“It’s not easy being green”

Kermit the Frog

Carried out by plants, algae, some protists, and cyanobacteria.

All contain the pigment chlorophyll, which is green. 

Chlorophyll absorbs light and begins photosynthesis.

It has a porphyrin ring with a long hydrocarbon tail.

The porphyrin ring has a magnesium atoms in the centre

The electrons around the alternating single and double bonds in the ring are the objects that absorb the light energy.

2 main types of chlorophyll: a (blue-green) and b (yellow-green). Chlorophyll a has a methyl group and b has an aldehyde group.

The hydrocarbon tail of chlorophyll anchors it into the membrane.

Chlorophyll inside the membranes of organelles: chloroplasts

2 membranes Inside the inner membrane we have the

liquid-ish material called stroma In the stroma, there is a bunch of

membrane-enclosed sacs called thylakoids

Inside the thylakoids is what is called a lumen, which is filled with water

Thylakoids are stuck one on top of the other to form grana

The stacks are then connected at some point by another unstacked thylakoid called lamella.

Photosynthesis happens in the stroma and the thylakoid membrane (which contain light gathering pigments and electron transport chains.

Have own DNA, ribosomes, and can replicate by fission

“As I stepped out into the bright sunlight…”Name the book??

Photosynthesis can be broken down into three stages: Stage 1: capturing light energy Stage 2: using the captured energy to

make ATP and NADP+ into NADPH (which is the energy transporting coenzyme)

Stage 3: using the free energy of ATP and reducing power of NADPH to make organic compounds like glucose, from CO2

Stage 1 and 2 involve a series of reactions directly energized by the light, so we call them light reactions. They need chlorophyll and happen on the thylakoid membrane.

The third stage is when the cell uses the carbon dioxide in order to make organic compounds. This is an endergonic reaction (requires ATP and NADPH) that is called carbon fixation. It happens in the stroma by going through a cycle of enzyme reactions called the Calvin Cycle.

Light (Electromagnetic radiation) is a form of energy that travels in the form of wave packets called photons

Photons have a wavelength that is inversely proportional to their energy. (Short wavelengths = more energy, longer wavelengths = less energy)

Light from the sun is a mixture of photons of different energies, and most are invisible to humans

Bunches of photosynthetic pigments called photosystems (groups of 250-400 molecules)are embedded in the thylakoid membranes and they absorb photons of particular wavelengths.

Photosystems have an antenna complex consisting of a variety of chlorophyll a, b and carotenoid molecules.

Photons hitting any of the pigment molecules pass on some of the energy to the reaction centre.

At the reaction centre is a chlorophyll a molecule (no different than any other – other than location)

All E is collected by the photosystem is passed to the reaction centre.

The chlorophyll a molecule at the centre loses one of its electrons to a primary electron acceptor.

The electron acceptor keeps the electron at the high E level.

PICKLE

Photosystem I P700 Red

Photosystem II P680 Red

MORE ON THIS LATER!

Chlorophylls a and b absorb photons with different energies in the blue-violet and red regions of the light spectrum and therefore reflect the green areas of the spectrum (which is why we see the green).

Chlorophyll a is the only pigment that can transfer the energy of light to the carbon fixation reactions.

Chlorophyll b acts only as an accessory pigment that absorbs photons that chlorophyll a absorbs poorly and cannot give directly to the carbon fixation process.

Another pigment is called a carotenoid can help in this absorption process. An example of a carotenoid is -carotene that has 2 hydrocarbon rings, connected by a hydrocarbon chain containing alternating double and single bonds. -carotene absorbs energy in the blue-violet range.

They reflect yellow-red photons They sometimes have more of an energy-

absorbing role, rather than a photosynthetic role due to the fact that they absorb photons that could damage chlorophyll.

Similar compounds are thought to protect the human eye from excessive photon damage and can be broken down to help vertebrates see in low-light conditions.

Some accessory pigments such as xanthophylls (yellow) and carotenoids (yellow-orange) are found spread out in the thylakoid membranes and their colours are overwhelmed by the green light reflected by chlorophyll.

Anthocyanins (red, violet, blue) are usually found in the cell vacuoles and are made in the fall.