Cellular Respiration

Topic 3.7 and 3.8

Assessment Statements: Core

3.7.1 Define cell respiration.3.7.2 State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP.3.7.3 Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP.3.7.4 Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP.

Assessment Statements: Higher Level

Energy metabolism and REDOX reactions

• Metabolism is the sum of all of the chemical reactions in an organism: catabolic (breakdown) and anabolic (synthetic)

• Respiration is a catabolic pathway

• Photosynthesis is an anabolic pathway

• The two processes are closely linked in plants

• REDOX (oxidation-reduction) reactions play a key role in energy flow

through organisms

• This is because the electrons flowing from

one molecule to another are carrying energy with

them

REDOX reactionsOXIDATION REDUCTION

Loss of electrons Gain of electrons

Gain of oxygen Loss of oxygen

Loss of hydrogen Gain of hydrogen

Results in C-O bonds Results in C-H bonds

Results in a compound with lower potential energy

Results in a compound with higher potential energy

OIL RIGLEO says GER

Definition of cellular respiration

Controlled release of energy from

organic compounds to produce ATP

• Cells break down organic compounds by SLOW oxidation

• Chemical energy is stored in covalent bonds

• By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP

REDOX reactions in respirationCells tap energy from electrons transferred from organic fuels to oxygen

Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water

The protons follow the electrons to produce water

Loss of hydrogen atoms

Energy

Gain of hydrogen atoms

Where Does Cellular Respiration Take Place?

glycolysis occurs in the cytoplasm

Krebs Cycle & ETC Take

place in the mitochondria

Cellular Respiration: Standard level

How does the process of cellular respiration yield ATP (chemical energy) from food?

1. What do you already know about cellular respiration?

2. What organelle in the cell is the “powerhouse” that makes energy for the cell?

What is ATP?• Energy ‘currency’ used by all cells• Adenosine triphosphate• Organic molecule containing high-energy

phosphate bonds

Chemical Structure of ATP

3 Phosphates

Ribose Sugar

Adenine Base

How Do We Get Energy From ATP?

By breaking the high- energy bonds between the last two phosphates in ATP

ATP hydrolase (ATP’ase) catalyses the breakdown of ATP into ADP + Pi

Each day, you hydrolyse 1025 ATP molecules

ATP-ase ATP Synthetase

H2O

HYDROLYSIS (Adding H2O)

How is ATP re-made?

• Substrate-level phosphorylation (using enzymes: in the cytoplasm of the cell and the matrix of the mitochondrion)

• Chemiosmosis (in the mitochondria, using ATP synthase)

Substrate level phosphorylation and chemiosmosis

GLYCOLYSIS

Glucose Pyruvicacid

KREBSCYCLE

ELECTRONTRANSPORT CHAIN

AND CHEMIOSMOSIS

Substrate Level Phos. Substrate Level Phos. Oxidative Phos.

REDOX reactions in respirationCells tap energy from electrons transferred from organic fuels to oxygen

Glucose gives up energy as it is oxidized: it transfers its electrons (and energy) to water

The protons follow the electrons to produce water

Loss of hydrogen atoms

Energy

Gain of hydrogen atoms

Enzymes remove electrons from glucose molecules and transfer them to a coenzyme

Hydrogen carriers such as NAD+ shuttle electrons in redox reactions

OXIDATION

Dehydrogenaseand NAD+

REDUCTION

• NADH delivers electrons to a series of electron carriers in an electron transport chain

• As electrons move from carrier to carrier, their energy is released in small quantities

Redox reactions release energy when electrons “fall” from a hydrogen carrier to oxygen

Energy released and now

available for making ATP

ELECTRON CARRIERS

of the electron transport chain

Electron flow

Two mechanisms generate ATP

• ATP can be made by transferring phosphate groups from organic molecules to ADP

• This process is called substrate-level phosphorylation

• Occurs in cytoplasm and in matrix of the mitochondrion

1. Cells use the energy released by “falling” electrons to pump H+ ions across a membrane• The energy of the

gradient is harnessed to make ATP by the process of chemiosmosis

• also known as oxidative phosphorylation

Two mechanisms generate ATP

Figure 6.7A

High H+concentration

ATP synthase uses gradient energy to make ATPMembrane

Energy from

Low H+concentration

ATPsynthase

Electron transport

chain

Definition of cellular respiration

Controlled release of energy from

organic compounds to produce ATP

• Cells break down organic compounds by SLOW oxidation

• Chemical energy is stored in covalent bonds

• By releasing energy in a controlled way, it can be trapped in the ‘useful’ form of ATP

Cellular RespirationBreakdown of one

glucose results in 36 to 38 ATP molecules

• Metabolic Pathway that breaks down carbohydrates

• Process is exergonic as high-energy glucose is broken into CO2 and H2O

• Process is also catabolic because glucose breaks into smaller molecules

Equations for aerobic respirationAll of these are fine!....

