Lesson 7: Protozoan and Virus
1.Video Lesson
2.Objective
At the end of this lesson you will be able to:-
- Define protozoan and viruses
- Categories protozoan and viruses
- Describe the common characteristic of protozoan and viruses
- Explain about classification of viruses
- Explain the reproduction of protozoan and viruses
- List common disease of protozoan and viruses
Brainstorming questions
- How do protozoan and viruses influence ecosystem dynamics and biodiversity, and what roles do they play in nutrient cycling?
- In what ways can fungi and viruses be harnessed for biotechnological advancements, such as in medicine, agriculture, or environmental remediation?
- How do protozoan and viruses adapt to changing environments or host defences, and what implications does this have for their evolution and our understanding of disease emergence?
key words
- Protozoa are chemoorganotrophic protists traditionally studied in the field of protozoology. They are unicellular microorganisms that lack a cell wall and can be either free-living or parasitic.
- Free-Living or Parasitic: Can live independently or as parasites.
- Aerobic: Require oxygen for survival.
- Locomotion: Movement via pseudopodia, flagella, cilia, or direct cell movements.
- Nutrition: Can be autotrophic, heterotrophic, or saprozoic.
- Habitat: Live in aquatic or terrestrial environments; can be free-living or symbiotic.
- Reproduction: Both asexual (fission, budding, cysts) and sexual (conjugation, syngamy)
- Asexual Reproduction: Includes fission (cell divides into two), budding (uneven division), and multiple fission (nucleus divides multiple times before cell division).
- Sexual Reproduction: Includes conjugation (exchange of micronuclei) and syngamy (fusion of gametes).
- Malaria: Caused by Plasmodium species.
- African Trypanosomiasis: Caused by Trypanosoma brucei.
- Amoebiasis: Caused by Entamoeba histolytica.
- Giardiasis: Caused by Giardia lamblia.
- Chagas Disease: Caused by Trypanosoma cruzi.
- Leishmaniosis: Caused by Leishmania species.
- Toxoplasmosis: Caused by Toxoplasma gondii.
- Cryptosporidiosis: Caused by Cryptosporidium species.
- Intracellular Parasites: Require a host cell for replication.
- Protein Coat (Capsid): Surrounds the nucleic acid core.
- Lack Cellular Organization: No cell wall, membrane, or organelles.
- Nucleic Acid: Genome consists of either DNA or RNA.
- Specific Attachment: High specificity for host cells.
- Capsid: Protein shell protecting the nucleic acid.
- Envelope: Some viruses have an outer lipoprotein layer derived from the host cell membrane.
- Capsomeres: Identical subunits that make up the capsid.
- Nucleocapsid: Combined core and capsid structure
Protozoa
The term protozoa [Greek protos, first, and zoon, animal] have traditionally referred to chemoorganotrophic protists, and protozoology generally refers to the study of protozoa.
Characteristics of protozoa
• Unicellular microorganisms that lacks cell wall.
• They may be free living or parasitic.
They are may be free living or parasitic.
• Aerobic.
• They have true nucleus.
• They are eukaryotic cells.
• Mostly microscopic, although some are
large enough to be seen with the unaided eye (Figure 10).
• Locomotion by pseudopodia, flagella, cilia, and direct cell movements.
• Nutrition of all types: autotrophic (manufacturing own nutrients by photosynthesis),heterotrophic (depending on other plants or animals for food), saprozoic (using nutrients dissolved in the surrounding medium)
• Aquatic or terrestrial habitat; free-living or symbiotic mode of life
• Reproduction asexually by fission, budding, and cysts and sexually by conjugation or by syngamy (union of male and female gametes to form a zygote).
Reproduction in protozoa
Protozoan reproduces in both sexual and asexual methods
Asexual reproduction in protozoa
Most reproduce asexually with one of three ways that represent in figure 11. These are:-
- Fission: Fission
- Budding
- Multiple fission (schizogony)
• ell.
Fission:-
Occurs when a cell divides evenly to form two new cells (Figure 2.20).
• Budding:-
Occurs when a cell divides unevenly.
