This document discusses viruses and provides information about their structure and life cycle. It defines viruses as non-cellular infectious particles composed of genetic material surrounded by a protein coat. Viruses are described as non-living because they contain no organelles and must use a host cell's machinery to replicate, but are also considered living because they can reproduce and mutate. The document outlines the differences between DNA and RNA viruses and describes viral capsids and envelopes. It explains the lytic and lysogenic replication cycles viruses use to infect host cells and how they are specific to certain kingdoms but not always specific species.

1. Virus

2. Virus
Laurence N. Ruedas
Advanced Topic in Biology for Teachers
MATS 305

3. V I R U S
-Non cellular infectious particles
made up of genetic material
packaged in a protein coat that
can invade living cells.
-Comes from the Latin word “virus”
which means “poison”

4. Are Viruses Living or
Non Living?

5. Viruses are Non Living
-they are acellular, that is, they contain
no cytoplasm or cellular organelles.
-They carry out no metabolism on
their own and must replicate using
the host cell's metabolic machinery.
-The vast majority of viruses possess
either DNA or RNA but not both.

6. Viruses are Living
-They reproduce at a fantastic rate,
but only in living host cells.
-They can mutate

7. Adolf Mayer

8. Martinus Beijerinck

9. Structure of virus

10. DID YOU KNOW THAT . . . .
The tiniest viruses are
only 20 nm in
diameter while the
largest known virus is
1500 nm

11. Wendell Stanley
Viruses could be
crystallized
It is an infectious
particle consisting of
one or more
molecules of a nucleic

12. DNA Virus RNA Virus
VIRAL GENOMES
Genomes are usually organized
as a single linear or circular
molecule of nucleic acid.
smallest virus
has 3 genes
(FMDV)
largest virus has
hundred to 2,000
genes (megavirus)

13. Capsids and Envelopes
Capsid
- protein shell enclosing the
viral genome
-Made up of large number of
large number of protein sub-
units called capsomeres

16. Capsids and Envelopes
Capsid
- protein shell enclosing the
viral genome
-Made up of large number of
large number of protein sub-
units called capsomeres

17. Capsids and Envelopes
Viral Envelopes
-Membranous envelope that
surrounds the capsids which
helps viruses in infecting their
host.
-Derived from the membranes of
the host cell; contains
phospholipids and membrane

18. Bacteriophages
Viruses that infect bacteria

19. HOST SPECIFICATION

20. HOST SPECIFICATION
•All kingdoms can be infected by
viruses
•Viruses are kingdom specific but
they may or may not be species
specific
•Spread is specific to the type of virus

21. VIRAL REPLICATION

22. VIRAL REPLICATION
Viruses lack metabolic enzymes
and equipment for making
proteins, such as ribosomes.
THEY CAN ONLY REPLICATE
WITHIN A HOST

23. SIMPLIFIED
VIRAL REPLICATIVE
CYCLES

24. VIRAL REPLICATIVE CYCLES
LYTIC CYCLE
LYSOGENIC CYCLE

25. Lytic cycle
A phage replicative cycle
that culminates in death
of the host cell
Virulent phage
A phage that
replicates only by a

26. LYTIC CYCLE

27. LYTIC CYCLE

28. LySOGENIC CYCLE
A phage replicative cycle
that allows replication
without destroying the
host.
Temperate phage
A phage capable of using
both modes of replicating

29. LYSOGENIC CYCLE

30. LYSOGENIC CYCLE

31. Thank you !!!