* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Unit 7
Survey
Document related concepts
Metalloprotein wikipedia , lookup
NADH:ubiquinone oxidoreductase (H+-translocating) wikipedia , lookup
Basal metabolic rate wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Adenosine triphosphate wikipedia , lookup
Citric acid cycle wikipedia , lookup
Electron transport chain wikipedia , lookup
Microbial metabolism wikipedia , lookup
Photosynthesis wikipedia , lookup
Biochemistry wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Transcript
Unit 7: Cellular Energetics Chapters 6-8 By Brook Wigginton Chapter 6 An Introduction to Metabolism Metabolic Pathways • In a metabolic pathway, a specific molecule is altered in a series of defined steps, resulting in a product. • Some metabolic pathways release energy by breaking down complex molecules to simpler ones. These degradative processes are called catabolic pathways. -Glycolysis • Anabolic pathways, in contrast, consume energy to build complicated molecules from simpler ones. Types of Energy • Energy is the capacity to cause change. • Kinetic energy can be associated with the relative motion of objects • Thermal Energy is the kinetic energy associated with the random movement of atoms or molecules • Thermal energy in transfer from one object to another is called heat. • Potential energy is energy that is not kinetic -Example • Chemical energy is a term used by biologists to refer to the potential energy available for release in a chemical reaction. Laws of Energy Transformation • According to the first law of thermodynamics, the total amount of energy in the universe is constant. It cannot be created nor destroyed. • The second law of thermodynamics states that the spontaneous directional energy flow is from high to low quality forms. Enzymes • Enzymes are catalysts that speed up certain reactions by lowering the activation energy. • Enzymes can be controlled by: -Temperature. High temperatures decrease reaction rates. -pH balance. They function best at a level of 7. -Salinity. If enzymes are dissolved in fluids that exceed the tolerance level, the hydrogen bonds will break, thus inactivating the enzyme. Endergonic vs. Exergonic • Endergonic reactions require energy input resulting in products with more energy than the reactants had. -Photosynthesis • Exergonic reactions release energy such that the products have less energy than the reactant. -Cellular Respiration Redox Reactions • In electron transfer chains, molecules accept and give up electrons in an orderly, stepwise manner to control the release of energy. • Oxidation-reduction reactions are simply electron transfers between molecules. The donor molecule loses and electron and is oxidized, then the donor molecule gains an electron and is reduced. • Bioluminescence comes from an enzyme called ‘luciferase’. • Reactions begin when ATP is in the presence of oxygen, which transfers a phosphate group to luciferin. • As the enzymes start to react, they release the extra energy in the form of fluorescent light at each step in the reaction. Chapter 7 Cellular Respiration and Fermentation Carbohydrate Breakdown Pathways • Anaerobic respiration and fermentation can release small quantities of energy without the use of oxygen • Aerobic respiration is the main energyreleasing pathway leading to ATP formation in eukaryotes. Aerobic Respiration • The formula for aerobic respiration is as following: C6H12O6 + 6O2 6CO2 + 6H2O • Three reactions are required for aerobic respiration: 1. 2. 3. Glycolysis- the breakdown of glucose to pyruvate; small amounts of ATP are generated. The Krebs Cycle- degrades the pyruvate to CO2, ATP is produced, and NAD+ and FAD accept H+ and electrons to be carried to the electron transfer chain. Electron Transfer Phosphorylation- processes the H+ and electrons to generate high yields of ATP; oxygen is the final electron acceptor. Fermentation vs. Aerobic Respiration • Anaerobic respiration and fermentation take place when there is no oxygen present. • Aerobic respiration takes place when in the presence of oxygen. Important Formulas • Glycolysis- glucose + oxygen oxygen and water • Fermentation- pyruvate acetyl aldehyde + NADH + alcohol • Krebs Cycle- acetyl Co A + hydrogen ATP + NADH + FADH + CO2 • Electron transfer phosphorylation- FADH2 + NADH H +ATP + H2O Glycolysis • Enzymes in the cytoplasm catalyze several steps in the breakdown of a 6 C sugar glucose into two molecules of pyruvate. • Glycolysis begins when glucose is first phosphorylated, then split to form two molecules of PGAL using two ATP molecules. • Then, enzymes remove H+ and electrons from PGAL to change NAD+ to NADH. -4 ATPs are produced • Overall, glycolysis produces 2 pyruvates, 2 ATP, and 2 NADH • Additionally, glycolysis occurs in the cytoplasm of the cell. After Glycolysis • Acetyl-Co A formation occurs as each pyruvate enters the mitochondria. 1 C is removed and attaches to the oxygen, forming carbon dioxide; the 2 C fragment remaining joins coenzyme A to form Acetyl-Co A • The Krebs Cycle/The Citric Acid Cycle - Begins when the two pyruvates are converted into two acetyl-coenzyme A (acetyl-CoA), two carbon dioxide molecules, and two NADH. Then, during the series of eight reactions that make up the citric acid cycle, the two acetyl-coA molecules are oxidized, yielding two more molecules of carbon dioxide and 2 ATP. After the Krebs Cycle • Electron Transfer Phosphorylation is when NADH and FADH2 give up their electrons to transfer systems embedded in the mitochondrial inner membrane. The energy is used to pump H+ out of the inner compartment. When H+ flow back through the ATP synthase in the channels, the cuopling of P to ADP yields ATP (cont.) • Oxygen joins with the used electrons from the glucose molecules and the H+ to yield water. • Without oxygen, the transfer chain becomes clogged, and no H+ gradient forms. No gradient means no ATP, which means the cell will die. Total