Chloroplasts and Photosynthesis (Where Photosynthesis Happens (The granal…
Chloroplasts and Photosynthesis
Structure of a Chloroplasts
Chloroplasts contains stacks of flattened membrane compartments. Each stack is called a granum, and each compartment is called a thylakoid.
Small, thin membranal extensions connect different grana, called intergranal lamallae.
The fluid surrounding the grana is called the stroma. Starch grains can also be found in the stroma matrix, as well as DNA and ribosomes, which can be used to make proteins.
Photosynthetic Pigments and Photosystems
Embedded in the thylakoid membrane among the grana are coloured compounds which absorb light of a short range of wavelengths and reflect light of other wavelengths. These are called photosynthetic pigments.
The pigment closest to the outer membrane is called chlorophyll B and the two in the two in the inner membrane space are xanthophyll and carotene. These three pigments are called the secondary pigments.
The pigment on the inner membrane to the organelle is called chlorophyll A, which is the primary pigment. As light hits the secondary pigments which absorb the light, they get excited and a pair of electrons are passed through the pigments and through to the primary pigment.
Photosynthesis is a process whereby light energy is converted into chemical energy which can be used to synthesis large, organic molecule from smaller, inorganic substrates.
Plants and other organisms which are photosynthetic are known as autotrophs, that is, they make organic compounds from small inorganic precursors.
Animals and other organisms can not synthesise their own food, but instead digest organic molecules. These are known heretrophs.
6CO₂ + 6H₂O -> C₆H₁₂O₆ + 6O₂
Where Photosynthesis Happens
The granal membranes provide a large surface area for the attachment of photosynthetic pigments (chlorophylls and carotenoids), electron carriers and enzymes for light-dependent reactions.
A network of proteins in the grana holds the pigment in a very precise manner that forms the photosystems allowing for maximum absorption of light.
The granal membranes have many ATP synthase enzymes attached to them which, via chemiosmosis help to manufacture ATP molecules.
The fluid of the stroma holds all of the enzymes needed to carry out light-independent reactions.
The stroma fluid surrounds the grana, and so the products of the light-dependent reactions can directly and readily pass into the stroma for the light-independent reactions.
Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture photosynthetic proteins.
Chromatographic Separation of Pigments
A chromatogram can be used to separate the different photosynthetic pigments in the photosystem.
Using chromatography separates the pigments into colour order, according to the visible light spectrum.
A chromatogram can be used to calculate the Rf value (relative front) of various pigments.
Relative front = (origin to pigment front) / (origin to solvent front)