The Great Life Processes Photosynthesis and Aerobic Respiration

Photosynthesis

Outline Flowering Plants Photosynthetic Pigments Photosynthesis –Light Reactions NoncyclicCyclic –Calvin Cycle Reactions –C4–C4–C4–C4 –CAM

Photosynthetic Organisms Photosynthesis transforms solar energy into the chemical energy of a carbohydrate. –All organisms use organic molecules produced by photosynthesizers as a source of chemical energy.

Flowering Plants The green portions of plants, particularly leaves, carry on photosynthesis. –Leaf of flowering plant contains mesophyll tissue. Contains cells specialized to carry on photosynthesis.

Flowering Plants CO 2 enters leaf through stomata. CO 2 and water diffuse into chloroplasts. –Double membrane surrounds fluid (stroma). Inner membrane system within stroma form flattened sacs (thylakoids). –Often stacked to form grana.

–Chlorophyll and other pigments within thylakoid membranes are capable of absorbing solar energy.

Photosynthetic Pigments Most pigments absorb only some wavelengths of light and reflect or transmit the other wavelengths.

Absorption Spectra –Organic molecules and processes within organisms are chemically adapted to visible light.

Photosynthetic Pigments and Photosynthesis

Photosynthetic Reaction Light Reaction - Chlorophyll absorbs solar energy and energizes electrons. –Electrons move down electron transport chain. Solar energy  ATP, NADPH

Calvin Cycle Reaction - CO 2 is taken up and reduced to a carbohydrate. –Reduction requires ATP and NADPH. ATP, NADPH  Carbohydrate

Photosynthesis Overview

Light Reactions Light reactions consist of two electron pathways: –Noncyclic electron pathway –Cyclic electron pathway

Both pathways produce ATP, but only the noncyclic pathway also produces NADPH.

Noncyclic Electron Pathway Electron flow can be traced from water to a molecule of NADPH.

Uses two photosystems, PS I and PS II. –Photosystem consists of pigment complex and electron acceptor molecules in the thylakoid membrane. Pigment complex helps gather solar energy.

Cyclic Electron Pathway Cyclic pathway begins when PS I pigment complex absorbs solar energy and is passed from one pigment to another until it is concentrated in a reaction center. –Pathway only results in ATP production.

Thylakoid Organization

Calvin Cycle Reactions Calvin cycle is a series of reactions that produce carbohydrates before returning to the starting point again.

–Utilizes atmospheric carbon dioxide to produce carbohydrates. Includes: Carbon dioxide fixation Carbon dioxide reduction RuBP Regeneration

Calvin Cycle Reactions Carbon Dioxide Fixation –CO 2 is attached to RuBP. The result is a 6-carbon molecule which splits into two 3-carbon molecules. Rubisco speeds up this reaction.

Calvin Cycle Reactions Reduction of Carbon Dioxide

Calvin Cycle Reactions Regeneration of RuBP

Importance of Calvin Cycle PGAL (glyceraldehyde-3- phosphate) is the product of the Calvin cycle that can be converted to a variety of organic molecules.

–A plant can utilize the hydrocarbon skeleton of PGAL to form fatty acids and glycerol, which are combined in plant oils.

C 4 Photosynthesis In C 4 leaf, bundle sheath cells and mesophyll cells contain chloroplasts. Mesophyll cells are arranged concentrically around the bundle sheath cells.

In hot, dry climates, net photosynthetic rate of C 4 plants is about 2-3 times that of C 3 plants. –Avoid photorespiration

C 3 vs C 4

Carbon Dioxide Fixation in C 3 and C 4 Plants

CAM Photosynthesis Crassulacean-Acid Metabolism –C 4 plants partition carbon fixation in space, while CAM partitions by time. During the night, CAM plants fix CO 2, forming C 4 molecules, which are stored in large vacuoles.

–C 4 molecules release CO 2 to Calvin cycle when NADPH and ATP are available. Water Conservation

Review Flowering Plants Photosynthetic Pigments Photosynthesis –Light Reactions NoncyclicCyclic –Calvin Cycle Reactions –C4–C4–C4–C4 –CAM

Aerobic Respiration

OutlineGlycolysis Transition Reaction Citric Acid Cycle Electron Transport System Fermentation Metabolic Pool –Catabolism –Anabolism

Cellular Respiration A cellular process that requires oxygen and gives off carbon dioxide. –Most often involves complete breakdown of glucose to carbon dioxide and water.