• Multiple fission(schizogony): –
The nucleus of the cell divides into multiple times before the rest of the cell divides. Then each nuclei separates into a daughter c
Sexual reproduction in protozoa
Sexual reproduction also occurs during the life cycle of most protozoa is called conjugation. A distinctive feature of ciliates is the presence of two types of nuclei: tiny micronuclei and large macronuclei. A cell has one or more nuclei of each type. Genetic variation results from conjugation (Figure 12), a sexual process in which two individuals exchange haploid micronuclei but do not reproduce. Ciliates generally reproduce asexually by binary fission, during which the existing macronucleus disintegrates and a new one is formed from the cell’s micronuclei. Each macronucleus typically contains multiple copies of the ciliate’s genome. Genes in the macronucleus control the everyday functions of the cell, such as feeding, waste removal, and maintaining water balance.
Nutrition in Protozoan’s
Protists receive nutrients by breaking down organic matter (heterotrophic) and can grow in both aerobic and anaerobic environments & live in the intestine of animals. Protists obtain food in one three ways: –
- Absorption
- Ingestion
- Engulf
• Absorption: – nutrient is absorbed across the protist’s plasma membrane.
• Ingestion: – Cilia outside the protist create a wave-like motion to move food into a mouth like opening in the protist called a cytosome. E.g. paramecmm. • Engulf: – food surrounded within their cytoplasmb using Pseudopods then engulf the food. This process is called phagocytosis. E.g. Amoeba. Food is digested in the vacuole after the food enters the cell. Waste products are excreted using a process called exocytosis
Common disease caused by protozoa
There are few disease-causing protozoans. Protozoans are beneficial in the environment because they help improve the quality of water by eating bacteria and other particles. Some of the human diseases caused by protozoans include: –
- Malaria
- African trypanosomiasis
- Amoebiasis
- Giardiasis
- chagas disease
- Leishmaniosis
- Toxoplasmosis
- Cryptosporidiosis
viruses
Viruses are small, obligate, intracellular particles; that is, most can be seen only with the electron microscope
lack chemical machinery to generate energy and synthesis large molecule due to this obligatory intracellular to be replicate. All virus’s species are parasitic
Common characteristic of viruses
- have inner core of nucleic acid surrounded by protein coat known as an envelope.
- They cannot be grown on artificial cell free media but grow in animals, eggs or tissue culture).
- have not cellular organization. like as cell wall or cell membrane or cellular organelles including ribosomes.
- obligate intracellular parasite of,bacteria, protozoa, fungi, algae, plants, and animals
- They lack the enzymes necessary for protein and nucleic acid synthesis
- They are unaffected by antibacterial antibiotics.
- Viruses are inert (nucleoprotein) filterable agents
- border between living and non-living, because they are crystallizable and non-living outside the body of host.
- Ultramicroscopic size, ranging from 20 nm up to 450 nm (diameter)
- Basic structure consists of protein shell (capsid) surrounding nucleic acid core.
- Nucleic acid of the viral genome is either DNA or RNA but not both.
- Nucleic acid can be double-stranded DNA, single-stranded DNA, single stranded RNA,
- Have high specificity for attachment to host cell.
- Multiply by taking control of host cell’s genetic material and regulating the synthesis and assembly of new viruses
- centra core is nucleic acid called genom& surrounded by protein coat called capsid. The envelope in some vires made up of glycoprotein and phospholipids outside capsid
Basic structural components of a virus
- Core-the genomic material, either DNA or RNA.
- Envelope- a few viruses, such as the HIV and influenza viruses, have lipoprotein layer around the capsid that derived from membrane of the host cell.
- Capsomeres- capsids are often built up of identical repeating subunits called capsomeres.
- Nucleocapsid-the combined formed by the core and capsid of protein structure
- Some virus contains enzymes which play central role during infection process.
E.g. Some bacteriophage contains an enzyme lysozyme, which makes small hole in
bacterial cell that allows viral nucleic acid to get in.
- Some virus contains their own nucleic acid polymerase which transcribe the viral genome into mRNA during replication process. E.g., Retrovirus are RNA virus that replicates inside host cell as DNA intermediate. These viruses posses RNA dependent DNA polymerase called reverse transcriptase.
