The History of a Lysosomal Enzyme Learning the Organelles

The creation of the protein starts in the Nucleus

The Nucleus The storehouse for DNA (deoxyribonucleic acid) in your cells. DNA contains the genes – which are instructions – for making proteins. The Nucleus must: Protect the DNA and Make the DNA available for use at the proper time (DNA transcription) for protein synthesis.

The Nucleus

The Nucleus The nucleus protects the cell’s DNA from molecules that might damage it. At the same time, the nucleus makes the DNA available to the many proteins that are involved in turning genes on and off. The nucleus is composed of the cell’s DNA enclosed in a nuclear envelope (a double membrane).

The Nucleus The nuclear envelope is pierced with pores (nuclear pores) which allow large molecules to pass between the nucleus and cytoplasm. RNA passes through the nuclear envelope between the nucleus and cytoplasm. The nucleolus is also found in the nuclear envelope. Its main purpose is producing the “subunits (the parts)” from which ribosomes are assembled.

Rough and smooth ER

Ribosomes Either found on the surface of the rough endoplasmic reticulum or independently suspended in the cytoplasm. Processes: they are the site of protein synthesis (and are made of ribosomal RNA and proteins). They link amino acids, found in cytoplasm, together to form proteins. They are built in the nucleolus in the nucleus.

Endoplasmic Reticulum (ER) An interconnected network of thin folded membranes (forms maze of enclosed spaces). Interior of the “maze” is the lumen. Fills a large part of a eukaryotic cell’s cytoplasm. The folds allow for lots of surface area to carry out its processes. Processes – production of proteins and lipids inside, in the lumen, and on the surface of it.

Ribosomes and Rough Endoplasmic Reticulum Work Together Ribosomes and rough endoplasmic reticulum (rough ER), work together. Ribosomes attached to the outside surface of the rough ER make proteins. The proteins enter the rough ER and are modified in the lumen. In the lumen, other molecules are added to the protein. The protein is folded, giving it its shape and determining its biological purpose, and sent to the Golgi apparatus.

Golgi Apparatus (GA) and Transport Vesicles

Transport Vesicles Vesicles are made when tiny pieces of protein-containing ER are pinched off - allowing the protein, finished and folded in the rough ER, to be safely transported to the Golgi apparatus. The transport vesicles make sure that the proteins are separated from the cytoplasm (so they aren’t “activated”). They are short-lived.

Golgi Apparatus (GA) From ER, proteins typically move to Golgi apparatus by transport vesicle. Process: they process, sort, “package,” and deliver proteins to where they need to go. GA is made of closely layered stacks of membrane-enclosed spaces. The packaged proteins can be stored in the GA; sent to other organelles in the cell; or shipped outside of the cell.

Lysosomes They contain enzymes, with which they break down damaged or worn-out cell parts. They also defend a cell from invading bacteria and viruses. They engulf and digest targeted molecules. The broken down molecule is then moved to the cytoplasm where its parts are used again by the cell. They are numerous in animal cells but rare in plant cells. Lysosomes are made by the Golgi apparatus.

Lysosomes The lysosomal enzymes are made in the rough ER in an inactive form. Transport vesicles pinch off from the rough ER and carry the enzymes to the Golgi apparatus. There, the enzymes are packaged, activated and pinched off from the Golgi membrane as formed lysosomes.