The plasma membrane, the membrane of the cell, is made up of two different layers of phospholipids, into which are embedded many different kinds of proteins. This cell membrane regulates everything that passes in and out of the cell using osmosis and diffusion. Proteins and amino acids made within the cytoplasm leave the cell via the plasma membrane, which also prevents unwanted substances from passing into the cytoplasm.
The cytoplasm takes up the larger part of the cell and is a thick liquid that contains organelles like mitochondria, which is the second biggest organelle in the cell beside the nucleus. Mitochondria are also filled with liquid and surrounded by a membrane separating them from the rest of the cytoplasm. Most cellular activities, such as cell division, conversion of glucose or glycolysis and the cell's metabolic process, occur within the cytoplasm. The body of cytoplasm is contained within the plasma membrane.
The nucleus is also contained in the cytoplasm, but it also has its own containing membrane called the nuclear membrane. The nucleus is the part of the cell that holds the genetic material. It is actually a membrane-enclosed organelle itself, present in all eukaryotic cells. The genetic material is organized as multiple long strands of linear DNA molecules with proteins that form the chromosomes within the DNA. The genes within the chromosomes themselves are the cell's genetic genome.
A ribosome is one of the organelles within the cell cytoplasm that synthesizes proteins from amino acids and RNA. Molecular biology is based on the chain of events where DNA is used to make RNA, which is in turn is used to make proteins. This process is how living cells replicate and evolve. Ribosomes contain both messenger RNA (mRNA) and transfer RNA (tRNA) and small and large proteins that bind to the mRNA and tRNA respectively using amino acids. This very small protein factory within the cell, the ribosome, is one of the most important features of the cell.