Key Area 1: Cellular respiration Glycolysis, Citric Acid Cycle, Electron Transport Chain Unit 2: Metabolism and Survival

Key Area 1: Cellular respiration

Glycolysis, Citric Acid Cycle, Electron Transport Chain

Unit 2: Metabolism and Survival

Glycolysis

CfE Higher BiologyMetabolism

and Survival

• In this series of reactions, the sugar _________ is broken down into __________.

• ________ control these reactions, which are called _____________.

• Glycolysis takes place in the __________ of the cell and _________ required oxygen.

Glycolysis


and Survival

• This process requires the energy from 2 ATP molecules in order to start it.

• This is an energy investment as the ATP is used to phosphorylate intermediates in glycolysis.

• The series of reactions in glycolysis produces four ATP molecules resulting in a net gain of two ATP (energy payoff)

Glycolysis


and Survival

Glucose 6C

Pyruvate 3C

2NAD

2NADH (reduced)

2 ATP

2 ADP + 2Pi

4 ADP + 4 Pi

4 ATP

Energy investment phase

Energy payoff phase

To electron transport system if oxygen present

Net gain of 2ATP molecules

Anaerobic respiration if oxygen absent

Glycolysis


and Survival

• Dehydrogenase enzymes have removed hydrogen ions and high energy electrons.

• These are passed to NAD or _______________________ which is a ____________,

• The reduced form of NAD is formed NADH.• This NADH will be used to produce ATP

later in respiration.• Two NAD molecules are involved at this

point producing two NADH

Glycolysis


and Survival

• Where does glycolysis take place in the cell?

• What is net gain in ATP from one glucose molecules during glycolysis?

• Is glycolysis anabolic or catabolic?

• Why?

After glycolysis what's next?


and Survival

• The pyruvate formed in glycolysis passes onto the CITRIC ACID CYCLE if Oxygen is present.

• Where does the Citric Acid Cycle occur?

Mitochondrion – the site of aerobic respiration


and Survival

Cristae – the site of electron transport chain

Matrix – the site of the Citric Acid Cycle (Krebs Cycle)

2CO2

Pyruvate

Acetyl coenzyme A

3NAD

FAD

FADH2

3NADH

ADP + PiATP

The Citric acid cycleNAD

NADH

2CO2

All the 2NADH2

go to the electron transfer system Citrate

Oxaloacetate

Coenzyme A


and Survival

Compound Number of carbons

Pyruvate

Acetyl coenzyme A

Citrate

Oxaloacetate

CO2

The Citric Acid Cycle

1. If oxygen is available pyruvate is broken down to carbon dioxide and an acetyl group.

2. Each acetyl group combines with coenzyme A to form acetyl coenzyme A. As this happens H ions are released and become joined to NAD forming NADH.

3. The acetyl group of acetyl coenzyme A combines with oxaloacetate to form citrate and enters the citric acid cycle.

4. After several enzyme-controlled steps oxaloacetate is regenerated.


and Survival

The Citric Acid Cycle5. During some of these steps dehydrogenase

enzymes remove H ions along with associated high-energy electrons. These H ions and high-energy electrons are passed to the coenzyme NAD to form NADH.

6. Also a similar reaction occurs but the coenzyme is FAD which becomes FADH2.

7. In addition, ATP is produced at one of the steps and carbon dioxide is released at two of the steps.

• This all occurs in the central matrix of the mitochondrion


and Survival

Electron Transport Chain• An electron transport chain consists of a group of

protein molecules attached to the inner membrane of the mitochondria. There are many of these chains in a cell.

1. NADH and FADH2, from glycolysis and the citric acid cycle release high-energy electrons and pass them to the electron transport chains.

2. The electrons begin in a high-energy state. As they flow along a chain of electron acceptors, they release energy. This is used to pump hydrogen ions across the membrane from the matrix side to the inter-membrane space to maintain a higher concentration of hydrogen ions.


and Survival


and Survival

3. When the hydrogen ions flow back down the concentration gradient to the matrix they pass through molecules of ATP synthase. This drives this enzyme to synthesise ATP from ADP and Pi.

4. Most of the ATP generated by cellular respiration is produced in mitochondria in this way.

5. When the electrons come to the end of the electron transport chain they combine with oxygen – the final hydrogen acceptor. At the same time, the oxygen joins to a pair of hydrogen ions to form water.

• In the absence of oxygen the electron transport chains do not proceed and ATP is not made at this stage.


and Survival

Substrates for respiration - carbohydrates

glucosemaltose

starch glycogen

sucrose

fructose

pyruvate

Substrates for respiration - fats

Fat

Glycerol

Fatty acids

glucose

intermediate

pyruvate

acetyl coenzyme A

Citric acid cycle

Substrates for respiration - proteins

Protein

Amino acids

Amino acids

glucose

pyruvate

acetyl coenzyme

A

Citric acid cycle

Amino acids

intermediate

urea

urea

urea

urea

deamination of amino acid to respiratory pathway intermediate

Absence of Oxygen


and Survival

• In the electron transport chain, oxygen and water combine to form metabolic or respiratory water.

• If oxygen is not present to act as the final hydrogen acceptor, then the hydrogen cannot pass through the system and complete oxidation cannot occur.

Fermentation


and Survival

• There is no oxygen present in anaerobic respiration and therefore no oxygen to act as the final hydrogen acceptor.

• Hydrogen cannot pass through the electron transport chain.

• This means that both the citric acid cycle and electron transport chain cannot take place.

• Glucose is only partially broken down and the only ATP produced is from glycolysis. This means that only 2 ATP are produced from one molecule of glucose that undergoes respiration.

Documents

Key Area 1: Cellular respiration Glycolysis, Citric Acid Cycle, Electron Transport Chain Unit 2: Metabolism and Survival