04 April 2025

The Lifecycle of Retrovirus

Lifecycle of Retrovirus

Lifecycle of Retrovirus

Introduction

Retroviruses are a type of RNA virus that replicate through a DNA intermediate. They integrate their genetic material into the host genome, enabling efficient replication. This lifecycle ensures their persistence and spread in host populations.

Source: Biorender.com [6,7]

Binding

The first step in the retrovirus life cycle is the binding of the virus to the host cell. This binding is mediated by specific viral surface proteins interacting with receptors on the host cell surface.

The list of specific receptors is provided in Table 1.

Table 1. List of Specific Receptors in Retroviruses
Name of Virus Name of Receptor References
Ecotropic MLV CAT-1 (amino-acid transporter) [1,10]
HIV CD4 (T-cell surface marker) [2]
HTLV GLUT-1 (glucose transporter) [3]
Amphotropic MLV PIT-2 (phosphate transporter) [4,9]
Gibbon Ape Leukemia Virus (GaLV) PIT-1 (phosphate transporter) [5]

Fusion

After binding to the host cell, the retrovirus must enter the host cell's cytoplasm to initiate infection. This is achieved through the fusion of the viral envelope with the host cell membrane. Fusion allows the viral core containing the viral RNA and associated enzymes to enter the host cell.

Reverse Transcription

Once inside the host cell, the retroviral RNA genome is reverse transcribed into double-stranded DNA by the viral enzyme reverse transcriptase. This process involves the synthesis of a complementary DNA (cDNA) strand from the viral RNA template, followed by the synthesis of a second DNA strand to form a double stranded DNA molecule. Reverse transcription takes place within the cytoplasm of the host cell.

Integration

The newly synthesized viral DNA is transported into the nucleus of the host cell, where it integrates into the host cell's chromosomal DNA. This integration is mediated by the viral enzyme integrase, which cleaves the host cell DNA and inserts the viral DNA into the host genome. Once integrated, the viral DNA is referred to as a provirus.

Transcription

Once integrated into the host genome, the proviral DNA can be transcribed by the host cell's RNA polymerase machinery. This results in the synthesis of viral messenger RNA (mRNA) transcripts, which can then be translated into viral proteins.

Translation

The viral mRNA transcripts produced by the host cell are translated by the host cell's ribosomes into viral proteins. These viral proteins include structural proteins (such as capsid proteins) and enzymes required for viral replication.

Assembly

The newly synthesized viral proteins and viral RNA molecules are assembled into new virus particles, or virions, within the cytoplasm of the host cell. The structural proteins encapsulate the viral RNA to form the viral core, while other viral proteins contribute to the formation of the viral envelope.

Budding

Once assembled, the new virus particles bud from the host cell membrane, acquiring a lipid envelope derived from the host cell membrane embedded with viral glycoproteins. This budding process allows the newly formed virus particles to acquire their final structure and become infectious.

Release

The mature virus particles are released from the host cell, either by budding off from the cell surface or through cell lysis, where the host cell is destroyed, releasing the viral particles into the extracellular environment. These released virus particles can then infect new host cells, continuing the cycle of infection.

Conclusion

This complete cycle allows retroviruses to efficiently infect host cells, replicate their genetic material, and produce new virus particles, facilitating the spread of infection within a host organism and between individuals.

References

1. Kim JW, Closs EI, Albritton LM, Cunningham JM. Transport of cationic amino acids by the mouse ecotropic retrovirus receptor. Nature. 1991;352:725–728.

2. Maddon PJ, Dalgleish AG, McDougal JS, et al. The T4 gene encodes the AIDS virus receptor. Cell. 1986;47:333–348.

3. Manel N, Kim FJ, Kinet S, et al. The ubiquitous glucose transporter GLUT-1 is a receptor for HTLV. Cell. 2003;115:449–459.

4. Miller DG, Miller AD. A family of retroviruses that utilize related phosphate transporters for cell entry. J Virol. 1994;68:8270–8276.

5. O'Hara B, Johann SV, Klinger HP, et al. Characterization of a human gene conferring sensitivity to infection by gibbon ape leukemia virus. Cell Growth Differ. 1990;1:119–127.

