Cellular Respiration

Cellular Respiration

Cellular Respiration A series of chemical reactions needed to break down carbohydrates and other molecules in order to release the energy they contain. C6H12O6 + 6O2 -----> 6CO2 + 6H2O + ATP

Energy in Living Organisms Energy harvested from the breakdown of sugar is stored in energy carrier molecules: • adenosine triphosphate (ATP) • nicotinamide adenine dinucleotide (NADH) • flavin adenine dinucleotide (FADH2).

Energy Carrier Molecule: ATP ATP consists of adenine (red), ribose (purple) and three phosphate groups (blue).

Energy Carrier Molecule: ATP • The bonds between the phosphate groups are high energy bonds. When energy is needed, the bond between the 2nd and 3rd phosphate groups is broken. • About 30 kJ/mol of ATP is released. The remaining molecule is now called adenosine diphosphate (ADP). ATP <-----> ADP + P + energy

Energy Carrier Molecules: NADH & FADH2 NADH carries an amount of energy equivalent to 3 ATP. FADH2 carries an amount of energy equivalent to 2 ATP.

Types of Cellular Respiration Aerobic respiration: • the process that requires sufficient O2 • produces 36 ATP Anaerobic respiration: • The process that occurs when there is insufficient O2 supply • Produces ONLY 2 ATP C6H12O6 + 6O2 -----> 6CO2 + 6H2O + ATP Sufficient: Aerobic Insufficient: Anaerobic

Aerobic Cellular Respiration 3 Main Phases: • Glycolysis • Krebs Cycle • Electron Transport Chain

Phase1:Glycolysis A series of 10 steps that breaks down glucose (6-carbon molecule) into two pyruvate molecules (3-carbon molecules) This process does not use oxygen.

Phase 1:Glycolysis Energy Yield 2 ATP are used 4 ATP are made (net of 2 ATP) 2 NADH are made The 2 ATP can be used directly, however, the 2 NADH need to go into the 3rd phase (ETC) to be converted into ATP. The process occurs in the cytoplasm.

Phase 2: Krebs Cycle A process by which 2 pyruvate molecules are sent through a cycle to release CO2. During the cycle, a 6-carbon molecule of citrate is produced, thus this cycle is also known as the citric acid cycle.

Phase 2: Krebs Cycle Energy Yield / pyruvate 1 ATP 4 NADH 1 FADH2 Since glycolysis produces 2 pyruvate molecules, the energy yield should be doubled. ADP ATP

Phase 2: Krebs Cycle The 2 ATP can be used directly. The 8 NADH and 2 FADH2 go into the 3rd phase (ETC) to be converted into ATP. CO2 is a waste product that is blown off when breathing. This phase occurs in the matrix of a mitochondria.

Phase 3: The Electron Transport Chain (ETC) Process by which NADH and FADH2 are converted into ATP. H2O molecules are also formed during this phase. This phase occurs on the cristae of the mitochondria.

Phase 3: ETC Details • NADH and FADH2 that are formed during glycolysis and Krebs cycle each have a pair of electrons. • These electrons are brought to the cristae of the mitochondria and transferred to proteins called cytochromes. • The electrons are passed down through a series of cytochromes known as the ETC. • As the electron pairs move through each cytochrome, 2 hydrogen ions (H+) are pumped out of the matrix into the intermembrane space. • This causes the intermembrane space to have a high concentration of H+ and so H+ want to diffuse back into the matrix. • They do this through a protein known as ATP synthase. Energy from H+ is provided to join ADP+ P ------> ATP . • At the end of the ETC, the electrons join with oxygen and 2 H+ to produce H2O.

Phase 3: ETC The electrons from NADH start at the beginning of the chain and pump 3 pairs of H+ across. The electrons from FADH2 start farther down the chain and only pump 2 pairs of H+ across. Since each pair of electrons passes through ATP synthase to make 1 ATP, each NADH can produce 3 ATP and FADH2 can produce 2 ATP.

Energy Yield Overview 2 ATP (glycolysis) 2 ATP (Krebs cycle) 2 NADH (glycolysis) ----> 4 ATP in ETC** 8 NADH (Krebs cycle) --> 24 ATP in ETC 2 FADH2 (Krebs cycle) --> 4 ATP in ETC 36 ATP from 1 glucose molecule **Krebs cycle and ETC both occur in the mitochondria therefore NADH made in Krebs cycle is converted into 3 ATP each. Glycolysis occurs in the cytoplasm and therefore the 2 NADH produced there must enter the mitochondria to get to the ETC. Thiscosts energy. Therefore, each NADH from glycolysis is only worth 2 ATP each.

Question How many ATP could a prokaryotic cell get from 1 glucose molecule? Explain. Answer: A prokaryotic cell could get 38 ATP from 1 glucose molecule because prokaryotes do not have mitochondrial membranes. Therefore, glycolysis, Krebs cycle, and ETC all happen in the cytoplasm. ALL NADH are worth 3 ATP. Since the NADH produced in glycolysis does not have to enter the mitochondria, there in NO energy cost!

Review: Cellular Respiration C6H12O6 + 6O2 -----> 6CO2 + 6H2O + ATP Glycolysis ETC Krebs Cycle ETC All Phases: 2 from glycolysis 2 from Krebs cycle 32 from ETC

Anaerobic Cellular Respiration Glucose is converted into 2 pyruvate molecules in glycolysis which will then go to the Krebs cycle IF O2 if available. Sometimes, the amount of O2 available is insufficient and the 2 pyruvate molecules undergo a process called fermentation.

Anaerobic Cellular Respiration During fermentation in eukaryotic cells, pyruvate will either be converted into: • Ethanol through Alcoholic Fermentation • Lactic Acid through Lactic Acid Fermentation

AlcoholicFermentation Ethanol: • produced when yeast cells ferment • A source of ethyl alcohol (beer and wine) Glucose ----------> 2 pyruvate ---------> ethanol + CO2 fermentation glycolysis 2 ATP

Lactic Acid Fermentation Lactic Acid • Produced by cells of multicellular organisms during O2 deficient times (exercise) • Lactic acid causes the “burn” felt in muscle cells • Blood circulation moves excess lactic acid fermentation glycolysis Glucose ----------> 2 pyruvate ---------> lactic acid 2 ATP

AnaerobicRespiration Consider that aerobic respiration can produce 36 ATP/ glucose molecule. Therefore, how efficient is anaerobic respiration at getting energy from glucose? 2 ATP / 36 ATP * 100% = 5.6% efficient

Cellular Respiration