Monalisa Manurung

08-114

OVERVIEW OF MOLECULAR CELL BIOLOGY

The beginning of modern medicine can be traced back to centuries

ago when physicians and scientists began studying human anatomy from

cadavers in morgues and animal physiology following

hunting expeditions. Gradually, from the study of animals

and plants in greater detail and the discovery of microbes,

scientific principles governing life lead to the emergence of

the biological sciences.

As biological science developed and expanded, scientists and

physicians began to utilize the principles of biological sciences

to solve challenges of human diseases

while continuing to explore the fundamentals of life in greater

detail. With ever-evolving state-of-the-art scientific tools, our

understanding of how cells, tissues, organs, and entire

organisms function, down to the level of molecular and

subatomic structure, has resulted in modern biology with an

enormous impact on modern healthcare and the discovery of

amazing treatments for disease at an exponential pace

Significant progress has been made in molecular studies of organ development, cell signaling, and gene regulation. The advent of recombinant DNA technology, polymerase chain reaction (PCR) techniques, and next-generation genomic sequencing, which resulted in the sequencing of the human genome, holds the potential to have a transformational influence on healthcare and society this century by not only broadening our understanding of the pathophysiology of disease, but also by bringing about necessary changes in personalized medicine

Today’s practicing surgeons are becoming increasingly aware that many modern surgical procedures rely on the information gained through molecular research (i.e., personalized surgery). Genomic information, such as deleterious BRCA and RET proto-oncogene mutations, is being used to help direct prophylactic procedures to remove potentially harmful tissues before they do damage to patients. Molecular engineering has led to cancer-specific gene therapy that could serve in the near future as a more effective adjunct to surgical debulking of tumors than radiation or chemotherapy,

• so surgeons will benefit from a clear introduction to how basic biochemical and biological

• principles relate to the developing area of molecular biology.

• This chapter reviews the current information on modern

• molecular biology for the surgical community.

Basic Concepts of Molecular ResearchThe modern era of molecular biology, which has been mainly concerned with how genes govern cell activity, began in 1953 when James D. Watson and Francis H. C. Crick made one of the greatest scientific discoveries by deducing the double helical

1 structure of deoxyribonucleic acid (DNA).1,2 The year2003 marked the 50th anniversary of this great discovery. In the same year, the

Human Genome Project completed with sequencing approximately 20,000 to 25,000 genes and 3 billion

2 base pairs in human DNA.3 Before 1953, one of the mostmysterious aspects of biology was how genetic material was precisely duplicated from one generation to the next. Although DNA had been implicated as genetic material, it was the base-paired structure of DNA that provided a logical interpretation of how a double helix could “unzip” to make copies of itself. This DNA synthesis, termed replication, immediately gave rise to the notion that a template was involved in the transfer of information between generations, and thus confirmed the suspicion that DNA carried an organism’s hereditary information.

Within cells, DNA is packed tightly into chromosomes. One important feature of DNA as genetic material is its ability to encode important information for all of a cell’s functions (Fig. 15-1). Based on the principles of base complementarity, scientists also discovered how information in DNA is accurately transferred into the protein structure. DNA serves as a template for RNA synthesis, termed transcription, including messenger RNA (mRNA, or the protein-encoding RNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). mRNA carries the information from DNA to make proteins, termed translation, with the assistance of rRNA and tRNA. Each of these steps is precisely controlled in such a way that genes are properly expressed in each cell at a specific time and location. In recent years,

New classes of noncoding RNAs (ncRNA), for example, microRNA (or miRNA), Piwi-interacting RNA (or piRNA), and long intergenic noncoding RNA (or lincRNA), have been identified. Although the number of ncRNAs encoded in the human genome is unknown and a lot of ncRNAs have not been validated for their functions, ncRNAs have been associated to regulate gene expression through posttranscriptional gene regulation such as mRNA degradation or epigenetic regulation such as chromatin structure modification and DNA methylation induction.4 Consequently, the differential gene activity in a cell determines its actions, properties, and functions.

Molecular Approaches to Surgical Research

Rapid advances in molecular and cellular biology over the past half century have revolutionized the understanding of disease and will radically transform the practice of surgery. In the future, molecular techniques will be increasingly applied to surgical disease and will lead to new strategies for the selection and implementation of operative therapy. Surgeons should be familiar with the fundamental principles of molecular and cellular biology so that emerging scientific breakthroughs can be translated into improved care of the surgical patient

Figure 15-1. The flow of genetic information from DNA to proteinto cell functions. The process of transmission of genetic information from DNA to RNA is called transcription, and the process of transmission from RNA to protein is called translation. Proteins are the essential controlling components for cell structure, cell signaling, and metabolism. Genomics and proteomics are the study of the genetic composition of a living organism at the DNA and protein level, respectively. The study of the relationship between genes and their cellular functions is called functional genomics.

The greatest advances in the field of molecular biology have been in the areas of analysis and manipulation of DNA.1 Since Watson and Crick’s discovery of DNA structure, an intensive effort has been made to unlock the deepest biologic secrets of DNA. Among the avalanche of technical advances, one discovery in particular has drastically changed the world of molecular biology: the uncovering of the enzymatic and microbiologic techniques that produce recombinant DNA. Recombinant DNA technology involves the enzymatic manipulation of DNA and, subsequently, the cloning of DNA. DNA molecules are cloned for a variety of purposes including safeguarding DNA samples, facilitating sequencing, generating probes, and expressing recombinant proteins in one or more host organisms.

DNA can be produced by a number of means, including restricted digestion of an existing vector, PCR, and cDNA synthesis. As DNA cloning techniques have developed over the last quarter century, researchers have moved from studying DNA to studying the functions of proteins, and from cell and animal models to molecular therapies in humans. Expression of recombinant proteins provides a method for analyzing gene regulation, structure, and function. In recent years, the uses for recombinant proteins have expanded to include a variety of new applications, including gene therapy and biopharmaceuticals. The basic molecular approaches for modern surgical research include DNA cloning, cell manipulation, disease modeling in animals, and clinical trials in human patients.