Introduction to Molecular Biology

 Introduction to Molecular Biology

Cells are fundamental building blocks of living organisms. Cells contain a nucleus, mitochondria and chloroplasts, endoplasmic reticulum, ribosomes, vacuoles, etc. 

The nucleus is important organelle because it houses chromosomes which include the DNA. 

The DNA is in essence a blueprint of the organism as it encodes information needed to synthesize proteins.

Molecular biologists would like to understand how human biology works with the hope to treat diseases like cancer. One can look at simpler organisms such as yeasts to understand how human biology works.

 Admittedly, unicellular yeasts are very different from humans who have approximately 1014 cells. However, the DNA is similar across all living organisms. For example, humans share 99% of DNA with chimps. Naturally, we would like to know what information contained in that 1% of DNA is so critical to determine all the distinguishing features of humans, 

DNA 

        DNA stands for deoxyribonucleic acid. 

DNA is an extremely long molecule that forms a double helix. 

The double-helix backbone of the molecule consists of sugars and phosphates, and there is one base attached to each sugar. There are four types of bases: cytosine (C), guanine (G), adenine (A) and thymine (T).

The DNA consists of two strands, and each base attached to one strand forms a bond with a corresponding base on the other strand. A only links with T and C links with G. A triplet of bases encodes an amino acid.

 Protein is a sequence of amino acids, and the functional subunit of DNA that encodes a protein is called a gene.

Gene Expression - from DNA to protein 

           Gene expression is a two-step process in which DNA is converted into a protein it encodes. The first step is DNA transcription. In this step, the information from the archival copy of DNA is imprinted into short-lived mRNA. 

The structure of RNA is a little different, it contains ribose instead of deoxyribose, and the four bases that bind to it are cytosine (C), guanine (G), adenine (A) and uracil (U).

During transcription, DNA unfolds, and mRNA is created by pairing mRNA bases with the bases of RNA. 

In this process C in DNA translates to G, G to C, A to U, and T to A. After mRNA is translated, it is transported to the ribosome.

The second step, protein translation occurs at the ribosome.

During translation, the sequence of codons (triplets of bases) of mRNA is, with the help of tRNA, translated into a sequence of amino acids. 

Gene expression seems to be a straightforward process, but it is the control of gene expression that causes most phenotypic differences in organisms. Since many diseases result from complex changes on the molecular level, we need to observe and model these processes.

DNA is the blueprint for living organisms on the system level. 

Gene regulatory circuits are an example of machinery that allows us to depict gene expression graphically. In this model, arrow from A and B to D indicates that if genes A and B are made into protein, so is gene D.