This summary is based on the 3rd edition of Essential Cell Biology from Alberts et al. The remaining chapters can be accessed when logged in and can be found here: Second part of the summary

1. Introduction to cells

Unity and diversity of cells

Cells are the fundamental units of life; all living things are made of cells. The present-day cells are believed to have evolved from an ancestral cell that excited more than 3 billion years age. Cells vary enormous in appearance and function, however all living cells have a similar basic chemistry.

With the invention of the microscope, it became clear that plants and animals are assemblies of cells, that cells can also exist as independent organisms, and that cells individually are living in the sense that they can grow, reproduce, convert energy from one form into another, respond to their environment, and so on. Although cells are varied when viewed from the outside, all living things are fundamentally similar inside. And in all living things, genetic instructions, called genes, are stored in DNA molecules. In every cell, the instructions in the DNA are read out, or transcribed, into a chemically related set of molecules made of RNA. The messages carried by the RNA molecules are in turn translated into yet another chemical form: they are used to direct the synthesis of a huge variety of large protein molecules that dominate the behaviour of the cell. In sum, the reproduction process exists of replication (DNA synthesis), transcription (RNA synthesis) and translation (protein synthesis). Unfortunately, the copying of DNA is not always perfect, and the instructions are occasionally corrupted. Later is this summary we will discuss this further.

Cells are enclosed by a plasma membrane that separates the inside of the cell from the environment. And all cells contain DNA as a store of genetic information and use it to guide the synthesis of proteins. Cells in a multicellular organism, though the all contain the same DNA, can be very different. They use their genetic information to direct their biochemical activities according to cues they receive from their environment.

Cells under the microscope

Cells of animal and plant tissues are typically 5-20 micrometer in diameter and can be seen with a light microscope, which also reveals some of their internal components (organelles). The electron microscope permits the smaller organelles and even individual molecules to be seen, but specimens require elaborate preparation and cannot be viewed alive. So, the invention of the light microscope led to the discovery of cells

The presence or absence of a nucleus is used as the basis for a simple but fundamental classification of all living things. Organisms whose cells have a nucleus are called eukaryotes. Organisms whose cells do not have a nucleus are called prokaryotes. Bacteria, the simplest of present-day living cells, are prokaryotes. Different species of prokaryotes are diverse in their chemical capabilities and inhabit an amazingly wide range of habitats. Prokaryotes are divided into two groups: eubacteria and archaea. As mentioned above eukaryotic cells possess a nucleus. They probably evolved in a series of stages from cells more similar to bacteria. An important step appears to have been the acquisition of mitochondria, origination as engulfed bacteria living in symbiosis with larger anaerobic cells.

There are a lot of organelles found in eukaryotic cells: the nucleus is the most prominent organelle in most plant and animal cells. It contains the genetic information of the organism, stored in DNA molecules. The rest of the cell’s contents, apart from the nucleus, constitute the cytoplasm. Chloroplasts are green organelles found only in the cells of plants and algae, not in the cells of animals or fungi. They perform photosynthesis and in the process they release oxygen as a molecular by-product. Other organelles are the mitochondria, which are generators of chemical energy for the cell. Mitochondria contain their own DNA and reproduce by dividing in two. Furthermore, they take the energy from the oxidation of food molecules to produce adenosine triphosphate (ATP). The endoplasmatic reticulum (ER) is the site at which most cell membrane components, as well as materials destined for export from the cell, are made.  The Golgi apparatus often modifies chemically the molecules made in the ER and directs them to various locations of the cell. Lysosomes are organelles in which intracellular digestion occurs and peroxisomes generate a dangerously reactive chemical, hydrogen peroxide. Finally, the cytoskeleton is responsible for directed cell movements.

Model organisms

Free-living single-celled eucaryotic micro organisms include some of the most complex eucaryotic cells known, and they are able to swim, mate, hunt and devour food. Other types of eukaryotic cells, derived from a fertilized egg, cooperate to form large, complex multicellular organisms composed of thousands of billions of cells.

Biologists have chosen a small number of organisms as a focus for intense investigation. These include the bacterium E. coli, brewer’s yeast, a nematode worm, a fly, a small plant, a mouse and the human species itself.
Although the minimum number of genes needed for a viable cell is probably less than 400, most cells contain significantly more. Yet even such a complex organism as a human has only about 30.000 genes – twice as many as a fly, seven times many as E. coli.

2. Chemical components of cells

Chemical bonds

The cell is the structural and functionalRead more