Intro to Cell and Molecular Biology for Non-Biologists
This post is targeted mainly at computer scientists, statisticians, engineers, physicists, data scientists, mathematicians, and any other professionals in a (esp. scientific) discipline who are interested in consuming the state-of-the-art literature in biology and medicine. Since lots of texts in biomedicine often use heavy jargons, non-biologists usually find it quite intimidating to read publications in this and related fields, let alone contribute their unique expertise to biology. Yet, recent technological advances in experimental techniques have led to a dramatic explosion of data, which in turn requires interdisciplinary collaboration between people of different know-how so as to make sense of these huge datasets and extract meaningful biological insights out of them. Therefore, it is now even more important than ever for scientists from other disciplines who have zero formal training in bioscience to be able to quickly understand the large body of work being produced in cell and molecular biology without having to spend four years in university majoring in life science. The purpose of this article is to give you a summary of the most important points that you need to know in order to intelligently understand the language of biologists.
Life is made of cells
The human body is made up of “just” 200–400 cell types, but we (i.e. you and I) have copious amount of each cell types. In fact, there is a mind-bogglingly 10¹⁴ cells (that’s 100 trillion of cells) in a human body, organized into tissues and organs that give rise to life. Cells come in thousands of shapes and sizes, but they are so small that 10,000 of our cells could all fit on the head of a pin. To sustain life, the cells in our body go through 5 x 10¹⁷ biochemical reactions per second (that’s 500 quadrillion every second!). That is why biochemistry plays such a crucial role in understanding cells (and life) and has important medical applications.
As a cell develops, it eventually divides itself, and as it divides itself, it ends up differentiating itself into groups. For example, an embryo is a group of cells; as the cells in the embryo go through further division, some genes are down-regulated and some others remain expressed, which leads to further cell differentiation. After ~10 rounds of division, the embryo takes the shape of a sphere-like structure known as blastocyst. The outer layer of the blastocyst, which will eventually become the placenta, is made up entirely of cells that express the gene CDX2.
The interior of the blastocyst is mainly made up of cells that express the gene OCT3/4. These cells are called pluropotent cells, as they are the ancestors of every one of the cells in an adult human body. That is, those cells ultimately differentiate into skin, blood, bone, muscle, etc. However, not all cells take on specialized functions by differentiating into such specific types. The cells that remain less differentiated and thus retain the ability to generate a wide range of other mature cell types (through self-renewal) are known as stem cells.
Stem cells are indispensable in their role at replenishing other cells in our body as they age and die off. For example, the hematopoietic stem cells in the bone marrow replace trillions of red blood cells every single day. That’s why hematopoietic stem cells are used to replenish blood supplies after a chemo- or radiotherapy. For the purpose of bioengineering, however, the multipotent stem cells in a human adult are limited in their ability to generate other cell lineages and challenging to maintain in culture. Hence, usually the embryonic stem (ES) cells are harvested and grown in-vitro due to their pluripotency. The ES cells in culture can be engineered under controlled conditions into certain lineages (e.g. neural lineage).
For more information on the biology of cells, check out the wiki on general biology or resources from The Biology Project. Multiple educational videos can also be found on YouTube (e.g. the one below on cell cycle).
Molecular Components of the Cell
The plasma membrane is made up of double-layer lipid molecules. It is the “flexible wall” that protects the cell from the outside world; the molecules of the membrane are constantly moving within the structure and never static. The plasma membrane plays a crucial role in cell signaling networks, namely it receives signals from the cell environment and transmits that information into the cell. For example, the MAPK signaling pathway is activated through the binding of a growth factor to the receptors in the cell membrane. This in turn recruits some signaling molecules to the intracellular domain of the docking site. This activation of the membrane is regulated by several proteins, leading to the translocation of a protein to the nucleus that triggers multiple transcription factors for mediating gene expression. Hence, MAPK signaling is contributing to the survival and proliferation of the target genes.
Chromatin, which contains the DNA, receives signals from the environment, which recruits proteins that regulate gene expression (which in turn results in cell phenotype). The study of chromatin structure and its role in regulating gene expression is also a major part of epigenetics.
Chromatin is basically just condensed DNA-protein complex that resides in the nucleus. In the zones of naked DNA, transcription factors can bind to the DNA directly and regulate gene expression. Bound to DNA, the transcription factor (TF) can interact with other proteins for transcription (i.e. the process of creating an mRNA molecule from a DNA sequence)
A gene is just a sequence of DNA instructions that ultimately gives life to flesh and blood. It all begins with the TF that interacts with other proteins at the start of a gene forming a bundle that triggers transcription. This process reads off the information needed to produce proteins by sliding along the DNA. As it slides along, it unzips the double helix and copies one of the two strands into RNA. See also: DNA v.s. RNA.
The single-stranded mRNA carries the gene information out of the nucleus to a ribosome, where the 3D protein that corresponds to the genetic message is made. Amino acids attached to transfer RNAs are carried into the ribosome as building blocks for the protein while the mRNA is read as codons (a codon is a group of three nucleotides). This process of joining chains of amino acids into proteins based on the mRNA sequence is called translation.
I hope this short article inspires you to learn more and ultimately contribute your expertise to help advance this field.