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Microbiology 315 > Lecture 7 > Flashcards

Lecture 7 Flashcards

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1
Q

LAST TIME WE DISCUSSED

Environmental influences on growth

A

• Temperature, pressure, pH, oxygen

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2
Q

Extremophiles

A

• Mesophiles, psychrophiles, thermophiles, barophiles

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3
Q

Antimicrobial control measures

A

• Sterilization, disinfection, antisepsis, and sanitation

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4
Q

Microbes that grow in ____ are called?

A

• Temperatures 0-20 C
(Psychropiles)
• High salt 2-4M NaCl
(Halophiles)

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5
Q

REVIEW FROM LAST TIME

Which of the following statements about microbes and temperature is FALSE?

A

ANSWER : D
A. Within a specific range, the microbial growth rate roughly doubles for every 10oC rise in temperature.
B. Changes in temperature affect membrane fluidity, and thus influence nutrient transport.
C. Thermophiles are microbes that grow at temperatures between 40oC and 80oC.
D. Microbes have mechanisms to control their temperature.

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6
Q

VIRUSES ARE EVERYWHERE

Viruses act as a ______ consumer of marine microbes

A

Dominant

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7
Q

When marine algae overgrow they generate a _____

A

Bloom

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8
Q

Bloom

A

is dissipated by viruses (lyse algae as they grow)

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9
Q

Human virome

A

• Most of our own viruses go unnoticed • Some contribute to our health

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10
Q

We hear about the viruses that cause epidemics

A

(influenza, HIV)

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11
Q

_______ have provided tools and model systems that led to discovery of fundamental principles of molecular biology

A

Viruses

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12
Q

WHAT IS A VIRUS ?

A

Non-cellular (non-living) particle that infect a host cell and use the cell’s machinery to replicate

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13
Q

Virion (virus particle) -

A

consists of a nucleic acid genome (DNA or RNA, single or double stranded)

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14
Q

Has a protein coat

A

capsid

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15
Q

Viruses may kill their host or copy their _____ into the host’s genome

A

Genes

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16
Q

All kinds of cells (bacteria, eukaryotes, archaea) can be infected by viruses

A

• Estimated 10^32 viruses on earth

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17
Q

EVEN SMALLER THAN A VIRUS

Vitriols
Don’t have a capsid

A

RNA genome is itself the infectious particle
• Infect plants
• RNA structure prevents degradation by host Rnases
[pic]

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18
Q

Prions-

Can make other misfold as well?

A

protein only (no nucleic acid)
• Abnormal protein structure
• Cause of “mad cow” disease
• Creutzfeldt-Jakob disease

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19
Q

VIRUS STRUCTURE- ICOSAHEDRAL VIRUSES

\_\_\_\_\_\_\_\_\_\_\_ are a type of symmetrical virus that packages their genome in an icosahedral capsid
A

Icosahedral viruses

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20
Q

Capsid

A

polyhedron with 20 identical triangular faces

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21
Q

Each triangle can be composed of three identical but asymmetrical
protein units

A

Each triangular face is determined by the same genes encoding the same protein subunit

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22
Q

Rotational symmetry

A

no matter what the pattern of the subunits

[pic]

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23
Q

VIRUS STRUCTURE- FILAMENTOUS VIRUSES

Filamentous viruses

A

are a type of symmetrical virus with helical symmetry

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24
Q

Pattern of capsid molecules forms a __________ around the genome, which is coiled inside

