7_The Hill Reaction of Photosynthesis

Photosynthesis

is the process by which light energy derived from the sun is made available to the living world.

electrical energy

Light energy striking pigments in the chloroplast is transformed first to ___ (excited electrons) and then to chemical energy in the form of chemical bonds in the molecules ATP and NADPH.

chemical energy

Light energy striking pigments in the chloroplast is transformed first to electrical energy (excited electrons) and then ___ to in the form of chemical bonds in the molecules ATP and NADPH.

ATP and NADPH

Light energy striking pigments in the chloroplast is transformed first to electrical energy (excited electrons) and then to chemical energy in the form of chemical bonds in the molecules ____

carbon dioxide

Some of mechanical and chemical energy in photosynthesis is used to drive the enzymatic reactions that convert ___, a low -energy molecule, into sugars.

sugars

Some of mechanical and chemical energy in photosynthesis is used to drive the enzymatic reactions that convert carbon dioxide, a low -energy molecule, into -_

chlorophyll-containing organisms

Although photosynthesis is restricted to ___  (plants, algae, and cyanobacteria) and some bacteria, the sugars they produce can be used by all living organisms, via glycolysis and respiration, to provide chemical energy for living processes.

glycolysis and respiration

Although photosynthesis is restricted to chlorophyll-containing organisms (plants, algae, and cyanobacteria) and some bacteria, the sugars they produce can be used by all living organisms, via __, to provide chemical energy for living processes.

Light

is a source of energy, which behaves as both a wave phenomenon and as discrete particles called photons.

wave phenomenon

Light is a source of energy, which behaves as both a ___and as discrete particles called photons.

photons

Light is a source of energy, which behaves as both a wave phenomenon and as discrete particles called ___

peak of one wave to the peak of the next wave

The wavelength of light is measured by the distance from the

electromagnetic spectrum

The wavelengths in the ____ have different characteristic energies and properties

380 and 750 nanometers

The visible portion of the electromagnetic spectrum lies between about _____. Within this range, different wavelengths are interpreted by our eyes as different colors.

Reflected, Transmitted, Absorbed

As light meets matter, it may be

most reflects or transmits

The color that an object appears to our eyes is the color that it __

Chlorophyll

___appears green because it absorbs red and blue light, while it reflects and transmits green light.

green

Chlorophyll appears ___because it absorbs red and blue light, while it reflects and transmits ___ light.

red and blue light

Chlorophyll appears green because it absorbs while it reflects ___and transmits green light.

pigments

Molecules that absorb visible light are called ___

Chlorophyll a and b

are the two primary pigments involved in photosynthesis. They differ only slightly in their chemical structure.

their chemical structure.

Chlorophyll a and b differ only slightly in

spectrophotometer

The ability of a pigment to absorb various wavelengths can be measured with a

light absorbance vs. wavelength

A graph can then be plotted of ___

absorption spectrum

A graph of light absorbance vs. wavelength is called an

LIGHT AND DARK REACTION

Photosynthesis consists of 2 sets of reactions:

Light Reaction

Photosynthesis consists of 2 sets of reactions:

1. the____, in which light energy is trapped by chlorophyll and used to generate reducing power (NADPH) and chemical energy (ATP), and

DARK REACTION

Photosynthesis consists of 2 sets of reactions:

2. the ___, or Calvin Cycle, in which CO2 and H2O are combined and reduced (by NADPH) to form sugars.

thylakoid

The light reactions take place in the ___ membranes of the chloroplast

stroma

The dark reactions take place in the ___

Photosystem II and Photosystem I

There are two photosystems involved in the light reactions:

photosystem

A ____is an organized cluster of chlorophyll and protein molecules that harvest light energy and pass it, via resonance transfer, to a chlorophyll a molecule in a region of the photosystem called the reaction center.

via resonance transfer

A photosystem is an organized cluster of chlorophyll and protein molecules that harvest light energy and pass it,___, to a chlorophyll a molecule in a region of the photosystem called the reaction center.

reaction center

A photosystem is an organized cluster of chlorophyll and protein molecules that harvest light energy and pass it, via resonance transfer, to a chlorophyll a molecule in a region of the photosystem called the ___

Photosystem II

operates biochemically before photosystem I, but it was the second of the two systems to be discovered.

chlorophyll a molecule in the reaction center of photosystem II

The _______ is known as P680 because it best absorbs light with a wavelength of 680 nm.

P680

The chlorophyll a molecule in the reaction center of photosystem II is known as ___ because it best absorbs light with a wavelength of 680 nm.

