Bre’ona Fergerson and Jaelon Harris Cellular Respiration Bre’ona Fergerson and Jaelon Harris

9.1 Catabolic pathways yield energy by oxidizing organic fuels

To keep working a cell must regenerate the ATP that it uses The breakdown of glucose and other organic fuels are exergonic ( accompanied by the release of energy) What is Cellular Respiration? It is the process in a cell’s mitochondria when food (sugar) is broken down using oxygen to produce energy. There are two main types of cellular respiration processes, aerobic and anaerobic.

Aerobic respiration and Anaerobic Respiration Aerobic respiration is the consumption of oxygen as a reactant along with organic fuel. Just think of it like this: Aerobic means “air” so this process needs air (oxygen) in order for it to work. Equation: Anaerobic Respiration is when a different substance is used in replace of oxygen as a reactant to harvest chemical energy. (*Also known as fermentation) For example, sometimes a plant or an animal doesn’t have enough oxygen to respire, but they still need energy to live so they perform respiration without oxygen to produce energy.

Redox Reactions In redox reactions the cell taps the energy stored in the food molecules, which causes one substance to partially or totally shift electrons to another substance. The substance that receives the electrons is reduced (becomes more negative) and the substance losing the electrons is oxidized (becomes more positive). During cellular respiration, glucose is oxidized to CO₂ and O₂ is reduced to H₂O. When electrons transfer from organic compounds to oxygen they lose potential energy; Electrons from the organic compound are usually first passed to NAD+ which reduces it to NADPH; the NADPH then passes the electrons to and Electron Transport Chain that connects them to O₂ in energy releasing steps. This energy is then used to make ATP.

Stages of Cellular Respiration: A Preview Glycolysis-The breakdown of enzymes by enzymes releasing energy and pyruvic acid; it produces 2 molecules of ATP. Citric Acid Cycle (Kreb’s Cycle)- the sequence of reactions in which most living cells generate energy during the process of aerobic respiration;takes place in mitochondria, consuming O₂, producing CO₂ and H₂O as waste products and converting ADP to energy-rich ATP. Glycolysis and the citric acid cycle supply electrons (through either NADH or FADH₂) to the electron transport chain, which drives oxidative phosphorylation ( metabolic pathway that cells use to oxidize nutrients which causes the release of energy which is used to reform ATP) . Oxidative phosphorylation then generates ATP.

9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

9.3 The citric acid cycle completes the energy-yielding oxidation of organic molecules

In eukaryotic cells, the importation of the pyruvate into the mitochondrion and its conversion to acetyl CoA links glycolysis to the citric acid cycle

9.4 During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis

Introduction Glycolysis (Concept 9.2) and the citric acid cycle(Concept 9.3) Glycolysis ⇒ 2 ATP (through substrate level phosphorylation) Citric Acid Cycle ⇒ 2 ATP (through substrate level phosphorylation) Concept 9.4: Oxidative Phosphorylation Oxidative Phosphorylation= Electron Transport Chain + Chemiosmosis ⇒ generating 34 ATP The most efficient and productive way in which cell harvest the energy from glucose and other nutrient 2 parts of process Electron Transport Chain Chemiosmosis NADH and FADH2 serve as electron carriers 34 ATP are produced

Electron Transport Chain Location cristae= the folded inner membrane of the mitochondria (in eukaryotes) Plasma membrane (in prokaryotes) Series of protein are embedded in the cristae 4 large protein complex (Complex I - IV) Cytochrome= electron carriers between ubiquinone and oxygen Electrons are passed down from one protein complex(less electronegative) to next protein complex(more electron negative) through the series of redox reaction As ETC progresses, reduction potentials increase until O2 Electron Transport Chain

The Pathway of Electron Transport NADH and FADH2 donate their electrons to ETC NADH (produced from Glycolysis and Citric Acid Cycle) FADH2 (produced from Citric Acid Cycle) FADH2 has less energy b/c it is added later in the chain Electrons are transferred along the ETC through the series of redox reaction ⇒ released energy Using that energy, H+ are pumped from matrix to intermembrane space ⇒ establish Proton Motive Force Proton Motive Force= high [H+] gradient in intermembrane space and low [H+] gradient in matrix Stored energy which can be used to make ATP through chemiosmosis At the end of ETC, oxygen serves as final electron acceptor by converting into water The Pathway of Electron Transport Cytochromes are electron carriers between ubiquinone and oxygen.

