Presentation on theme: "HAPPY THURSDAY Bellwork: What is a virus? How do viruses make us sick? How are viral infections treated? Can viral infections be prevented? Write 37 words."— Presentation transcript:
I. Viruses A. All viruses have one thing in common: 1. They enter living cells and use the cell to produce more viruses.
B. Virus Structure -A virus is made of: a) a core of DNA or RNA b) A virus has either a capsid or an envelope surrounding its genetic information. -The capsid allows viral DNA or RNA to enter a host cell. Envelope Capsid
Viral components – Nucleic acids DNA or RNA – Capsid Protein – Envelope Lipid – Spikes Used to attach to cell ONLY SOME VIRUSES 7
Generalized Structure of Viruses virions having envelopes = enveloped viruses virions lacking envelopes = naked viruses
Cellular Organisms vs Acellular Particles Eukaryotic Nucleus Prokaryoti c Cell Viru s Eukaryotic Cell 1 ųm (1000 nm)
C. Virus Specificity -Viruses are highly specific to the cells they infect Examples: 1) plant viruses infect plant cells 2) animal viruses infect only certain related species of animals 3) bacterial viruses infect only certain types of bacteria. So, what about zombies?
E. Retroviruses 1. Retroviruses are viruses that contain RNA as their genetic information. -Retroviruses get their name from the fact that their genetic information is copied backward, from RNA to DNA. 2. HIV is the most infamous retrovirus. AZT is a medication used to treat HIV by stopping an enzyme called reverse transcriptase Write this on your notes!
F. Viruses are parasites (use other organisms to grow and reproduce) 1. Viruses are NOT alive because they do not: a) grow and develop b) obtain and use energy c) respond to the environment
G. Vaccines 1. Viral diseases cannot be treated with antibiotics. 2. Vaccines are the best way to protect against viruses a) A vaccine is a dead or weakened version of a virus that is injected into a person to stimulate the immune system. b) Vaccines provide protection only if they are used before an infection begins.
D. Most viruses are not harmful to humans. 1. A pathogen is a disease-causing agent. 2. Viruses cause disease by disrupting the body’s normal equilibrium. 3. Viruses attack and destroy certain cells in the body, causing the symptoms of the disease.
H. Viral Reproduction 1. Once viral genes are inside the host cell, two processes may occur: the lytic cycle or the lysogenic cycle.
a) Lytic Cycle 1. Viral genes are inserted into a host cell and take control of the cell 2. After more viruses are made, the host cell bursts and is destroyed 3. New viruses infect new host cells
b) Lysogenic Cycle 1. Virus makes its DNA a part of the host cell’s DNA (integrates) 2. Virus’s genetic information (DNA or RNA) replicates with the host cell’s DNA. 3. The DNA remains dormant in the host cell. 4. Virus’s DNA activates and switches back to the lytic cycle.
- Since viruses can transport DNA and RNA into cells, scientists are exploring Gene Therapy - In Gene Therapy, viral genetic material is replaced with new DNA - In time, this could be used to cure genetic diseases. Currently we have no cure for these types of illnesses
Sage and Scribe: Cycle Steps Get into partners—decide who is partner A and who is partner B. – Partner A: Describe the steps for the Lytic cycle. – Partner B: Draw each step. After a few minutes, we will switch to the Lysogenic Cycle and you will switch roles.