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جبار. بشرى دmedical biologyالمادة:

Definition of viruses

microscopic particles that can replicate only within a living cell, so widely considered not to be themselves truly 'living', and not possible to destroy directly without also destroying the host cells. For those that cause human diseases, antiviral drug treatment is limited (antibiotics have no effect) but vaccination can provide immunity and in the second half of the 20th century this eradicated smallpox worldwide and much reduced the incidence of poliomyelitis. Viral conditions include colds, influenza, chickenpox, measles, hepatitis and herpes of different types (e.g. cold sores, shingles). See also human

immunodeficiency virus (HIV) .

General Properties of Viruses

.Nucleic acid -contains 3-400 genes 1 -

Deoxyribonucleic Acid (DNA) -unique features

Single and/or double stranded-

Glycosylated and/or methylated-

Gaps present in double stranded molecule-

Circular or linear-

Bound protein molecules-

Unique purine and/or pyrimidine bases present-


Ribonucleotides present-

Ribonucleic Acid (RNA) - Unique features

Single or double stranded-

Segmented or unsegmented-

Bound protein molecules-

Unique purine and/or pyrimidine bases present-

Folding pattern -

2 -Capsid -The capsid accounts for most of the virion mass. It is the protein coat of the virus. It is a complex and highly

organized entity which gives form to the virus. Subunits called protomeres aggregate to form capsomeres which in turn aggregate to form the capsid.

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. 3 -Envelope -this is an amorphous structure composed of lipid, protein and carbohydrate which lies to the outside of the capsid It contains a mosaic of antigens from the host and the virus. A naked virus is one without an envelope.

4 -Spikes. These are glycoprotein projections which have enzymatic and/or adsorption and/or hemagglutinating activity. They arise from the envelope and are highly antigenic.


Morphology (Symmetry)

1 -Icosahedral -The protomeres aggregate in groups of five or six to form the capsomere. In electron micrographs capsomeres are recognized as regularly spaced rings with a central hole. The shape and dimensions of the icosahedron depends on characteristics of its protomeres . All icosahedral capsids have 12 corners each occupied by a penton. capsomere and 20 triangular faces, each containing the same number of hexon capsomeres. Icosahedral symmetry is identical to

cubic symmetry.

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2-Helical -The protomeres are not grouped in capsomeres, but are bound to each other so as to form a ribbon-like structure.

This structure folds into a helix because the protomeres are thicker at one end than at the other. The diameter of the helical capsid is

determined by characteristics of its protomeres .

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3-Complex -e.g., that exhibited by poxvirus and rhabdovirus..

Replication Cycle

1-Adsorption -Viruses can enter cells via phagocytosis, viropexis or adsorption. Adsorption is the most common process and


the most highly specific process. It requires the interaction of a unique protein on the surface of the virus with a

highly specific receptor site on the surface of the cell.

Penetration -This occurs by one or more processes. 2-

Enveloped viruses fuse their envelope with the membrane of the host cell. This involves local digestion of the viral and cellular membranes, fusion of the membranes and concomitant release of the nucleocapsid into the cytoplasm.

Naked viruses bind to receptor sites on the cellular membrane, digest the membrane and enter into the cytoplasm intact.

Both naked and enveloped viruses can be ingested by phagocytic cells. However, in this process they enter the cytoplasm enclosed in a cytoplasmic membrane derived from the phagocytic cell.

3 -Uncoating -During this stage cellular proteolytic enzymes digest the capsid away from the nucleic acid. This always occurs in

the cytoplasm of the host cell. The period of the replication cycle between the end of the uncoating stage and maturation of

new viral particles is termed the eclipse. Thus during the eclipse stage, no complete viral particles can be viewed within the cell


4-Replication of nucleic acid. Replication of viral nucleic acid is a complex and variable process. The specific process depends on the nucleic acid type.

