How cells harvest chemical energy ATP Cell respiration intro video Cellular Respiration How cells harvest chemical energy ATP Cell respiration intro video

Introduction to Cellular Respiration Cell respiration is how we derive energy from our food, specifically glucose Nearly all cells in our body break down sugars for ATP production The aerobic harvesting of energy from sugar is called cellular respiration Glucose Oxygen gas Carbon dioxide Water Energy 38 ATPs

Respiration and Cellular Respiration are linked Breathing supplies oxygen to our cells for cellular respiration, it also removes CO2 as a waste product BREATHING Muscle cells carrying out Cellular Respiration Sugar + O2  ATP + CO2 + H2O

Respiratory System Purpose What is respiration? The process by which oxygen and carbon dioxide are exchanged between cells, the blood, and air in the lungs The respiratory system is where gas exchange occurs Picks up oxygen from inhaled air Expels carbon dioxide lungs

Cellular Respiration banks energy in ATP Cellular respiration breaks down glucose molecules and banks their energy in ATP The process uses O2 and releases CO2 and H2O Glucose Oxygen gas Carbon dioxide Water Energy Introduction Animation

Redox Reactions Redox (oxidation-reduction) Reactions Oxidation describes the loss of an electron by a molecule, atom or ion; loss of hydrogen (H) or gain of oxygen (O) OIL: Oxidation Is Losing H atoms Reduction describes the uptake of an electron by a molecule, atom or ion; loss of oxygen (O) or gain of hydrogen (H) RIG: Reduction Is Gaining H atoms Give an example.

Cellular Respiration is a redox reaction Loss of hydrogen atoms Energy Glucose Gain of hydrogen atoms Glucose  Carbon dioxide is a oxidation reaction OIL Oxygen  Water is a reduction reaction RIG

Once again… Cellular Respiration banks energy in ATP Cellular respiration breaks down glucose molecules and banks their energy in ATP The process uses O2 and releases CO2 and H2O Glucose Oxygen gas Carbon dioxide Water Energy

What is ATP? ATP: adenosine triphosphate Currency of biological energy When ATP becomes ADP, it gives off energy A – P – P – P + H2O  A – P – P + P + energy Therefore, when ATP is created, energy is stored! Adenosine is made of adenine and ribose

How can we generate ATP ? Two different ways: 1. Substrate-level phosphorylation 2. Chemiosmosis An enzyme transfers a phosphate group from an organic molecule to ADP.

Generating ATP continued… 2. Chemiosmosis Oxidative phosphorylation ATP synthase (a protein) synthesizes ATP using the energy stored in concentration gradients of H+ ions across membranes Occurs in a membrane High H+ concentration ATP synthase uses gradient energy to make ATP Membrane Electron transport chain ATP synthase Energy from Low H+ concentration ATP synthesis

Cell Respiration occurs in 3 stages Glycolysis occurs in the cytoplasm of the cell Krebs cycle occurs in the mitochondria Electron transport chain occurs in the mitochondria High-energy electrons carried by NADH GLYCOLYSIS ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS KREBS CYCLE Glucose Pyruvic acid Cytoplasm Mitochondrion

Mitochondria Purpose of Cristae: The inner membranes of mitochondria fold many, many times. These folds are called cristae. These cristae are important because they make more surface area where chemical reactions can take place. The molecules and some of the enzymes responsible for making ATP are located in and on the folds of these inner membranes (cristae) Intermembrane space

Glycolysis Breaking down of sugar * Detailed Handout *

Glycolysis: breaking down of glucose Process by which 1 glucose molecule is broken down into 2 molecules of pyruvic acid. Does not require oxygen Occurs in the cytoplasm Glucose is broken in half, producing two molecules of pyruvic acid, a 3-carbon compound.

Glycolysis does release some energy Must invest two molecules of ATP to get the reaction started. During the reaction, 4 ATP are created = Net gain of 2 ATP NADH is an electron carrier NAD+ is a molecule that helps to pass energy from glucose to other pathways NAD+ + 2e - + H + = NADH

NADH, an electron carrier

After Glycolysis… Products of glycolysis: 2 ATP 2 NADH 2 pyruvic acid At the end of glycolysis, 90% of chemical energy that is available in glucose is still unused and locked in pyruvic acid. In the presence of oxygen, pyruvic acid passes to the Krebs Cycle. Glycolysis Animation

Acetyl CoA (acetyl coenzyme A) Convert pyruvic acid  Acetyl CoA Preparatory step between glycolysis and Krebs cycle Products: 2 Acetyl CoA 2 NADH 2 CO2 Each pyruvate molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle Acetyl CoA (acetyl coenzyme A) pyruvate CO2

TAKES PLACE IN THE MATRIX OF THE MITOCHONDRIA Krebs Cycle Completes the oxidation of organic fuel, Generates many nadh and fadh2 molecules TAKES PLACE IN THE MATRIX OF THE MITOCHONDRIA

Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from acetyl CoA Acetyl group (2C) combines with 4C compound = citric acid (6C) Citric acid is broken down and electrons released into 3 NADH and FADH2 4C compound ready to restart cycle Citric Acid C-C-C-C-C-C Oxaloacetic Acid C-C-C-C KREBS CYCLE CO2 Acetyl group of acetyl CoA combines with a 4C molecule = 6C citric acid Citric acid is broken down into 4C molecule, more CO2 is released and electrons transferred to energy carriers The 4c is ready to continue in the cycle, join with another acetyl group and start the cycle over. 5 carbon compound C-C-C-C-C CO2

Energy Tallies from Krebs Cycle One pyruvic acid Two pyruvic acid 1 ATP 4 NADH One from pyruvic  acetyl CoA 3 from citric acid  4C 1 FADH2 2 ATP 8 NADH 2 from prep stage 6 from citric  4C 2 FADH2 In the presence of oxygen, these high energy electrons can be used to generate HUGE amounts of ATP Krebs Animation

Electron Transport Chain Chemiosmosis powers ATP PRODUCTION

Electron Transport Chain NADH and FADH2 are passed to the electron transport chain (ETC) ETC is located in the inner membrane of the mitochondria ETC uses high energy electrons from these molecules to convert ADP  ATP How?! Pumping H+ ions! (sound familiar?)

