C1.2_Cell_respiration

C1.2 Cell respiration

Interaction and interdependece - Molecules

• What are the roles of hydrogen and oxygen in the release of energy in cells?
• How is energy distributed and used inside cells?

C1.2.1—ATP as the molecule that distributes energy within cells

ATP is a nucleotide (A1.2.1):

ATP

Adenosin TriPhosphate

ATP is a high energy molecule that functions as an immediate power source for cells. It transfers chemical energy between metabolic reactions.

C1.2.1—ATP as the molecule that distributes energy within cells

ATP is an excellent energy storage molecule to use as "currency" due to the phosphate groups that link through phosphodiester bonds.

What do we need the energy for?

C1.2.2—Life processes within cells that ATP supplies with energy

C1.2.2—Life processes within cells that ATP supplies with energy

C1.2.3—Energy transfers during interconversions between ATP and ADP

Hydrolysis

Regeneration

Exergonic reaction

Endergonicreaction

Used in endergonic reactions (anabolism)

Released from exergonic reactions (catabolism)

_ __

C1.2.4—Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds

What is respiration?

C1.2.4—Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds

Main substrates of cell respiration:

Cell respiration is a series of metabolic reactions that break down organic molecules, releasing energy (used to produce the ATP) that power all other processes in the cell

C1.2.4—Cell respiration as a system for producing ATP within the cell using energy released from carbon compounds

CELL RESPIRATION VS GAS EXCHANGE

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans

Aerobic respiration glucose + oxygen → carbon dioxide + water (+ATP) Anaerobic respiration glucose → lactate (+ATP)

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans

C1.2.6—Variables affecting the rate of cell respiration

Rate of respiration

Respiration rate = Variable measured / timeVariables:

• O2 consumed
• CO2 produced

Factors that affect respiration rate:

• Temperature
• Concentration of substrates (O2, glucose)
• pH
• ...

C1.2.6—Variables affecting the rate of cell respiration

Respirometer

C1.2.6—Variables affecting the rate of cell respiration

C1.2.6—Variables affecting the rate of cell respiration

Rate of respiration virtual lab

Go to the virtual lab and complete the Teams Forms

C1.2.7—Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration.

Redox reaction:

OIL RIG – Oxidation Is Loss (of electrons) ; Reduction Is Gain (of electrons)

C1.2.7—Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration.

Redox reaction:

Vital role in several steps of cell respiration

Nicotinamide adenine dinucleotide (NAD) is a key molecule in cell respiration. It functions as a coenzyme, a molecule that is required for an enzyme to carry out its function. NAD’s ability to be reduced and oxidised allows it to perform the critical role of a hydrogen/electron carrier.

C1.2.7—Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration.

Redox reaction:

NAD’s ability to be reduced and oxidised allows it to perform the critical role of a hydrogen/electron carrier.

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans AND C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Aerobic cell respiration 1. Glycolysis - Cytoplasm - Shared with anaerobic2. The link reaction - Mitochondrial matrix 3. Krebs cycle - Mitochondrial matrix4. Electron transport chain and chemiosmosis - Mitochondrial inner membrane

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Glycolysis - Cytoplasm - Shared with anaerobic respiration - Metabolic pathway (catalyzed by enzymes) - Includes the following processes: 1. Phosphorylation 2. Lysis 3. Oxidation 4. ATP formation

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Glycolysis 1. Phosphorylation: a phosphate group (PO43-) is added to an organic molecule

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Glycolysis 2. Lysis: 1 glucose molecule (6 C) is splitted into two molecules of pyruvate (2 x 3 carbon)

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Glycolysis 3. Oxidation: - 1 H isremoved from each of the 3C sugars (oxidation) to reduce NAD+ to NADH + H+ - Two molecules of NADH are produced in total (one from each 3C sugar)

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Glycolysis 4. ATP formation: - Substrate level phosphorylation: Some of the energy released from the sugar intermediates is used to directly synthesise ATP -In total, 4 molecules of ATP are generated during glycolysis by substrate level phosphorylation (2 ATP per each 3C sugar)

C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

C1.2.9—Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration

Anaerobic cell respiration 1. Glycolysis 2. NAD regeneration (fermentation)

