viruses; section 18-1
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By, Mackenzie Pabst. Viruses; Section 18-1. What is a Virus?. disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsid A virus replicates inside living cells called host cells. Why are Viruses Non-Living?. Viruses are nonliving because: - PowerPoint PPT PresentationTRANSCRIPT
VIRUSES;SECTION 18-1
By, Mackenzie Pabst
What is a Virus?
disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsid
A virus replicates inside living cells called host cells
Why are Viruses Non-Living? Viruses are nonliving because:
They don't exhibit all the criteria for lifeCriteria for life includes:
Respiration, growth and development All viruses can do is replicate
Replication is making exact copies of themselves with the help of living cells
How are Viruses Named? Some Viruses are
named after the disease they cause Example: Rabies
Virus Other viruses were
named for the organ or tissue they infect. Example: The
Adenovirus effects the adenoid tissue
Rabies Virus
How does a Virus attach to a Host Cell?
For a virus to replicate, it must enter a host cell
When a virus’ proteins interlock with the receptor site, the virus is attached to its host cell
The attachment process is like two pieces of a jigsaw puzzle fitting together
Virus Attachment
Each virus has a specifically shaped attachment protein
Viruses are species specific Some Viruses are cell-type specific
Example: polio viruses normally infect only intestinal and nerve cells.
Lytic Cycle:A. Attachment:
The Virus attaches to the Host Cell
B. Entry:The Bacteriophage injects its nucleic acid into the bacterial cell
C. Replication :The host’s metabolic machinery makes the virus’ nucleic acid and proteins
A Viral Replication Process
Lytic Cycle:
D. Assembly:New Virus Parts are made
E. Lysis and Release:The host cell breaks open and releases new viruses• This results in the
killing of the host cell
A Viral Replication Process
Another Viral Replication Process…
Of an Enveloped Virus: After attachment, the
membrane of the host cell surrounds the virus
This produces a virus-filled vacuole inside the host cell's cytoplasm.
The virus bursts out of the vacuole and releases its nucleic acid into the cell.
The Lysogenic Cycle
The Lysogenic Cycle:
Begins the same way as the Lytic Cycle
The virus attaches to the host cell and its nucleic acid is injected into the cell.
Then the viral DNA is integrated into the host cell's chromosomes This is done instead of immediately
taking over the host's genetic material (As in the Lytic Cycle)
This Cycle does not kill its host cell
RNA Viruses:
Many Viruses, including HIV, are RNA viruses This means their only nucleic acid is RNA
The RNA virus with the most complex replication cycle is the Retrovirus
The Retrovirus - uses reverse transcriptase to make DNA from viral RNA the retroviral DNA is then integrated into
the host cell's chromosome
Retrovirus Cycle:
Retrovirus Cycle:
Once inside a host cell, the retrovirus makes DNA from its RNA with reverse transcriptase
Reverse transriptase produces double-stranded DNA from the viral RNA. The double-stranded viral DNA
becomes part of the host cell’s chromosome and it becomes a provirus
Human Immunodeficiency Virus(HIV) HIV infects white blood cells in
humans The infected cells still function
normally Because the viral genetic material is a
provirus that only produces a small number of new viruses at a time
An infected person will not appear sick Can infect others with the virus through body
fluids
Human Immunodeficiency Virus(HIV) Most people with HIV
will get AIDS Over time, more white
blood cells are infected and killed
White Blood cells are essential to our immune system Their destruction
reduces the body’s ability to protect itself from other viruses
Virus’ link to Cancer:
Some viruses have been linked to certain cancers in humans and animals
Viruses can disrupt the normal growth and division of cells in a host This causes abnormal
growth and creates tumors
Prions: Are composed of
proteins but have no nucleic acid to carry genetic information
Are thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioning
Responsible for many animal diseases Example: Mad Cow
Disease
Viroids:
Composed of a single circular strand of RNA with no protein coat
Shown to cause infectious diseases in several plants.
Have less RNA than most viruses
Plant Viruses: There are more than
400 plant viruses Plant Viruses can
cause stunted growth and yield losses in their host plants.
The first virus to be identified as a plant virus was the tobacco mosaic virus
Plant Viruses:
Do not undergo lytic or lysogenic phases
Plant Viruses are named according to their host plant.
Not all viral plant diseases are fatal or even harmful.
The Mosaic virus, as seen in the following picture, cause patterns of color in the flowers of plants.