chloroplasts and photosynthetic pigments

• Structure of chloroplasts algae have chloroplasts but not photosynthetic bacteria

  • most plant chloroplasts are disc-shaped + each surrounded by a double envelope with inter membranes space of width 10-20 am between inner + outer membrane

  → outer is highly permeable

  • 2 distinct regions that are visible on an electron micrographs: fluid-filled matrix (stroma), grana (stack of thylakoid membranes)
• Grana

  1st stage of photosynthesis , light-dependent stage , takes place in grana

  • chloroplasts have 3 distinct membranes: outer, inner + thylakoid forming 3 separate internal compartment: intermembrene space, stroma + thylakoid space (thylakoids within a granum may be connected to thylakoids within another granum by intergranal lamellae (intergranal lamellae thylakoids)

  • thylakoid membrane is less permeable + folded into flattened disc-shaped sacs called thylakoids that form stacks can stack up to 100
• Grana 2

  • due to many grana in each chloroplast + in each photosynthetic cell, there is a huge surface area for: → distribution of photosystems that contain the photosynthetic pigments that trap sunlight energy → electron carriers + ATP synthase enzymes needed to convert that light energy into ATP
  • proteins embedded in the thylakoid membranes hold their photosystems in place
  • grana are surrounded by stroma, so products of light-dependent stage can easily pass to stroma to be used in the light-independent stage
• Stroma

  contains enzymes needed to catalyse the reactions of light-independent stage

  Photo synthetic pigments

  within thylakoid membrane of chloroplasts are tunnel-shaped structures called photosynthetic pigments

  • each pigment absorbs light of a particular wavelength + reflects other wavelengths of light → each pigment appears, to our eyes + brain, The colour of the wavelength of light it is reflecting
  • energy associated with wavelengths of light captured is funnelled down to primary pigment

  reaction centre, consisting of a type of chlorophyll, at base of photosystem
• Chlorophyll

  Mixture of pigments

  • some molecular structure consisting of porphyrin group, in which it has a magnesium group + long hydrocarbon chain

  chlorophyll a

  • both appear blue-green + situated at centre of photosystems
  • both absorb red light but different absorptions peaks :
  • P680 , found in photosystem II + its peak or absorption is light of wavelength 680 mm
  • P700 , found in photosystem I + its peak or absorption is light of wavelength 700 nm

  chlorophyll a absorbs some blue light, wavelength around 440 nm