NET yeald: 2 ATP molecule

C1.2.9—Conversion of pyruvate to lactate as a means of regenerating NAD in anaerobic cell respiration

Anaerobic cell respiration in humans:

• If oxygen is not present, pyruvate is not broken down further and no more ATP is produced (incomplete oxidation)
• The pyruvate remains in the cytosol and is converted into lactic acid

• Glycolysis involves oxidation reactions that cause hydrogen carriers (NAD+) to be reduced (becomes NADH + H+)
• Typically, the reduced hydrogen carriers are oxidised via aerobic respiration to restore available stocks of NAD+
• In the absence of oxygen, glycolysis will quickly deplete available stocks of NAD+, preventing further glycolysis
• Fermentation of pyruvate involves a reduction reaction that oxidises NADH (releasing NAD+ to restore available stocks for glycolysis)
• Hence, anaerobic respiration allows small amounts of ATP to be produced (via glycolysis) in the absence of oxygen

C1.2.10—Anaerobic cell respiration in yeast and its use in brewing and baking

Anaerobic cell respiration in yeast

• In yeast pyruvate is converted to ethanol and CO2
• Fermentation of pyruvate involves a reduction reaction that oxidises NADH (releasing NAD+ to restore available stocks)
• Although the NADH regeneration reaction is different than the one in humans
• In yeast, Ethanol and CO2 is formed (alcoholic fermentation)
• Again here, anaerobic respiration allows small amounts of ATP to be produced (via glycolysis) in the absence of oxygen

Compare and contrast anaerobic respiration in humans and yeast

C1.2.10—Anaerobic cell respiration in yeast and its use in brewing and baking

• Bread :Carbon dioxide causes dough to rise (leavening), the ethanol evaporates during baking

• Alcohol: Ethanol is the intoxicating agent in alcoholic beverages (concentrations above ~14% damage the yeast)

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans AND C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Aerobic cell respiration 1. Glycolysis - Cytoplasm - Shared with anaerobic2. The link reaction - Mitochondrial matrix 3. Krebs cycle - Mitochondrial matrix4. Electron transport chain and chemiosmosis - Mitochondrial inner membrane

C1.2.11—Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration

C1.2.11—Oxidation and decarboxylation of pyruvate as a link reaction in aerobic cell respiration

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans AND C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Aerobic cell respiration 1. Glycolysis - Cytoplasm - Shared with anaerobic2. The link reaction - Mitochondrial matrix 3. Krebs cycle - Mitochondrial matrix4. Electron transport chain and chemiosmosis - Mitochondrial inner membrane

B2.2.4 Adaptations of the mitochondrion for production of ATP by aerobic cell respiration

C1.2.12—Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD

• Citrate is produced by transfer of an acetyl group to oxaloacetate
• Oxaloacetate is regenerated by the reactions of the Krebs cycle, including:
• four oxidations (dehydrogenation)
• two decarboxylations.
• Output (per Acetyl CoA):
• 2 CO2
• 3 NADH+H
• 1 FADH2
• 1 ATP

C1.2.12—Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD

• Citrate is produced by transfer of an acetyl group to oxaloacetate
• Oxaloacetate is regenerated by the reactions of the Krebs cycle, including:
• four oxidations (dehydrogenation)
• two decarboxylations.
• Output (per Acetyl CoA):
• 2 CO2
• 3 NADH+H
• 1 FADH2
• 1 ATP

C1.2.12—Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD

C1.2.5—Differences between anaerobic and aerobic cell respiration in humans AND C1.2.8—Conversion of glucose to pyruvate by stepwise reactions in glycolysis with a net yield of ATP and reduced NAD.

Aerobic cell respiration 1. Glycolysis - Cytoplasm - Shared with anaerobic2. The link reaction - Mitochondrial matrix 3. Krebs cycle - Mitochondrial matrix4. Electron transport chain and chemiosmosis - Mitochondrial inner membrane

C1.2.7—Role of NAD as a carrier of hydrogen and oxidation by removal of hydrogen during cell respiration.

Redox reaction:

Vital role in several steps of cell respiration

Nicotinamide adenine dinucleotide (NAD) is a key molecule in cell respiration. It functions as a coenzyme, a molecule that is required for an enzyme to carry out its function. NAD’s ability to be reduced and oxidised allows it to perform the critical role of a hydrogen/electron carrier.

