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Cellular Respiration
IB DP Biology: Higher Level/ Option C
Stephen TaylorBandung 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. 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
Image source unknown
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 1NAD+ 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
Krebs Cycle 1. Acetyl CoA (2C) enters the cycle & joins a 4C molecule2. In a series of steps, the remaining H and high energy electrons are removed from the Acetyl CoA3. 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-
• A Quick Review• Quiz
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