Cellular Respiration IB DP Biology: Higher Level/ Option C Stephen Taylor Bandung International School

Respiration Cell respiration: controlled release of energy from organic molecules (most often glucose) by oxidation in order to generate ATP ATP: Adenosine TriPhosphate – Energy carrying molecule. Carries measured doses of energy. Used to facilitate many cell reactions. ADP + P + energy ATP

Other Energy Carrying Molecules NADH: A second energy carrying molecule in the mitochondria. NADH is a coenzyme. NAD+ + 2H → NADH + H+ FADH2: A third energy carrying molecule in the mitochondria. FADH2 is also a coenzyme. Coenzymes are nucleotides which act as enzyme helpers. They accept hydrogen and electrons from substances at one reaction site transfer them to a second reaction site. Adenine is the nucleotide found in both NADH and FADH2

Structure of the Mitochondria The cell organelles where the bulk of aerobic respiration occurs Have 2 bilayer membranes with the inner membrane folded Cristae: folded inner membrane increases surface area. Electron transport and oxidative phosphorylation occur here Matrix: fluid-filled inner compartment. Contains enzymes for the Krebs cycle.

Outer Compartment: Space between inner and outer membranes Outer Compartment: Space between inner and outer membranes. Protons pumped here to create a high proton concentration (used to power creation of ATP – chemiosmosis) The first step of respiration, glycolysis, occurs just outside the mitochondria in the cytoplasm

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As a result of oxidation reactions in living cells, hydrogen atoms tend to carry electrons and energy to the substance to be reduced. NAD+ + 2H NADH + H+ Example 1 NAD+ is reduced to NADH by addition of 1H and 1 electron from the 2nd H. The 2nd H is oxidized to H+ by the loss of and electron

Glycolysis The first series of reactions that break glucose apart to liberate the energy it holds in its covalent chemical bonds. Glycolysis occurs in both aerobic and anaerobic respiration Occurs solely in the cytoplasm

Summary of the Steps of Glycolysis 2 ATP added to glucose (6C) to energize it Glucose split to 2 PGAL (3C) (phosphoglyceraldehyde) H+ and e- taken from each PGAL and given to make 2 NADH NADH is energy and e- carrier Each PGAL rearranges into pyruvate (3C), with energy transferred to make 4 ATP (substrate phosphorylation)

Although glycolysis makes 4 ATP, the net ATP production by this step is 2 ATP because 2 were used to start glycolysis. The 2 net ATP are available for cell use. If NO oxygen is available to the cell, pyruvate will be fermented by addition of 2H from the NADH (to alcohol + CO2 in yeast or lactate in muscle cells). This changes NADH back to NAD+ so it is available for the 3rd step above. This keeps glycolysis going

Summary Table of Glycolysis Summary of Glycolysis 1. One glucose (6C) converted into 2 pyruvate (3C) 2. Net yield of 2 ATP for use by cell 3. Two NAD+ are converted into 2 NADH & 2H+ (these go to electron transport) During glycolysis, addition of a phosphate to ADP to make ATP is known as substrate phosphorylation

If oxygen is available to the cell, the pyruvate will move into the mitochondria and aerobic respiration will begin.

Anaerobic Respiration Respiration without O2 = Fermentation Lactate Fermentation: in muscle – glucose partially broken down into lactate (3C) & 2 net ATP Alcohol Fermentation: in yeast & bacteria – glucose partially broken down into ethyl alcohol (2C), CO2 & 2 net ATPS

After glycolysis occurs, pyruvate enters the mitochondria and diffuse to the matrix At the matrix, the Krebs Cycle occurs. Here, the remaining hydrogen atoms and their rich electrons are removed In one turn of the Krebs Cycle, 1 ATP, 1FADH2, and 3 NADH are made In one turn of the Krebs Cycle, 2 CO2 are released

The 2 ATP are available for use by the cell The FADH2 and 3 NADH proceed to the Cristae where they provide energy for Electron Transport (also known as oxidative phosphorylation) The energy provided by all the NADH and FADH2 is used To pump H ions into the outer compartment This creates a charge imbalance across the cristae (high potential energy) As H ions diffuse back to the matrix, they pass through a protein channel with an enzyme, ATP synthase, which takes the energy released by the H ions and uses it to create ATP (from ADP + P) Oxygen bonds with 2 hydrogen ions (removing then so aerobic respiration can continue) to form water.

Summary of One Turn of the Krebs Cycle 1. Acetyl CoA (2C) enters the cycle & joins a 4C molecule 2. In a series of steps, the remaining H and high energy electrons are removed from the Acetyl CoA 3. Three NAD+ are converted into 3 NADH & 3H+ 4. One FAD is converted into 1 FADH2 5. One ATP is made (by substrate phosphorylation-addition of phosphate to ADP to make ATP) 6. Two CO2 are released 7. At the end of the cycle, nothing remains of the original glucose molecule

Electron Transport/Oxidative Phosphorylation The purpose of the Electron Transport Chain is to receive the high energy electrons carried by the coenzymes NADH &FADH2 and use the energy from these electrons to pump protons out of the matrix. A high concentration of protons results. As the protons diffuse back to the matrix, their energy is used by the ATP synthase to create 32 ATP. Oxidative phosphorylation (electron transport) - The creation of ATP via chemiosmosis as a result of electron transport.

Electron Transport Occurs at cristae (inner membrane) NADH & FADH2 deliver H+ and e- to cristae Electrons “transport” along cristae through electron acceptors, provide energy to pump H+ from matrix to outer compartment Concentration of H+ is now higher in outer compartment. H+ pass through ATP synthases in cristae back to matrix. 32 ATP are made. This is known as chemiosmosis Last step involves H+ & e- added to oxygen. This frees NAD+ to return to glycolysis & Krebs Cycle to pick up more H+ & e-

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