VIRUSES

Lecture 11 Exam 1

UIC BioS 101 Nyberg

VIRUSES

Viruses can replicate only in a living cell. They require molecules made by their hosts for transcription and translation. Virus are, therefore, not considered to be organisms.

Speaker Notes:

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Reading Assignment

Chapter 35 up to p. 786, including Box 35.3.
Read Bioskills 8, B14- B16 on electron microscopy.

- Monday, 16 Feb 09, is the first BioS 101 exam.
- There will be a seating chart (according to your teaching assistant).
- Complete the scantron answer sheet information at the beginning of the exam. Do not wait until the end of the exam.

Speaker Notes:

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Why viruses don’t have scientific names

Viruses can multiply only within the cells of host organisms.
Viruses don’t have any metabolism outside of a host cell.
Viruses don’t have an independent ‘tree of life’ that links them all together, but viruses definitely evolve.

Speaker Notes:

Viruses had to evolve after there were organisms. In many cases they seem to be minimal collections of genes.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Plasmids

Plasmids, usually circular DNA, can infect certain cells.
Plasmids never form a capsid (protective cover). –that distinguishes them from viruses.
The R plasmid carries resistance to many antibiotics and spreads from benign bacteria to species that cause disease.

Speaker Notes:

Benign = a mild type that does not threaten health

R plasmids protect bacteria from antibiotics. Human disease is increased when bacteria are protected.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Viruses are smaller than cells

Because they are small, the abundance of viruses is very high (see picture on p 769).
Small particles essentially float in air.
Viruses get from person to person by air and direct contact. I know of no human viruses primarily transmitted by water.

Speaker Notes:

Though viruses are typically specific to a type of cell, they often can attack many species.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Viral diseases

When a disease effects a large number of individuals at the same time it is referred to as an epidemic.
A virus or organisms that is able to kill the host after infection is called virulent.
A big epidemic was the ‘Spanish Flu” of 1918-1919.

Speaker Notes:

Viral diseases need to find uninfected hosts to persist. Vaccination has made it possible to eliminate some diseases.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Structure of Viruses

All viruses store hereditary information in nucleic acids, but only a small proportion of viruses use double-stranded DNA.
All viruses have a protein coat called a capsid.
Enveloped viruses are surrounded by a lipid layer derived from the host. The others are said to be nonenveloped.

Speaker Notes:

Double stranded DNA is the hereditary material in all organisms.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Reverse transcriptase

Some viruses use RNA to store information.
Many of these viruses, HIV included, make DNA complementary to the RNA. This is done with an enzyme call ‘reverse transcriptase’ (because it copies info from RNA to DNA the opposite of transcription.)
Reverse transcriptase has been a very important enzyme for research.

Speaker Notes:

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Entry of viruses into cells

Breathing, wounds and bites are ways viruses can initially get inside an individual, but this does not tell us how the virus spreads among cells of the body.
Cells have proteins on their surface (doing many tasks). Most viruses attach to particular proteins and enter the cell thru that attachment.

Speaker Notes:

Most viruses can infect a host only in certain ways. As the paths of infection are understood one can devise protection schemes that are more effective.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Ways of slowing disease spread

Public health involves protecting the population from disease.
Quarantine is an effective means of stopping the spread of many viral diseases.
For diseases that spread by intimate contact developing a list of contacts is information that can be used to combat the spread.

Speaker Notes:

The spread of venereal disease can be limited by finding probable infected individuals and treating them.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Vaccination & Immune system

The immune system defends the body against ‘exotic’ molecules.
- One’s own molecules were inventoried early in life.
The immune system primarily recognizes proteins as they have many shapes.
Continued detection of the exotic molecule results in a stimulation of the cells that recognize it to grow and become more abundant.

Speaker Notes:

Box 34.1 provides a good explanation to how immunization of an individual works.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Vaccination

Viral proteins, killed viruses or attenuated viral particles are injected into an individual.
The injected material stimulates the immune system to produce antibodies. The molecule the antibodies recognize is called an antigen.

Speaker Notes:

See Box 35.1

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Vaccination

Vaccination prepares the immune system to respond to a disease that it has not yet encountered.
People who have been vaccinated will respond by quickly producing antibodies if the virus infects them later.
Vaccinated individuals are said to be immune to a particular disease.

Speaker Notes:

What diseases have you been immunized against?

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Population dynamics

Contagious diseases typically can spread from individual to individual only a a particular stage or time period.
If many individuals are immune to a disease the rate of spread is reduced. At some point the disease dies out because it can find no never-infected individuals.

Speaker Notes:

Timing is almost always important in biology.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

The Lytic Cycle of bacteriophage

Nucleic acid injection
Nucleic acid replication
Translation into protein
Capsid proteins surround nucleic acid.
Host cell bursts open and the viral particles are released.

Speaker Notes:

Viruses that infect bacteria are known as phages.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Lysogenic replication is alternative to lytic cycle

Sometimes viral DNA integrates into the host DNA instead of replicating and making more viruses.
In that state it causes no problems to host and does not produce viral proteins -until something causes it to ‘pop out’ of host DNA.

Speaker Notes:

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Emerging viruses emerging diseases

Diseases are NOT permanent components of the human ‘landscape’.
Most of the viral diseases that we are concerned with today did not exist as human diseases a few hundred years ago.
A pathogen that jumps from animal into human populations is called a zoőnosis.

Speaker Notes:

Viruses most particular proteins to enter cells. Many species may share the same protein family.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

New Viral Diseases

Hanta virus
Ebola virus
West Nile virus
HIV
SARS
- Severe acute respiratory syndrome
  - Severe = serious, really sick
  - Acute = rapid progression from onset to really sick

Speaker Notes:

Syndrome = set of concurrent things that from an identifiable pattern

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Origin of a new disease

How does one figure out the probable source of a new viral disease?
- Identify the earliest cases.
- Look for common elements shared among the earliest cases.
- Use knowledge/experience of other epidemics to focus on likely common elements.
- Look for homologous nucleic acid sequences in the putative source(s).

Speaker Notes:

Trying to figure out the animal ‘reservoir’ of a new human disease.

Lecture 11 Exam 1

UIC BioS 101 Nyberg

Vocabulary

Acute
Antibody
Antigen
Epidemic
Host
Lysis
Mutation

Plasmid
Public health
Reverse transcriptase
Severe
Syndrome
Vaccination
Virulent

Speaker Notes: