Embed Size (px)
Citation preview
Chapter 5. Viruses (at the threshold of life)
1. Discovery and Structure of viruses
What is virus ?
- virus : living things or not ? -> “organules” “molechisms”
- Golden age of microbiology (1880 - 1915)
-> increased understanding of infectious disease (tuberculosis, typhoid fever..)
-> industrial utilization of microbes
-> importance of microbes in environments
Yet unknown causation of some disease (measles, chickenpox, polio, hepatitis)
“ i ” d t f t k id tit f i f ti di“virus” was used to refer to unseen or unknown identity for infectious disease
- bacterium for tuberculosis d b i ?bacterium for tuberculosis- protozoan for malaria
caused by virus ?
The true nature of virus remained a mystery
Chapter 5. Viruses (at the threshold of life)
1) Development of virology1) Development of virology
- 1892, Dmitri Iwanowski :
-> attempting to isolate bacterial cause of tobacco mosaic diseasep g
-> use filter to trap smallest known bacteria
-> filtered juice contained infectious agent -> called filterable virus
- 1898, Martinus Beijerinck , j
-> diluted filtered juice -> still infectious -> called contagious living fluid
- 1930s, Wendell M. Stanley : crystalization of tobacco mosaic virus
-> implies that TMV is chemical molecule> implies that TMV is chemical molecule
-> viral disease caused fever, a response by immune system or other symptom
- 1933, electron microscope 발명 -> TMV 전자사진
Chapter 5. Viruses (at the threshold of life)
2) Structure of viruses2) Structure of viruses
- size : 27nm(poliovirus) ~ 250nm(smallpox virus)
- 500 or more viruses fit inside a single bacterial cellg
Chapter 5. Viruses (at the threshold of life)
2) Structure of viruses2) Structure of viruses
- shape : helical, icosahedral, complex type
HIV
Chapter 5. Viruses (at the threshold of life)
3) Component of viruses3) Component of viruses
- genome : core of nucleic acid
-> DNA or RNA, not both
-> long and helical, or folded
-> single molecule, occasionally segmented
- capsid : coat of protein -> consisted of capsomerescaps p capsom r s- nucleocapsid : combination of genome and capsid
- envelope : membrane-like envelope enclosing nucleocapsid
- no cytoplasmno cytoplasm
☞ spikes : projections on the envelope
-> contacting virus to its host
-> assist penetration into host cell
Chapter 5. Viruses (at the threshold of life)
Chapter 5. Viruses (at the threshold of life)
☞ 생물체로서의 미생물의 특징
- 성장을 위한 영양분의 흡수, 소화
소화산물의 배설- 소화산물의 배설
- 독립적 생식능력
- 환경변화에 대한 적응능력
생물계 구성원의 공통특징
- 자극에 대한 반응능력
☞ virus의 생화학적 특징- no chemistry going on within a virus
- no intake of nutrientno intake of nutrient
- no production of waste
- no increase or decrease in size
- no metabolism
- but, they replicate
-> programs a host cell biochemically to produce hundreds of copiesp g y p p
Chapter 5. Viruses (at the threshold of life)2 Viral replication2. Viral replication
- virus : inert particle outside a host cell
-> becomes highly efficient replicating machine in the host cell
-> utilize metabolism of the cell-> utilize metabolism of the cell
-> produces multiple copies of itself in several stages
1) Stages of replication(1) attachment stage
- high degree of specificity for a certain host
- 1. protein molecule in envelope keys off receptor sites(lock) in the host cell
- 2. or viral tail attaches to receptor sites
- 3. or blending of viral envelope with host cell membrane
- 4. or by phagocytosis
X 200,000
Viral attachmnet
X 70,000
Chapter 5. Viruses (at the threshold of life)
(2) penetration stage
- nonenveloped virus is left outside the host cell, the genome passes into the cell
(3) uncoating stage
- within the cell, cellular protein removes the protein capsid from the viral genome
(4) synthesis stage
- viral proteins are synthesized from viral genome using cellular machinery
(5) assembly stage
- viral parts are combined to form new viral particles after synthesis is completed
(6) release stage
- viral envelope is built from cellular membrane
-> disrupt cell membrane => lytic cycle
Replication of Enveloped virusReplication of Enveloped virusp pp p
Cli k iClick to view animation.
animation
Unenveloped virusUnenveloped virus
Chapter 5. Viruses (at the threshold of life)
2) L tic and l s enic c cle2) Lytic and lysogenic cycle
- some times, virus enters a host cell but do not replicate immediately =>lysogeny- lysogenic cycle : y g y
-> virus incorporates its genes into the host genes and becomes part of it
-> multiply together with host genes => becomes provirus(oncogene)
Chapter 5. Viruses (at the threshold of life)
Lytic and lysogenic cycleLytic and lysogenic cycle
Chapter 5. Viruses (at the threshold of life)
Lysogenic and lytic cycleLysogenic and lytic cycle
Cli k i Cli k iClick to view animation.
Click to view animation.
animation
Chapter 5. Viruses (at the threshold of life)3) Viriods and prions3) Viriods and prions
- Viriods : single-stranded molecules of RNA without protein coat
-> infect plants causing disease
- Prions : proteineous infectious particle
-> composed solely of protein, extremely stable
-> transformed from prion protein(PrP, harmless protein in itself in brain cell)
-> PrP : protect cells by helping rid of dangerous chemicals
-> prion : clump together -> block molecular traffic
3 Viruses and Cancer3. Viruses and Cancer- Cancer : results from uncontrolled reproduction of cells
-> grows into abnormal, functionless mass of cells => tumor- body’s response to the tumor
-> surrounding it with a capsule of connective tissue => benign-> outgrowth and break out of the capsule and spread => malignant
- Properties of cancer cell differing from normal cells
-> more rapid growth than normal cell
-> stick together less firmly than...
-> undergo dedifferentiation (reverting to an early stage to divide indefinitely
-> fail to exhibit contact inhibition -> not stop growing when contacted
Chapter 5. Viruses (at the threshold of life)
Contact inhibitionContact inhibition
Chapter 5. Viruses (at the threshold of life)
☞ How viruses transform cells☞ How viruses transform cells
- oncogene : transforming genes normally reside in the chromosomal DNA of cells
-> not viral in origin but part of the genetic endowment
> over 60 oncogenes were identified-> over 60 oncogenes were identified
- proto-oncogene : fore-runners of oncogenes
-> can be converted to oncogenes by carcinogens including viruses
