Microtubules are hollow rods made up of thousands tubulin protein subunits. There form long tube-like structures in the cell and are responsible for guiding the movement of organelles. Note that microtubules have other functions such as guiding chromosomes during mitosis and meiosis via the spindle fibers, which are made of microtubules.

A vegetarian diet without the proper supplements places one at risk for anemia. Without the proper amount of protein, iron, folate, and vitamin B12, the body is unable to produce enough red blood cells. To compensate, inactive bone marrows will be reactivated. The activity of the hematopoietic stem cells will lower the concentration of the fat cells in the bone marrow. 

The nucleolus is a specialized structure within the nucleus that is the site of ribosome synthesis and assembly. The nucleolus is not directly involved in DNA replication, translation, or ATP synthesis. While the DNA of eukaryotic cells is stored in the nucleus, it is not stored in the nucleolus since this part of the nucleus is specialized for ribosome assembly.

The process of vesiculation (the production of vesicles) requires “coat” proteins. These coat proteins provide 2 essential functions for the vesicles: #1: they allow the formation of the vesicle to occur and #2: act as signals that tell the vesicle where to go once inside the cell. There are 3 different coat proteins found on these vesicles. COPI, COPII and clathrin. COPI mediates transfer from the Golgi apparatus to the endoplasmic reticulum (ER); COPII meditates transfer from ER to the Golgi apparatus; clathrin mediates transfer from plasma membrane to the lysosome or Golgi apparatus. Therefore, if proteins were radio-labeled inside this vesicle coated with clathrin, we would expect them to be found in the lysosome.

The 2 main functions of the smooth endoplasmic reticulum (ER) are #1 synthesis of bio-lipids and #2 detoxification reactions. 3 general classes of molecules synthesized here are lipids, phospholipids, and steroids. Sphingolipids are types of lipids that protect the cell with their chemical charges. Phosphatidylcholine is a phospholipid found on the cell membrane of cells. Testosterone is a steroid protein most commonly found in high concentrations in male organisms like humans. Cardiolipin is an important protein found on the inner mitochondrial membrane. Cardiolipin is exclusively produced by the mitochondria and does not require the Golgi apparatus to produce it. 

Within a typical cell, the intracellular concentration of ionized calcium is roughly 100 nM, but is subject to increases of 10 to 100-fold during various cellular functions. The intracellular calcium level is kept relatively low with respect to the extracellular fluid, by an approximate magnitude of 12,000-fold. The cell is able accomplish this by storing the calcium within the endoplasmic reticulum via an active calcium channel pump called sarcoplasmic/endoplasmic reticulum calcium-ATPase (SERCA).

The process of secretion of a newly synthesized molecule destined for use outside of the cell follows the following path: Rough endoplasmic reticulum, smooth endoplasmic reticulum, Golgi apparatus, secretory vesicle. This pathway must be accomplished for proper secretion to occur as vital peptides are added in the process in different organelles to make sure they are properly delivered.

Glycosylation is an enzymatic process that occurs in the rough endoplasmic reticulum and the Golgi apparatus as a co-translational or post-translational modification. There are also O-Linked Glycosylation reactions that can also occur in the nucleus and cytoplasm. These glycans serve a variety of structural and functional roles of both membrane and secretory proteins and are therefore very important to the integrity of the proteins.

Lysosomes are organelles responsible for programmed cell death and the site of intracellular digestion. They do not occur in plant cells. Chloroplasts occur only in plant cells. Peroxisomes, mitochondria, and golgi apparatus are found in all eukaryotic cells, which includes plants.

The endomembrane system consists of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and plasma membrane. Though the endoplasmic reticulum has ribosomes embedded into it, they are not considered a part of the endomembrane system. Also, the mitochondria are responsible for metabolic functions, but it does not remain continuous with the endomembrane system physically or through vesicle transport. Though the endomembrane system does have a structural role, the cytoskeleton and centrosome are not considered in that structural role as they also are not continuous with the endomembrane system.