Lytic and Lysogenic cycle of viral reproduction

Viral reproduction process:

Viruses can reproduce within the host cell in two processes of a cycle. The multiplication of virulent phages is called lytic cycle and the multiplication of template phages is called lysogenic cycle.

Lytic cycle:

It is considered the main cycle of viral reproduction as most of the viruses replicate in this process. At this cycle, viruses are entered their genetic material within the host cell. Then it transcribes itself into the host cell's messenger RNAs and uses them to direct the ribosome. The host cell's DNA is destroyed and the virus takes over the cell's metabolic activities. The virus starts using the cell energy because of its own propagation. The virus produces progeny phages. These replicate fast, and soon the cell is filled with approximately 100-200 new viruses. As the cell starts getting overcrowded, the initial virus releases enzymes to destroy the cell wall. The cell wall bursts - this method is called lysing - and the new viruses are released.

Lysogenic cycle:

 In this cycle, the viral genetic material enters the host cell and integrates into the host DNA as a new set of genes called prophage. So, the viral DNA becomes part of the cell's genetic material. No progeny particles, like in the lytic phase, are produced. Each and every time the host cell DNA chromosome replicates during cell division, the passive and non-virulent prophage replicates too. This can modify the cell's characteristics, but it does not destroy it.

Read More

What is gram-negative bacteria?

Gram-negative bacteria

The gram staining characteristics of bacteria are denoted as negative or positive, dependent on if the bacteria take up and retain the crystal violet stain or not. Gram-negative bacteria lose the crystal violet stain in Gram's technique of staining. This is characteristic of bacteria that have a cell wall made up of a thin layer of a particular substance (called peptidoglycan).  The thin peptidoglycan layer in their cell wall is sandwiched between an inner cytoplasmic cell membrane and also a bacterial outer membrane. Just after staining with crystal violet, an alcohol wash is utilized which decolorizes the bacteria showing that their peptidoglycan layer is too thin to retain the stain and enabling identification.

 Cell envelope:

The Gram-negative cell envelope contains a different outer membrane composed by phospholipids and lipopolysaccharides which face the external environment. The highly charged nature of lipopolysaccharides confers a total negative charge towards Gram-negative cell wall. The chemical structure of the outer membrane lipopolysaccharides is normally unique to specific bacterial strains and is responsible for most of the antigenic properties of these strains. Many species of Gram-negative bacteria are pathogenic. This pathogenicity is usually associated with the lipopolysaccharide (LPS) layer of the Gram-negative cell envelope.

Gram-negative bacteria include:

• Actinobacillus
• Brucella
• Campylobacter
• Cyanobacteria
• Enterobacter
• Erwinia
• Escherichia coli
• Franciscella
• Helicobacter
• Hemophilus
• Klebsiella
• Legionella
• Moraxella
• Neisseria
• Pasteurella
• Proteus
• Pseudomonas
• Salmonella
• Serratia
• Shigella
• Treponema
• Vibrio

Read More

Gram-positive bacteria....

Bacteria are mainly divided into two main groups, gram-positive and gram-negative, depending on their Gram stain retention property.The phrase ‘gram-positive’ is usually a term used by microbiologist to classify bacteria into two groups (gram-positive or gram-negative). This positive/negative reference is dependent on the bacterium’s chemical and physical properties of the cell wall.

To determine whether a bacteria is gram-positive or gram-negative a microbiologist will perform a special type of staining technique, called a Gram Stain. The name comes from its inventor, Han Christian Gram (1884). This stain will either stain the cells in purple (for positive) or pink (for negative) color.

Gram-positive bacteria retain the color of the crystal violet stain while in the Gram stain. This is certainly characteristic of bacteria which have a cell wall made up of a thick layer of the particular substance called peptidoglycan.

Usually, gram-positive bacteria are the helpful, probiotic bacteria. They are the satisfied ones that live in our gut and help us digests food.But Gram-positive bacteria will also be pathogenic. Clostridium botulinum, the bacterium responsible for producing neurotoxins which could kill in hours is a gram-positive bacterium. The Gram-positive bacteria include staphylococci ("staph"), streptococci ("strep"), pneumococci, and the bacterium responsible for diphtheria(Cornynebacterium diphtheriae) and anthrax (Bacillus anthracis). The archetypal hospital "superbug", methicillin-resistant S. aureus (MRSA), regularly attracts mass-media interest.

In general, the characteristics are present in gram-positive bacteria are include:

·       Cytoplasmic membrane made up of lipid.

·       Thick peptidoglycan cell wall.

·       Teichoic acids and lipoids exist, forming lipoteichoic acids, which function as chelating agents, and also for several kinds of adherence.

·       Peptidoglycan chains are cross-linked to make rigid cell walls by the bacterial enzyme DD-transpeptidase.

·       A smaller volume of periplasm than that in gram-negative bacteria.

Read More

Definition of bacteria:

Definition of bacteria:

Bacteria are single-celled microscopic organisms discovered by Leeuwenhoek in 1676 through his microscope. He first called them animalcules. Bacteria are prokaryotic microbes and, therefore, have no nucleus or membrane bound organelles. They have simple cell structure and varied in shape.They are huge in number approximately 5×10³⁰ on earth.

Bacteria are sometimes maligned because of human and animal disease like Leptospira, that causes serious disease in livestock. However, several bacteria, the actinomycetes, produce antibiotics such as streptomycin and nocardicin; others live symbiotically in the guts of animals or elsewhere within their bodies, or on the roots of certain plants, converting nitrogen in a usable form. Bacteria help to break down dead organic matter, bacteria make up the base of the food web in numerous environments. Bacteria are of such immense importance for their extreme flexibility, ability to rapid growth and reproduction, and great age - the oldest fossils were known, nearly 3.5 billion years old, are fossils of bacteria-like microorganisms.

Read More

What is virus?

Virus is an ultramicroscopic infectious agent mainly composed of nucleic acid and wrapped by a  protein coat.They replicate and grow only within the living host cell mainly bacteria, plants and animals.The word virus comes from Latin means poison. Main modern meaning of virus is "any agent that cause infectious disease" first recorded in 1728. A virus invades living cells and uses their chemical machinery to help keep itself alive in order to replicate itself. Virus causes a number of diseases that may lead severe condition of animals or plants. "Common cold" is caused by a specific virus called  rhinoviruses, AIDS caused by HIV and many specific RNA and DNA virus caused specific diseases. Many viruses are species specific.

Read More