Thylakoid

Thylakoids are special parts inside tiny structures called chloroplasts and in tiny blue-green plants called cyanobacteria. They are very important because this is where plants catch sunlight and turn it into energy, a process called photosynthesis.

Thylakoids are like little bags made of a thin layer called the thylakoid membrane, and they hold a watery space inside called the thylakoid lumen. In plants, these bags often stack up like coins and are called grana, with each stack being called a granum. These stacks are linked together by other thylakoid parts called intergranal or stromal thylakoids, so they all work together.

Inside the thylakoid membranes, there are special green molecules called chlorophyll that catch the light. These chlorophyll molecules are grouped into tiny clusters known as quantasomes.

Etymology

The word Thylakoid comes from a Greek word, thylakos or θύλακος, which means "sac" or "pouch". So, thylakoid describes something that looks like a little sac or pouch.

Structure

Thylakoids are tiny parts inside chloroplasts. They look like stacks of coins and help plants make food from sunlight.

The thylakoid membrane holds special colors that catch sunlight. Inside the membrane is a space called the lumen, which stores energy. In plants, these stacks are linked by thin layers, giving chloroplasts a large area to catch sunlight.

Formation

Chloroplasts grow from small structures called proplastids when seedlings come out of the ground. Thylakoids need light to form. In young plants that haven't seen light yet, proplastids turn into structures with special membranes called prolamellar bodies. When these plants get light, the prolamellar bodies change into thylakoids. But if plants grow in the dark, they can't make thylakoids and won't grow well.

A special protein called VIPP1 is needed for thylakoids to form. Without enough VIPP1, plants grow more slowly and look paler because they can't make food as well. VIPP1 is important for making the thylakoid membranes but not for adding the proteins that sit on them. VIPP1 is found in all plants and algae that have thylakoids, like Chlamydomonas and Arabidopsis thaliana.

Isolation and fractionation

Thylakoids can be separated from plant cells using special spinning techniques called centrifugation. Breaking apart the thylakoids can release their inside material. We can also take out certain proteins from the thylakoid membranes using sodium carbonate (Na₂CO₃), detergents, and organic solvents. These help separate proteins that stick to the membrane surface from those that are part of the membrane itself, like peripheral membrane proteins and integral membrane proteins.

Proteins

Thylakoids have many important proteins in their membranes and inside them. We now know that thylakoid contain at least 335 different proteins. Some of these proteins are inside the thylakoid space, while others are part of the thylakoid membrane.

Thylakoid membranes hold special proteins that help plants capture light and turn it into energy. There are four main groups of these proteins: Photosystems I and II, the cytochrome b6f complex, and ATP synthase. Photosystem II is mostly found in certain parts of the thylakoid, while Photosystem I and ATP synthase are in other areas. The cytochrome b6f complex is spread evenly. These proteins work together to help move energy and make important energy-rich molecules.

Photosystems are groups of proteins that collect light energy using special green pigments. This energy is passed to a center point where it helps create energy carriers needed for plant growth. The cytochrome b6f complex moves energy between the two photosystems. ATP synthase uses energy differences to create ATP, a key energy molecule for plants.

Inside the thylakoid space, there are proteins that help move energy and create important molecules for the plant. Plants control how these proteins are made and placed inside the plant cells. Some instructions come from the plant’s own DNA, while others come from DNA that originally came from old bacteria living inside the plant’s cells long ago. This helps the plant keep everything working properly.

Function

Thylakoids are tiny bags inside plant cells. They help plants use sunlight to make food through a process called photosynthesis. This process turns sunlight, water, and air into energy for the plant.

Inside the thylakoids, water is split to give energy and make oxygen, which we need to breathe. The thylakoids also help move tiny particles called electrons. This makes special energy-rich molecules like ATP. This process helps plants grow using sunlight.

Thylakoid membranes in cyanobacteria

Cyanobacteria are tiny organisms that can make their own food using sunlight. Inside them, there are special layers called thylakoid membranes. These layers help the cyanobacteria turn sunlight, water, and air into food through a process called photosynthesis.

Unlike bigger plants, the thylakoid layers in cyanobacteria form many round shells that connect together. This creates a network that helps important things move around easily. The layers also have small holes, which let tiny parts of the cell travel through. Scientists study these tiny organisms to learn more about them.