Lesson 4: Viruses Flashcards
What are the structural features of viruses?
Small and fixed in size and shape
capsid
x cytoplasm
Few enzymes
Why are viruses not considered living?
Cannot replicate independently.
Does not have a metabolism
what is a viral Capsid?
protein shell that encloses and protects the genetic material
what are the functions of viral capsid?
In some viruses the capsids contain proteins which can penetrate the cell membrane of the host and insert their genetic information.
In what ways can viruses differ in structurally?
DNA or RNA
Structure of capsid
Single or double stranded DNA/RNA.
Why are viruses so hard to treat?
Viruses are found inside our cells, so it is hard to treat them without interfering with normal cell function.
What are the steps in the lytic Cycle?
The virus attaches itself to the host cell’s membrane.
It injects its viral genome (virus genetic material) into the host cell.
Breaks down host’s genome.
Replication of viral genome and synthesis of viral proteins.
Assembly of viral particles.
Release of new viruses and death of host cell.
Lysogenic cycle
Phage attaches to bacterium.
Injects phage DNA.
Phage DNA integrates with host’s DNA creating a prophage.
Prophage replicates when bacterial DNA replicates.
Compare and contrast lysogenic and lytic cycle
Integration: lysogenic cycle involves integration of host and viral genome while the lytic cycle does not.
Cell fate: In the lytic cycle, the host cell dies while in the lysogenic cycle, it lives and divides along with the integrated phage DNA.
Speed: the lytic cycle is a lot faster.
What is convergent evolution?
organisms that share similar traits but do not share a common ancestor.
What is divergent evolution?
when two or more species sharing a common ancestor become more different over time
Viruses evolve very quickly due to their _____ _________ , _______ ___________ ______and ______ ________.
large population, short generation times, high mutations
What is antigenic drift?
small changes in the genetic material over a long period of time.
What is antigenic shift?
Two or more different viral strains or viruses infect the same cell and combine their genetic material producing major changes in a short time.
what are the evidences for viruses having a convergent evolution?
Some viruses that infect different cell types have evolved to have….
similar ways of entering and replicating in cells.
similar ways of evading the host’s immune system and spreading to new hosts.
similar shapes and size.