Parasites

Medical parasitology : deals with the parasites which infect man, the diseases they produce, the response generated by him against them and various methods of diagnosis and prevention and included the study of three major groups of animals: parasitic protozoa, parasitic helminths (worms), and those arthropods that directly cause disease or act as vectors of various pathogens. A parasite is an organism which lives in/on the body of a host. A host is that which harbors the parasite. There is usually some association such as mutualism , commensalisms, or parasitism between the parasite and the host. This association may produce a variety of effects and the host usually tends to react to it.


Life cycle of the malaria parasite))

CLASSIFICATION OF MEDICAL PARASITOLOGY

Parasites of medical importance come under the kingdom called protista and animalia Protista includes the microscopic single-celled eukaroytes known as protozoa. In contrast, helminthes are macroscopic, multicellular worms possessing welldifferentiated.

Parasitology is generally classified into Medical

1 -Medical Protozoology - Deals with the study of medically important protozoa.

2 -Medical Helminthology - Deals with the study of helminthes (worms) that affect man.


3 -Medical Entomology - Deals with the study of arthropods which cause or transmit disease to man..

DIFFERENT KINDS OF PARASITES

Ectoparasite – a parasitic organism that lives on the outer surface of its host, e.g lice,ticks,mites etc ..

Endoparasites – parasites that live inside the body of their host, e.g. Entamoeba histolytica .

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Obligate Parasite - This parasite is completely dependent on the host during a segment or all of its life cycle, e.g. Plasmodium spp

Facultative parasite – an organism that exhibits both parasitic and non-parasitic

modes of living and hence does not absolutely depend on the parasitic way of

life, but is capable of adapting to it if placed on a host. E.g. Naegleria fowleri

Accidental parasite – when a parasite attacks an unnatural host and survives. E.g Hymenolepis diminuta (rat tapeworm).

Erratic parasite - is one that wanders in to an organ in which it is not usually found E.g. Entamoeba histolytica in the liver or lung of humans. .

EFFECT OF PARASITES ON THE HOST

The damage which pathogenic parasites produce in the tissues of the host may be described in the following two ways:


a) Direct effects of the parasite on the host

Mechanical injury - may be inflicted by a parasite by means of pressure as it grows larger, e.g. Hydatid cyst causes blockage of ducts such as blood vessels producing infraction.

b) Indirect effects of the parasite on the host:

Immunological reaction: Tissue damage may be caused by immunological response of the host, e.g. nephritic syndrome following Plasmodium infections.

FUNGIFungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds as well as the more familiar mushrooms. These organisms are classified as a kingdom

Fungi, which is separate from plants, animals, protists and bacteria.

The fungi are more evolutionarily advanced forms of microorganisms, as compared to the prokaryotes (prions, viruses, bacteria). They are classified as eukaryotes, i.e., they have a diploid number of chromosomes and a nuclear membrane and have sterols in their plasma membrane. Genetic complexity allows morphologic complexity and thus these organisms have complex structural features that are

used in speciation .

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General Properties of fungi


1 -Fungi are eukaryotic organisms .

They reproduce by means of spores 2-

3-Depending on the species and conditions both sexual and asexual spores may be produced .

Fungi exhibit the phenomenon of alteration of generation 4 -

5 -The vegetative body of the fungi may be unicellular or composed of microscopic threads called hyphae.

6 -The structure of cell wall is similar to plants but chemically the fungi cell wall are composed of chitin.

. Fungi are heterotrophic organisms 7-

8 -They fungi digest the food first and then ingest the food, to accomplish this the fungi produce exoenzymes

. Fungi store their food as starch 9-

. Biosynthesis of chitin occurs in fungi 9-

The nuclei of the fungi is very small 10-

. During mitosis the nuclear envelope is not dissolved 11-

Nutrition in fungi - they are saprophytes, or parasites or symbionts.

Reproduction in fungi is both by sexual and asexual means. Sexual state is referred to as teleomorph, asexual state is referred to as

anamorph .

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