Thylakoid

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Thylakoids (from ancient Greek θύλακος thylakos "bag") are in the biology membrane systems in the chloroplasts of plant cells and in phototrophic bacteria ( cyanobacteria ), in which the light reaction of photosynthesis takes place.

In phototrophic bacteria, thylakoids arise from inwardly directed invaginations of the cytoplasmic membrane , which are typically located near the inside. Inside the chloroplasts of green plants , the thylakoids also arise from membrane invaginations, namely on the inner chloroplast membrane. They run through the chloroplast interior, the so-called stroma .

Thylakoids also occur in other plant plastids that can be derived from chloroplasts.

Granum

TEM image from Grana

In chloroplasts, roll-like lamellae stacks, the so-called grana (from the Latin granum "grain", pl. Grana ), are formed by superimposing disc-shaped thylakoid lobes. The granular thylakoid lobes are called granathylakoids ; they have a particularly high pigment content . The thylakoid parts, which run not in the grana but individually in the stroma, are called stromathylakoids ; they contain fewer pigments and are not as involved in the light reaction of photosynthesis.

construction

Scheme of the photosynthesis apparatus in a thylakoid membrane
PS I, PS II: Photosystem I and II,
Cyt b 6 f: Cytochrome b 6 f complex,
ADP: adenosine diphosphate , ATP: adenosine triphosphate

The thylakoids consist of a membrane that encloses an interior space, the lumen . The light-collecting complexes PS are located in the membrane .

The granathylakoids contain a particularly large number of light-harvesting complexes ( photosystem I and photosystem II ) and also cytochrome b 6 f complexes , ATP synthase , plastoquinone , plastocyanin , ferredoxin and NADP + reductase , all of which are protein molecules . There are chlorophyll , carotene and phospholipid molecules in the lumen . The pH in the lumen is around 4.

literature

  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Biochemistry. 6 edition, Spektrum Akademischer Verlag, Heidelberg 2007. ISBN 978-3-8274-1800-5 .
  • Donald Voet, Judith G. Voet: Biochemistry. 3rd edition, John Wiley & Sons, New York 2004. ISBN 0-471-19350-X .
  • Bruce Alberts , Alexander Johnson, Peter Walter, Julian Lewis, Martin Raff, Keith Roberts: Molecular Biology of the Cell , 5th Edition, Taylor & Francis 2007, ISBN 978-0815341062 .