Cellular Respiration

Chemical Energy and Food PHOTOSYNTHESIS ___________ + _________ + ___________ →_______________ + __________ 6 CO2 6 H2O C6H12O6 6O2 CELLULAR RESPIRATION C6H12O6 6 CO2 _____________ + _________ →________ + __________ + __________ 6O2 6 H2O The two equations are exact opposites! Discovery School - The Mitochondria (2:44)

Comparing Photosynthesis & Cellular Respiration: Which type(s) of organisms carry out photosynthesis? Autotroph Heterotroph Which type(s) of organisms carry out cellular respiration?

Organisms that do CELLULAR RESPIRATION: Bacteria Protists Fungi Plants Animals In short – almost ALL organisms undergo cellular respiration (also known as AEROBIC RESPIRATION)!

EXCEPT FOR… SOME bacteria, who undergo a similar process called ANAEROBIC RESPIRATION, which does NOT require oxygen. Instead, this process may use nitrate, sulfate, or carbonate… HOWEVER, it does not result in as much ATP production as when oxygen is used

Energy (Adenosine triphosphate) Reactants Products O2 + C6H12O6 → CO2 + H2O + ATP Oxygen Carbon Dioxide Water Glucose/sugar Energy (Adenosine triphosphate) Yields/ produces Cellular respiration is the process that releases energy from food in the presence of oxygen.

Structure of the Mitochondria:

Chemical Energy and Food Cellular respiration happens slowly and in many steps. If all the energy was release in one step… Most would be lost as light and heat! Cellular respiration breaks down glucose molecules and banks their energy in ATP

Chemical Energy and Food Unit for measuring energy in food = Calorie 1 Calorie = 1 kilocalorie = 1,000 calories Energy Consumption - Virtual Cell Animation (4:41)

Anaerobic Vs Aerobic Respiration Anaerobic Respiration Does NOT require oxygen Makes less ATP (than aerobic) Ex:Glycolysis Aerobic Respiration Requires oxygen Makes more ATP Ex: Krebs cycle and electron Transport chain

3 Stages of Cellular Respiration Glycolysis Krebs Cycle (Citric Acid Cycle) Electron Transport Chain (ETC)

Glycolysis ATP (Glykos = sweet, Lysis = split apart) The first step in cellular respiration Happens in the CYTOPLASM outside the mitochondria Does not require oxygen, BUT it needs some energy to get it started. What molecule is going to supply the energy? ATP Glycolysis Overview - Virtual Cell Animation (3:00)

Glycolysis Reactions - Virtual Cell Animation (5:00) Produces pyruvic acid (pyruvate = 3-carbon compound) Cell needs to invest some energy to get a higher return (2 ATP gained) Occurs quickly, in milliseconds to respond to increased energy demand Produces 2 NADH Glycolysis Reactions - Virtual Cell Animation (5:00)

Put in 2 ATP and get back 4 ATP Glycolysis ________ ↓ ___________ → → _____________ ____________________ + _______________ GLUCOSE 2 PYRUVIC ACID ATP ATP ATP ATP NADH NADH Put in 2 ATP and get back 4 ATP Net gain of 2 ATP and 2 NADH

The Advantages of Glycolysis Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase. Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.

Mitochondria Structure Has a double membrane, with an intermembrane space between the two layers. Cristae are folds of the inner membrane The matrix is the innermost compartment, which is filled with a gel-like fluid.

