What is an Organelle?

Organelles, meaning little organ, are tiny structures inside of a cell that carry out specific jobs, such as  protein synthesis, which creates proteins that control every cell function. This allows an organism to live and function properly. There are eight organelles that allow for protein synthesis: the mitochondria, nucleus, nucleolus, ribosome, endoplasmic reticulum, golgi apparatus, vesicle, and lysosome.

First, energy must be used up in order for the organelles to be powered up and function properly. The mitochondria (aka the powerhouse of the cell) is in charge of generating this energy, which is in the form of ATP. 

The Mitochondria:

Function

The Mitochondria:

ATP

ATP, adenosine 5'-triphosphate, is an energy source and storage at the cellular level. Through cellular respiration fueled by glucose, ATP is created. It is used to drive many processes in living cells, including protein synthesis. 

The mitochondria has a double membrane, which separates the organelle into 4 compartments. The double membrane also helps increase surface area for energy creation. The outer membrane contains porins that allow  diffusion of molecules between the two membranes. The intermembrane contains the proteins. The inner membrane contains the transporters for carrying proteins into the matrix. Lastly, the matrix contains enzymes responsible for chemical reactions.

The Mitochondria: 

Structure

Protein synthesis first begins in the nucleus of the cell. The nucleus stores and protects the cell's DNA and RNA. DNA is the genetic code that make up an organism; it is the blueprint of instructions for all the organelles in the cell to carry out its functions. The DNA cannot leave the nucleus. On the other hand, RNA can leave the nucleus. It is a disposable copy of the DNA that carries out the instructions for protein synthesis. There are 3 types of RNA; rRNA, tRNA, and mRNA. 

The Nucleus: Function

The Nucleus: RNA

rRNA stands for ribosomal RNA. It creates ribosomes (see page 12), which is essential to protein synthesis. mRNA stands for messenger RNA. It contains the genetic blueprint for amino acid sequences that create proteins. mRNA binds to the ribosome, bringing it the blueprint instructions. Finally, tRNA stands for transfer RNA. It is in charge of translating mRNA to proteins, bringing in the correct amino acids to the ribosome.

The Nucleus: Structure

A nuclear envelope surrounds the nucleus, which is a double membrane that keeps the contents inside the nucleus protected. It is perforated with pores, each lined with different proteins knowns as the nuclear pore complex. The pore complex regulate the movement of macromolecules, including RNA proteins. The movement of molecules is called nuclear transport. Smaller molecules are 

allowed to passively go through the pores; however, larger molecules, like RNA and most proteins, must actively move through the nucleus through protein channels. Through active transport, proteins and RNA are continuously being recognized and transported to specific directions. These different forms of transportation ensures that the correct molecules are going in and out or staying inside of the nucleus.

The Nucleolus:Function

The nucleolus is the spherical structure found inside of the cell's nucleus. This is the site where rRNA genes are transcribed, making up the nucleolus' primary function: producing and assembling the cell's ribosomes. Once the ribosomes are assembled, they are transported to the cell cytoplasm (gel-like fluid inside the cell where chemical reactions take place) to begin creating the actual proteins itself.

Once the ribosome has been created through rRNA, the ribosome reads the mRNA sequence. Then, it uses tRNA to translate the mRNA code into a specific sequence of amino acids. These amino acids will form into long, polypeptide chains that fold to form proteins. Ribosomes are in charge of protein production.

The Ribosome: Function

The Ribosome: 

Free vs. Bound

There are 2 types of ribosomes: free and bound ribosomes. Free ribosomes are inside of the cytosol, synthesizing proteins the cell needs for itself; it is not attached to rough endoplasmic reticulum (ER). Bound ribosomes synthesize proteins mainly for export and is attached to the rough ER (see page 18); however, it also synthesizes proteins that require a membrane surrounding it.

The Ribosome:

Structure

Ribosomes consist of 2 subunits: the small and large subunits. The smaller subunit decodes mRNA during translation, while the larger catalyzes peptide bonds to create long chains of amino acids that later get folded into proteins in the endoplasmic reticulum. 

The Endoplasmic Reticulum:

Function

When the proteins are assembled in the ribosome, the proteins are then transferred into the endoplasmic reticulum (ER) to modify the proteins: folding and adding other entities. There are two parts to the endoplasmic reticulum: the smooth and rough endoplasmic reticulum. 

The ER:

Rough vs. Smooth

The smooth ER is in charge of a plethora of jobs: membrane production, the synthesis of lipids and steroids, and the hydrolysis of glycogen into glucose, which detoxifies drugs, alcohols, and poisons. The rough ER has an attachment to the ribosome. Here, it does all the protein modifications such as folding and extra additions.