Cellular Respiration Energy for life’s activities

Overview of Cellular Respiration The life processes of ALL organisms require energy. The potential energy held in the bonds of food molecules CANNOT be used directly by the cell. Energy from food must be converted to the ONLY energy source that cells can use … ATP!

Review of ATP Adenosine Triphosphate Result of the bonding of a free phosphate w/free ADP molecule The bond between the phosphates is where the actual energy is stored

Review of ATP, cont. When the bond between the phosphates is broken, energy is released

Cellular Respiration Defined Respiration is the process by which the energy in the bonds of nutrients are used to synthesize ATP. Respiration occurs continuously in all cells of all organisms. The energy needed to synthesize ATP comes from an organism’s food

Summary of Cell Respiration ATP ADP + P energy (out) energy (in) cellular respiration cell activities ATP energy (out) cellular respiration cell activities The whole process is an enzyme controlled reaction.

Aerobic Respiration Aerobic Respiration – respiration with oxygen C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O energy (to make ATP)

Aerobic Respiration, cont. Happens in 2 stages:  Stage 1 – Glycolysis  glyco – glucose lysis – splitting  In glycolysis, a glucose molecule is broken into 2 pyruvic acids  This requires the input of 2 ATP molecules as activation energy

energy released to make small quantity of ATP (2 molecules) series of enzyme controlled reactions pyruvic acid glucose Glycolysis does not require oxygen

Aerobic Respiration, cont.  Stage 2 – Breakdown of pyruvic acid  The pyruvic acid made in glycolysis still contains a lot of energy  It can only be broken down to release the rest of the energy in the presence of oxygen

energy released to make large quantity of ATP (34 molecules) series of enzyme controlled reactions pyruvic acid carbon dioxide + water

Summary of ATP production Stages 1 and 2 release all the chemical energy in one molecule of glucose to make a total of 36 molecules that can be used by the organism  There is actually enough energy in a glucose molecule to make ~90 ATP, but the rest is lost as heat

ATP production – summary 34 ADP + 34 P = 34 ATP glucose pyruvic acid carbon dioxide + water 2 ADP + 2 P = 2 ATP ~56 ATP (heat)

The Mitochondrion

The Role of the Mitochondrion In order for the cell to capture as much energy as it possibly can from it’s food, a series of controlled reactions requiring the input of oxygen is necessary These reactions are directed by the mitochondrion

The Role of the Mitochondrion, cont. Glycolysis occurs in the cytosol (cytoplasm) of the cell The aerobic reactions occur in the mitochondria of the cell and are divided into 2 stages

The Role of the Mitochondrion, cont. Stage 1 – The Krebs (Citric Acid) Cycle  Discovered by Hans Krebs in 1937  Pyruvic acid is broken down into CO 2 in a series of energy-extracting reactions  The first compound formed in this series of reactions is citric acid  This is the stage that is the source of all the CO 2 that you exhale

Krebs Cycle  The Krebs Cycle occurs in the matrix of the mitochondrion

The Role of the Mitochondrion, cont. Stage 2 – The Electron Transport Chain  The Krebs Cycle generates many high- energy hydrogen atoms  Oxygen is added as an electron carrier at this stage  When the oxygen binds with the hydrogen, energy is released to form ATP and water is made

Electron Transport Chain  The electron transport chain occurs in the cristae of the mitochondrion.

Anaerobic Respiration Also called fermentation Happens in low/no oxygen conditions 1 Glucose only partially broken down to form waste products and 2 ATP

Anaerobic Pathways Pathway 1- Lactic Acid Fermentation  Glucose  2 lactic acid + 2 ATP –Happens in muscle cells when they run out of oxygen –Happens in bacteria that make yogurt, cheese, dill pickles

glycolysis still happens as it does not require oxygen in absence of oxygen pyruvic acid is turned into lactic acid. pyruvic acid lactic acid glucose 2 ADP + 2 P 2 ATP

Anaerobic Pathways, cont.  A build up of lactic acid produces muscle fatigue  This makes the muscles ache and contract with less power  A recovery period is needed; during this time more O 2 is taken in which converts lactic acid back into pyruvic acid  The volume of O 2 needed is called oxygen debt

Anaerobic Pathways, cont. Pathway 2 – Alcoholic Fermentation  Glucose  2 ethanol + 2 CO ATP  process in which sugars are converted into alcohol and carbon dioxide by the action of various yeasts, molds, or bacteria

glycolysis still happens, producing 2 ATP molecules This time in absence of oxygen, pyruvic acid is turned into carbon dioxide and ethanol glucose pyruvic acid ethanol + carbon dioxide This is irreversible 2 ADP + 2 P 2 ATP

Comparing Aerobic & Anaerobic Cellular Respiration Pathways Aerobic (needs oxygen) Anaerobic (no oxygen) Occurs in:Most organismsMostly yeast and bacteria 1 glucose makes: 6 CO H 2 OEthanol + CO 2 Or Lactic acid + CO 2 Net ATP production: 362

Adaptations for Respiration Bacteria, protists & fungi –Respiratory gases are exchanged by diffusion Plants –Respiratory gases are exchanged through leaves, stems, and roots –Moves in and out of cells by diffusion but leaves and stems also have openings to the environment (stomata)

Adaptations for Respiration in Animals Techniques vary: –Simple diffusion across cell membranes –Diffusion across moist skin into a circulatory system –Openings to the environment that can be flapped open and closed with a circulatory system to transport gases –Specialized respiratory structures (e.g. lungs) to speed exchange of respiratory gases