Viral symmetry
Based on morphological structures, there are three types of viruses. These are:-
- Helical symmetry
- Complex symmetry
- polyhedral symmetry
Helical symmetry
There are several viruses found with a helical morphology. These viruses consist of identical protein subunits or protomers which assembled in a helical structure around the genome. Generally rigid nucleocapsid. Moreover, some helical structure provides flexibility to the filaments. The most common example is tobacco mosaic virus and Sendai virus is also reported to have a helical structure.
Polyhedral (Icosahedral) Symmetry
These structure refers to a type of polyhedron with 20 equilateral triangular faces and 12 vertices. The rigid structure provides protection to the genome. The common examples are papovavirus, picomavirus, adenovirus, toga virus, etc.
Complex Symmetry
These groups of viruses do not come under the above-motioned groups. These viruses consist of complex structural components which made it different from the other two groups A common example pox virus.
The difference between DNA & RNA Viruses
- RNA viruses have RNA genetic material & DNA virus have DNA genetic material.
- RNA viruses are single-stranded and DNA virus have double stranded .
- RNA virus higher mutation rate than the DNA.
- DNA viruses replicate in the nucleus while RNA viruses takes place in the cytoplasm.
Viruses infect all cellular life forms: eukaryotes and prokaryotes (bacteria and archaea). The viruses that infect prokaryotes are often referred to as bacteriophages, or phages for short.
HIV (human immunodeficiency virus) is a virus that attacks the body’s immune system. If HIV is not treated, it can lead to AIDS (acquired immunodeficiency syndrome). Leaming the basics about HIV can keep you healthy and prevent HIV transmission.
Classification of Viruses
The primary criteria for delineating the main viral taxa are:-
A. the type and character viral genome i.e DNA viruse and RNA virus.
B. the strategy of viral replication
C. the types of organisms that infect.
Viral replication
Virus invades a living host cell, hijacks the metabolism of the cell to produce copies of itself, and often destroys the host cell when new virions are released.
Replication has been studied in a wide range of viruses and their host cells. We examine the bacteriophages first and then discuss the animal viruses One of the best studied,processes of replication is that carried out by bacteriophages of T-even group (T for “type”).
Viruses have five replication steps. These are:-
- Adsorption:- the attachment of viruses to host cells.
- Penetration:- the entry of virions into host cells.
- Synthesis:- the synthesis of new nucleic acid molecules, capsid proteins, and other viral components within host cells while using the metabolic machinery of those cells.
- Maturation:- Assembly of newly synthesized viral components into complete virons.
- Release:- Departure of new virions from host cells. Release generally, but not always, kills (lyses) host cells.
Bacteriophage (phages).
- are bacterial vm1ses.
- They are the viruses that infect bacteria.
They are obligate intracellular parasites that multiply inside bacteria by making use of some or all of the host biosynthesis machinery
Phages exhibit two different types of life cycle. These are:-
- Lytic cycle
- lysogenic cycle
Lytic cycle
- Also known as virulent cycle. In this cycle,
- Intracellular multiplication of the phage results in the lysis of host bacteria then release virions (Figure 11).
- The enzyme lysozyme, breaks down the cell wall, allowing viruses to escape.
- In the process the bacterial host cell is lysed. Thus, phages such as T4 are called virulent (lytic) phages because they lyse and destroy the bacteria they infect.
- The released phages can now infect more susceptible bacteria, starting the infection process all over again.
- Lytic cycle of bacteriophage (Replication of a virulent bacteriophage).
- A virulent phage undergoes a lytic cycle to produce new phage particles within a bacterial cell.
- Cell lysis releases new phage particles that can infect more bacteria).
Lysogenic cycle
- Infection with every phage does not result in lysis of the host cells .
- Unlike virulent phages, which cause lysis of the host cell, some phages (such as temperate phages) integrate into the genome of the bacterial chromosome without causing any lysis of the bacteria.
- The integrated phage nucleic acid is known as the prophage.
- The prophage behaves like a segment of the host chromosome and multiplies synchronously with it. This phenomenon is known as lysogeny.
The bacterium that carries a prophage within its genome is called lysogenic bacterium and such phages are called lysogenic or temperate phages
The difference between Lytic & Lysogenic Cycle
Common viral disease in Ethiopia
A viral disease is any condition that’s caused by a virus. There are several types of viral disease, depending on the underlying virus. the common viral diseases listed the below table
