Chapter 19 Flashcards
(7 cards)
List and describe the basic components of viral particles. Make sure to identify which components are only present in some viruses.
*Nonliving particle consists of nucleic acid genome enclosed in a protein coat capsid and sometimes an envelope. Vary greatly in their characteristics:
*Viral Particle Structure:
-All viruses have a capsid (protein coat) but it varies in shape and complexity.
-Some also have a viral envelope derived from the host cell plasma membrane
*Genome:
-DNA vs. RNA, Single stranded vs Double stranded, linear vs circular
*Host range
-Number of species and cell types that can be infected
Outline the steps of basic viral reproductive cycle. Which step of the cycle determines host range?
*Attachment
-A molecule on the virus binds to a specific molecule on the surface of the host cell
*Entry
-Some viruses inject only genome
-Others fuse their envelope with the host membrane and whole capsid enters
-Virus may proceed to synthesis of viral components OR integrate into host chromosome
*Integration
-Some viruses have to integrate their genome into the host genome:
-HIV AND Phage Lysogenic Cycle
-Viral protein Integrase cuts host chromosomal DNA and inserts viral genome
-HIV have RNA genome so it has to use viral reverse transcriptase to make complementary DNA strand that will be used to create double stranded DNA that integrates into the host genome
*Synthesis of Viral Components
-Host Cell DNA replication for viruses with DNA genomes
-Host cell transcription makes viral RNA
-Host cell translation makes viral proteins
*Viral Assembly
-Capsid proteins enclose viral genome
-Other proteins may modify capsid proteins or serve as scaffolding for assembly
*Viral Release
-Phages must lyse their host cell to escape
-Enveloped viruses like HIV bud from the host cell membranE
Make sure to define reverse transcriptase and explain why HIV needs it, but many other viruses don’t.
*2 copies of single-stranded RNA and two molecules of reverse transcriptase in viral particle
*Packaged into a capsid
*Surrounded by a viral envelope
*HIV Reproductive Cycle:
-Must integrate
-Uses reverse transcriptase to produce viral DNA from RNA that can be integrated into the host cell
genome
-Reverse transcriptase lacks a proofreading function and makes more errors leading to lots of strains of HIV
Define viroids and prions.
*Other Non-Living Infectious Particles
*Viroids
-Composed ONLY of a single-stranded circular RNA molecule a few hundred nucleotides in length
-Infect plant cells
-RNA genome does not code for proteins
-Disease mechanism not well understood
-Can be a significant problem in agriculture
*Prions
-Composed entirely of protein
-Disease causing protein shape PrPSc
-Normal protein PrPC expressed at low levels on surface of nerve cells
-Prion protein converts normal proteins to abnormal protein shape
-Causes several types of neurodegenerative diseases of human and livestoc
Define a plasmid and give examples of traits that might be carried on a plasmid.
*Plasmids are small, circular pieces of DNA that exist independently of the bacterial chromosome
-Not usually necessary for survival, but can provide growth advantages like drug resistance, create pathogenic traits or the ability to do conjugation
-Some plasmids can integrate into and become part of the bacterial chromosome
Distinguish bacterial cell division from eukaryotic cell division
Mitosis:
Binary Fission:
Bacteria asexually reproduce but still have genetic diversity. Describe two sources of genetic diversity in bacteria:
Describe the three mechanisms of horizontal gene transfer:
Conjugation (include F factor and sex pilus in your description):
*Direct physical interaction transfers genetic material from donor to recipient cell
*Donor cell must have the Fertility plasmid (F+) to create sex pilus and attach and transfer DNA to F-recipient cell
Transformation:
*DNA released from a dead bacterium into the environment is taken up by another bacteria, that then incorporates the DNA into its chromosome
*Only “competent” cells have the ability to pick up pieces of DNA from the environment
*DNA must be from somewhat related bacteria
Transduction:
*A virus unintentionally transfers genetic information from one bacterium to another
*Error in Viral reproductive cycle puts piece of bacterial DNA into viral particle instead of viral DNA
*When Viral particle goes to infect new host, it instead passes a piece of bacterial DNA
