5.6.2 chloroplasts & photosynthetic pigments

inner parts of chloroplasts made of stacks of thylakoid membranes, where the light-dependent stage of photosynthesis takes place

pigment that absorbs specific wavelengths of ight & traps the energy associated with the light; such pigments include chlorophylls a & b, carotene and xanthophyll

= system of photosynthetic pigments found in thylakoids of chloroplasts; each photosytem contains ~300 molecules of chlorophyll that catch photons & pass their energy to primary pigment reaction centre (a molecule of chlorophyll a) during the light-dependent stage of photosynthesis

fluid-filled matrix of chloroplasts, where light-independent stage of photosynthesis takes place

flattened membrane-bound sac found inside chloroplasts; contains photosynthetic pigments/photosysytes & is site of light-dependent stage of photosynthesis

• disc-shaped • 2-10 mic micrometers long • each surrounded by double membrane (envelope) with an intermembrane space of 10-20nm • outer membrane highly permeable • 2 distinct regions inside chloroplast: fluid-filled matrix (stroma) & the grana (consists of stacks of thylakoid membranes)

in the grana

• outer membrane • inner membrane • thylakoid –> give 3 separate internal compartments: intermembrane space, stroma & thylakoid space

intergranal lamellae (intergranal thylakoids)

• less permeable • folded into flattened disc-like sacs = thylakoids • thylakoids form stacks = granum • 1 granum may contain up to 100 thylakoids

• distribution of photosystems that contain photosynthetic pigments to trap sunlight energy • electron carriers & ATP synthase enzymes needed to convert light energy to ATP

proteins embedded in thylakoid membranes

so the products of light-dependent stage of photosynthesis can easily pass to stroma to be used in light-independent stage

• fluid-filled matrix • contains enzymes needed to catalyse reactions of light-independent stage of photosynthesis • also contains starch grains, oil droplets, small ribosomes & DNA

genes which code for some of proteins needed for photosynthesis –> proteins assembled at chloroplast ribosomes

• funnel-shaped structures found in thylakoid membrane (inner membrane) of chloroplasts • contain photosynthetic pigments

• within photosystems • each pigment absorbs light of particular wavelength & reflects other wavelengths of light • each pigment appears (to eyes/brain), the colour of wavelength of light it’s reflecting • energy associated with wavelengths of light is captured & funnelled down to primary pigment reaction centre

• energy associated with wavelengths of light is captured & funnelled down to this centre • consists of type of chlorophyll, at base of photosystem

• mixture of pigments • all have similar molecular structure which consists of porphyrin group (in which is a magnesium atom) & a long hydrocarbon chain

• 2 types which both appear blue-green • both situated at centre of photosystems • both absorb red light, but have different absorption peaks: • P680 = found in photosystem II & peak of absorption is light of wavelength 680 nm • P700 = found in photosystem I & its peak of absorption is light of wavelength 700nm • chlorophyll a also absorbs some blue light, of wavelength ~440nm

• absorbs light of wavelengths 400-500nm & ~640nm • appears yellow-green

• carotenoids - absorb blue light of wavelengths 400-500nm & reflect yellow/orange light • xanthophylls - absorb blue & green light of wavelengths 375-550nm - reflect yellow light

• separate pigments in chlorophyll by scraping/mashing green leaf • use 2 microscope slides • spot chlorophyll onto a slide coated with thin layer chromatography material • when solvent creeps up the slide the pigments separate out as have different Rf values

distance travelled by pigment divided by distance travelled by solvent