ATP Synthase What? Protein complex ⇒ made up of multiple polypeptides Location the inner membrane of the Mitochondrion 4 Components Stator Rotor internal rod Knob How it works? Hydrogen ions flow down between the stator and rotor and causes the rotor and rod to rotate The spinning rod causes changes in the stationary knob, activating three catalytic sites that make up the knob It catalyzes the addition of inorganic phosphate to ADP, generating ATP

Chemiosmosis: The Energy-Coupling Mechanism Chemiosmosis = Proton Motive Force ⇒ ATP(through ATP synthase) Chemiosmosis= energy stored in form of hydrogen ion gradient across a membrane to synthesize ATP H+ flow from high concentration gradient (intermembrane space) to low concentration gradient (matrix) through ATP synthase ATP synthase generates 34 ATP In total, cellular respiration generate 38 ATP Glycolysis⇒ 2 ATP (Substrate Level Phosphorylation) Citric Acid Cycle⇒ 2 ATP (Substrate Level Phosphorylation) ETC + Chemiosmosis⇒ 34 ATP (Oxidative Phosphorylation) https://www.youtube.com/watch?v=kN5Mtq AB_Yc Chemiosmosis is energy stored in form of hydrogen ion gradient across a membrane to synthesize ATP

9.5 Fermintation and anaerobic respiration enables cells to produce ATP without Oxygen.

Fermentation At the end of Glycolysis, pyruvate, ATP, and NADH are produced Pyruvate can undergo 2 different pathway (depending whether or not O2 is present) O2 is present⇒ Aerobic cellular respiration No O2 is present⇒ Fermentation 2 Types of Fermentation Alcohol Fermentation Lactic Acid Fermentation Purpose: regeneration of NAD+, which can be reused in Glycolysis

Types of Fermentation Alcohol Fermentation(Pyruvate⇒ ethanol) 2 Steps Pyruvate⇒ Acetaldehyde (by releasing CO2) Acetaldehyde⇒ Ethanol (reduced by NADH) Final electron acceptor: Acetaldehyde Produce 2 ATP (substrate level phosphorylation) Ex. yeast

Type of Fermentation 2) Lactic Acid Fermentation One Step Pyruvate⇒ lactate (reduced by NADH) Final electron acceptor: Pyruvate Produce 2 ATP (substrate level Phosphorylation) Example Fungi bacteria (used to make cheese and yogurt) human muscle cells

Aerobic Respiration Fermentation Environment Environment O2 is present Final Electron Acceptor Oxygen Net ATP Production (38 ATP) Glycolysis⇒ 2 ATP Citric Acid Cycle⇒ 2 ATP ETC + Chemiosmosis⇒ 34 ATP Types of organism that use Aerobic Respiration Obligate Aerobic= organism that can survive with O2 Fermentation Environment No O2 Final electron acceptor Organic molecule (Pyruvate or Acetaldehyde) Net ATP Production (4 ATP) 2 ATP (Glycolysis) 2 ATP (Fermentation) Type of Organism that use fermentation Obligate Anaerobe= organism that cannot survive in the presence of O2 Common pathway Glycolysis (to oxidize glucose) Type of Organism that can use either pathway Facultative Anaerobe= organism that can use either use either fermentation or aerobic respiration

9.6 Glycolysis and the citric acid cycle connect to many other metabolic pathways

Catabolic Pathway Breakdown complex molecules into monomers(used as fuels⇒ generate ATP) Carbohydrates (enter) Glycolysis and Citric Acid Cycle Proteins⇒ Amino acid ⇒ Deamination(removal of amino group) need to occur first Converted into intermediates of Glycolysis and Citric Acid Cycle Fat (broken down into) ⇒ Glycerol + Fatty Acid Glycerol(converted into)⇒Glyceraldehyde-3-Phosphate (intermediate of Glycolysis) Fatty Acid ⇒ beta oxidation(breakdown FA into acetyl CoA) ⇒ (enter) Citric Acid Cycle (produce) NADH and FADH2⇒ generate ATP (through Oxidative Phosphorylation)

Anabolic Pathway Monomers⇒ Complex molecules (consume ATP) Amino Acid⇒ Protein (build up muscle) Pyruvate⇒ Glucose Acetyl CoA⇒ Fatty Acid Connection between Glycolysis and Citric Acid Cycle Dihydroxyacetone Phosphate (from glycolysis) ⇒ (converted into) precursor of fat ⇒ used in Citric Acid Cycle

Feedback Mechanisms⇒ Regulation Feedback Inhibition= end product of pathway inhibits the enzyme that is used for early reaction step Ex. increase ATP⇒ slow down respiration; Decrease ATP⇒ speed up respiration (by regulating Enzyme activity) Enzyme pathway regulates: Phosphofructokinase(enzyme for step 2 glycolysis) Allosteric enzyme(has sites for specific activator and inhibitor to bind) Activator: AMP⇒ speed up Glycolysis Inhibitor: ATP and Citrate⇒ slow down Glycolysis

Chapter Question What is the reducing agent in the following reaction? The immediate energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylation is the? What metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule? In mitochondria, exergonic redox reactions do what? The final electron acceptor of the electron transport chains of mitochondria, which of the following changes occur? When electrons flow along the electron transport chains of mitochondria, what changes occur? Cells do not catabolize carbon dioxide because? Which of the following is a true distinction between fermentation and cellular respiration Most CO2 from catabolism is released during?

Answers NADPH Hᐩ concentration across the membrane holding ATP synthase Glycolysis Provide the energy that establishes the proton gradient. Oxygen The pH of the matrix increases CO₂ is already completely oxidized NADH is oxidized by the electron transport chain in respiration only The citric acid cycle