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VirusesViruses are NOT cells. A virus is an infectious agent made up of:
•a core of nucleic acid (RNA or DNA)
•a protein coat (capsid)
•Genetic material carries information for multiplication
•Hijacks biochemical machinery of host cell to carry these processes out•So…viruses are NOT LIVING
CELLCELL VIRUSVIRUS
Made of cells YES NO
Obtain & use energy
YES NO
Grow & develop
YESOnly inside a living cell
Reproduce YESOnly inside a living cell
Respond & adapt
YES YES
Contain RNA or DNA
YES YES
Characteristics
of life
Re-CapViruses are NOT ALIVE. Viruses do not:•Grow
•Have homeostasis
•Metabolize
Viruses do:•Infect cells and use the cell to make more
viruses
•Cause disease in many organisms
Structureof a virus• Envelope (part of
the protein coat)• Capsid (part of
the protein coat)• Nucleic acid
(either DNA or RNA)
ENVELOPE
NUCLEIC
ACIDCAPSID
Retrovirus• A virus that
contains RNA instead of DNA
• Human Immunodeficiency Virus (HIV) is a retrovirus
• HIV causes AIDS
ENVELOPE
RNA
CAPSID
Ticking time bombs . . .
Viruses do not reproduce by themselves. They invade a living cell and let the cell do the work for them.
Lysogenic Cycle
The viral infection that enters a cell, remains harmless for a period of time (sometimes years), and then becomes harmful later is called the lysogenic cycle.
In the lysogenic cycle, the virus reproduces by first injecting its genetic material, indicated by the red line, into the host cell's genetic instructions.
Lysogenic Cycle
Role of viruses
• All viruses act like parasites, harming the host cell.
• Viruses cause disease in every kind of organism—animals, plants, fungi, protists, and bacteria.
• HIV• Measles• Smallpox• Influenza• Chicken pox
• Common cold• Herpes• Warts• Mononucleosi
s• Mumps
Some viral diseases
HIV• A retrovirus• Infects human helper T-cells, which
are associated with the immune system.
• Modes of transmission: – Sexual contact with an infected person– Sharing needles with an infected person– Blood transfusions (rare)– Breast feeding– Etc.
HPV• Human Papilloma Virus• Causes warts• Most common STD in the United
States• 80% of women by the age of 50 will
have acquired some strain of genital HPV.
• HPV vaccine
Influenza (flu)• Symptoms: body aches, fever,
coughing, runny nose, fatigue, usually lasting about a week.
• Mode of transmission– Airborne (air droplets)
People still die from influenza.
Bacteria
Bacteria are Prokaryotes.
Prokaryotic Cells:• Have no nucleus• Do not have membrane
bound organelles• Are very small• Often have a flagellum
for movement
Shapes of bacteria
Bacteria are classified according to their shape:
• Round is called cocci
• Rod shaped is called bacilla
• Spiral shaped is called spirilla
Role of bacteria• Some bacteria are helpful
– E. coli– Yeast– V.streptococci– Lactobacillus
• Some bacteria are harmful– E. coli– S. pyogenes– S. aureus– Y. pestis
Streptococcus
• Causes strep throat, pneumonia, and other infections.
• Named based on the shape and orientation of the bacteria.
Staphylococcus • Cause of staph infections that occur
on the skin or in wounds. (ex. MRSA)
• But, Certain types of staph reside normally on the skin.
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