Obtaining energy from sunlight to synthesize organic compounds for nutrition
Heterotrophic
An organism that eats other plants or animals for energy and nutrients
Prokaryotic cells
Lack a nucleus and membrane-bound organelles
Bacteria and related microorganisms
Eukaryotic cells
Contain a nucleus and membrane-bound organelles
Animals, plants, fungi, and protists
Viruses
Microscopic particles that infect cells of other organisms
Carry conventional genetic material in the form of DNA or RNA but they cannot reproduce on their own
Virus Classification Hierarchy
Realm
Kingdom
Phylum
Class
Order
Family
Genus
Species
Morphological Types of Viruses
Helical Viruses
Icosahedral Viruses
Enveloped Viruses
Complex Viruses
Helical Viruses
The viral nucleic acid coils into a helical shape and the capsid proteins wind around the inside or outside of the nucleic acid, forming a long tube or rod-like structure
Icosahedral Viruses
The icosahedron is made up of equilateral triangles fused together in a spherical shape
The genetic material is fully enclosed inside of the capsid
Viruses with icosahedral structures are released into the environment when the cell dies, breaks down and lyses, thus releasing the virions
Enveloped Viruses
Has an outer wrapping or envelope
The envelope comes from the infected cell or host in a process called "budding off"
Complex Viruses
Structurally complex viruses incorporate a larger variety of components into their capsids than simple viruses
They may contain accessory proteins with specific architectural or functional roles or incorporate non-proteic elements such as lipids
Genome Types
DNA Viruses
RNA Viruses
Reverse-Transcribing Viruses
DNA Viruses
Made of deoxyribonucleic acid
Present everywhere, especially in the marine ecosystem
Divided into three major categories: double-stranded (ds) DNA viruses, single-stranded (ss) DNA viruses, and pararetroviruses
RNA Viruses
Made of ribonucleic acid
dsRNA has many hosts, such as bacteria, animals, fungi and humans
Have a higher mutation rate when compared to DNA viruses
Their genetic diversity makes it difficult to produce effective vaccines against them
Reverse-Transcribing Viruses
A process by which viruses generate complementary DNA (cDNA) from an RNA template, using enzymes called reverse transcriptases
Baltimore Classification Groups
Group I - dsDNA viruses
Group II - ssDNA viruses
Group III - dsRNA viruses
Group IV - positive-sense ssRNA viruses
Group V - negative-sense ssRNA viruses
Group VI - ssRNA viruses with a life cycle intermediated with DNA
Group VII - dsDNA viruses with a life cycle intermediated with an RNA
Bacteriophages
Viruses that infect bacteria
Viral Multiplication in Bacteriophages
1. Adsorption
2. Penetration
3. Assembly
Uses of Bacteriophages
Destroy bacterial pathogens
Treat bacterial infection
Prevent food contamination
Steps in Animal Virus Multiplication
1. Adsorption
2. Penetration
3. Uncoating
4. Replication
5. Assembly
6. Release
Viral Infections
Abortive Infections
Cytocidal Infection
Persistent Infection
Abortive Infections
Infections of nonpermissive cells where no viral production occurs
Cytocidal Infection
An infection that results in cell death either from cell lysis, apoptosis, or the accumulation of cytopathic effects
Persistent Infection
Characterized as those in which the virus is notcleared but remains in specific cells of infected individuals
Do not cause cell death
Types of Persistent Infections
Chronic infections that are not lytic but productive
Latent infections with limited macromolecular synthesis but no virus synthesis
Slow infections, characterized by a prolonged incubation period without prominent morphological and physiological changes to the host cell
Transforming infections, in which the viral nucleic acid may remain in specific eukaryotic host cells indefinitely, and a virus may or may not be produced
Viroids
Short, naked fragments of single-stranded RNA, which can interfere with the metabolism of plant cells
Transmitted between plants in the same manner as viruses
Examples of plant diseases caused by viroids are potato spindle tuber and citrus exocortis
Do not cause animal disease
Virusoids
Essentially viroids that have been encapsulated by a helper virus coat protein
RNAs, have genomes from 220 to 338 nucleotides long, their genomes are circular and single-stranded, and they have ribosome activity
Replicate in the cytoplasm of their host, using an RNA-dependent RNA polymerase
Require that the host cell be infected with a specific helper virus
Associated with plant infections
Prions
Infectious agents that do not have a nucleic acid genome
A normal protein in animal tissue, but when these particles become abnormally folded and shaped they become proteinaceous infectious particles that are not cellular organisms or viral particles
Prion diseases are transmissible from host to host of a single species
Size of viruses varies from very small, from 20nm to 450nm.