MCAT Biology

Cellular Organelles

MCAT Biology > Cellular Organelles


The cell is the most basic structure of life. Each cell is composed of specific organelles which act just like human organs do in the body. Each organelle serves a specific function within the cell.

There are many different organelles throughout the cell that are necessary to know for the MCAT exam. These organelles include:

MCAT Cellular Organelles - Animal Cell

Organelles between plant and animal cells are generally similar with the exception of the cell wall and chloroplasts in plants. These provide the unique structure and ability to perform photosynthesis that distinguish plants and are not found in animal cells.


Endoplasmic Reticulum

See Endoplasmic Reticulum


See Ribosomes

MCAT Cellular Organelles - Ribosomes

The ribosome is responsible for protein production. It takes orders from the nucleus and mRNA. It then sends out the products to the endoplasmic reticulum to be processed and sent out throughout the cell.

There are two types of ribosomes, bound and unbound. Bound ribosomes are bound to the endoplasmic reticulum while unbound ribosomes can float freely throughout the cytoplasm.

Eukaryotic ribosomes consist of 60s/30s subunits while prokaryotic ribosomes have 50s/30s and deal with the newly created rRNA molecule.

Ribosomes contain three major binding sites, (1) for mRNA, and (2) for tRNA.

  • The A-site holds the aminoacyl-tRNA complex
  • The P-site binds to tRNA attached to a growing polypeptide chain
MCAT Cellular Organelles - Ribosome MRNA Translation

Proteins are distinguished based on the signal sequence on the cells surface or a unique carbohydrate chain. If there is no signal, the protein is excreted from the cell. At the end, the vesicle of a protein is released to mature in the lysosomes

Click here to learn more about ribosomes and protein synthesis through transcription and translation.

Golgi Apparatus

See Golgi Apparatus


See Lysosomes


See Vesicles


See Mitochondria


See Centrioles


See Cytoskeleton

Plant Cell Organelles

See Plant Cell Organelles

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