What fuel do we have headed into ETC? From glycolysis: 2 ATP (substrate-level phosphorylation) 2 NADH From prep stage and Krebs cycle 8 NADH 2 FADH2

Electron Transport Chain: composed of carrier proteins located in inner membrane High energy electrons from NADH and FADH2 travel down the electron transport chain to an oxygen atom At the end of ETC, an enzyme combines the electrons with H+ ions and oxygen to form WATER Oxygen is the final electron acceptor Protein complex Intermembrane Space Electron carrier High energy electrons are passed from one carrier protein to the next. Oxygen serves as final electron acceptor of ETC. Inner membrane Electron flow 2e- + 2 H+ + ½ O2  H2O Matrix

Electron Transport Chain: composed of carrier proteins located in inner membrane As electrons move down the chain, H+ ions are pumped into the intermembrane space of mitochondria (High H+ concentration) Protein complex Intermembrane Space Electron carrier High energy electrons are passed from one carrier protein to the next. Oxygen serves as final electron acceptor of ETC. Inner membrane Electron flow Matrix

Chemiosmosis H+ ions go down concentration gradient (highlow) through ATP synthase forming ATP H+ ions that have come through ATP synthase are now ready to move across the membrane again via the electron transport chain = giant circle.

Each glucose molecule yields up to 38 molecules of ATP Each NADH has enough energy to create 3 ATP each Each FADH2 has enough energy to create 2 ATP each Total ATP count with oxygen: Process Initial Input ATP output Glycolysis 2 ATP 2 NADH 6 ATP Krebs Cycle 8 NADH 24 ATP 2 FADH2 4 ATP TOTAL ATP = 38 ATP ETC animation

ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS REVIEW Cytoplasmic fluid Mitochondrion Electron shuttle across membranes GLYCOLYSIS 2 Acetyl CoA ELECTRON TRANSPORT CHAIN AND CHEMIOSMOSIS 2 Pyruvic acid KREBS CYCLE Glucose by substrate-level phosphorylation used for shuttling electrons from NADH made in glycolysis by substrate-level phosphorylation by chemiosmotic phosphorylation Maximum per glucose:

Anaerobic Respiration Without Oxygen

Fermentation is an anaerobic alternative to aerobic respiration After glycolysis, if there is no oxygen then fermentation occurs. Fermentation releases energy from food molecules by producing small amounts of ATP in the absence of oxygen. Glycolysis will stop when all NAD+ electron carriers are full…how can NAD + be replenished? Pyruvic acid Glucose

Converting NADH to NAD + During fermentation, cells will convert NADH to NAD+ by passing high energy electrons back to pyruvic acid. By converting NADH to NAD+, glycolysis can continue and small amounts of ATP are created. Two types: Alcoholic Fermentation Lactic Acid Fermentation

Alcoholic Fermentation In alcoholic fermentation, pyruvic acid is converted to CO2 and ethyl alcohol. This recycles NAD+ to keep glycolysis working Pyruvic acid + NADH  ethyl alcohol + CO2 + NAD+ GLYCOLYSIS 2 pyruvic acid 2 Ethanol Glucose

Lactic Acid Fermentation In lactic acid fermentation, pyruvic acid is converted to lactic acid This recycles NAD+ to keep glycolysis working Pyruvic acid + NADH  lactic acid + NAD+

Lactic Acid Buildup During strenuous exercise, our cells require energy faster than our bodies can deliver oxygen Lactic Acid Fermentation (anaerobic): Our body begins to convert pyruvic acid into lactic acid to continue glycolysis to generate ATP. This as lactic acid builds up at high levels in our muscles High lactic acid = high acidity = pain and burning sensation This often painful sensation also gets us to stop overworking the body, thus forcing a recovery period in which the body clears the lactate and other metabolites. Once the body slows down, oxygen becomes available and lactate reverts back to pyruvate, allowing continued aerobic metabolism and energy for the body’s recovery from the strenuous event.

Exercise and ATP

During exercise there are 3 sources of ATP 1. Stored ATP 2. Lactic Acid Fermentation 3. Cell Respiration During a 200m sprint: Stored ATP is gone in a few seconds of intense activity Lactic Acid supplies enough energy for about 90 seconds Only way to get rid of lactic acid Heavy breathing to increase oxygen consumption 1oom final

What about a longer race? 2OOOm race Need to use cell respiration = continuing supply of ATP Respiration releases energy slowly which is why even well-conditioned athletes pace themselves. Where does the supply of glucose come from? GLYCOGEN in the muscles Glycogen stores enough glucose to last 15-20min Then it starts using other energy such as fats.

One final point All organisms have the ability to harvest energy (ATP) from organic molecules (glucose) However, only plants can make organic molecules (glucose) from inorganic sources by the process of photosynthesis

Photosynthesis vs. Cell Respiration Function Energy Capture in Foods Energy Release from Foods Location Chloroplasts mitochondria Reactants Carbon dioxide, water and light energy Glucose and oxygen Products Carbon dioxide, water and ATP energy Equation 6CO2 + 6H2O + light  C6H12O6 + 6O2 C6H12O6 + 6O2  6CO2 + 6H2O + ATP