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 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 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 reactions OIL RIG LEO says GER OXIDATION 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 RIG LEO 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 respiration Cells 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? What do you already know about cellular respiration? 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 Adenine Base 3 Phosphates Ribose Sugar

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

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 ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Substrate Level Phos. Substrate Level Phos. Oxidative Phos.

REDOX reactions in respiration Cells 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

Hydrogen carriers such as NAD+ shuttle electrons in redox reactions Enzymes remove electrons from glucose molecules and transfer them to a coenzyme OXIDATION Dehydrogenase and NAD+ REDUCTION

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

Two mechanisms generate ATP 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 High H+ concentration ATP synthase uses gradient energy to make ATP Membrane Electron transport chain ATP synthase Energy from Low H+ concentration Figure 6.7A

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

Breakdown of one glucose results in 36 to 38 ATP molecules Cellular Respiration Breakdown 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 respiration All of these are fine!....

Equation for Cellular Respiration C6H12O6 + 6O2 YIELDS 6CO2 + 6H20 + e- + 36-38ATP + heat

Stages of Cellular Respiration Glycolysis ALWAYS OCCURS Anaerobic pathways if no oxygen available (Lactic acid and Ethanol fermentation) 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 Occurs in the cytoplasm of the cell Two ATP molecules are used to start the process (‘energy investment phase’) A total of 4 ATP’s are produced (net gain of 2 ATP) 2 molecules of NADH are produced Involves substrate level phosphorylation, lysis, oxidation and ATP formation Controlled by enzymes: when ATP levels in the cell are high, feedback inhibition will block the first enzyme in the pathway 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

Fermentation 1. Alcoholic fermentation Pyruvate is converted into ethanol plus carbon dioxide and NAD+ 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 oxygen 8.1.5: 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 The ‘link’ reaction The Krebs cycle The electron transport chain Chemiosmosis and oxidative phosphorylation

The Link Reaction After glycolysis, when there is ample oxygen… 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 2 Krebs Cycle 2

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

The Krebs Cycle (Citric Acid/TCA cycle) 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

Krebs cycle turns TWICE for each molecule of glucose Each molecule of glucose produces 2 pyruvates in glycolysis Leading to 2 acetyl CoA molecules in the link reaction

Fill in your table! Substance Oxidised/Reduced/Neither Reason NAD+ NADH FADH2 FAD

How did you do? Substance Oxidised/Reduced/Neither Reason NAD+ NADH FADH2 FAD oxidised reduced neither +ve due to lost electron gained H from organic molecule no loss/gain of H/electrons

Production PER glucose molecule 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

and finally…. The electron transport chain, chemiosmosis and oxidative phosphorylation

The movie…

Chemiosmosis in the mitochondrion Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Poisons interrupt critical events in cellular respiration Rotenone Cyanide, carbon monoxide Oligomycin ELECTRON TRANSPORT CHAIN ATP SYNTHASE

Chemiosmosis powers most ATP production 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

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?

ELECTRON TRANSPORT CHAIN Chemiosmosis/ ETC occurs on the inner membrane of the mitochondria Protein complex Intermembrane space Electron carrier Inner mitochondrial membrane Electron flow Mitochondrial matrix ELECTRON TRANSPORT CHAIN ATP SYNTHASE Figure 6.12

Final checks and balances Process ATP used ATP produced Net ATP gain Glycolysis Krebs cycle Electron Transport Chain/ Chemiosmosis Total

Final checks and balances Process ATP used ATP produced Net ATP gain Glycolysis 2 4 Krebs cycle Electron Transport Chain/ Chemiosmosis 32 Total 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

ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS For each glucose molecule that enters cellular respiration, respiration produces up to 38 ATP molecules Cytoplasmic fluid Mitochondrion Electron shuttle across membranes KREBS CYCLE GLYCOLYSIS 2 Acetyl CoA 2 Pyruvic acid KREBS CYCLE ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS Glucose by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis by substrate-level phosphorylation by chemiosmotic phosphorylation 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)