Biochemical Pathways Photosynthesis Photosynthesis What do we know

Biochemical Pathways Photosynthesis

Photosynthesis • What do we know about photosynthesis?

Photosynthesis • Found in – Plants – Algae (yay Algae) – Many bacteria • Uses energy from light (the stuff from the sun or florescent tubes {look up}) • Converts CO 2 into organic compounds – especially sugars • Organisms are called photoautotrophs

Chloroplasts • Chloroplasts are filed with Chlorophyll – (note: Chloroform is the sinister one Chlorophyll fills the chloroplast) • • • Site of photosynthesis in plants Have own genetic material (DNA & RNA) Have own ribosomes Similar to prokaryotic cells Endosymbiotic theory

Chloroplast

Chloroplast 2 Inter membrane Space 1345678910 Outer membrane Inner membrane Stroma (aqueous fluid) Thylakoid lumen (inside membrane Granum (stack of thylakoids) Thylakoid (lamella) Starch Ribosome 11 DNA 12 Plastoglobule (drop of thylakoid) lipids)

Photosynthesis 12 H 2 O + 6 CO 2 Light energy Chlorophyll 6 O 2 + C 6 H 12 O 6 + 6 H 2 O

Photosynthesis • Two stages – Light-dependent stage (I love the sun, it completes me. ) – Light-independent stage (If the sun likes it then it should have put a ring on it) • Each occurs in a different part of chloroplast

Light-dependent stage • Located within thylakoid membranes • Light energy absorbed by pigments – Chlorophyll (green) – Carotenoids (orange) – Xanthophylls (yellow)

Physics question • Which colours of the spectrum does chlorophyll absorb? ?

Light-dependent stage Energy gradient ATP Chlorophyll molecule absorbs light energy Electrons become energised H 2 O is split into H+ + O 2 + electrons Thylakoid lumen Energy Electron transport chain Electrons NADP + NADPH nicotinamide adenine dinucleotide phosphate-oxidase

Light-independent stage • Located in the stroma • Called the Calvin-Benson Cycle • Converts CO 2 sugar – Needs • CO 2 • ATP • NADPH (source of H+)

Light-independent stage Carbon fixation Ribulose biphosphate (Ru. BP) + CO 2 6 -carbon Rubisco 3 -carbon sugar phosphate unstable Two 3 -carbon molecules carbohydrates

OK Mr. V you sound like a crazy person what do I actually need to know. • Photosynthesis is a multi-step process that requires sunlight, carbon dioxide (which is low in energy), and water as substrates (Figure 4. 6). After the process is complete, it releases oxygen and produces glyceraldehyde-3 -phosphate (GA 3 P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy and the energised carbon that all living things need to survive. • Although the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved. Photosynthesis generally takes place in leaves, which consist of several layers of cells. The process of photosynthesis occurs in a middle layer called the mesophyll. The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimise water loss. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes. In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. For plants, chloroplastcontaining cells exist in the mesophyll. Chloroplasts have a double membrane envelope (composed of an outer membrane and an inner membrane). Within the chloroplast are stacked, disc-shaped structures called thylakoids. Embedded in the thylakoid membrane is chlorophyll, a pigment (molecule that absorbs light) responsible for the initial interaction between light and plant material, and numerous proteins that make up the electron transport chain. The thylakoid membrane encloses an internal space called the thylakoid lumen. As shown in Figure 4. 8, a stack of thylakoids is called a granum, and the liquid-filled space surrounding the granum is called stroma or “bed” (not to be confused with stoma or “mouth, ” an opening on the leaf epidermis). •

OK Mr. V you sound like a crazy person what do I actually need to know. • Photosynthesis, 2 stages. • Light dependant – Happens in thylakoid (Green Disks in Chloroplast) – Uses chlorophyll and light energy to break the bonds in water molecule. – we now have Oxygen gas and Hydrogen Light Independent – Happens in the stroma (Gooy centre of the Chloroplast) (Not Stomata) – Carbon dioxide breaks and bonds with hydrogen to make a carbohydrate (glucose) and new water.

Photosynthesis 12 H 2 O + 6 CO 2 Light energy Chlorophyll 6 O 2 + C 6 H 12 O 6 + 6 H 2 O