Genetic Mechanism and Gene Regulation

Key Concepts

• Genes, Genome
• Genetic Mechanism
• Gene Regulation
• Lac Operon
• Human Genome Project

Recall: 

• Genes
• DNA replication  

Introduction: 

Genes and genomes are replicated and DNA repairs to damage. Genes are expressed properly and generate the proteins and also the other molecules that do the work of the cell. The series of gene expression starts with the production of mRNA and continue the process of protein synthesis. Each step is exquisitely regulated to control gene expression. The levels of proteins within cells are affected not only by rates of protein synthesis but also by rates of degradation of the protein. 

Explanation: 

Gene mechanism is involved in the gene expression, starting with the production of an mRNA (transcription), followed by its processing and localization, and continuing to protein synthesis (translation). 

The process of the genetic codes is used for managing the protein synthesis, which is required for our body to produce the cell structures. Genes carry information required for sequences of amino acids that are termed structural genes. This process has two main steps: 

Transcription- with the help of RNA polymerase enzymes, the messenger RNA is produced, which results in the process of mRNA molecule. 

Translation-The main function of RNA is to synthesize the protein, which results in the translational process of the protein molecules. 

Gene regulation  

Gene regulation is the formation of a polypeptide; it can be regulated at several levels. In eukaryotes, the regulation could be exerted at: 

1. Transcriptional level (formation of primary transcript),  

2. Processing level (regulation of splicing),  

3. Transport of mRNA from the nucleus to the cytoplasm, 

4. Translational level. 

Prokaryotic cells  

Prokaryotic organisms are single-celled organisms that lack a nucleus, and their DNA floats freely in the cytoplasm. To synthesize proteins, processes of transcription and translation occur simultaneously. When the protein is not required, the transcription process stops. The primary method to control the type of protein and how much of each protein is expressed in a prokaryotic cell is the regulation of DNA transcription. When more proteins are required, more transcription occurs. Therefore, in prokaryotic cells, the gene expression control is at the transcriptional level. 

Lac operon 

Lac refers to lactose in the lac operon. The lac operon is one regulatory gene, the i gene codes for the repressor of the lac operon and the three structural genes (z, y, and a). The z gene codes for beta-galactosidase (β-gal); it hydrolyses disaccharide lactose into galactose and glucose. y gene codes permease, it increases the permeability of the cell to β-galactosides. Gene encodes a transacetylase. Lactose is termed as inducer; lactose is the substrate for the enzyme beta-galactosidase, which regulates the on and off of the operon during the absence of inducer. Repressor of the operon is synthesized (all-the-time – constitutively) from the i gene. The repressor protein binds with the operator region of the operon and prevents RNA polymerase from transcribing the operon. During the presence of inducer, the repressor is inactivated with the interaction of inducer, which allows RNA polymerase to promoter transcription. 

Eukaryotic cells 

In eukaryotic cells, the DNA is present inside the cell’s nucleus, and it is transcribed into RNA. The synthesized RNA is transported out of the nucleus into the cytoplasm; ribosomes translate the RNA into protein. The process of transcription and translation are separated by the nuclear membrane; transcription occurs within the nucleus, and translation occurs outside the nucleus in the cytoplasm. The regulation of gene expression can occur at all stages of the process. Regulation may occur when the DNA is not coiled, and nucleosomes bind transcription factors. When the RNA is transcribed, the RNA is processed and exported to the cytoplasm. The RNA is translated into protein. 

Human genome project :

The scientific project that deals with the study of sequences of DNA molecules to complete the set of chromosomes is called the human genome project. 

Goals of Human Genome Project 

• To identify approximately 20,000-25,000 genes in human DNA. 
• Determining the sequences of the 3 billion chemical base pairs which make up human DNA. 
• To store this information in databases. 
• To improve tools for data analysis. 
• Transfer related technologies to other sectors, such as industries. 
• To address the ethical, legal, and social issues (ELSI) that may arise from the project.