Equation for Cellular Respiration

6CO2 + 6H20 + e- + 36-38ATP

+ heat

C6H12O6 + 6O2

YIELDS

Stages of Cellular Respiration1. Glycolysis ALWAYS

OCCURS

2. Anaerobic pathways if no oxygen available (Lactic acid and Ethanol fermentation)

3. Aerobic pathways if oxygen available (Link reaction, Krebs cycle, electron transport chain)

Where Does Cellular Respiration Take Place?

glycolysis occurs in the cytoplasm

Krebs Cycle & ETC Take

place in the mitochondria

Glycolysis: Always the initial stage of respiration

• Location: cytoplasm• Substrate: glucose• Requires input of 2 ATP• Products: pyruvate,

(NADH), 4 ATP Glycolysis is an anaerobic process: no oxygen required

the movie...

Glycolysis

Summary of glycolysis

1. Occurs in the cytoplasm of the cell2. Two ATP molecules are used to start the process

(‘energy investment phase’)3. A total of 4 ATP’s are produced (net gain of 2 ATP)4. 2 molecules of NADH are produced5. Involves substrate level phosphorylation, lysis, oxidation

and ATP formation6. Controlled by enzymes: when ATP levels in the cell are

high, feedback inhibition will block the first enzyme in the pathway

7. Produces 2 pyruvate molecules at the end

If no oxygen is available, glycolysis

(anaerobic) is followed by

fermentation (anaerobic)

Why fermentation?

In the absence of oxygen, glycolysis soon stops unless there is an alternative

acceptor for the electrons produced from the glycolytic pathway

Fermentation1. Alcoholic fermentation Pyruvate is converted into ethanol plus carbon dioxide and NAD+

2. Lactate fermentation

Pyruvate is converted into lactate and NAD+

Alcoholic fermentation in yeast

Alcoholic fermentation in yeast

• Pyruvate is produced from glycolysis• 3-carbon pyruvate is converted to 2-carbon ethanol and

carbon dioxide• Generation of carbon dioxide helps bread products to rise• Yeast is used to produce ethanol

Lactate fermentation in mammals

• Lactate is a 3-carbon molecule

• NAD+ is regenerated to allow glycolysis to continue

Aerobic respiration: Higher level

8.1.4: Explain aerobic respiration: the Link reaction, the Krebs cycle, the role of NADH and H+, the electron transport chain and the role of oxygen8.1.5: Explain oxidative phosphorylation in terms of chemiosmosis

Aerobic respiration

• Takes place in the mitochondria of eukaryotic cells

• Substrate: pyruvate• Produces LOTS of ATP (28 –

38 ATP): 90% of total ATP from respiration

• Also produces carbon dioxide, water and heat

• Oxygen is the final electron acceptor

Aerobic respiration

• 2 pyruvate molecules enter the mitochondrion

• Pyruvate loses a CO2 molecule and becomes acetyl CoA

• Krebs cycle produces 2 ATP, 4 CO2, 6 NADH and 3 FADH2

• Electron transport chain produces 34 ATP and water

• Aerobic respiration completely oxidises glucose

• Anaerobic respiration does not completely oxidise glucose – ethanol, lactate and carbon dioxide are by-products

Get to know your mitochondrial structure!

Stages of aerobic respiration

1. The ‘link’ reaction2. The Krebs cycle

3. The electron transport chain4. Chemiosmosis and oxidative phosphorylation

The Link Reaction

Steps 2 in aerobic respiration (step 1 is glycolysis in the cytoplasm)

After glycolysis, when there is ample oxygen…2 pyruvate molecules from glycolysis move into the matrix of the mitochondrion for the Link reaction and the Krebs cycle

Matrix – Link Reaction

Krebs Cycle

2

2

The Link reaction

The link reaction converts pyruvate (3C) into acetyl Coenzyme A (2C), producing carbon dioxide and NADH in the process

• Krebs: The walk-through...• Krebs: the movie…• The 2C acetyl Coenzyme A enters the Krebs cycle • It joins oxaloacetate (4C) to form citrate (6C). • Two carbon atoms are then lost as carbon dioxide

and the cycle repeats.• Hydrogen is released during this cycle to reduce

the coenzymes NAD+ and FAD to 3 NADH and 1 FADH2 for each cycle

• ATP is also released

The Krebs Cycle (Citric Acid/TCA cycle)

Each molecule of glucose produces• 2 pyruvates in

glycolysis• Leading to 2 acetyl CoA

molecules in the link reaction

Krebs cycle turns TWICE for each molecule of glucose

Fill in your table!

