Virus Lysogenic Cycle

[mai Algamdi]

Viral Genetics

Phage T4 - invades e.coli
Viruses are rather simple. They usually consist of DNA or RNA packed into a protein head. They are incapable of many metabolic tasks by themselves and hence must invade a host cell in order to reproduce.

Virus Structure
I am sure all of you guys have seen those pictures of viruses which makes them look like martian spaceships, some of them indeed do look like that but their structure is vary varied.
They are rather small and range between 20 to 14000 nm in length

A virus structure can be split into two parts

1. Viral Nucleic Acid
2. The Protein Coat

Viral Nucleic Acid - It is very varied. It can be single-stranded, double-stranded, DNA or RNA. The genetic material can be found to be either linear or circular

Protein Coat - The main function of the protein coat or capsid is to protect the nucleic acid from the environment. The capsid is made up of repeating units called capsomeres which are proteins synthesized by the viral nucleic acid. Some viruses are proteceted by addition layers containing lipids and carbohydrates. The structure of the protein coat is coded in the viral DNA sequence and varies from virus to virus.

As we already said viruses can only reproduce within the host cell?
How do they recognize the host cell? The host cell has particular receptors which are recognized by the virus, which then allows it to enter the cell. The types of cell a virus can invade varies; some viruses can invade only one type of host cell while other types of viruses can invade a range of host cells.
A typical Viral Life cycle:

1. Recognize host cell

2. Enter host cell

3. Replicate using host cell machinery (nucleotides, ribosomes, tRNA, etc)

4. Self-assemble capside and pack genome into capsid head

5. Release itself from host cell (possibly killing the host cell)

Bacteriophages - are viruses that invade bacteria. Examples include T4 and lambda which

infect E.coli.

T4 - multiplies by the lytic cycle which kills the host

Lambda - multiplies by the lysogenic cycle. It stays put as a prophage until due to some trigger enters the lytic cycle.

Lytic Cycle - We briefly mentioned the lytic cyle in the last section when talking about

bacterial transduction. Now we are going to describe the steps in further detail. Nasty Stuff.

1. Complex fibers on the tail of T4 allows it to contact and bind the correct receptor on
2. the surface of e.coli virus. The virus is only weakly adhered to bacteria.

The T4 releases an enzyme called lyzoszyme which breaks the cell wall at the place of injection and allows the T4 virus to inject its DNA into the bacteria. The empty capsid remains outside

Host protein synthesis is stopped and T4 uses host nucleotids to replicate its DNA

It uses the host protein machinery to synthesize capsid proteins and other important proteins
A trigger is sent out that the T4 is matured, which causes the spontaneous self-assembly of the DNA as well as capsid and the tail fibers
T4 virus releases lysoszyme which breaks the cell wall and allows the virus to leave the cell, in effect killing the cell.
Lysogenic Cycle

The lambda virus can enter either the lytic or lysogenic cycle, these types of phages are referred to as 'temperate phages'

1. When lambda enters the lysogenic cycle, its DNA combines with the host DNA via recombination

2. This is called a propahge

3. Genes called repressor proteins are synthesized by the bacteria which prevents the
synthesis of most viral genes

4. A random event triggers the bacteria to enter the lytic cycle and break out of the cell. The

prophage can remain as one for many generations, and is passed on each time the bacterial chromosome is replicated.
HIV - HIV is a unique virus is that its genetic material is a single-stranded RNA. These types of viruses are called retroviruses.
Once the HIV virus enters the cell, it activates an enzyme called reverse transcriptase.

This enzyme uses the RNA of the virus to synthesize complimentary double stranded DNA. The process of reverse transcription is very error-prone, hence there is a large degree of mutation which is why finding a cure for AIDS is so difficult.

المصدر

http://images.google.com.sa/imgres?i...D1&safe=active

[mai Algamdi]

Link shows :

1 - lysogenic cycle

http://www.youtube.com/watch?v=_J9-xKitsd0

2 _ lytic cycle

http://www.youtube.com/watch?v=UsZ0m2Iamhk&feature=related

[mai Algamdi]

Golgi apparatus

or Golgi network, massive Golgi (Golgi Camillo Golgi also writes), is an organelle found in cells of organisms with complex cellular structure of genetic material are organized saluted in the form of a membrane around the nucleus of the cell. Named these organelles relative to the Italian Camillo Golgi, who discovered in animal cells of a cat and some birds in 1898. Is the primary function of the Golgi apparatus is the formation and the production of some molecules such as proteins and lipids. It is also a site on which the creation of Many break-ups, such as mucus. He described the installation Golgi network as an object highly flammable nitrate to precipitate the silver and Osmium tetroxide.