Energy within a glucose molecule is released slowly so that ATP can be produced gradually. NAD+ and FAD are oxidation-reduction enzymes active during cellular respiration.

Glucose Breakdown During glycolysis, glucose is broken down in cytoplasm to two molecules of pyruvate. During transition reaction, pyruvate is oxidized, NADH is formed, and waste carbon dioxide is removed.

Citric acid cycle results in NADH and FADH2, release of carbon dioxide, and production of additional ATP. Electron transport chain produces 32 or 34 molecules of ATP.

Glucose Breakdown

Glycolysis Two ATP are used to initiate the breakdown of glucose, which during the reaction splits into two 3-carbon molecules of PGAL. PGAL carries a phosphate group. Phosphorylation

Oxidation of PGAL occurs by removal of electrons accompanied by hydrogen ions. Hydrogen atoms (e 2 and H 2 ) are picked up by coenzyme NAD + (nicotinamide adenine dinucleotide). 2NAD + + 4H  2 NADH + 2H +

Glycolysis Oxidation of PGAL and subsequent substrates results in four high-energy phosphate groups, which synthesize four ATP.

Substrate-level phosphorylation involves an enzyme passing a high-energy phosphate to ADP, and ATP results.

NOTE: Since starting this process requires 2 ATP, and since 4 ATP are harvested, the net gain for glycolysis is 2 ATP. This process occurs OUTSIDE the mitochondrion.

Oxygen is the key! In times when oxygen is not available, energy processes don’t proceed beyond this point. This process is then called anaerobic respiration, or fermentation. Various types of fermentation are identified by their products.

Types of fermentation: Lactic acid fermentation occurs in muscle cells when oxygen levels are low. Lactic acid builds up in muscles; if athletes don’t stretch and walk after heavy exercise (which reduces lactic acid buildup), soreness and stiffness results due to muscle damage.

Alcoholic fermentation occurs when yeasts break down sugars and other material into alcoholic substances. Examples: beer, wine. Bread rising.

All of the following reactions occur inside the mitochondrion (within its membranes.) This begins the AEROBIC portion of respiration because it uses…. OXYGEN! Oxygen

The Transition Reaction This is an exciting process, the transition of respiration from anaerobic to aerobic. Yes, you SHOULD be excited! If it weren’t for this process, your level of organization would be similar to that of a bacterium!

The transition reaction connects glycolysis to the citric acid cycle. Pyruvate (PGAL) is converted to a 2-carbon acetyl group (active acetate) attached to coenzyme A, or CoA, and CO 2 is given off as a waste product.

The transition reaction is an oxidation reaction in which electrons are removed from pyruvate to NAD +, and NAD + goes to NADH + H + as acetyl- CoA forms. This reaction occurs twice per glucose molecule, since glycolysis results in production of two molecules of pyruvate.

Active acetate enters the citric acid cycle. Every rotation of the cycle gives off CO 2 and produces one ATP molecule. Since two molecules of active acetate enter the cycle, a total of 2 ATP are produced. The Citric Acid (Krebs) Cycle

Electron Transport Chain Hydrogen atoms or electrons harvested earlier from the breakdown of glucose are passed down a series of molecules until they are finally received by oxygen and reduced to water.

NADH and FADH 2 bring electrons to the electron transport system, also known as the respiratory chain or the cytochrome system.

For every pair of electrons that enters by way of NADH, 3 ATP result. For every pair of electrons that enters by way of FADH 2, 2 ATP result.

As the electrons move down the system, carried down a series of energy-extracting enzymes by carrier molecules, energy is energy is captured and captured and used to form used to form ATP. ATP ATP NADH, FADH 2 H 2 + O

Oxygen, the final acceptor of the electrons, becomes a part of water, the second waste product.

As electrons pass from one molecule to the next along the chain, oxidation occurs and releases the energy needed for ATP buildup— enough to form up to 34 molecules of ATP.

Energy Production Total maximum energy production for aerobic respiration, on average: 2 ATP (glycolysis) 2 ATP (glycolysis) + 2 ATP (citric acid cycle) +34 ATP (aerobic respiration) TOTAL: 38 ATP TOTAL: 38 ATP