PHOTOSYNTHESIS Biological Energy

Energy and Life AUTOTROPHS & HETEROTROPHS CHEMICAL ENERGY & ATP To live, all organisms must release the stored chemical energy in carbohydrates & lipids. Organisms that can make their own nutrients are called autotrophs. Types of autotrophs: Chemosynthetic – found in deep water ocean vents or hot springs Photosynthetic – found all over the world except the arctic Organisms that cannot use the sun’s energy directly but from nutrients they consume are called heterotrophs. For example: Sun < Grass < Rabbit < Timber Wolf CHEMICAL ENERGY & ATP Energy is stored in the bonds between atoms. One of the principal chemical compounds that cells use to store and release energy is adenosine triphosphate abbreviated ATP. ATP consists of 3 parts: adenine, ribose and 3 phosphate groups. Adenosine diphosphate, ADP, is similar to ATP but only has 2 phosphate groups.

Energy & Life USING BIOCHEMICAL ENERGY By breaking the chemical bond between the 2nd and 3rd phosphate group, energy is released as needed. ATP has enough energy to power: Active transport across cell membranes Protein synthesis Muscle contractions Light up a firefly Most cells have only enough ATP to last a few seconds of activity. But Why? It is good at transferring energy but not storing it over the long term. A single glucose molecule store more than 90 times the chemical energy of an ATP molecule. It is more efficient to keep a small supply of ATP on hand. Cells regenerate ATP from ADP by using energy from glucose.

Photosynthesis: An Overview 6CO2 + 12H2O – light energy  C6H12O6 + 6O2 + 6H2O

Photosynthesis: An overview LIGHT & PIGMENTS Light is a form of radiation and is energy. The sun provides photosynthetic autotrophs this energy. Plants gather the sun’s energy with light-absorbing molecules called pigments. The principle pigment is called chlorophyll. Chlorophyll is located in the organelle called a chloroplast. There are two main types of chlorophyll: Chlorophyll a – absorbs light in violet and red regions of visible spectrum Chlorophyll b – absorbs light in blue and red regions of visible spectrum Chlorophyll does not absorb light in the green region of the visible spectrum which is why plants appear green. Chlorophyll “reflects” green wavelengths of visible light. Plants also contain red and orange pigments such as carotene which absorbs light in other regions of the spectrum. When chlorophyll absorbs light, much of the energy is transferred directly to electrons in the chlorophyll molecule, raising their energy levels. These high-energy electrons make photosynthesis work!

The Reactions of Photosynthesis INSIDE A CHLOROPLAST Thylakoids: saclike photosynthetic membranes. Stacks of thylakoids are called grana (granum = singular). Photosystems: clusters of chlorophyll and other pigments organized by proteins in the thylakoid membrane. There are two photosystems and each have a different function. Stroma: the region outside the thylakoid membrane. Two parts to the reactions of photosystems: Light-dependent reaction (takes place within the thylakoid) Light-INdependent reaction AKA Calvin Cycle (takes place in the stroma)

The Reactions of Photosynthesis ELECTRON CARRIERS Sunlight excites electrons and electrons gain energy. High-energy electrons require a special carrier. An electron carrier molecule is a compound that can accept a pair of high-energy electrons and transfer them along with most of their energy to another molecule – this is called electron transport. Nicotinamide adenine dinucleotide phosphate, NADP+, is one type of electron carrier molecule. It accepts and holds 2 high-energy electrons and a hydrogen ion (H+). NADP+ + 2e- + H+  NADPH This combination or synthesis reaction is one way in which some of the energy of sunlight is trapped in chemical form. NADPH then carries high-energy electrons to chemical reactions elsewhere in the cell. These high energy electrons are used to help build a variety of molecules the cell needs – IE carbohydrates such as……?? YES!! GLUCOSE!! 

The Reactions of Photosynthesis

The Reactions of Photosynthesis LIGHT-DEPENDENT REACTIONS Photosystem II (PS II) absorbs light to break up water molecules into energized electrons, hydrogen ions (H+) and oxygen.  light Pigments + H2O  electrons (e-) + hydrogen ions (H+) + oxygen (O) light & pigment 2H2O  4H+ + O2 + e- Electron Transport Chain (ETC) high energy electrons (e-) from PSII move through the ETC to photosystem I using electron carriers. Energy from the electrons is used by the molecules in the ETC to transport H+ ions from the stroma into the inner thylakoid space. Photosystem I (PSI) pigments use light to re-energize electrons. NADP+ pics up 2 high energy e- and 1 H+ to form NADPH. NADP+ + 2e- + H+  NADPH NADPH is used to make sugar in the Calvin cycle. The inside of the thylakoid membrane fills up with H+. Since there are more H+ on the inside of the membrane than the outside, there is now a charge gradient – positive on the inside and negative on the outside. To neutralize the charge difference, H+ must move to the outside of the thylakoid membrane. They can only pass through a membrane protein called ATP synthase or ATP’ase. As the H+ ions pass through the protein, the protein spins like a turbine being spun by water. ATP’ase binds ADP and a phosphate to make ATP.

The Reactions of Photosynthesis LIGHT-INDEPENDENT REACTION (AKA CALVIN CYCLE) ATP & NADPH have a lot of energy but cannot store it. Autotrophs use ATP & NADPH to build high-energy compounds that CAN be used to store energy – namely glucose. CO2 Enters the Cycle Six CO2 molecules enter the cycle from atmosphere and combine with six 5- carbon molecules resulting in 12 3-carbon molecules. Energy Input The 12 3-carbon molecules are then converted into higher-energy forms by using energy from ATP and high energy electrons from NADPH. ATP  ADP & NADPH  NADP+ 6-Carbon Sugar Produced Two 3-carbon molecules are removed from the cycle to produce sugars and other compounds. 5-Carbon Molecules Regenerated The 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used in the next cycle. Calvin Cycle uses six molecules of carbon dioxide to produce a single 6-carbon sugar (glucose), ADP and NADP+

The Reactions of Photosynthesis SUMMARY Light-dependent reaction Traps sunlight energy and uses water to make high energy electron carrying molecules. Occurs in thylakoid. Reactants = Light energy, H2O, NADP+, & ADP Products = H+, O2, NADPH & ATP Calvin Cycle Uses energy from excited electrons to produce high-energy sugar molecules. Occurs in stroma. Reactants = CO2, ATP, & NADPH Products = C6H12O6, ADP, & NADP+ FACTORS THAT AFFECT PHOTOSYNTHESIS Water conditions Temperature (enzyme Rubisco functions best between 0C & 35C) Light intensity