Configuration
Golgi complex objects consist of a membrane known Balsesterna bags, and is a narrow membrane bags arranged in parallel, and curved to give a form similar to the cup length of 0.5 to 2 microns are formed from the internal network Alheiolip buds, which constantly secretory vesicles to form shallow, and surrounded by Several surmounted by vesicles, and there are usually 5 8 of the grafted membranes Bahoislat, there are sources indicate that the number may reach the range of 60 [1]. There are about the composition above a number of spherical vesicles that bud from the membrane Asturna. Astiria membrane consists of five areas of importance Olaohy: Network Cisse (CIS), the Cess and corresponding to the cell nucleus, the central region, the Trans (TRANS) and corresponding to the cell membrane, and network Trans. Exists between the nucleus and the Golgi apparatus is called the network install the latest Albulasmip the Interior, which also contain vesicles and integrate this network with the Golgi apparatus, and specifically with the network of pipes through Cisse minutes until it reaches the network within the Trans-Golgi where the delivery of materials between the internal network Albulasmip [2] the Golgi apparatus. And summed up the post of membrane Asturna modify the installation of some materials produced by the cell and the classification and stored until used by the cell later or secreted to the outside. So frequent Golgi bodies in cells with endocrine activity.

In terms of chemical structure with the Golgi apparatus of fatty substances and protein united with each other and no fatty part of the device is not convincing in the case of the phenomenon is surrounded by a thin layer of protein, but it can expose the fat and show it by treating the cells, especially enzymes digest proteins of Foreign Affairs and dissolved and This occurs naturally in some cells usually older animals, and in some cases of disease

No device Kolchi in different types of cells of vertebrates, with the exception of germ cells in the form of a network installation The germ cells and all the cells of invertebrates, as well as plant cells, the Golgi apparatus where there is in the form of curved objects called Acanutyoussomat.

Differs from the exact location of the Golgi network is slightly different depending on the cell For example, there is a Kolchi in endocrine pole of the cell, ie between the nucleus and the free edge of the cell in the parts of the pancreas Alguenoip while taking a Kolchi in the nucleus of nerve cells. In addition to the difference in the site Kolchi also differs in appearance depending on the physiological status of the animal appears for example in the epithelial cells of the gut in the form of a hungry animal body of a small heavy occupies a small area of cytoplasm (the cytoplasm), but after feeding, gradually increasing in size to occupy more space of the cytoplasm . Kolchi also shows the changes in shape during the formation and growth of animal cells in small animals is the Golgi apparatus in the form of a small network installation is located at the central pole of the cell, and increase the size of this structure gradually with the growth of the animal, even surrounded the nucleus fully informed, and as animal age, crumble the network and divided into small granules appear scattered throughout the cell

The exact structure

Golgi apparatus and appears under the microscope in the form of the dark color in the cytoplasm, but under the electron microscope appears in the form of groups of flat gaps that relate to the internal soft retina by a number of vesicles containing secretory granules, and differs in appearance from one cell to another, and usually takes a Golgi a party to the kernel, Vjuath surface (upper) swollen and circular (surface Cisse), while the lower Vmenbstp, soft and dual-membrane wall (surface Trans).

Function

It appears that the primary function of this device is the secretion and production of materials inside the cell, due to the presence of granular glands attached to the seafloor, may have a secretory function as high as in the Goblet cell in the intestine and blueberry Acinar cell in the pancreas.

Has been confirmed by imaging of this post articles, Color Vifraz a whole cell protein Jellicoe Glyco - Protein no protein united with sugar and then leave the cell. Thus, the Golgi apparatus is a compulsory passage for all materials produced by the cell. This is done by unloading vesicles hyphen between the device and the cell surface. Thus, we can sum up the post of the Golgi apparatus as an addition of proteins and sugars composition of the final composite, and then put this compound outside the cell
across the surface of the vesicles with the hyphen.

http://ar.wikipedia.org/wiki/%D8%AC%...84%D8%AC%D9%8A

[Prof. Nagwa Aref]

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