Energy for Life 12/11/14. Light Absorption in Chloroplasts

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1 Energy for Life Biochemical pathways A series of reactions where the products of one reaction is used in the next reaction Light Absorption in Chloroplasts Chloroplasts Two membranes Grana- layered stacks of thylakoids which contain chlorophyll There is a solution called the stroma which surrounds the grana 1

2 Light Absorption in Chloroplasts Light and Pigments Electromagnetic radiation What is white light? Light Absorption in Chloroplasts Pigments A compound that absorbs certain wavelengths and reflects others Chloroplast pigments Thylakoids contain chlorophylls and carotenoids Two types of chlorophylls Chlorophyll a absorbs more red Chlorophyll b absorbs more blue Light Absorption in Chloroplasts 2

3 Photosystems Clusters of chlorophylls and carotenoids 2 types Photosystem I Photosystem II Reactions fueled by light start when pigments in both photosystems absorb light The energy from light is transferred until it reaches chlorophyll a molecules 5 steps Step 1- Light forces electrons to go to a higher energy level in photosystem II Step 2- Excited electron leaves chlorophyll a Oxidation/Reduction reaction (OIL RIG) A molecule called the primary electron acceptor, found in the thylakoid membrane, takes electron Step 3- Primary electron acceptor passes electron on to a group of molecules called the electron transport chain As electron moves along chain, protons move into the thylakoid Step 4- Light is also absorbed at the same time by photosystem I. Electrons move from chlorophyll a to another primary electron acceptor Electron lost is replaced by electron from photosystem II 3

4 Step 5- The primary electron acceptor of photosystem I releases electron to a different electron transport chain which takes it to outside of thylakoid membrane that faces stroma The electron then combines with NADP+ to make NADPH Restoring Photosystem II An enzyme inside the thylakoid splits water to replace the missing electrons 2H 2 O à 4H + + 4e - + O 2 Proton stays inside thylakoid to be used later Electrons are put into photosystem II Oxygen diffuses out of chloroplast 4

5 Chemiosmosis Chemiosmosis is the synthesis of ATP A protein called ATP synthase, located in the thylakoid membrane, uses the protons to change ADP to ATP It is like a dam letting water out turning turbines Protons flow from high concentration to low concentration Calvin Cycle The carbon atoms released from CO2 during photosynthesis are bonded into organic compounds Through a series of steps the carbon is bonded to make compounds such as amino acids, lipids, and carbohydrates 5

6 Glycolysis The organic compounds produced by plants will be broken down by heterotrophs to gain energy Glycolysis is the process of turning glucose into 2 pyruvic acid molecules One NADH molecule is made per pyruvic acid Once pyruvic acid is produced there are two possible pathways Anaerobic respiration Aerobic respiration Anaerobic respiration occurs when there is an absence of oxygen Anaerobic respiration is also known as fermentation There are two types of fermentation Lactic acid fermentation Ethyl alcohol fermentation Lactic Acid Fermentation An enzyme converts pyruvic acid into lactic acid by taking two hydrogen atoms from NADH and H+ This allow glycolysis to continue 6

7 Lactic Acid Fermentation This process helps to produce certain foods like yogurt and cheese Also occurs during strenuous exercise What happens when you have too much lactic acid in your blood? Ethyl Alcohol Fermentation A two step process occurs to create CO2 and ethanol Not very efficient at converting pyruvic acid into energy Only about 3.5% of the potential energy is created through the anaerobic pathway Why do organisms use anaerobic respiration if it is inefficient? 7

8 Aerobic Respiration The process of creating energy when oxygen is present There are two major stages Krebs cycle Chain Occurs inside the mitochondria First step after glycolysis Pyruvic acid reacts with coenzyme A to form acetyl coenzyme A (acetyl CoA) NADH is produced Aerobic Respiration The Krebs Cycle Acetyl CoA is used to produce CO2, hydrogen atoms, and ATP Done in 9 steps Only 2 ATP directly produced 3 NADH molecules produced 1 FADH 2 molecule is produced 8

9 Aerobic Respiration Chain The mitochondria takes all the NADH and FADH 2 and turns it into ATP Aerobic Respiration How much Energy is produced? Glycolysis and the Krebs cycle produce 2 ATP 4 ATP Every NADH molecule makes 3 ATP Total of 10 NADH = 30 ATP Every FADH 2 molecule makes 2 ATP Total of 2 FADH 2 = 4 ATP Grand total = 38 ATP 9