4.4.c - Ribosomes + Endomembrane + Golgi + Lysosomes + Vacuoles

What is the function of ribosomes in both prokaryotes and eukaryotes?

It act as a workbench for protein synthesis. They use the information from mRNA to assemble polypeptide chains. Ribosomes are present in both prokaryotes and eukaryotes.

What are ribosomes made of and how are they structured?

They are composed of two subunits: one large and one small. Each subunit contains a mixture of proteins and ribosomal RNA (rRNA), which are essential for the ribosome’s function.

What happens to polypeptides synthesized by ribosomes attached to the endoplasmic reticulum (ER)?

After the ribosome binds to a receptor on the ER, the synthesized polypeptide enters the lumen of the ER. There, it may be modified and assumes its final shape before further transport.

What are the components of the endomembrane system, and what is its main function?

It includes the nuclear envelope, endoplasmic reticulum (ER), Golgi apparatus, and vesicles. Its main function is to compartmentalize the cell, enabling specific enzymatic reactions in different regions, thus increasing efficiency.

What is the role of the rough ER in protein synthesis?

It has ribosomes on its surface, allowing it to synthesize polypeptides. These polypeptides are then modified in the ER's lumen, and transport vesicles carry the proteins to other parts of the cell, like the plasma membrane or the Golgi apparatus.

What are the functions of smooth ER, and how do they vary by cell type?

It synthesizes lipids (e.g., phospholipids and steroids) and forms transport vesicles. Its functions vary: in the testes, it produces testosterone, while in the liver, it helps detoxify drugs. It also sends molecules to the Golgi apparatus.

What is the function of the Golgi apparatus in the endomembrane system?

It is composed of a stack of flattened structures. It receives transport vesicles from the rough and smooth ER, modifies the molecules inside (e.g., adding or removing sugars from proteins), and then sorts and packages them into new vesicles for transport to their destinations, such as the plasma membrane or lysosomes.

What are lysosomes, and what is their function in the cell?

They are vesicles produced by the Golgi apparatus that digest molecules entering the cell and break down damaged organelles. They can also fuse with vesicles formed at the plasma membrane to digest their contents. In diseases like Tay-Sachs, missing enzymes in lysosomes lead to harmful lipid accumulation, causing cell dysfunction.

What are vacuoles, and how do their functions vary in different cells?

They are larger than vesicles and are specialized for different functions. In aquatic protists, vacuoles remove excess water or help digest nutrients. In plant cells, vacuoles store water, nutrients, salts, pigments, and toxic molecules, which help protect plants and give flowers their colors.