Microbio Exam 2

Viral structure

10 → 100 nm in diameter

bacteria/archaea

500 - 5000 nm

Poxviruses

200 nm

Virus → Genome

• Deoxyribonucleic acid

• Ribonucleic acid

• Linear or circular

capsid

The protein structure surrounding the viral genome.

 composed of protein subunits called capsomeres.

how many nucleotides do humans have?

about 3 billion

_______ are the fully assembled infectious viral particles.

Virions

viruses uncoats ____ to start replication cycle

capsid

Helical

Rod shape

Most plant viruses

Diverse virion size

Icosahedral

spherical, 20-sided polygon

the ____ are required for viral entry into other hosts; without _______ the virus is non-infectous.

envelope`

Enveloped viruses → _______

influenza

Coevolution hypothesis

Viruses originated prior to or at the same time as primordial cells and continued to coevolve with these hosts. RNA

Regressive hypothesis

Virus lost some of its essential features and has become dependent on a host. MITOCHONDRIA

Progressive hypothesis →

plasmids

• allowed the DNA or RNA to replicate and be transmitted in a semi-autonomous fashion.

Bacteriophages

Viruses that infect bacteria

• Plaques → zones or claridges where phage killed bacteria

Animal viruses

Use adherence cells

Cytopathic effects (rounding/detachment)

Viral purification

• Filtration (0.2 µm)

• Differential centrifugation (separates by size)

• Gradient centrifugation

Direct count

determines absolute # of viral particles; does not differentiate

Hemagglutination assay

same viruses stick to erythrocytes causing them to agglutinate (stick together) and form a gel mat.

NAKED EYE!!!

Plaque assay

Most common method for determining infectious titer; plaque forming unit

Tissue culture infectious dose 50 (TCID50)

amount of virus to infect 50%of the cultured host cells.

Lethal Dose 50 (LD50)

amount of viruses needed to kill 50% of the hosts.

Classification of viruses

A simple letter/number combo

The organism they infect

Location of discovery

Apperance

Disease they cause

viruses have _____; not domains

realms

The International Committee on Taxonomy of Viruses (ICTV)

-morphology (virion size)
-genomic structure
-biological feature

The Baltimore classification system:

classifies viruses based on their mRNA production method

-group viruses into 7 classes

Electron microscopy

first method to ID viruses (determine morphology)
-many viral groups have distinctive shapes

Nucleic acid analysis

PCR the viral genome (DNA viruses)
Reverse transcriptase PCR the viral genome (RNA viruses)
* You will PCR a conserved gene

Viroids

Are infectious agents of plants composed of naked RNA.

Potato spindle tubor viroid

Satellite viruses

are infectious agents of plants composed of an RNA genome containing a gene that codes for its protein coat.

hepatitis D virus

Satellite RNAs

are infectious agents of plants composed of an RNA genome and a protein coat that is encoded by a helper virus.

Virophages

are virus-like particles that replicates in host cell co-infected with helper virus and is detrimental to the helper virus.

Prions

are infectious agents composed of protein that can replicate within a host cell and cause transmissible spongiform encephalopathies.

mad cow disease

normal prion →

PrP^c

infectious prion →

PrP^Sc

misfolded protein

DNA replication -

DNA must remain intact so each new daughter cell gets the same copy

Transcription

DNA must be copies into ssRNA, which provides the instructions for protein synthesis

Translation

mRNA must be read and decoded for protein synthesis

___________ is a type of horizontal gene transfer in which a piece of free DNA is taken up by a cell

Transformation

Frederick Griffith, 1928

demonstrated that hereditary info could be transferred horizontally

S strain

pathogenic

smooth appearance

R strain

non-pathogenic

rough appearance

The Avery, MacLeod, and McCarty experiment

Isolated the live, pathogenic S strain, heat-killed it, then digested certain macromolecules one at a time

DNA tube did ___ show transformation

NOT

Radiolabeled capsids w/______

sulfur-35 

DNA was radiolabeled w/ ________

phosphorus-32

Purines ( 2 ring structure)

Adenine and Guanine

Pyrimidines (1 ring structure)

Thymine and Cytosine and Uracil

Same strand = phosphodiester bonds

→ a covalent bond (STRONG)

Archaea and Eukarya have _____

histones (causes supercoiling and packaging)