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Cell Energy ATP and Enzymes Respiration Photosynthesis Energy • Energy – the ability to do work • ATP – molecule that stores energy in which organisms use; adenosine triphosphate • Calorie – the unit used to measure the amount of energy food contains • Metabolism – the collection of the chemical reactions that occur in a cell; anabolism and catabolism Energy • Potential energy – stored energy, energy that results from position – Food has potential, stored, energy • Kinetic energy – energy of motion – Our bodies convert food into kinetic energy ATP and ADP • ADP – adenosine diphosphate turns into ATP through the process of phosphorylation, addition of a phosphate group to a molecule Energy from food Synthesis of ATP ADP + P ATP Energy used by cell Hydrolysis of ATP Role of Enzymes • Proteins that help chemical reactions in living organisms and help control the chemical environment at cell’s level • Catalyst – a chemical that helps a chemical reaction, but is not consumed or changed in the reaction – Enzymes act as a catalyst in biochemical reactions Role of Enzymes Role of Enzymes • Reactant – the reactant molecule in which the enzyme reacts • Substrate – the area on the enzyme where the substrate fits in shape and chemistry • Active site – where substrate fits • Product – the molecule produced in the enzyme reaction • Pepsin – an enzyme produced by the stomach for digestion of proteins • Amylase – an enzyme produced in the salivary glands for the digestion of carbohydrates Role of Enzymes • Enzymes lower the activation energy required for chemical reactions to take place Cellular Respiration • The process by which living things release energy from food C6H12O6 + 6O2 6CO2 + 6H2O + ATP glucose + oxygen carbon + water + energy dioxide Cellular Respiration • Redox reaction – a chemical reaction in which electrons are transferred between atoms • Reduction – a chemical reaction that results in a gain of electrons – Glucose loses electrons and hydrogen • Oxidation – a chemical reaction that results in a loss of electrons – Oxygen gains electrons and hydrogen C6H12O6 + 6O2 6CO2 + 6H2O + ATP Cellular Respiration • Electron carriers – special molecules that carry electrons from one set of reactions to another • NADH (nicotinamide adenine dinucleotide) – the main electron carrier involved in cellular respiration Stages of cellular respiration • Glycolysis – Glucose is split • Kreb’s Cycle – Produces ATP, NADH, and FADH2 • Electron Transport Chain – Produces ATP Glycolysis • Uses 2 ATP molecules to split glucose into two 3-carbon compounds. • Bonds rearrange and produce NADH from NAD+, along with two 3-carbon compounds. • Two 3-carbon compounds are converted into pyruvic acid, along with 4 ATP. • In order to move into the mitochondria, pyruvic acid is converted into acetic acid, which bonds to coenzyme A to create acetyl CoA. It releases acetic acid into mitochondria Glycolysis NADH 3-carbon NAD+ compound 3-carbon compound 2 ATP Pyruvic Acid 2 ATP Glucose 3-carbon compound 3-carbon compound Pyruvic Acid NAD+ NADH 2 ATP Kreb’s Cycle • Acetic acid enters the matrix of mitochondria. • The cycle also uses 3 NAD+ and 1 FAD molecule through a series of chemical reactions. • The products are 2 CO2, 1 ATP, 3 NADH, and FADH2 molecules. Kreb’s Cycle Electron Transport Chain • NADH transfers electrons to first electron carrier. High energy electrons passed down chain. • Energy is released each time electrons are moved down the chain, which pumps H+ across the membrane. Water is also formed. • The energy released, with ATP synthase, produces ATP by adding phosphate to ADP Fermentation • Anaerobic – not requiring oxygen • Fermentation – process for making ATP not requiring oxygen • Lactic acid – an organic waste produced by anaerobic fermentation – Occurs during periods of intense exercise “side ache) • Ethyl alcohol – a liquid waste produced by anaerobic fermentation – Occurs in yeasts when making bread and alcoholic beverages. Controlling Respiration • Feedback inhibition – process used by cells to control metabolic pathways – Too much of a substance creates a pathway to stop the production of the substance – Too little of a substance creates a pathway to increase production of a substance – Ex. - Hyperventilate, Hunger, Increased respiration during exercise Photosynthesis • Heterotrophs – organisms that cannot make their won food and must obtain energy from the foods they eat • Autotrophs – a self-nourishing organism that makes its own food • Photosynthesis – process by which autotrophs harvest energy to make glucose 6CO2 + 12H2O + light C6H12O6 + 6O2 + 6H2O Leaf Anatomy • Stoma – an opening on the underside of a leaf for gas exchange • Vascular bundle – a vein in a leaf that transports water and food • Mesophyll – the green tissue inside a leaf • Chlorophyll – the pigment that absorbs light in autotrophs Leaf Anatomy Top Layer Mesophyll Vascular Bundle Stoma Light Absorption Light Absorption • The first step in photosynthesis is the absorption of light energy • Plant cells convert energy from light to chemical energy; called the light reaction • Produces ATP and NADPH Light Reaction Light Reaction • Electrons gain energy when light strikes chlorophyll. • Excited electrons transferred to a reaction center and enter an electron transport chain. • An assembly of proteins and pigments through which electrons are transferred to reaction centers is called a photosystem Light Reaction • Photosystem I – chlorophyll absorbs red light and produces ATP; electrons return to reaction center • Photosystem II – chlorophyll absorbs red light and moves electrons to Photosystem I; electrons are replaced by the splitting of water and oxygen is released • Energy enriched electrons produce ATP by adding a phosphate to ADP • No glucose is produced after the light reaction. Dark Reaction (Calvin Cycle) • The first step of the Calvin cycle, CO2 molecules combine with the sugar RuBP (ribulose bisphosphate) to make PGA (phophosglycerate). – The source of carbon in photosynthesis is CO2 in the air. • The second step of the Calvin cycle, energy from ATP combines with electrons from NADPH to form G3P, and energy rich sugar molecule. Dark Reaction (Calvin Cycle) • The third step of the Calvin cycle, G3P produces glucose and other compounds needed for growth and metabolism. • The fourth step of the Calvin cycle, energy from ATP is added to G3P to make RuBP. The cycle is complete and begins again. Dark Reaction (Calvin Cycle) Making Glucose in Difficult Conditions • C4 plants – a plant that photosynthesizes in hot, dry weather – Special enzymes convert CO2 into a fourcarbon compound – Ex. corn and crabgrass • CAM plants – a plant that takes in CO2 only during the night. – Open stomata at night and store CO2 for use in the day – Ex. Cacti and pineapple