CHAPTER 13 LEARNING OBJECTIVES

Differentiate a virus from a bacterium

General characteristicsof viruses

- Contain DNA or RNA

- No ribosomes or ATP generating mechanisms

- have a protein coat

- obligatory intracellular parasites

-

General characteristicsof bacterium

- living

- contain DNA or RNA

- has organelles

-reproduces via binary fission

DIFFERENCES:

- Bacteria are living, viruses are not

- bacteria are free living, viruses NEED a host

- viruses are tiny, the largest ones are smaller than the smallest bacteria

- bacterium are composed of cells, viruses are not

- bacterium can (usually) be treated with antibiotics while viruses cannot be

Describe a chemical and physical structure of both an enveloped and a non enveloped virus

non enveloped

enveloped

Physical

chemical

Physical

Chemical

composed of capsid (protein) and nucleic acid (DNA or RNA)

capsid protect the viruses from nuclease enzymes in biological fluids and promotes the viruses attachment to susceptible host cells.

envelope that covers capsid consists of lipids, proteins, and carbs

envelope (lipid bilayer) covers capsid

capsid made of capsomeres

nucleic acid - Capsomeres - Envelop - Spikes (only on some)

capsids are NOT covered by an envelope

nucleic acid - capsid (made of capsomeres

Describe how bacteriophages are cultured

media type

bacteriophages can be grown in liquid OR solid media

How they are grown

bacteriophages form viral plaques on a lawn of bacteria. The bacteriophage viruses replicate and spread in order to form regions of cell destructions aka visible plaques

Describe how animal viruses are cultured

living animals

embryonated eggs

a hole is drilled into shell, virus is then injected into the fluid of the egg. Viral growth is indicated by the death of the embryo or embryo cell damage.

animal is infected with virus then observed

cell structures

cells grown in culture media using continuous cell lines and observed at lab

list three techniques used to identify viruses

cytopathic effects

serological tests

nucleic acids

detect antibodies against viruses in a patient

looks for structural changes in host cells that had been invaded

use antibodies to identify viruses in neutralization tests, viral hemagglutination, and western blot

using PCR/sequencing

Describe the lytic cycle of T-even* bacteriophages

1. Attachment: Phage attaches to host cell

2. Penetration: Phage penetrates host cell and injects its DNA

3. Biosynthesis: Phage DNA directs synthesis of viral components by the host cell

4. Maturation: Viral components are assembled into virions

5. Release: Host cell lyses (breaks down) , and new virions are released

*T2, T4, T6 etc.

Describe the lysogenic cycle of bacteriophage lambda

1. Phage attaches to host cell and injects DNA

2. Phage DNA circularizes and enters the lysogenic cycle

3. Phage DNA integrates within the bacterial chromosome through recombination, becoming a prophage

4. Lysogenic bacterium reproduces normally

5. Many cell divisions occur; occasionally the prophage may excise from the bacterial chromosome by another recombination event, initiating a lytic cycle

Compare and contrast the multiplication cycle of DNA and RNA containing animal viruses

DNA

RNA

1. Attachment: virion attaches to host cell

1. Attachment

2. Entry and uncoating: virion enters the cell and DNA is uncoated

2. Entry and uncoating: ssRNA: + or sense strand, ssRNA: - or antisense strand, dsRNA: + or sense strand with - or antisense strand

3. A portion of viral DNA is transcribed, producing mRNA that encodes early viral proteins.

4. Biosynthesis- Viral DNA is replicated, and some viral proteins are made.

5. Late translation: Capside proteins are synthesized.

6. Maturation- virions mature.

7. Release- virions are released.

3. RNA replication by viral RNA-dependent RNA polymerase.

4. Translation and synthesis of viral proteins

5. maturation and release

Define oncogene and transformed cell

Oncogene: a gene that has the potential to cause cancer

Transformed cell: Cells that acquire properties that are distant from the properties of unaffected cells; increased growth, loss of contact inhibition

Discuss the relationship between DNA and RNA containing viruses and cancer

Around 10% of cancers are caused by viruses

Genetic material of oncogenic viruses becomes integrated into the host cells DNA

DNA viruses include: HPV and Hep B

RNA retroviruses are oncogenic: HTLV 1 and 2

activated oncogenes transform normal cells into cancer cells

Discuss how a protein can be infectious

Prions: Proteinaceous infectious particle

Inherited and transmissible by ingestion, transplant and surgical instruments

Normal proteins are PrP^c and abnormal is PrP^Sc

PrP^Sc enter a cell and change PrP^c to PrP^Sc which causes a buildup of the infectious protein

Describe the structure of influenza and how strains evolve due to antigenic shift and drift

Structure

Single stranded RNA

(-) strand

multiple RNA strands

types A, B and C

Antigenic shift:

the swapping of different forms

Antigenic drift:

the mutation of existing genes

Describe the structure and life cycle of SARS- CoV-2

structure

lifecycle

enveloped

+ ssRNA virus

unsegmented, ~ 30,000 base genome

structural proteins

spikes: helps virus gain entry into host cell

nucleocapsid: packages genomic RNA

envelope and membrane: assemble encapsidated RNA into viral particles

1. spike interacts and promotes viral uptake and fusion

2. release and uncoating of RNA

3. translation of non structural proteins

4. biogenesis of viral replication organelles

5. assembly/maturation, budding, exocytosis/viral release

Describe the evolution of SARS-CoV-2 from other coronaviruses and the emergence of new variants

zoonotic origin: transferred from animals (in this case bats) to humans

genetic recombination occurred

new variants emerged from shift and drift

List three positive roles of viruses in nature

they serve as predators in microbial communities to help maintain microbial diversity and stimulate nutrient cycling

They help stimulate genetic diversity because they can carry useful genes

domesticated retroviruses play a major role in eukaryotes

commensal viruses and human health: enteric viruses restored immune function and normal intestinal morphology in mice