 Welcome back! Today we will be following the journey of a protein through the various organelles in a eukaryotic cell. Eukaryotic cells contain a nucleus and several membrane-bound organelles that perform different functions for the cell. To start, let's follow the journey of a protein through the cell. The information for how to build the protein is encoded in DNA, which is packaged in the nucleus. Little messengers called mRNA take a copy of this DNA out of the nucleus and to the ribosomes. These ribosomes build the protein. In eukaryotic cells, ribosomes are attached to an organelle called the endoplasmic reticulum, or the ER. The rough ER, which is covered in ribosomes, forms a kind of highway to transport these new proteins around the cell. The smooth sections of the ER are actually involved in lipid synthesis instead. Our protein will then be shipped to the Golgi apparatus for processing. Here it is modified, decorated and packaged up to ship to its final destination. For example, if it's a plasma membrane protein, this is where it will be shipped. Now, this long process must be powered by something. That power is provided by an energy-rich molecule that is made in the mitochondria, which is why it is often called the powerhouse of the cell. When components of the cell reach the end of their life, they are dismantled and recycled by organelles called lysosomes. Lys means to break, and these organelles are filled with enzymes that break things down. Another organelle which helps to break things down is the peroxisome. Specifically, it chemically breaks down fats. In the cell, you will also find vacuoles. These water-filled organelles are used for the storage of nutrients or waste. So this is a typical animal cell, but plant cells are slightly different. One of the biggest differences is a strong cell wall around the plasma membrane. It gives the cell structure, strength and protection. The strength provided by the cell wall is the reason why wood is so strong and trees can be hundreds of metres tall. In addition, plant cells also contain large vacuoles. These push tightly up against the cell wall like an inflated balloon, making the cells turgid. If the plant doesn't have enough water, the vacuoles will deflate and the plant will wilt. The next organelle found only in plants is the reason why they're normally green. This is the chloroplast, which contains the green pigment chlorophyll involved in photosynthesis. The chloroplast is where photosynthesis happens. Light energy and CO2 are converted into oxygen and sugars. The chloroplast is also an example of endosymbiosis with blue-green algae. Both plant and animal cells are examples of eukaryotic cells that contain organelles. These organelles perform specific and important functions for the cell, creating life as we know it.