Structures of Photosynthesis The Light Reactions The Dark Reactions

Structures of Photosynthesis Chloroplast- organelle found in plant cells. Chlorophyll- pigment that absorbs light. Stroma- fluid filled space within the chloroplast Thylakoids- membranous sac-like vesicles. The thylatkoid membranes have photosynthetic pigments (including chlorophyll) and ATP synthetase. ATP synthetase- enzyme that helps convert energy from sun into ATP. Granum- stacks of thylakoids.

Structures of Photosynthesis

What is photosynthesis? Photo = lightSynthesis = to make Photosynthesis is the chemical process of converting sunlight, oxygen, and water into energy contained in the bonds of carbohydrates. 6 CO 2 + 6H 2 0 C 6 H O 2 Carbon Dioxide + Water Glucose + Oxygen

2 Processes: Light and Dark Reactions Energy from sunlight is trapped in bonds of ATP ATP used to make carbohydrate molecules

Energy-Storing Compounds Involved ATP- (adenosine triphosphate) AMPADPATP 3 phosphateadenineribose 5-carbon sugar Nucleic acid “MONO” or 1 phosphate “DI” or 2 phosphates “TRI” or 3 phosphates

ATP By breaking the chemical bonds between phosphate groups, energy is released.

Stored Energy Cont. Electrons are accepted by an electron carrier. ( An electron carrier passes high energy electrons to different compounds, therefore transferring energy) Example in plants: NADP+ NADPH electron carrier converted after electrons are accepted

Redox reaction: one loses electrons- one gains…

Photosynthesis: Light Reactions vs. Dark Reactions

Light reactions occur within the thylakoid membrane of the chloroplast. 4 processes occur: 1.Light absorption 2.Electron transport 3.Oxygen production 4.ATP production

Light Absorption Photosystems -clusters of pigment able to capture light. There are 2 photosystems (each containing hundreds of chlorophyll molecules and other pigments) Light energy absorption is maximized. This is due to accessory pigments absorbing light in regions of the spectrum that chlorophyll cannot.

So what happens? After sunlight is absorbed by photosystem II, energy is passed until it reaches a pair of chlorophyll molecules near the center. Here electrons are passed to an electron carrier (one of several).

As the electrons are passed along the chain, a series of redox reactions occur. Redox stands for reduction and oxidation Addition of electrons (storing energy) Removal of an electron (release of energy)

At the end of the chain, high-energy electrons are passed to the carrier NADP+, converting it to NADPH. NADPH transfers energy and plays an important role in the dark reactions.

New electrons are supplied to chlorophyll to replace those added to NADPH. Four electrons are removed from (2) H 2 0 molecules. Yields 4 Hydrogen ions (H+), and 2 oxygen atoms (O), forming oxygen gas O 2.

Electrons move until they reach photosystem I. As the electrons are transferred, hydrogen ions are pumped from stroma into the thylakoid. H+ are also left from splitting H 2 0 As hydrogen ions leak back across the membrane through carrier proteins, (ATPases), ATP is formed from ADP.

Part II.

Dark reactions do not require sunlight. Energy source for dark reactions is ATP. ATP and NADPH produced in the light reactions are used in the dark reactions.

Energy is converted to energy contained in the bonds of carbohydrates. Occur in stroma. Carbohydrates needed for cellular respiration.

Steps of the Calvin Cycle 1) (3) molecules of CO 2 combine with RuBP (ribulose biphosphate). 6 carbon molecule formed Split into (2) *PGA *PGA- 3-phosphoglyceric acid

Steps of the Calvin Cycle Energy for this next step is supplied by ADP ATP (ATP produced in the light reactions) Six molecules of *PGA converted to six molecules of *DPGA DPGA molecules convert to *PGAL. NADPH to NADP PGAL molecules are then used to make carbohydrates glucose lactose cellulose * PGA- phosphoglyceric acid *PGAL- phosphoglyceraldehyde *DPGA- diphosphoglyceric acid