Chapter 13

Chapter 13 - Chapter13pg.283289 Virusesarenotcells

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 13 pg. 283-289 Viruses are not cells Acellular:  they are not cells and do not consist of cells o Composed of a few proteins and nucleic acids o Do no regulate transmission in/out o Do not perform metabolic functions o Much smaller than bacteria Reproduce only with the help of living cells Develop and reproduce within living cells o Use host cell’s DNA machinery to reproduce Virions:  basic unit of a virus outside of a cell, consist of DNA/RNA  surrounded by  proteins called  capsid B/c they lack cell walls and ribosomes antibiotics are useless with viruses Classified by a number of factors: o DNA or RNA o Single or Double stranded o Shape (Simple or Complex) o Membrane or Not Bacteriophage – lytic/lysogenic cycle Bacteriophage:  viruses that infect bacteria 1. Recognize host by means of proteins on capsid 2. Inject viral DNA into bacteria; 2 things can happens Lytic Cycle:  infected bacteria lyses releasing progeny phage Lysogenic cycle:  postpones reproduction; infected bacteria does not  lyse – harbors viral DNA Lytic Cycle Virulent virus:  virus that reproduces only through the Lytic cycle Process: 1. Early stage Viral DNA contains promoters that attract host RNA polymerase; viral  genes adjacent to promoter are transcribed Code for proteins that shut down host transcription; stimulate viral  genome replication/viral gene transcription Viral nucleases digest host’s chromosomes and use nucleotides for own  synthesis 2. Late Stage Late genes code for proteins of the viral capsid and those that lyse host  cell to release to virions
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Whole process takes ½ hour – needs careful control; premature lysis before late stage  stops infection 2 viruses can infect cell at the same time although rare – crossing over occurs causing  mutation and variation in viruses Lysogenic Cycle Lysogenic bacteria:  bacteria harboring viruses that are not lytic Deems host “immune” to same viral strand Prophage:  non-infective entity in lysogenic bacteria; molecule of phage DNA that has  been integrated into bacterial genome – can remain inactive for many replications  Once activated – lytic cycle begins Process of influenza virus: 1. Viral glycoprotein bind to receptor on host cell’s plasma membrane 2. Virus enter cell by endocytosis 3. Viral and vesicle membrane fuse   capsid breaks down 
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/17/2011 for the course MCDB 101 taught by Professor Unknown during the Spring '08 term at UCSB.

Page1 / 5

Chapter 13 - Chapter13pg.283289 Virusesarenotcells

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online