6. Origin of viruses. Nature.

7. Team, B. (2020). Retrovirus Life Cycle. BioRender.

8. Van Zeijl M, Johann SV, Closs E, et al. A human amphotropic retrovirus receptor is a member of the gibbon ape leukemia virus receptor family. Proc Natl Acad Sci U S A. 1994;91:1168–1172.

22 March 2025

Techniques for Microbial Taxonomy and Phylogeny

Techniques for Microbial Taxonomy and Phylogeny

Techniques for Determining Microbial Taxonomy and Phylogeny

Technique Description Applications
Morphological Analysis Involves studying the physical characteristics of microorganisms, such as shape, size, color, and arrangement. Preliminary classification based on basic visible traits (e.g., cocci, bacilli, spirilla).
Gram Staining A differential staining method that classifies bacteria into Gram-positive (purple) or Gram-negative (pink). Initial identification and classification based on cell wall composition.
Biochemical Tests Tests that identify microbial enzymes, fermentation patterns, and metabolic products. Differentiation of bacteria based on metabolic activities (e.g., lactose fermentation, catalase test).
Fatty Acid Profiling Analysis of the fatty acid composition of the bacterial cell membrane. Chemotaxonomic classification, especially useful for identifying species in environmental samples.
Protein Profiling (e.g., MALDI-TOF) Mass spectrometry-based method that identifies microorganisms by analyzing their protein patterns. Fast identification of bacterial species, particularly in clinical microbiology.
DNA-DNA Hybridization (DDH) Measures the genetic similarity between two DNA samples by hybridizing them and assessing the degree of pairing. Determining relatedness between bacterial species or strains; used to confirm species designation.
16S rRNA Gene Sequencing Sequencing of the 16S ribosomal RNA gene to identify and classify bacteria based on evolutionary relationships. Highly accurate identification of prokaryotes; a cornerstone in bacterial phylogeny and taxonomy.
Whole Genome Sequencing (WGS) Sequencing the entire genome of a microorganism to obtain comprehensive genetic data. Provides in-depth phylogenetic and taxonomic resolution; helps define novel species.
Multilocus Sequence Typing (MLST) Sequencing several "housekeeping" genes to create a sequence type for comparison between strains. Useful for in-depth strain comparison and epidemiological tracking.
Polymerase Chain Reaction (PCR) Amplifies specific regions of microbial DNA to identify species or strains. Used for species identification, detection of specific genes (e.g., virulence, resistance genes).
Restriction Fragment Length Polymorphism (RFLP) DNA fragments are generated by digesting DNA with restriction enzymes, and the fragment patterns are analyzed. Helps identify genetic diversity within microbial populations; used for species or strain differentiation.
Phylogenetic Tree Construction Based on sequence data (e.g., 16S rRNA or whole genome) to create a tree showing evolutionary relationships. Used for understanding the evolutionary history and relationships of microbial species.
DNA Microarray A tool that detects the expression of thousands of genes simultaneously by hybridizing DNA or RNA samples. For functional analysis, identification of specific microbial strains, and analysis of gene presence.
Fluorescent in situ Hybridization (FISH) Uses fluorescent probes that bind to specific nucleic acid sequences to identify microorganisms directly in samples. Identification and quantification of specific microorganisms in complex environmental or clinical samples.
Comparative Genomics Involves comparing the entire genome of different strains to study genetic similarities and differences. Used to examine evolutionary relationships, functional genomics, and strain-level diversity.

04 March 2025

Overview of Immune System

Overview of Immune System

Overview of Immune System

1. Introduction to Immune System

The immune system is a complex network of cells, tissues, and organs that work together to protect the body from harmful pathogens such as bacteria, viruses, fungi, and parasites. In addition to defending against infections, the immune system also plays a critical role in eliminating damaged or abnormal cells, such as cancerous cells. The immune system has two main types of defenses: innate immunity and adaptive immunity, each with its own specialized functions and characteristics.

Figure 1. Innate Immunity Versus Adaptive Immunity (Source: Biorender.com)

Innate Immunity: The body's first line of defense, offering immediate but nonspecific protection against pathogens.

Adaptive Immunity: A more specific and adaptable defense mechanism that is activated upon exposure to pathogens and improves with subsequent exposures.

Figure 2. Stages of Adaptive Immune Response (Source: Biorender.com)

© 2025 Overview of Immune System- MBLOGSTU

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