A

Helical tube

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25
Genome can be _______ stranded DNA or RNA
Single
26
Examples
M13 phage, Ebola, tobacco mosaic virus
27
VIRUS STRUCTURE- TAILED VIRUSES Tailed viruses
Multipart structure
28
Icosahedral capsid or “head” containing the genome attached to a helical “neck” that channels the ___________ into the host
Nucleic acid
29
Example
T4 bacteriophage | [pic]
30
VIRUS STRUCTURE - ASYMMETRICAL VIRIONS Asymmetrical viruses –
lack capsid symmetry | • Examples: Influenza, poxviruses
31
Vaccinia poxvirus (cowpox)
• Core envelope encloses the nucleo capsid-coated DNA and accessory proteins • Proteins can be found inside the capsid or between the core envelop and outer membrane [PIC]
32
VIRUS STRUCTURE- ENVELOPES Viruses may have a _______
lipid envelope
33
Allows fusion to host cell membrane
• Occurs if host cell is not covered by cell wall | *Bacteriophages and plant viruses are NON-enveloped
34
Envelope lipids come from the host membrane
• Not encoded by the viral genome
35
Envelope proteins usually encoded by virus
Coats viral capsid as virus leaves cell or organelle | [pic]
36
VIRAL GENOMES
* DNA or RNA * Single- or double-stranded * Linear or circular
37
..
• Includes genes encoding viral proteins * Capsid * Envelope proteins if virus is enveloped * Any polymerase not found in host cell [PIC]
38
Size varies greatly
• Small – fewer than 10 genes • Large – 500-2,500 genes
39
CLASSIFICATION OF VIRUSES International Committee on Taxonomy of Viruses (ICTV) Criteria:
• Genome composition – classified by the Baltimore method • Capsid symmetry (helical, icosahedral) • Envelope *Presence of host-derived envelop and structure • Size of the virus particle • Host range *Closely related viruses typically infect the same or related hosts
40
THE BALTIMORE VIRUS CLASSIFICATION Based on genome composition and means of mRNA production
[important pic]
41
[pic]
[another pic] | [another pic]
42
MOLECULAR EVOLUTION OF VIRUSES How do we compare virus genomes?
No rRNA
43
Comparison is based on _________ – genes of common ancestry in two genomes that share the same function
Orthologs | [pic]
44
_______ classification is useful for viruses because their small genomes encode few proteins
Proteomic
45
Statistical comparison of phage proteins predicted major evolutionary categories of phage species that share common host _________
Bactria | [pic]
46
VIRAL LIFE CYCLES All viruses require a host for reproduction and require:
* Host recognition and attachment * Cell surface receptors * Genome entry * Enter and gain access to machinery * Replicate genome * Make viral proteins
47
Continued...
* Assemble capsids * Exit and transmission * Release progeny viruses from host cell
48
BACTERIOPHAGE LIFE CYCLE Host recognition and attachment *Cell- surface receptors
proteins on the host cell surface that are specific to the host species and bind to a specific viral componen
49
Typically a protein with an important function for the host cell
.[pic]
50
• Genome _____
Entry
51
Most phages inject only their genome into the cell through the ________
Cell envelope
52
The phage capsid remains outside, attached to the cell surface
• “ghost” – empty capsid | [pic]
53
Lytic cycle
• Phage injects its genome into a cell and immediately reproduces as many progeny phage particles as possible • Expression of phage genes • “Early genes” – to produce new phage capsids etc • “Late gene” – expressed once capsids are assembled; produces enzyme that lyses the host cell – killing the host and releasing new phage particles • Lysis is also referred to as a burst and the number of particles released is called the burst size
54
Lysogenic cycle
* Temperate phage * Integrates its genome into the host genome (prophage) * Presence of prophage prevents further infection of host by other virions of the same type * Prophage DNA is replicated along with the host
55
Continue...
• Prophage can reactivate to become lytic by excising from the host genome * Can occur at random *Triggered by environmental stress(senses when host is about to die) • During exit from lysogeny the phage can acquire host genes that it then passes on to another cell (transduction)
56
Lysis and Lysogeny
[PIC] | [VIDEO]
57
Slow-release cycle
* Phage particles reproduce without killing the host cell * Phage M13 * Slow generation of progeny genomes and assembly of phage particles * Phage particles extrude through the envelope without lysing the cell
58
DISCUSSION: SLOW RELEASE VS. TEMPERATURE PHAGE What are the advantages and disadvantages (from virus perspective) of slow-release vs alternating between lysis and lysogeny?
Slow release- take long - host destroyed by something else -don’t need big population of host cells Lysogeny-host reused Slow release- environment might not conclusive so it waits *uses a lot of host resources Lyric- more viruses Lysogeny- uses little/ no resources —> many ... The slow release actually uses a lot of cellular resources
59
BACTERIAL HOST DEFENSES Bacteria have evolved several forms of defense against ______________
Bacterialphage infection
60
Genetic resistance
Altered host receptor proteins (phage can’t bind)
61
Restriction endonucleases
Cleaves viral DNA which lacks methylation
62
CRISPR
• Clustered Regularly Interspaced Short Palindromic Repeats • Bacterial immune system • Copy a tiny piece of the phage – “remembers” the phage *Detects this phage DNA in the next infection and cleave sit
63
ANIMAL VIRUSES Host recognition and attachment
* Cell surface receptors * Tropism – ability to infect a particular tissue type within a host * Broad tropism – infect many kinds of host tissues (e.g. Ebola)
64
Entry into cell
``` • Inject genome directly (similar to bacteriophage) • Most animal viruses enter the cell as virions • Taken up via endocytosis *Brought into the cell as an endosome *Requiresuncoating • Viral envelope fuses to host membrane * Releases capsid into cell ```
65
Genome replication
DNA viruses must get DNA into the nucleus to use the host polymerase (e.g. HPV) • ORreplicateincytoplasmwithaviralpolymerase
66
Genome replication RNA viruses encode a viral polymerase
- RNA to RNA :RNA-dependent RNA polymerase | - RNA to DNA:Reverse transcriptase (RNA-dependent DNA polymerase) – carried within the virion (Retroviruses)
67
(+) ssRNA viruses – translated directly by host ribosomes
• Produces RNA-dependent RNA polymerase ,which generates the | (-) RNA strand that is used as a template for progeny genomes
68
(-) ssRNA viruses
used as a template to create mRNA and progeny genomes
69
Exit and transmission
``` • Lysis of cell * Similar to bacteria • Budding *Viruspassesthrough membrane * Membrane lipids surround capsid * All enveloped viruses bud from a membrane * Plasma membrane or organelle membrane [pic] ```

Microbiology 315 (7 decks)

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