Energy • Overall, electron transfer yields 32 ATP, glycolysis yields 2 ATP, and the Krebs cycle yields 2 ATP for a total of 36 ATP per glucose molecule! That is a lot of energy. Anaerobic Pathways • Anaerobic pathways operate when there is no oxygen present. Pyruvate from glycolysis is metabolized to produce molecules other than acetyl CoA. • Fermentation pathways -Fermentation yields enough energy for many single-celled anaerobic organisms and is sufficient for some aerobic organisms when oxygen levels are diminished, but as a whole, is ineffective for large, multi-celled organisms. Types of Fermentation • Alcoholic fermentation begins with glucose degradation into pyruvate. Then, cellular enzymes convert pyruvate to acetaldehyde, which then accepts electrons from NADH to become alcohol. • Lactate fermentation occurs when certain bacteria, such as milk, and muscle cells have the enzymes capable of converting pyruvate into lactate. No additional ATP beyond the net 2 from glycolysis is produced, but NAD+ is regenerated. Twitches • Slow twitch muscle fibers support steady, prolonged activity because they have an abundance of mitochondria making lots of ATP. • Fast twitch muscle fibers have few mitochondria and produce small amounts of ATP by lactate fermentation, so they support quick, non-sustainable demands for energy. Alternate Energy Sources • Excess fats are stored in adipose tissue, which is digested into glycerin, which enters glycolysis. • Fatty acids enter the Krebs cycle, and since they have so many carbon and hydrogen atoms, they are broken down more slowly and yield more ATP. • Amino acids travel in the blood, and after the amino group is removed, the amino acid is fed into the Krebs cycle. Chapter 8 Photosynthesis Light Properties • Light energy is packaged as photons, which vary in energy as a function of wavelength. The light reflected in each pigment gives the pigment it’s color. • Only a small range (380-750) of wavelengths are used in photosynthetic reactions Taste the Rainbow • Chlorophyll is the most common pigment used in photosynthesis by plants, photosynthetic protists, and cyanobacteria. • A pigment absorbs light of specific wavelengths by acting as an antenna for receiving photon energy. • Photosynthesis begins when photosynthetic pigments absorb a photon of light. Photo Flat • Photosynthesis takes place in the chloroplast. • The semifluid interior, the stroma, is the site for the second stage of reactions • Thylakoids, which are like flattened sacs, are interconnected by channels weaved through the stroma. Two Types of Reactions • Light dependent reactions convert light energy to chemical bond energy of ATP • Light independent reactions assemble sugars and other organic molecules using ATP, NADPH, and CO2 Light Dependent Reactions • Begins when light is ‘harvested’ by pigments in the chloroplasts. -One pathways begins when chlorophyll P680 in photosystem II absorbs energy. A boosted electron moves through a transport system, which releases energy for ATP. -The other pathway begins when chlorophyll P700 in photosystem I absorbs energy. The boosted electron from P700 passes to the acceptor, then the electron transport chain, and finally joins NADP+ to form NADPH. Noncyclic Photophosphorylation • Step 1: • Electrons trapped by P680 in photosystem II are energized by light. • Step 2: • Two energized electrons are passed to a molecule called the primary electron acceptor. This electron acceptor is called “primary” because it is the first in a chain of electron acceptors. Electron Transport Chain • Step 3: • Electrons pass through an electron transport chain. This chain consists of proteins in the thylakoid membrane of the chloroplast that pass electrons from one carrier protein to the next. Some carrier proteins, such as the cytochromes, include nonprotein parts containing an ion. The electron transport chains in photosynthesis are analogous to those in the inner mitochondrial membrane. Phosphorylation • Step 4: • As the two electrons move “down” the electron transport chain, they lose enrgy. The energy lost by the electrons as they pass along the ETC is used to phosphorylate, on average, about 1.5 ATP molecules Photosystem I & NADPH • Step 5: • The ETC terminates with P700. Here the electrons are again energized by sunlight and passed to a primary electron acceptor. • Step 6: • The two electrons pass through a short ETC. At the end of the chain, the two electrons combine with NADP+ and H+ to form NADPH. NADPH is a coenzyme, electron acceptor, and forms an energy rich molecule. Parting the Red Sea • Step 7: • The two electrons that originated in PS II are now incorporated into NADPH. The loss of these two electrons from PS II is replaced when H2O is split into two electrons, 2 H+, and ½ O2. The two electrons from the water replace the lost electrons from PS II, one of the H+ provides the H in NADPH, and the ½ O2 contributes to the oxygen gas that is released. Calvin-Benson Cycle • Step 1: Carbon fixation -6 carbon dioxide combine with 6 RuBP to produce 12 PGA. The enzyme rubisco catalyzes the merging of carbon dioxide and RuBP. The Calvin Cycle is referred to as C3 Photosynthesis because the first product formed, PGA, contains three carbon atoms. Step 2 • Reduction: 12 ATP and 12 NADPH are used to convert 12 PGA to 12 G3P. The energy in the ATP and NADPH molecules is incorporated into G3P, thus making it a very energized molecule. Step 3 • Regeneration: 6 ATP are used to convert 10 G3P to 6 RuBP. Regenerating the 6 RuBP originally used to combine with 6 CO2 allows the cycle to repeat. Step 4 • Carbohydrate synthesis: Note that 12 G3P were made in step 2, but only 10 were used in step 3. These two remaining G3P are used to build glucose. Other monosaccharides, like fructose and maltose, can also be formed. In addition, glucose molecules can be combined to form disaccharides, like sucrose, and polysaccharides, like starch and cellulose.