Unit III - Bioenergetics - Cellular Respiration

All chemical reactions occurring with the cells of an organism. Metabolism includes processes that build complex substances from simpler ones and processes that break down complex substances into simpler ones. It also involves the continuous release and use of energy. Many biologists consider metabolic activity to be the single most important characteristic of life.

The process by which energy stored in food is released in the cells. This release of energy takes place inside the cells of both autotrophs and heterotrophs. Organisms as diverse as plants, animals, and microorganisms show remarkable similarities in the way they obtain energy from food.

Glucose(C₆H₁₂O₆) and Oxygen(O₂) from the plants is converted in the mitochondria into ATP (a form of energy), Carbon Dioxide(CO₂), and Water(H₂O).

Glucose is too large and to powerful for the cells parts to use . It must be converted to something the cell can accommodate. One example of this would be: A 20 dollar bill in a coke machine.

ATP is used by cells and cell organelles to complete the processes necessary for life. ATP is the only form of energy that cells can use for these life processes.

Mitochondria are round or slipper-shaped organelles that release the energy in food molecules for use by the cell. It is a double membrane structure. It's inner membranes have folds called Cristae. It is on these folds that many biochemical reactions that produce ATP occur.

The mitochondrion is the location where Kreb's Cycle takes place. The mitochondria take in two carbon acetyl groups attached to Coenzyme A. The acetyl Co-A transfers the acetyl groups to Kreb's cycle. Krebs Cycle, also known as the Citric Acid Cycle, is the splitting of the two acetyl groups to make four carbon dioxides, six NADH₂, two FADH₂, and two ATP.

The sources of the glucose(C₆H₁₂O₆) and Oxygen(O₂) needed for cellular respiration is photosynthesis.

Aerobic respiration = Cellular respiration that occurs in the presence of O₂. Anaerobic respiration = Cellular respiration that occurs when no O₂ is present.

Alcoholic Fermentation

Alcoholic Fermentation is also known as Yeast Fermentation. Alcoholic fermentation occurs through anaerobic respiration after glycolysis occurs. After glycolysis produces the pyruvic acid it is changed into yeast cells. These specific yeast cells can be converted into other substances such as ethyl alcohol and Carbon Dioxide. Breweries use the ethyl part of alcoholic fermentation while bakeries use the carbon dioxide to make the bread rise.

Electron Transport or Chemiosmosis

Chemiosmosis is the last step of the process of aerobic respiration. It consists of a chain of electron carriers located on the inner membrane of the mitochondrion of a cell. NADH₂ and FADH₂ add hydrogen to the chain. The hydrogen breaks into electrons (e^-) and hydrogen ions (H⁺). Through the process of electrons passing from carriers to other carriers, ATP is formed. In the end, free oxygen combines with the electrons and the H⁺ ions to form molecules of water. This process produces 32 ATP molecules from each molecule of glucose.

Factor for Comparison	Anaerobic Respiration	Aerobic Respiration
Reactants	Glucose	Glucose + Oxygen
Activation Energy	2 ATP	2 ATP
Location in the Cell	Cytoplasm	Mitochondrion
Total amount of ATP Produced	4 ATP	38 ATP
Net Energy Profit from Reaction	2 ATP	36 ATP

Alcohol Fermentation

Alcohol fermentation is the formation of alcohol from sugar. Yeast, when no oxygen is present, converts glucose to pyruvic acid by using the glycolysis pathway, then converting pyruvic acid into ethanol, a two carbon compound.

Fermentation and Cellular Respiration

The process of fermentation and aerobic process of cellular respiration are similar because both metabolic pathways use glycolysis to oxidize glucose and other substrates to pyruvate, producing a net profit of 2 ATP's by substrate phosphorylation, and the use NAD+ as the oxidizing agent that accepts electrons from food during glycolysis.

Glycolysis

Glycolysis is the process of breaking down the glucose molecule into two three-carbon pyruvic acid molecules. Glycolysis is a metabolic process (series of chemical reactions) that splits the glucose molecule(6c) into 2 pyruvic acid(3c) molecules. Two ATP'S are required to start the reaction (activation energy). Glycolysis releases enough energy to make a total of 4 ATP'S (a net profit of 2 ATP'S). In addition, transfer of hydrogen produces 2 NADH molecules. Glycolysis occurs in the cytoplasm not in the mitochondrion.

Aerobic and anaerobic respiration release energy as heat. In aerobic respiration glucose is completely oxidized to carbon dioxide and water. Complete oxidation allows the maximum amount of energy to be removed from the glucose as heat.

Glycolysis

glycolysis, which occurs in the cytoplasm is a metabolic process(a series of chemical reactions) that splits the glucose molecule (6 carbon) into 2 pyruvic acids (3 carbon) molecules. 2 ATP's are required to start the reaction (activation energy). Glycolysis releases enough energy to make a total of 4 ATP's ( a net profit of 2 ATP's). In addition, transfers of hydrogen produces 2 NADH molecules. At the same time,the hydrogen removed from PGAL is accepted by the coenzyme NAD, forming NADH. The process of breaking down the glucose molecule into 2 3-carbon pyruvic acid molecules is called Glycolysis.
For every pyruvic acid molecule produced by glycolysis, 2 ATP molecules are formed. Since the splitting of 1 glucose molecule produces 2 pyruvic acid molecules, a total of 4 ATP molecules are formed per glucose molecule. Remember, however, that 2 ATP molecules were used to energize the glucose molecule.
The net energy output of glycolysis, then, is 2 ATP molecules for each molecule of glucose, + the energy in the coenzyme NADH. The energy carried by NADH maybe used to form more ATP at a later stage but only if oxygen is present.

Humans switch back and forth between aerobic systems. Rhythmic activity utilizes the efficient aerobic respiration, while intense sudden bursts of activity utilize the anaerobic system. This system yields less energy in ATP so therefore restricts activity length.

Cellular respiration & photosynthesis depend on each other. Each provides the necessary requirements for the other & this ensures the flow of energy & cycling of matter in nature.