Cellular Respiration

Topic 3.7 and 3.8

Assessment Statements: SL

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.

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

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

Each day, you hydrolyse 1025 ATP molecules

ATP-aseATP-ase ATP ATP SynthetaseSynthetase

H2O

HYDROLYSIS (Adding HHYDROLYSIS (Adding H22O)O)

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

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 Breakdown of one

glucose results in glucose results in 36 36 to 38 ATPto 38 ATP molecules molecules

• Metabolic Pathway Metabolic Pathway that breaks down that breaks down carbohydratescarbohydrates

• Process is exergonic as Process is exergonic as high-energy glucose is high-energy glucose is broken into CObroken into CO22 and and HH22OO

• Process is also catabolic Process is also catabolic because glucose breaks because glucose breaks into smaller moleculesinto smaller molecules

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

Equation for Cellular Respiration

6CO6CO22 + 6H + 6H220 + e0 + e-- + 36-38 + 36-38ATP ATP

+ heat+ heat

CC66HH1212OO6 6 + 6O+ 6O22

YIELDSYIELDS

Stages of Cellular Respiration1.1. Glycolysis ALWAYS Glycolysis ALWAYS

OCCURSOCCURS

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

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

Where Does Cellular Respiration Take Place?

glycolysis occurs glycolysis occurs in the cytoplasmin the cytoplasm

Krebs Cycle & ETC TakeKrebs Cycle & ETC Take

place in the mitochondriaplace 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

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

• 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: the most efficient pathway for ATP generation

Aerobic respiration

• 2 pyruvate molecules enter the mitochondrion

• Pyruvate loses a CO2 molecule and becomes acetyl CoA

• Krebs cycle produces 2 ATP and CO2

• Electron transport chain produces 34 ATP and water

• Aerobic respiration completely oxidises a glucose molecule

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

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)