5.6.2 chloroplasts & photosynthetic pigments Flashcards
define granum (pl: grana)
inner parts of chloroplasts made of stacks of thylakoid membranes, where the light-dependent stage of photosynthesis takes place
photosynthetic pigment
pigment that absorbs specific wavelengths of ight & traps the energy associated with the light; such pigments include chlorophylls a & b, carotene and xanthophyll
photosystem
system of photosynthetic pigments found in thylakoids of chloroplasts; each photosytem contains ~300 molecules of chlorophyll that that photons & pass their energy to primary pigment reaction centre (a molecule of chlorophyll a) during the light-dependent stage of photosynthesis
describe stroma
fluid-filled matrix of chloroplasts, where light-independent stage of photosynthesis takes place
describe thylakoid
flattened membrane-bound sac found inside chloroplasts; contains photosynthetic pigments/photosysytes & is site of light-dependent stage of photosynthesis
structure of chloroplasts
- 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)
where does the first stage of photosynthesis occur (light-dependent stage)
in the grana
what are the three distinct membranes of a chloroplast
- outer membrane
- inner membrane
- thylakoid
–> give 3 separate internal compartments: intermembrane space, stroma & thylakoid space
what may connect the thylakoids of one granum with another thylaokoid in another granum
intergranal lamellae (intergranal thylakoids)
describe the thylakoid membrane (inner membrane)
- less permeable
- folded into flattened disc-like sacs = thylakoids
- thylakoids form stacks = granum
- 1 granum may contain up to 100 thylakoids
due to the number of grana in each chloroplast, and the number of chloroplasts in each synthetic cell, what is there a huge surface area for?
- distribution of photosystems that contain photosynthetic pigments to trap sunlight energy
- electron carriers & ATP synthase enzymes needed to convert light energy to ATP
what hold the photosystems in place
proteins embedded in thylakoid membranes
why are the grana surrounded by the stroma
so the products of light-dependent stage of photosynthesis can easily pass to stroma to be used in light-independent stage
describe the stroma
- fluid-filled matrix
- contains enzymes needed to catalyse reactions of light-independent stage of photosynthesis
- also contains starch grains, oil droplets, small ribosomes & DNA
what does the loop of DNA in the stroma contain
genes which code for some of proteins needed for photosynthesis
–> proteins assembled at chloroplast ribosomes
describe photosystems
- funnel-shaped structures found in thylakoid membrane (inner membrane) of chloroplasts
- contain photosynthetic pigments
describe 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
describe the 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
describe chlorophylls
- mixture of pigments
- all have similar molecular structure which consists of porphyrin group (in which is a magnesium atom) & a long hydrocarbon chain
describe chlorophyll a
- 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
describe chlorophyll b
- absorbs light of wavelengths 400-500nm & ~640nm
- appears yellow-green
name 2 accessory pigments & describe them
- carotenoids - absorb blue light of wavelengths 400-500nm & reflect yellow/orange light
- xanthophylls - absorb blue & green light of wavelengths 375-550nm - reflect yellow light
how to separate photosynthetic pigments using thin layer chromatography (TLC)
- 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
how to calculate Rf value
distance travelled by pigment divided by distance travelled by solvent
