What Are Thylakoids Made Of?

Thylakoids are membranous compartment structures which contain substances in cells. While a type of vesicle, they are distinguished between other vesicles in cells. While other vesicles in cells are free floating, thylakoids form a continuous and closed system which are stacked within the chloroplast of cells. While both vesicles and thylakoids have a bilipid layer which encloses a lumen, thylakoids are more specialized.

As they are involved in photosynthesis, thylakoids can be found in cyanobacteria and chloroplasts. They are believed to have their origin in photosynthetic bacteria and are closely related to the development of photosystem II, which allows oxygenic photosynthesis. In vascular plants, chloroplasts emerge from undifferentiated proplastids that initially possess few internal membranes. As chloroplasts differentiate, a thylakoid membrane system is formed that requires continuous synthesis for its maintenance during cell division.

Thylakoids are the main structure within mature chloroplasts. Their composition and architecture are closely linked to the evolution of chloroplasts from simple proplastids. These membranes are lipid bilayers with a specific glycerolipid composition, notable for a high content of galactolipids which are almost exclusive to plastid membranes. These include as galactosyl diglyceride. Galactolipids have two chains of unsaturated fatty acids, unlike other lipids that commonly contain one.

Thylakoid formation is a complex process, which may include invagination of the inner envelope in young plastids. In fully developed chloroplasts, the thylakoid membrane proves to be a dynamic system that adapts to light variations by protein movement.

Plastids are cell organelles found in plants and some other eukaryotes which are essential for their survival. To learn more, check out our related article asking what are plastids in plant cells?

As thylakoids are contained within chloroplasts and cyanobacteria, their purpose is closely linked to photosynthesis. You can bear this in mind as we look at the functions of thylakoids:

• They capture light energy and transform it into the chemical energy forms ATP and NADPH. During this process, water is oxidized and oxygen is released. These functions are performed by five major protein complexes which are photosystem I with attached antennae, photosystem II with attached antennae, light-harvesting complex II, cytochrome b 6 f and ATP synthase.
• Thylakoids absorb photons from sunlight to initiate the photochemical phase of photosynthesis.
• The chemical energy produced during photosynthesis will later be used in cellular respiration.
• Thylakoids contain chlorophyll, xanthophylls and carotenoids, which are also used to capture light and during the photosynthetic process.
• It has enzymes, lipids and proteins necessary to carry out photosynthetic reactions.
• They are responsible for the production of ATP (adenosine triphosphate) and facilitating the electron transport chain.
• The energy produced in plant cells is necessary for survival.
• The granule-like structure of the thylakoids provides a large surface area to maximize light collection, which improves the efficiency of the photosynthetic process.

Learn more about what is a chloroplast and its function to see how thylakoids are important within the cell.

We can understand the structure of thylakoids by looking at what they are made of. Thylakoids are surrounded by a thylakoid membrane which houses the multiprotein complexes essential for the light reactions of photosynthesis. It is composed primarily of photosystems I and II, together with their associated light-harvesting complexes, cytochrome b6f and ATP synthase.

These complexes consist of numerous peripheral and integral proteins, as well as a variety of pigments and cofactors. The distribution of components in the thylakoid membrane is not homogeneous. Photosystem I is predominantly found in the unstacked stromal lamellae, whereas photosystem II is the major component in the grana stacks.

Protein components in thylakoid membranes are distributed in a specific manner. For example, photosystem II is predominantly localized in the stacked regions, whereas photosystem I and ATP synthase are found in the stromal thylakoids and in the non-stacked areas. This asymmetric arrangement is crucial to maximize the efficiency of photosynthetic reactions.

The thylakoid membrane is rich in glycolipids, especially galactolipids. These represent about 70% of the lipid fraction. Together with plastoquinone and other components, this lipids maintain membrane fluidity, despite a high protein/lipid ratio. Furthermore, the thylakoid system allows the translocation of protons to the lumen, which is essential for the generation of ATP through ATP synthase.

Now that you know what thylakoids are made of and their function, you may want to know some general information about what are cell organelles?

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