Study eCentre

SAQ 1 a) What is gene mapping? How do the linked genes help in gene mapping? Gene mapping is the method used to determine the location of genes on a chromosome and the distance between them. It helps in identifying the exact position of a gene responsible for a particular trait or disease. The concept started with the work of Thomas Hunt Morgan in the early 1900s when he studied Drosophila melanogaster (fruit fly) and observed that some traits are inherited together. This was because the genes responsible for those traits were located close to each other on the same chromosome. This phenomenon is known as linkage. There are two main types of gene mapping: 1. Genetic Mapping (Linkage Mapping): Genetic mapping uses the frequency of recombination or crossing over between genes to estimate their distance on a chromosome. It gives a relative position of genes rather than their exact physical location. 2. Physical Mapping Physical mapping uses molecular biology techniques to determine the e...

To distinguish between primary and secondary cell culture, we must first understand what each term represents and how they differ in terms of origin, growth behavior, life span and application. Primary cell culture  refers to the initial culture that is directly derived from animal or plant tissues by mechanical or enzymatic disaggregation. The cells in this culture closely resemble the in vivo state both genetically and functionally. However, these cells have a limited capacity to divide and usually undergo senescence after a few passages. On the other hand,  secondary cell culture  is derived from the subculturing or passaging of primary cells. After several passages, the cells that adapt better to in vitro conditions may give rise to a more stable population. In some cases, these cells may undergo transformation and acquire the ability to proliferate indefinitely, forming a cell line. Now, based on several key features, we can distinguish between primary and secondary ...

Lysosomal degradation is one of the two major  intracellular pathways  responsible for maintaining  protein homeostasis  in eukaryotic cells, the other being the  ubiquitin-proteasome system.  While the  proteasome  primarily degrades  short-lived  or misfolded proteins that are tagged with  ubiquitin,  lysosomal degradation mainly targets  long-lived  cytoplasmic proteins, membrane proteins, protein aggregates, damaged organelles and extracellular proteins taken up by the cell. It plays a key role not only in general protein turnover but also in specialized physiological processes such as antigen presentation, cellular remodeling and metabolic adaptation during stress. Proteins targeted for lysosomal degradation are transported into the lysosome through four distinct routes, each with its own mechanism of substrate selection, delivery, and regulation. These include: Macroautophagy Microautophagy Chaperone-Mediated Au...

Ubiquitin is a highly conserved protein made up of  76 amino acids.  It functions as a regulatory molecule in cells by  tagging  specific proteins for degradation. This tagging ensures that unnecessary, misfolded, damaged, or short-lived proteins are identified, and removed in a selective and controlled way. This process is essential for maintaining cellular balance and preventing harmful accumulation of proteins. Ubiquitin does not perform the degradation itself, but by attaching to target proteins, it directs them to the proteasome, where they are broken down. This tagging function allows ubiquitin to play multiple crucial roles across different cellular processes. The major roles of ubiquitin in protein turnover can be classified as follows: 1. Protein Tagging for Degradation The most well-established role of ubiquitin is in  targeting proteins for degradation  via the ubiquitin-proteasome system (UPS). In this process, multiple ubiquitin molecules are c...

Protein turnover is a continuous and regulated process in which proteins inside a cell are broken down and replaced by newly synthesized ones. It is not just a recycling mechanism, but also a core regulatory process that helps maintain cellular homeostasis. Through protein turnover, cells can remove misfolded, damaged, or excess proteins and replace them with functional ones. It also allows the cell to adapt to environmental stress, control the cell cycle, regulate signaling pathways, manage growth and apoptosis. Hence, the pathways responsible for protein turnover such as the  ubiquitin-proteasome system  and  lysosomal degradation system,  both are designed with specific properties that ensure precision, efficiency and control. The properties of protein turnover pathways can be systematically classified in two ways: Based on biochemical properties Based on physiological-level properties 1. Biochemical Properties of Protein Turnover Pathways There are three fundamen...

The type of cell junction that is similar to plasmodesmata is the  gap junction.  Both allow the direct transfer of ions, small molecules and chemical signals between neighboring cells.  Plasmodesmata  are found in  plant cells,  while  gap junctions  are their functional counterparts in  animal cells. Gap Junction Gap junctions are a type of communicating cell junction found in animal cells. These structures form direct channels between adjacent cells, allowing for the transfer of ions, metabolites and small signaling molecules. They play a crucial role in maintaining tissue homeostasis, cell communication and coordinated cellular responses. These junctions are especially important in tissues that require rapid and synchronized communication like cardiac muscle, smooth muscle and certain neural tissues. Structure of Gap Junctions Gap junctions are composed of transmembrane protein subunits known as  connexins.   Six connexin molecu...

SAQ 1 i) Define Recon, Muton and Cistron. The terms Recon, Muton and Cistron were introduced by Seymour Benzer during the 1950s to study the detailed structure and function of genes at the molecular level. He worked on the rII region of T4 bacteriophage and used bacteriophage genetics to analyze how small changes in DNA affect phenotypes. At that time, the gene was considered as a single indivisible unit. But Benzer showed that a gene has a finer internal structure and can be divided into smaller functional units. Based on this, he proposed three molecular units: Recon, Muton and Cistron, each having a specific role related to recombination, mutation and expression. Recon Recon is defined as the smallest unit of recombination. It refers to the smallest segment of DNA within which crossing over cannot occur, but recombination can occur between two such units. According to modern molecular understanding, recombination between two genes or within a gene occurs at the level of nucleotid...