B2.2.4 Adaptations of the mitochondrion for production of ATP by aerobic cell respiration

C1.2.13—Transfer of energy by reduced NAD to the electron transport chain in the mitochondrion

• Reduced NAD and FAD from:
• Glycolysis
• Link reaction
• Krebs cycle

• Are oxidized as they transfer 2e- to the electron carrier proteins of the ETC
• NAD delivers the e- to the first and FAD to the second carrier.

C1.2.14—Generation of a proton gradient by flow of electrons along the electron transport chain

• The e- move along the ETC (are transferred from one protein to the next)
• The e- lose energy, which is used to pump H+ to the intermembrane space
• The membrane is impermeable to H+ and the H+ are pumped against gradient
• The accumulation of H+ in the intermembrane space generates a proton gradient.

C1.2.15—Chemiosmosis and the synthesis of ATP in the mitochondrion.

• The membrane is impermeable to H+

• The H+ can only go back to the matrix (with the gradient) using a specialised protein channel: the ATP synthase

• This flow of protons (aka proton motive force), generates the energy required to phosphorylate ADP using inorganic phosphate (Pi) to form ATP.

• Hence, ATP synthase couples release of energy from the proton gradient with phosphorylation of ADP.

• This process of forming ATP is called oxidative phosphorilation

C1.2.15—Chemiosmosis and the synthesis of ATP in the mitochondrion.

• The ATP synthase has a structure on it that rotates like a turbine.

• As the H+ flow through, it rotates and generates the ATP.

• This flow of protons down their electrochemical gradient is called chemiosmosis.

• Between 2 and 4 H+ are needed to phosphorilate 1 ATP

C1.2.15—Chemiosmosis and the synthesis of ATP in the mitochondrion.

C1.2.16—Role of oxygen as terminal electron acceptor in aerobic cell respiration.

• Oxygen accepts electrons from the ECT
• allowing continued flow of electrons along the chain.

• Oxygen accepts protons from the matrix of the mitochondrion
• producing metabolic water
• this helps to maintain the proton gradient between the intermembrane space and the matrix.

C1.2.17—Differences between lipids and carbohydrates as respiratory substrates.

1. What molecules can be substrates of cell respiration?

C1.2.17—Differences between lipids and carbohydrates as respiratory substrates.

1. What molecules can be substrates of cell respiration?
• Carbohydrates (glucose)
• Fatty acids
• Proteins
2. Which substrate provides more energy?

C1.2.17—Differences between lipids and carbohydrates as respiratory substrates.

1. What molecules can be substrates of cell respiration?
• Carbohydrates (glucose)
• Fatty acids
• Proteins
2. Which substrate provides more energy?

3. What determines the energy content of the different substrates? (Tip: think about the whole cellular respiration process)

C1.2.17—Differences between lipids and carbohydrates as respiratory substrates.

3. What determines the energy content of the different substrates? (Tip: think about the whole cellular respiration process)

• The amount of hydrogen available when the molecule is broken down.
• The more hydrogen, the more NAD can be reduced.
• The more reduced NAD produced, the more protons can be transported across the inner mitochondrial membrane
• Generating a greater proton motive force, and therefore more ATP.

C1.2.17—Differences between lipids and carbohydrates as respiratory substrates.

• Lipids contain more hydrogen than carbohydrates and les oxygen, so they provide more energy per gram.

• But fatty acids do not enter glycolysis, so only carbohydrates can be used for anaerobic respiration

• Fatty acids are broken down into acetyl groups and through the link reaction become units of acetyl CoA, ready to enter the Krebs cycle

C1.2.12—Oxidation and decarboxylation of acetyl groups in the Krebs cycle with a yield of ATP and reduced NAD

• Citrate is produced by transfer of an acetyl group to oxaloacetate
• Oxaloacetate is regenerated by the reactions of the Krebs cycle, including:
• four oxidations (dehydrogenation)
• two decarboxylations.
• Output (per Acetyl CoA):
• 2 CO2
• 3 NADH+H
• 1 FADH2
• 1 ATP

Linking Questions

Interaction and interdependece - Molecules

• In what forms is energy stored in living organisms?
• What are the consequences of respiration for ecosystems?