1. Viruses, Viroids, and Prions13
Viruses, Viroids, and Prions

2. Attachment, Penetration, and Uncoating
Pinocytosis
Figure 13.14a

3. Attachment, Penetration, and Uncoating
Fusion
Figure 13.14b

4. Release of an Enveloped Virus by Budding
Figure 13.20

5. Multiplication of DNA Virus
Figure 13.15

6. + Sense Strand (+ Strand) RNA Virus
Maturation
and release
Entry
and uncoating
Translation and synthesis
of viral proteins
RNA replication by viral RNA-
dependent RNA polymerase
Uncoating releases
viral RNA and proteins.
Nucleus
Attachment
Viral
protein
Capsid
Cytoplasm
Host cell
– strand is transcribed
from + viral genome.
+ strand
mRNA is transcribed
from the – strand.
RNA
genome
(RNA)
ssRNA; +
or sense strand;
Picornaviridae
(a)
Figure 13.17a

7. — Antisense Strand (— Strand) RNA Virus
Maturation
and release
Entry
and uncoating
Translation and synthesis
of viral proteins
RNA replication by viral RNA-
dependent RNA polymerase
Uncoating releases
viral RNA and proteins.
Nucleus
Attachment
Viral
protein
Capsid
Cytoplasm
Host cell
– strands are
incorporated
into capsid
The + strand (mRNA) must first
be transcribed from the – viral
genome before proteins can
be synthesized.
Additional – strands are
transcribed from mRNA.
RNA
genome
(RNA)
ssRNA; – or
antisense strand;
Rhabdoviridae
(b)
Figure 13.17b

8. Multiplication of a Retrovirus
PLAY
Animation: Viral Replication
Figure 13.19

9. Cancer
Activated oncogenes transform normal cells into cancerous cells.
Transformed cells have:
increased growth
loss of contact inhibition
tumor specific transplant
antigens

10. Latent viral infections
Virus remains in asymptomatic host cell for long periods.
Cold sores, shingles
Persistent viral infections
Disease processes occurs over a long period; generally is fatal.
Subacute sclerosing panencephalitis (measles virus)
Figure 13.21

11. Table 13.5

12. Prions Infectious proteins
Inherited and transmissible by ingestion, transplant, and surgical instruments
Spongiform encephalopathies: Sheep scrapie
Creutzfeldt-Jakob disease
Mad cow disease
PrPC: Normal cellular prion protein, on cell surface
PrPSc: Scrapie protein; accumulates in brain cells forming plaques
PLAY
Animation: Prion Reproduction

13. Prions
Figure 13.22

14. Plant viruses: Enter through wounds or via insects.
Viroids: Infectious RNA; e.g., potato spindle tuber disease.
Figure 13.23

15. Some Plant Viruses
Table 13.6

16. Crossing the Species Barrier
UN 13.3