen ions and electrons, passing them to NAD to form NADH

The hydrogen ions and electrons from NADH are removed and passed onto the next stage of respiration, the electron transport chain

What Happens Where?

Stage 3: Electron Transport Chain

• The Electron Transport Chain occurs in the inner mitochondrial membrane

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• Only occurs if oxygen is present and uses the Hydrogen ions and electron from NADH to generate ATP and form water

Stage 3: Electron Transport Chain

• The Electron Transport Chain is a series of carrier proteins attached to the inner mitochondrial membrane

• As the electrons move along the chain, energy is released

• That energy is used to pump the Hydrogen ions (H+) across the inner mitochondrial membrane from the matrix

• These hydrogen ions flow through the ATP synthase protein back through the inner membrane

Stage 3: Electron Transport Chain

• Each pyruvate produced during glycolysis enters the matrix of a mitochondrion, where it is converted to a compound called acetyl co-enzyme A (Acetyl co-A).

During this conversion:

• Carbon dioxide is released.

Pyruvate

CO₂

NAD

NADH

Hydrogen molecules are removed, which immediately combine with NAD to form NADH

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Hydrogen cannot exist in a cell on its own – it must always be combined with a coenzyme/hydrogen acceptor such as NAD

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Link Reaction

Krebs Cycle / Citric Acid Cycle

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• Acetyl co-A combines with a Oxaloacetate to form Citrate.

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CO₂

CO₂

Krebs’

Cycle

• Citrate is then gradually converted back to Oxaloacetate which is then ready to begin the process again

Acetyl co-A

During this process: -

• CO₂ is released (decarboxylation)

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CO₂

CO₂

Krebs’

Cycle

FADH

FADH₂

• Dehydrogenation occurs - pairs of hydrogen atoms are removed and combine with NAD to form NADH

• Also a similar reaction occurs but the coenzyme is FADH which becomes FADH₂.

• 1 ATP is produced

Pyruvate

Citric acid acid

CO₂

CO₂

CO₂

Citric acid cycle

3NAD

3NADH

FAD

FADH₂

NAD

NADH

Important points

• Each glucose molecule gives two turns of the Krebs’ cycle – one for each of the pyruvates produced during glycolysis

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Give an account of the structure of the inner membranes of mitochondria and the function of the electron transport chain in cellular respiration. (8)

Title: The Electron Transport Chain

LO: Describe and explain the role of the electron transport chain in producing ATP.

Starter: Which part of the question below can you already answer? By the end of the lesson today you should be able to do all of it! ☺

In pairs, remind ourselves….. What are the glycolysis and the Krebs cycle?

Electron transport chain

• An electron transport chain is a group of protein molecules attached to the inner membrane of the mitochondria. There are many of these in a cell.

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• NADH and FADH, from glycolysis and the citric acid cycle release high-energy electrons and pass them to the electron transport chains.
• As the high energy electrons flow along a chain of electron acceptors, they release energy.
• This pumps hydrogen ions across the membrane from the matrix into the inter-membrane space to maintain a higher concentration of hydrogen ions.

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Electron transport chain

• Hydrogen ions flow back down the concentration gradient into the matrix, they pass through the ATP synthase and drive this enzyme to synthesise ATP from ADP and P_i.
• Most of the ATP generated by cellular respiration is produced in mitochondria in this way.

(Each pair of hydrogens passing along the chain yields 3 ATP)

• Oxygen is the final hydrogen acceptor it combines with H and electrons to form water.
• In the absence of oxygen the electron transport chains do not proceed and ATP is not made at this stage.

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Give an account of respiration under the following headings: (10 marks)

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• Glycolysis; 4
• The Citric acid cycle 6

 Any 4 from:

• Occurs in cytoplasm
• Glucose broken down into 2 molecules of pyruvate
• ATP required to start process
• Net gain of 2ATP
• Hydrogen carried away by NAD*
• Does not require oxygen/is anaerobic

Any 6 from:

• Occurs in the matrix of the mitochondria
• Pyruvate is converted to acetyl-CoA
• Oxaloacetate joins acetyl group to form citric acid
• Carbon dioxide produced as a waste product
• Hydrogen carried away by NAD*
• Requires oxygen/is aerobic
• Oxaloacetate breaks down in a series of reactions back to citrate/cyclical reaction

* award only once

Aim: To use Resazurin dye to investigate Respiration

Resazurin is blue coloured dye. When it is oxidised it remains blue, when it is in the presence of respiring cells it will turn to pink or white depending on the amount of respiration.

No respiration

Some respiration

Lots of respiration

A

B

C

Tube C

• 3ml distilled water.
• 3ml 5% glucose solution
• 3ml Resazurin

• Set up your test tubes
• Incubate all in a water bath at 35°C for 30 minutes.
• Record your results

Tube A

• 3ml 2.5% boiled yeast
• 3ml 5% glucose solution
• 3ml Resazurin

Tube B

• 3ml 2.5% yeast
• 3ml 5% glucose solution
• 3ml Resazurin

Results Table:

Conclusion Questions:

• Which tube showed the most respiration?
• How did you know this?
• Why did this show the most respiration?
• How could we improve our experiment?

No respiration

Lots of respiration

Give an account of the structure of the inner membranes of mitochondria and the function of the electron transport chain in cellular respiration. (8)

Test your knowledge

1a) What compound is represented by the letters ATP? (1)

b) What is the structural difference between ATP and ADP? (1)

c) Give a word equation to indicate how ATP is regenerated in a cell. (2)

2. Explain each of the following:

• During the glycolysis of one molecule of glucose, the net gain is two and not four molecules of ATP. (1)
• Living organism have only small quantities of oxaloacetate in their cells. (1)
• A human body can produce ATP at a rate of around 400gh^-1, yet at any given moment there are only about 50g present in the body. (2)

3. Using the letters G (Glycolysis), C (Citric Acid cycle) and E (Electron Transport Chain). Indicate where each of the following statements refers to, more than one letter may apply to some statements.

• It bring about the breakdown of glucose to pyruvate.
• It ends with the production of water.
• It begins with acetyl from acetyl coenzyme A combining with oxaloacetate.
• It involves a cascade of electrons which are finally accepted by oxygen.
• It has an energy investment phase and energy payoff phase.
• It results in the production of NADH
• It involves the release of carbon dioxide.
• It results in the production of ATP.

Fermentation

• Where does it occur?

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• What conditions are needed for fermentation to take place?

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• How much ATP is generated?

What can you remember from Nat 5?

Fermentation in Animal Cells

Pyruvate

Lactate

In the absence of oxygen fermentation takes place in the cytoplasm.

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Pyruvate is instead converted into Lactate and only the 2 molecules of ATP from glycolysis are generated .

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If oxygen becomes available again, lactate can be converted back into pyruvate for aerobic respiration to occur.

Pyruvate

ethanol

CO₂

During fermentation in plant or yeast cells, the molecules of pyruvate are all converted into ethanol and carbon dioxide.

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Again, only 2 molecules of ATP are generated.

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What can we use fermentation for in industry?

Fermentation in Plant and yeast Cells

Bingo

Glycolysis

pyruvate

acetyl

investment

ATP

ADP

Pi

Pay off

Dehydrogenase

NAD

NADH

Citric Acid Cycle

Cytoplasm

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Co Enzyme A

Acetyl Co. A

Oxaloacetate

Citrate

Carbon Dioxide

Matrix

Membrane

Oxygen

Protein pumps

electrons

Hydrogen

ATP synthase

acceptor

diffusion