very small non-living particle made up of nucleic acid and proteins can only reproduce by...
TRANSCRIPT
VIRUSES
WHAT IS A VIRUS? Very small
Non-living particle
Made up of nucleic acid and proteins
Can only reproduce by infecting living cells
Do not carry out respiration, grow or develop
STRUCTURE Viruses have an inner core which
contains either RNA or DNA
The core consists of the viruses genetic material.
Has outer coat called a capsid that is made up of proteins
STRUCTURE
Nucleic Acid: DNA or RNA
Capsid
Viruses have different shapes and sizes.
The arrangement of the proteins in the capsid of a virus determines the virus’s shape
HOST CELL The cell in which a virus replicates Before a virus can replicate it must
enter a host cell
Before it can enter a host cell it must first recognize and attach to a receptor site on the plasma membrane of the host cell.
VIRAL INFECTION Most viruses are highly specific to the
cells they infect. Ex: Plant viruses only infect plants
Bacteriophages are viruses that infect bacteria Ex: bacteriophage T4
Viruses have two ways of infecting the host cell: -Lytic Infection -Lysogenic Infection
BACTERIAPHAGE T4
LYTIC INFECTION Lytic Cycle
virus injects its nucleic acid into the host takes over the host cells metabolismcauses host cell to start replicating the
viruses proteins and nucleic acids virus secretes enzymes that “lyse” the host
cell’s cell wall and releases new virus particles
these particles can attack other host cells
Lytic Infection causes host cell to be “lysed” and destroyed.
LYSOGENIC INFECTION Lysogenic cycle
Lysogenic virus injects its nucleic acid into a host cell
Viral DNA is integrated into the host cell’s chromosome→ provirus
Every time host cell reproduces, the provirus is replicated along with it → every cell that originates from the infected host cell has a copy of the provirus
The lysogenic cycle can take place for many years
At any time the provirus can be activated and enter a lytic cycle
↓ host cell is killed
VIRUSES AND DISEASES Viruses cause human diseases such as
polio, measles , influenza, and AIDS.
Viruses attack and destroy certain cells in the body → causing symptoms of the disease
The best way to prevent against viral diseases is to prevent infection through vaccination.
WHAT IS A VACCINE? A preparation of a weakened or killed
virus or viral protein
When injected into the body, it stimulates the immune system in an effort to create permanent immunity to the disease
For vaccines to be most effective it must be used before an infection begins.
Vaccines are used for the prevention of viral infections
Vaccines are NOT used for bacterial infections
Disease Symptom Incubation
Measles Rash, fever 9-11 days
Shingles Pain, itching on skin
Years
Warts Bumpy areas on skin
Months
Coryza (cold) Sneezing, runny nose, fever
2-4 days
HIV Fatigue, weight loss
2-5 years
The symptoms and incubation time of a disease can indicate how the virus acts inside its host cell.
Which diseases may be caused by lytic viruses?Which diseases may be caused by lysogenic viruses?
RETROVIRUSES Viruses that contain RNA as their genetic
material
When retroviruses infect a cell they produce a DNA copy of their RNA.
Called retroviruses because their genetic information is copied backwards
From RNA to DNA instead of DNA to RNA
Retroviruses are responsible for some types of cancer and HIV
RETROVIRUSES AND CANCER Retroviruses can cause some cancers
Retroviruses that convert, or transform, normal cells → tumor viruses
These viruses carry genes that disrupt the normal controls over cell growth and division
RETROVIRUSES AND CANCER
HIV
PLANT VIRUSES
TOBACCO MOSAIC VIRUS Was the first
virus to be identified
Causes disease in tobacco plants
KNOWLEDGE CHECK
What characteristic do viruses share with all living organisms?
a. Respiration b. Metabolism c. Replication d. Movement
KNOWLEDGE CHECK
A lytic infection occurs when a
a. Virus infects a bacterium and kills it immediately
b. Virus embeds its genome into the DNA of the host cell
c. Virus enters a cell, makes copies of itself, and causes the cell to burst
d. Virus inserts its DNA into the DNA of the host cell and remains part of the host cell for many generations
KNOWLEDGE CHECKOne group of viruses that contain RNA as their genetic information are
a. Oncogenetic virusesb. Retrovirusesc. Capsidsd. Prophages
KNOWLEDGE CHECKFill in the blanks
The nucleic acid core of a virus contains ________ or __________
All viruses contain a coat of ________ and a core of _________
VIDEOS http://www.pbs.org/wnet/secrets/previou
s_seasons/lessons/lp_virus_videos.html#