Energy in the Cell!

1. Energy in the Cell!

2. Energy • Ability to do Work/Ability to Cause Change • AMP – adenosine monophosphate • ADP – adenosine diphosphate • ATP – adenosine triphosphate – contains the energy used by the cell trapped between the second and third phosphate groups. Also contains adenine and a ribose sugar that form the “adenosine” base. • Why here? • The cell receives the greatest amount of energy in return for what it “cost” to form the bond between the second and third phosphate groups. Remember, the phosphate groups don’t want to be close together because they carry the same charge! When ATP binds to a protein, this specific bond is broken, releasing energy. Thus ATP functions as a cellular “battery”

3. Energy Sources • Sunlight • Photosynthesis • 6CO2 + 6H2O  C6H12O6 + 6O2 • Light Dependent Reactions • Light  Chemical Energy • Light Independent Reactions (Calvin Cycle) • Chemical Energy  Sugar

4. Chloroplast • Structure: • Photosystem – protein complex embedded within the thylakoid membrane; functions to capture the excited chlorophyll electrons • Chlorophyll – green pigment found in chloroplasts that provides the electrons in the light-dependent reactions. Green because it reflects the wavelengths that correspond to the “green” portion of the visible spectrum; absorbs other wavelengths. • Thylakoid Disk – site of light dependent reactions • Membrane • Lumen – cytoplasmic like fluid inside the thylakoid disk • Grana – stacks of flattened thylakoid disks • Stroma – cytoplasmic like fluid found inside the chloroplasts (different from the lumen due to the proteins and other constituents that are dissolved in water) • Double Membrane – surrounds chloroplasts

5. Light Dependent Reactions • Light  Chemical Energy

6. Light Dependent • Results: • ATP – provides the energy used in the light independent reactions to form PGAL • Oxygen – released into the atmosphere after photolysis (see next slide) • Protons – establish positive charge gradient inside the thylakoid disk (see next slide) • NADPH (nicotinamide adenine dinucleotide phosphate) • Transports electrons back to stroma for use in the LIR’s

7. What happens to the electrons? • Photolysis – splitting of water due to powerful oxidizing effect of chlorophyll • Half molecule of O (released into atmosphere) • Two H+ ions (back to thylakoid!) • Establish gradient; diffuse to produce more ATP in stroma through a channel protein called ATP Synthase. ATP Synthase captures the kinetic energy generated in diffusion and uses it to couple ADP and Pi in the stroma. This process is called chemiosmosis. • Two Electrons (back to chlorophyll!) so the LDR’s can occur again

8. Light Independent Rxn’s • Calvin Cycle • 3CO2 + 6NADPH + 5H2O + 9ATP  G3P + 2H+ + 6NADP+ + 9ADP + 8Pi • Carbon Fixation by RuBP • Unstable intermediates (first 6 carbon then two 3-carbon. These two unstable, 3-carbon molecules use the energy provided by ATP and the raw materials provided by NADPH and H2O to form a stable, 3-carbon compound called PGAL) • Results in 2 molecules of PGAL; 5/6 of PGAL is recycled to become more RuBP; 1/6 is used to form glucose (final product of photosynthesis). Thus, it requires 6 cycles of the “Calvin Cycle” to create one molecule of glucose (a stable, 6-Carbon sugar that provides energy)

9. Cellular Respiration • Glycolosis – anaerobic; occurs in the cytoplasm • Citric Acid Cycle – aerobic – occurs in the mitochondria • Electron Transport Chain – aerobic – occurs in the mitochondrial membrane

10. Glycolosis • Glucose  Pyruvic Acid • C6H12O6 + 2NAD+ + 2Pi + 2ADP  2 Pyruvate molecules + 2NADH + 2ATP + 2H+ + 2H2O • Pyruvate Decarboxylation by PDH (pyruvate dehydrogenase complex)  Acetyl-CoA + CO2 • This step must occur before our compound can enter the mitochondria for the aerobic reactions. It is an intermediate step.

11. Citric Acid Cycle and ETP • Acetyl-CoA  CO2 + ATP + NADH + FADH2 • Acetyl-CoA is broken down to release Carbon Dioxide, 2 ATP molecules, and two electron carriers that transport electrons to the electron transport chain (NADH and FADH2). This is the Citric Acid Cycle. It requires oxygen, and occurs in the mitochondria • Electron Transport Chain: 32 ATP Molecules • Location? • Membrane of the mitochondria

12. Lactic Acid Fermentation • Occurs when O2 is scarce! • Conversion between Lactic Acid and Pyruvic Acid occurs in Kidneys to produce ATP • Results in muscle fatigue (lactic acid buildup) • If oxygen is present, cellular respiration will proceed because it is so much more efficient at providing energy.