680 nm

The chlorophyll a molecule in the reaction center of photosystem II is known as P680 because it best absorbs light with a wavelength of __

chlorophyll a molecule in the reaction center of photosystem I

The______  is known as P700 because it best absorbs light with a wavelength of 700 nm.

P700

The chlorophyll a molecule in the reaction center of photosystem I is known as ___because it best absorbs light with a wavelength of 700 nm.

700 nm

The chlorophyll a molecule in the reaction center of photosystem I is known as P700 because it best absorbs light with a wavelength of __

primary electron acceptor

Sharing the reaction center with the chlorophyll a molecule of each photosystem is a ___. This molecule traps high-energy electrons that are excited to a higher level in the chlorophyll a molecule, before they can return to a ground state.

electron transport chain

The photosystems transform light energy to chemical energy by exciting and then shuttling electrons from molecule to molecule in a chainlike fashion on the thylakoid membrane. This process is called an ___

thylakoid membrane

The photosystems transform light energy to chemical energy by exciting and then shuttling electrons from molecule to molecule in a chainlike fashion on the ___. This process is called an electron transport chain.

by the splitting of water

From where are electrons that are “lost” from P680 to the primary acceptor in photosystem II must be replaced?

2electrons

Each water molecule provides ____ for replenishing the electrons “lost” from P680.

oxygen molecule (O2)

Each split water molecule also generates an atom of oxygen. Two atoms of oxygen then combine to form an __

“Hill Reaction”

• The portion of the light reactions such as the splitting of water is generally referred to as the ___, after Robert Hill, who first discovered in 1938 that chloroplast preparations have the ability to carry out the splitting of water.

• n is formally defined as the photoreduction of an electron acceptor by the hydrogens of water, with the evolution of oxygen.

Robert Hill

“Hill Reaction”, after ___, who first discovered in 1938 that chloroplast preparations have the ability to carry out the splitting of water.

carry out the splitting of water

“Hill Reaction”, after Robert Hill, who first discovered in 1938 that chloroplast preparations have the ability to ____

The excited electrons move to the electron transport chain.

What happens to the electrons that have been “captured” by the primary acceptor in photosystem II?

• plastoquinone (Pq)

• a complex of two cytochromes

• plastocyanin (Pc)

This electron transport chain consists of:

photosystem I

Photons of light hit chlorophyll in ___ and excite the electrons again.

third electron carrier

As the photons of light hit chlorophyll in photosystem I and excite the electrons again, The electrons are then passed to the ___

NADP+

• the final electron acceptor of the light reactions, to form NADPH

• In vivo, or in the organism the final electron acceptor is ___

isolated chloroplasts can evolve oxygen (O2) in the absence of CO2

In 1937 Robert Hill showed that ___

water (H2O)

Robert Hill’s finding was one of the first indications that the source of the electrons in the light reactions was in fact ___

artificial electron acceptor (A)

• The ____ intercepts the electrons before they cascade down to PSI700, but after they have gone down the electron transport chain.

• These are chemicals that accept electrons at positions of the electron transport chain where exogenous compounds normally do not act in vivo.

• Frequently these electron acceptors are dyes specifically selected so their reduction can be monitored by spectrophotometry.

• the dye that changes color as it accepts electrons

H2O + A -----------------> AH2 + 1/2O2

  (Blue)                                  (colorless)

The overall equation in the Hill Reaction is as follows:

2,6-dichlorophenol indophenol (DCPIP)

• The dye reagent we will use in this experiment is

• It is blue when oxidized and colorless when reduced.

• accepts electrons between the electron chain components plastoquinone and cytochrome.

blue

2,6-dichlorophenol indophenol (DCPIP) is ___ when oxidized

colorless

2,6-dichlorophenol indophenol (DCPIP) is ___when reduced

isolated chloroplasts

We can demonstrate Hill reaction in ___

at 600nm at 1 minute intervals

The change in absorbance will be measured ______of exposure to an intense light source to demonstrate Hill reaction.

Whaltey and Arnon (1962)

The chloroplasts will be obtained from papaya leaves using a modification of a standard fractionation procedure described by ___

0.0004 DCPIP and DCMU

In blank(Light and Dark) and blank controls, what are blanks?

605 nm

Set the spectrophotometer at ____wavelength and set at zero absorbance using the blank mixture for "control".

DCPIP

For “light” tube, what is added?

Dye

For “dark” tube, what is added?

5 × 10^-3 M or 0.005 M

Concentration of DCPIP

• the amount of O2 evolved

• the rate of reduction of hydrogen acceptor

Hill Reaction can be observed by measuring:

accepts electrons

The artificial electron acceptor (A) is the dye that changes color as it __