Substance Oxidised/Reduced/Neither Reason

NAD+

NADH

FADH2

FAD

How did you do?Substance Oxidised/

Reduced/NeitherReason

NAD+

NADH

FADH2

FAD

oxidised

reduced

reduced

neither

+ve due to lost electrongained H from organic moleculegained H from organic moleculeno loss/gain of H/electrons

Glycolysis: 2 ATP, 2 NADH, 2 pyruvate

Link: 2 NADH, CO2

Krebs : 2 ATP, 6 NADH, 2 FADH2, 2 CO2

Overall: 4 ATP, 10 NADH, 2 FADH2

Production PER glucose molecule

and finally….

The electron transport chain, chemiosmosis and oxidative

phosphorylation

• The movie…

Chemiosmosis in the mitochondrion

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex

Electroncarrier

Electronflow

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Rotenone Cyanide,carbon monoxide

Oligomycin

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Poisons interrupt critical events in cellular respiration

• The electrons from NADH and FADH2 travel down the electron transport chain to oxygen

• Energy released by the electrons is used to pump H+ (protons) into the space between the mitochondrial membranes

• In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase, which capture the energy to make ATP

Chemiosmosis powers most ATP production

Questions…

• What is the role and the position of oxygen in the electron transport chain?

• What is the benefit of having cristae in the mitochondria?

Chemiosmosis/ ETC occurs on the inner membrane of the mitochondria

Figure 6.12

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex

Electroncarrier

Electronflow

ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Final checks and balancesProcess ATP used ATP produced Net ATP gain

Glycolysis

Krebs cycle

Electron Transport Chain/

ChemiosmosisTotal

Final checks and balances

Process ATP used ATP produced Net ATP gain

Glycolysis 2 4 2

Krebs cycle 0 2 2

Electron Transport Chain/

Chemiosmosis

0 32 32

Total 2 38 36

Review of mitochondrial structure and function

Outer mitochondrial membrane

Matrix

Cristae

Inner mitochondrial membrane

Space between inner and outer membranes

Review of mitochondrial structure and function

Outer mitochondrial membrane Separates contents of mitochondrion from rest of cell

Matrix Like cytoplasm: enzymes for the Link reaction and the Krebs cycle

Cristae Increases surface area for oxidative photophosphorylation

Inner mitochondrial membrane Carriers for electron transport chain and ATP synthase and

Space between inner and outer membranes

Reservoir for protons (H+ ions) to create concentration gradient

For each glucose molecule that enters cellular respiration, respiration produces up to 38 ATP molecules

KREBSCYCLE

Electron shuttleacrossmembranes

Cytoplasmic fluid

GLYCOLYSIS

Glucose2

Pyruvicacid

2AcetylCoA

KREBSCYCLE

ELECTRONTRANSPORT CHAIN

AND CHEMIOSMOSIS

Mitochondrion

by substrate-levelphosphorylation

used for shuttling electronsfrom NADH made in glycolysis

by substrate-levelphosphorylation

by chemiosmoticphosphorylation

Maximum per glucose:

Some practice questions on respiration…

1. How do cells capture the energy released by cell respiration?

A. They store it in molecules of carbon dioxide.

B. They produce glucose.

C. The energy is released as pyruvate.

D. They produce ATP.

(Total 1 mark)

Some practice questions on respiration…

2. Which process produces the most ATP per molecule of glucose?

A. Anaerobic respiration in a yeast cell

B. Aerobic respiration in a bacterial cell

C. Glycolysis in a human liver cell

D. The formation of lactic acid in a human muscle cell

(Total 1 mark)

Some practice questions on respiration…

3. Which of the following is the best definition of cell respiration?

A. A process needed to use energy, in the form of ATP, to produce organic compounds

B. A process used to provide oxygen to the atmosphere

C. A controlled release of energy, in the form of ATP, from organic compounds in cells

D. A controlled release of energy in the production of food from organic compounds

(Total 1 mark)

Some practice questions on respiration…

4. Which of the following processes produces CO2?

I. Glycolysis

II. Alcohol (ethanol) fermentation

III. Lactic acid production

A. I only

B. II only

C. I and II only

D. I, II and III

(Total 1 mark)

Some practice questions on respiration…

4. Which of the following processes produces CO2?

I. Glycolysis

II. Alcohol (ethanol) fermentation

III. Lactic acid production

A. I only

B. II only

C. I and II only

D. I, II and III

(Total 1 mark)

Some practice questions on respiration…

4. State a word equation for anaerobic cell respiration in humans.

(1 mark)