Viruses

Page
2

Tail

sheath

Tail

fiber

50 nm

50 nm

50 nm

20 nm

(a) Tobacco mosaic

virus

(b) Adenoviruses

(c) Influenza viruses

(d) Bacteriophage T4

Slide 10

Fig. 19-3a

(a) Tobacco mosaic

virus

20 nm

18  250 nm

Capsomere

of capsid

RNA

Slide 11

Fig. 19-3b

DNA

Capsomere

Glycoprotein

70–90 nm (diameter)

50 nm

(b) Adenoviruses

Slide 12

Fig. 19-3c

Membranous

envelope

RNA

Capsid

Glycoproteins

80–200 nm (diameter)

50 nm

(c) Influenza viruses

Slide 13

Fig. 19-3d

Head

DNA

Tail

sheath

Tail

fiber

80  225 nm

50 nm

(d) Bacteriophage T4

Slide 14

Some viruses have membranous envelopes that help them infect hosts

These viral envelopes surround the capsids of influenza viruses and many other viruses found in animals

Viral envelopes, which are derived from the host cell’s membrane, contain a combination of viral and host cell molecules

Slide 15

Bacteriophages, also called phages, are viruses that infect bacteria

They have the most complex capsids found among viruses

Phages have an elongated capsid head that encloses their DNA

A protein tail piece attaches the phage to the host and injects the phage DNA inside

Slide 16

Concept 19.2: Viruses reproduce only in host cells

Viruses are obligate intracellular parasites, which means they can reproduce only within a host cell

Each virus has a host range, a limited number of host cells that it can infect

Slide 17

General Features of Viral Reproductive Cycles

Once a viral genome has entered a cell, the cell begins to manufacture viral proteins

The virus makes use of host enzymes, ribosomes, tRNAs, amino acids, ATP, and other molecules

Viral nucleic acid molecules and capsomeres spontaneously self-assemble into new viruses

Animation: Simplified Viral Reproductive Cycle

Slide 18

Transcription

and manufacture

of capsid proteins

Self-assembly of

new virus particles

and their exit from

the cell

Entry and

uncoating