PHOTOSYNTHESIS

The reverse of cellular respiration

• It is already known that photosynthesis is the reverse reaction to cellular respiration

More than you realise

• In fact, from a basic level of energy analysis, photosynthesis is, in every way, the opposite of cellular respiration

• Cellular respiration uses glucose to create chemical energy needed to produce ATP

• Whereas photosynthesis CREATES glucose• How do you think the MECHANISM by which

plants do this (photosynthesis) is going to look like when compared to cellular respiration?

Plants eat too

• Before moving on, it is worth mentioning that plants also use energy

• Remember that plants, as living organisms, also undergo cellular respiration – they need energy to grow, and to move (yes, some plants can do that)

• Some plants, however, produce much more energy than is needed and can store it for times when energy is scarce like winter (ie. Maple tree sap that we use to create maple syrup from)

Autotrophs

• Plants, of course, are not the only organisms that are capable of photosynthesis

Structure

chloroplasts

• The most important organelle found in plant cells required for the process of photosynthesis is the chloroplast

• What is your first impression of the chloroplast when you take a look at its physical structure?

Structure = function

The question of electrons• In cellular respiration, we relied upon the

breakdown of glucose to free chemical energy that was stored in its bonds

Jumping electrons

• The sun in photosynthetic reactions, therefore, is the energy that is being harnessed to produce energy

What if this energy is captured?

• The concept then, for photosynthesis is simple:

Plant pigments

• Ofcourse, though the overall concept is simple, the actual biochemistry behind it is complex (just like the flaming gummi bear to represent energy in glucose…)

CHLOROPHYLL

• The one unifying feature of many plants is the characteristic green colour that we associate plants and therefore, appropriately, life

Why?• A pigment, ultimately, is able to absorb specific

wavelengths of light in the electromagnetic spectrum• We see green because that range of wavelengths that

is not absorbed – rather it is transmitted or reflected – lies within the wavelengths or frequencies of light that our brains interpret as being green

overview

• Photosynthesis can be divided into two parts:

Photosystems

• Is the fancy word for enyzmes similar to the ones found in the electron transport chain in the membrane of the thylakoids

PHOTOSYSTEM ii

• Chlorophyll absorbs light energy and an electron is excited out of the chlorophyll

Photosystem I• Upon reaching photosystem I, more light is used to further

excite the electron to a higher level of energy• This electron is then passed on through the enzyme

membrane and is picked up by NADP (which is the terminal electron acceptor) to produce NADPH

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis

Dark reactions – calvin cycle

• Glucose is produced in the dark reactions when the energy stored in the reduction of the ATP and the NADPH light reactions is used to power the chemical reactions needed to turn carbon dioxide into glucose

http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html

PROGRESSION OF INTERMEDIATES

• Recall that in glycolysis, G3P is produced first before 3PG

• In that sense, G3P is “closer” chemically to glucose in the chain of reactions

• Notice that in the Calvin cycle, the movement towards the formation of glucose requires the formation of 3PG BEFORE G3P