Citric Acid Cycle An Overview (3:17) The Krebs Cycle 2nd stage of cellular respiration also known as the Citric Acid Cycle (The Krebs Cycle is because citric acid is the first compound formed in this series of reactions.) Citric Acid Cycle An Overview (3:17)

Kreb’s Cycle (preparation stage) Pyruvic acid from glycolysis enters the matrix NAD+ accepts 2 high- energy electrons to form NADH. One molecule of CO2 is also produced. The remaining 2 carbon atoms react to form acetyl- CoA. Diagram by Riedell The Citric Acid Cycle The Reactions (4:13)

The Citric Acid Cycle The Reactions (4:13) The Krebs Cycle Acetyl-CoA combines with a 4-carbon molecule (oxaloacetic acid) to produce citric acid. The Citric Acid Cycle The Reactions (4:13) Diagram by Riedell

The Citric Acid Cycle The Reactions (4:13) The Krebs Cycle Citric acid is broken down into a 5-carbon compound and then a 4-carbon compound. Two molecules of CO2 are released. The 4-carbon compound can then start the cycle again by combining with acetyl-CoA. The Citric Acid Cycle The Reactions (4:13)

KREBS CYCLE KREBS CYCLE PRODUCES ____ 3 1 1 4 Krebs Cycle Animation

Energy Extraction Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle. So each molecule of glucose results in 2 complete “turns” of the Krebs cycle.

Electron Transport Chain Final step in the breakdown of glucose Where occurs across the inner membrane of the mitochondria. Energy Yield Total of 32 ATP H2O NAD+ NADH ATP H+ Controlled release of energy for synthesis of ATP Electron transport chain 2 O2 2e + 1 Electron Transport Chain (2:00)

Electron Transport Chain Most of the energy in glucose is stored in electron carriers NADH and FADH2 Only 4 total ATP produced per glucose after complete breakdown in the Krebs Cycle

Electron Transport Chain NADH and FADH2 deposit electrons into electron transport chains in the inner mitochondrial membrane Electrons join with oxygen gas and hydrogen ions to made H2O at the end of the ETCs

FIGURE 8-8 The electron transport chain of mitochondria NADH and FADH2 donate their energetic electrons to the carriers of the transport chain. As the electrons pass through the transport chain, some of their energy is used to pump hydrogen ions from the matrix into the intermembrane space. This creates a hydrogen ion gradient that is used to drive ATP synthesis. At the end of the electron transport chain, the energy-depleted electrons combine with oxygen and hydrogen ions in the matrix to form water.

Chemiosmosis Energy is released from electrons as they are passed down the electron transport chain Released energy used to pump hydrogen ions across the inner membrane Hydrogen ions accumulate in intermembrane space

Chemiosmosis Hydrogen ions form a concentration gradient across the membrane, a form of stored energy Hydrogen ions flow back into the matrix through an ATP synthesizing enzyme Process is called chemiosmosis

Chemiosmosis Flow of hydrogen ions provides energy to link 32-34 molecules of ADP with phosphate, forming 32-34 ATP ATP then diffuses out of mitochondrion and used for energy-requiring activities in the cell

Overview of Cellular Respiration

Cellular Respiration Glycolysis, Krebs cycle, Electron Transport (6:01)

Fermentation When pyruvic acid moves to the next step, if there is no oxygen = anaerobic if there is oxygen = aerobic

Fermentation Fermentation – process by which cells release energy in the absence of oxygen Glycolysis produces ATP quickly and does not require O2 Without O2 the ETC does not run – no where for NADH to deposit its electrons Without NAD+ the cell cannot keep glycolysis going and ATP production stops.

Two types of fermentation: Alcoholic Fermentation Lactic Acid Fermentation

Alcoholic Fermentation Occurs in yeast cells: Yeast is added to bread– CO2 produced in fermentation make air spaces in bread and therefore bread rises. Alcohol evaporates during cooking Alcohol is toxic to cells. If too much fermentation occurs, alcohol will kill yeast cells. Happens when: Yeast make beer Bacteria make wine How Stuff Works - Bread (2:35) How Stuff Works - Whiskey (2:32)

Lactic Acid Fermentation Happens in muscles during exercise when body can’t get oxygen to tissues fast enough. Lactic acid builds up in muscles causing soreness. Bacteria use lactic acid fermentation to make: yogurt, cheese, sour cream, pickles, sauerkraut

The Totals Cellular Respiration (aerobic: with oxygen) 1 glucose → 36 ATP Fermentation (anaerobic: without oxygen) 1 glucose → 2 ATP