A Tour of the Cell

Words to know before you read

Do all cells look the same?

Cells come in many shapes and sizes. We are made up of about 200 different types of cells. Some cells are covered by a cell wall, other are not, some have slimy coats or elongated structures that push and pull them through their environment. Some cells have a thick layer surrounding their cell. This layer is called the capsule and is found in bacteria cells. 

In our body too, there are many different kinds of cells. Our body has various non living materials such as hair, finger nails, and the hard part of the bone and teeth. All these materials are made up of cells.

The cells in our body are different sizes. Our red blood cells are about 1/25,000^th of an inch across. Our kidney and liver cells are about 1/2500^th of an inch. Our muscle cells are thin filaments that are a few inches long. The record holders are our nerve cells that begin at the base of the spine and run all the way down to the tip of the big toe, a distance of several feet !!.

Taking a look inside a cell

Have you ever wondered what the inside of a cell looks like? If you think about the rooms in our homes, the inside of any animal or plant cell has many similar room-like structures called organelles. 

Some cells have a lot of these organelles, while others do as many of them. All organelles in a cell perform different functions. Here are some names and descriptions of organelles commonly found in cells:

Plasma membrane- The membrane enclosing a cell. This membrane is made up of two lipid layers held together. The lipids that are present in the plasma membrane are called phospholipids. These lipid layers are made up of a number of fatty acid building blocks. The fatty acid that makes up this membrane has two different parts to it- a small water loving head- hydrophilic head. Hydro stands for water and philic means liking or loving. The other part of this fatty acid is a long water-repelling or water hating tail. This tail is hydrophobic- Hydro stands for water and phobic means fear. The plasma membrane is arranged in such a way so that the tails face each other on the inside and the heads face towards the outside of the membrane.

Channels/pores- A channel in the cell's plasma membrane. This channel is made up of certain proteins whose function is to control the movement of food and water into the cell. These channels are made up of certain proteins.

Cytoplasm- A term for all the contents of a cell other than the nucleus. The cytoplasm contains mostly water.

Nucleus- The nucleus is the control center of the cell. It is the largest organelle in the cell and it contains the DNA of the cell. The DNA of any cell is made up of chromosomes. Inside the nucleus another organelle called nucleolus is present.

Ribosomes- Organelles that help in the synthesis of proteins. Ribosomes are made up of two parts, called subunits. One subunit is called large subunit because it is bigger in size, and the other subunit is called the small subunit because it is smaller in size. Both these subunits are necesary for protein synthesis in the cell. The ribosomes themselves are synthesized in the nucleolus of the cell.

Endoplasmic reticulum (ER)- It is a network of membranes throughout the cytoplasm of the cell. The ER is called rough ER when ribosomes are attached and smooth ER when there are no ribosomes attached. The rough endoplasmic reticulum is where protein synthesis occurs in the cell. The function of the smooth endoplasmic reticulum is to synthesize lipids in the cell. The smooth ER is also helps in the detoxification of harmful substances in the cell.

Golgi complex- It is organelle in the cell that is responsible for sorting and correctly shipping the proteins produced in the ER. Just like our postal packages which should have a correct shipping address, the proteins produced in the ER, should be correctly sent to their respective address. This shipping and sorting done by the Golgi complex is a very important step in protein synthesis, because, if the Golgi complex makes a mistake in shipping the proteins to the right address, certain functions in the cell may come to a halt. This organelle was named after an Italian physician-Camillo Golgi. He was the first person to describe this organelle in the cell.

Mitochondria- This is the cell’s powerhouse. This organelle packages the energy of the food into ATP molecules. Every cell has many mitochondria. The amount of mitochondria present in different tissues differ. There are more number of mitochondria in cells that have to perform lots of work, for example- your leg muscle cells, heart muscle cells etc.

Chloroplast- The cell organelle in which photosynthesis takes place. In this organelle the light energy of the sun is converted into chemical energy. Chloroplasts are found only in plant cells not animal cells. The chemical energy that is produced by chloroplasts is finally used to make carbohydrates like starch, that get stored in the plant. Chloroplasts contain tiny pigments called chlorophylls. Chlorophylls are responsible for trapping the light energy from the sun.

Vesicles- This term literally means "small vessel". This organelle helps store and transport products produced by the cell.