8. Viruses, retroviruses, reverse transcription
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10 Terms
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virus?
infectious, parasitic agent that can only replicate within other host cells
viruses doesn’t really fit our definition of living organisms, as they are unable to replicate without a host cell
all viruses have a genome and a capsid
the viral genome can be single or double stranded, DNA or RNA, linear or circular
the capsid is a protein coat surrounding the genome. it consist of several copies of one protein, coded by only one gene
viruses doesn’t really fit our definition of living organisms, as they are unable to replicate without a host cell
all viruses have a genome and a capsid
the viral genome can be single or double stranded, DNA or RNA, linear or circular
the capsid is a protein coat surrounding the genome. it consist of several copies of one protein, coded by only one gene
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retroviruses?
some RNA viruses contains an RNA-dependent DNA pol called reverse transcriptase
on infection, the single stranded RNA genome and the enzyme enters the host cell
the reverse transcriptase first synthetize on DNA strand, complementory to the RNA strand. the primer for this reaction is tRNAlys
the RNA is then degraded, except for a small portion, which acts as the primer for the synthesis of the second DNA strand
3 functions of rev. trans.: RNA-dep., DNA-pol. and RNA degradation. DNA dep. DNA pol.
this resulting DNA duplex often becomes incorporated into the genome of the host cell
the integrated viral genes can be activated and transcribed, and the products, viral genome and proteins, can be packed as new viruses
on infection, the single stranded RNA genome and the enzyme enters the host cell
the reverse transcriptase first synthetize on DNA strand, complementory to the RNA strand. the primer for this reaction is tRNAlys
the RNA is then degraded, except for a small portion, which acts as the primer for the synthesis of the second DNA strand
3 functions of rev. trans.: RNA-dep., DNA-pol. and RNA degradation. DNA dep. DNA pol.
this resulting DNA duplex often becomes incorporated into the genome of the host cell
the integrated viral genes can be activated and transcribed, and the products, viral genome and proteins, can be packed as new viruses
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LTR-Ψ-GAG-Pol-Env-LTR?
most retroviruses contains the Ψ-Gag-Pol-env. the LTR sequences are needed for initiation and regulation of transcription
the Ψ sequence is important for packing of retroviral RNA into mature viral particles
the sequence which contains the Gag (group associated antigen) and pol is translated into a large polyprotein which is cleaved into six proteins w. distinct features
the gag gene proteins are structural proteins, the pol gene codes for integrase, protease and reverse transcriptase
the env gene codes for the viral envelope proteins
the Ψ sequence is important for packing of retroviral RNA into mature viral particles
the sequence which contains the Gag (group associated antigen) and pol is translated into a large polyprotein which is cleaved into six proteins w. distinct features
the gag gene proteins are structural proteins, the pol gene codes for integrase, protease and reverse transcriptase
the env gene codes for the viral envelope proteins
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retroviruses that causes cancer and AIDS?
some retroviruses contains oncogene, that when expressed can cause the cell to grow abnormally: rous sarcoma is such a RNA-tumor virus
in addition to the typical retroviral genes Rous sarcoma virus also contains “src” which codes for a tyrosine-specific protein kinase, which is known to affect cell-division, cell-cell interaction
HIV causes AIDS. the tropism of HIV is the CD4 of T-cells
HIV genome contains many genes, other than the usual ones, like net involved in penetration, tat is a protein which “steals” transcription factors from the host, in order to express viral genes
in addition to the typical retroviral genes Rous sarcoma virus also contains “src” which codes for a tyrosine-specific protein kinase, which is known to affect cell-division, cell-cell interaction
HIV causes AIDS. the tropism of HIV is the CD4 of T-cells
HIV genome contains many genes, other than the usual ones, like net involved in penetration, tat is a protein which “steals” transcription factors from the host, in order to express viral genes
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Drugs for HIV?
AzT (azidodideoxy thymidine) reverse transcriptase. causes problem in bone marrow → anemia
dideoxyinosine - protease inhibitor
dideoxyinosine - protease inhibitor
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transposons?
Transposons are DNA sequences that can move within a genome. They can cause genetic changes and contribute to genetic diversity. They play a role in genome evolution and can have both beneficial and harmful effects on organisms.
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retrotransposons?
cut and paste
first transcribed to RNA, which is then transcribed back into the DNA, which will incorporate into the genome
the retrotransposons themselves codes for reverse transcriptase, which will reverse transcribe the RNA back into the DNA
first transcribed to RNA, which is then transcribed back into the DNA, which will incorporate into the genome
the retrotransposons themselves codes for reverse transcriptase, which will reverse transcribe the RNA back into the DNA
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DNA transposons?
cut and paste
these transposons simply relocate from one location in the genome, to another
these transposons simply relocate from one location in the genome, to another
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Telomeres?
Telomeres are repetitive DNA sequences found at the ends of chromosomes.
They protect genetic material during cell division and prevent damage.
Telomeres gradually shorten with each cell division, but an enzyme called telomerase can replenish them.
Shortened telomeres are associated with aging and disease.
They protect genetic material during cell division and prevent damage.
Telomeres gradually shorten with each cell division, but an enzyme called telomerase can replenish them.
Shortened telomeres are associated with aging and disease.
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Homing?
certain introns contains a gene for enzymes which promote homing or retrohoming
in type I and endonuclease is expressed
if allele a of a gene contains a homing intron white allele b doesn’t
endonuclease cuts the allele b at the site where the intron is in allele a. double strand break repair will insert a intron at the site
in type II a endonuclease/reverse transcriptase is needed. Allele a of gene Y contains a type II intron while allele b doesn’t
the spliced intron inserts itself and cuts the non-coding strand
it produces a self-complimentary DNA strand the RNA is removed and the second strand is synthesized
in type I and endonuclease is expressed
if allele a of a gene contains a homing intron white allele b doesn’t
endonuclease cuts the allele b at the site where the intron is in allele a. double strand break repair will insert a intron at the site
in type II a endonuclease/reverse transcriptase is needed. Allele a of gene Y contains a type II intron while allele b doesn’t
the spliced intron inserts itself and cuts the non-coding strand
it produces a self-complimentary DNA strand the RNA is removed and the second strand is synthesized