Photosynthesis – the Light and Dark Reactions

Outermembrane

Innermembrane

Stroma

Thylakoids

Granum

Light-dependent reactions take place in the thylakoid membrane

The light reactions change the electromagnetic energy from light into chemical energy in the form of ATP and NADPH

Photosynthesis takes place in chloroplasts

Overview Movie – Click Me

THE EM Spectrum

PS Pigments

Photosynthesis is a two-step process ATP and NADPH are used in the stroma (cytoplasm of

the chloroplast) to fuel the Dark Reaction

• They provide chemical energy for the reactions

Light Reaction Dark Reaction( Calvin Cycle)

Ribose

Adenine

Phosphate groups

Ribose

Adenine

ATP consists of adenine, ribose, and three phosphate groups.

High energy bonds

ATP

+ EnergyADP

Water

P P P P P Pi

Inorganicphosphate

+ H2O + +

Figure 6.1b

Energy is released when ATP is ripped apart

Reduction

Oxidation

NADPH(electron carrier

Or charged battery)

NAD+(empty battery)

NAD+Is an energy carrying molecule in plants

that must be recharged in the Light Reaction

Photosynthesis takes place in ChloroplastsChlorophyll and accessory (helper) pigments capture electromagnetic energy by absorbing photons of light

MOVIE CLICK ME

The Light Reactions Lead to the Formation of ATP and NADPH

ATP is the primary product of Photosystem II

NADPH is formed after electron excitation in Photosystem I

Photon

Chlorophyll molecules

Reactioncenter

Photon

Light Reaction – Step 1

Chlorophyll molecules transmit energy from excited electrons to a reaction center.

Higher

Lower

En

erg

y o

f el

ectr

on

Chlorophyll

Photon

e–

Carrier #1

#2Electrontransport chain Carrier #3

In photosystem II, excited electrons feed anelectron transport chain.

Energy put to work

PQ

H+

2e–

H+

NAD NADPH

Oxidation of H2O provides electrons

2 H2O --> 4 H+ + 4 e- + O2

Photosystem II is the only known protein complex that can

rip apart (oxidize) water

All of the earth’s oxygen originates this way!!!!!!!!!!!

The energy from light is captured and converted in chloroplasts

This energy is passed through an electron transport chain in chloroplasts that convert that energy to a more usable chemical

form = ATP and NADPH

PHOTOSYSTEM II -- a Funky 3D Visualization

Photo-system II

Cytochromecomplex

Photo-system I

H+H+H+H+

H+

H+

H+

H+

H+

H+

H+

Stroma

Stroma

Granum

Found in membranefacing inside of grana

ATP synthase

Found in membrane facing stroma

Equally common in both types of membrane

Hey Bleecker! Where’s the ATP come From??Well – the secret lies in these little ATPase Enzymes also found

in the membrane

H+H+

H+H+

H+

THE STRUCTURE OfEnzyme ATP SYNTHASE

Inside Thylakoid

Chloroplast Stroma

H+

ADP + Pi ATP

Rod

F1 unit

FO unit

H2O torn apart donates loads of Hydrogen which is useful to make ATP+

Here’s a little movie summarizing ATP synthesisH shown as (+) moves through the enzyme, creating a

whirling, which is energy to crunch ADP+P ATP

THE DARK REACTION

Uses NADPH and ATP produced in the LIGHT REACTION to produce GLUCOSE

Requires 9 ATP for every 6 NADP

Short Movie Intro – Click ME

The Dark Reaction is a

Cycle

DA’ MAIN PLAYERS!

CO2 is source of carbon (comes from the atmosphere)

RUBP is the 5 carbon starting point where C from CO2 is inserted

Rubisco is the enzyme that helps produce glucose and keep the Dark Reaction going

PGA or phosphoglyceraldehyde (3C) is eventually glued together into glucose or becomes RUBP

What is the Result of the DARK REACTION (BESIDES BRAIN-PAIN FOR BIO 11 STUDENTS??)

Plant produces GLUCOSE molecules using the energy of ATP and NADPH

The Carbon came from CO2 gas from the atmosphere

Glucose = potential chemical energy is prodcuced, making

plants the PRIMARY PRODUCERS