Download Lecture 19

Unit 4
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Proteins
Transcription (DNA to mRNA)
Translation (mRNA to tRNA to proteins)
Gene expression/regulation (turning genes on and off)
Viruses
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Yesterday’s Exit Ticket
• Eukaryotic genes all have enhancers, made
up of control elements.
• Specific combinations of specialized
transcription factors (called activators) bind
to the control elements and help RNA
polymerase initiate transcription.
• Without that specific combination of
activators, a gene won’t be transcribed.
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Today’s Plan
• Viruses
– What are viruses?
– General viral reproduction
– Host specificity
– Variety in viral reproduction
• Exam 4 Review
http://www.upworthy.com/long-shot-doctors-inject-fatal-virus-into-dying-girl-this-100-true-story-will-amaze-you
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Today’s Plan
• Viruses
– What are viruses?
– General viral reproduction
– Host specificity
– Variety in viral reproduction
• Exam 4 Review
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Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 19-1
• Viruses are not cells and are not alive
• Dependent on host cells to reproduce
0.5 µm
Structure of Viruses
• Consist of nucleic acid enclosed in a protein coat (capsid)
• Some viruses are surrounded by a membranous envelope
DNA
Capsid
RNA
DNA
Membranous
envelope
RNA
Capsid
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Viral Genomes
• Viral genomes can be:
– Double-stranded DNA
– Single-stranded DNA
– Double-stranded RNA
– Single-stranded RNA
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Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
• Bacteriophages, also called phages, are viruses that infect
bacteria
• 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
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Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Today’s Plan
• Viruses
– What are viruses?
– General viral reproduction
– Host specificity
– Variety in viral reproduction
• Exam 4 Review
9
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Viruses reproduce only in host cells
• Each virus has a limited number of host cell types
that it can infect
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Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
General Features of Viral Reproductive Cycles
• Viruses insert their genomes into a host cell
• The cell manufactures viral proteins
• The virus uses host enzymes, ribosomes, tRNAs,
amino acids, ATP, and other molecules
• Viral nucleic acids and proteins spontaneously selfassemble into new viruses
Basic Virus Reproduction Animation
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Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 19-5-1
1 Attachment
Fig. 19-5-2
1 Attachment
2 Entry of phage
DNA and
degradation of
host DNA
Fig. 19-5-3
1 Attachment
2 Entry of phage
DNA and
degradation of
host DNA
3 Synthesis of viral
genomes and
proteins
Fig. 19-5-4
1 Attachment
2 Entry of phage
DNA and
degradation of
host DNA
Phage assembly
4 Assembly
3 Synthesis of viral
genomes and
proteins
Head
Tail Tail fibers
Fig. 19-5-5
1 Attachment
2 Entry of phage
5 Release
DNA and
degradation of
host DNA
Phage assembly
4 Assembly
3 Synthesis of viral
genomes and
proteins
Head
Tail Tail fibers
Fig. 19-4
VIRUS
1 Entry and
DNA
uncoating
Capsid
3 Transcription
and manufacture
of capsid proteins
2 Replication
HOST CELL
Viral DNA
mRNA
Viral DNA
Capsid
proteins
4 Self-assembly of
new virus particles
and their exit from
the cell
Today’s Plan
Viruses
– What are viruses?
– General viral reproduction
– Host specificity
– Variety in viral reproduction
Exam 4 Review
Viral Envelopes
Many animal viruses have
a membranous envelope
Membranous
envelope
RNA
Capsid
(c) Influenza viruses
Viral Envelopes
Viruses use cellular communication mechanisms
to their advantage
Cell-cell recognition
galaxywire.net
Viral Envelopes
Viral glycoproteins on the envelope bind to specific
receptor molecules on the surface of a host cell
Viruses imitate identifiers on the outside of host
cells to “trick” cells into letting them attach
Membranous
envelope
RNA
Capsid
Cell-cell recognition
Glycoproteins
Viral Envelopes
Many viral envelopes are formed from the host cell’s
plasma membrane as the viral capsids exit
Fig. 19-7
Capsid and viral genome
enter the cell
Capsid
RNA
HOST CELL
Envelope (with
glycoproteins)
Viral genome (RNA)
Template
mRNA
Capsid
proteins
ER
Glycoproteins
Copy of
genome (RNA)
New virus
Today’s Plan
Viruses
– What are viruses?
– General viral reproduction
– Host specificity
– Variety in viral reproduction
Exam 4 Review
Nucleic Acids and Viral Reproduction
• The type of nucleic acid in a virus determines how
it reproduces
DNA
transcribed
translated
RNA
translated directly as mRNA
copied to produce mRNA
translated
reverse transcribed into DNA
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RNA as Viral Genetic Material
• Retroviruses use reverse transcriptase to copy their RNA genome into DNA
• HIV (human
immunodeficiency virus)
is a retrovirus that causes
AIDS (acquired
immunodeficiency
syndrome)
– HIV infects helper t-cells,
and others, compromising
the immune system
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Fig. 19-8a
Glycoprotein
Viral envelope
Capsid
RNA
Reverse
transcriptase
HOST CELL
HIV
Reverse
transcriptase
Viral RNA
RNA-DNA
hybrid
DNA
NUCLEUS
Provirus
Chromosomal
DNA
RNA genome
for the
next viral
generation
New virus
mRNA
Because
reverse
transcriptase
doesn’t exist
naturally in
animal cells,
the virus
brings it to
the party
• The viral DNA that is integrated into the host
genome is called a provirus
• The provirus remains a permanent resident of the
host cell
HIV Reproduction Animation
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So what did doctors really do to save Emma?
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Today’s Exit Ticket
What are the key parts of a virus?
What extra component do retroviruses contain?
Today’s Plan
Viruses
– What are viruses?
– General viral reproduction
– Host specificity
– Variety in viral reproduction
Exam 4 Review