Genetics of Viruses and BacteriaCh 19 & 20

Everything you need to know about

viruses.

Infected? With What?How can you tell?• Start with Symptoms: illness is abrupt and is

characterized by fever, headache, joint and muscle aches, sore throat, and weakness, followed by diarrhea, vomiting, and stomach pain. A rash, red eyes, internal and external bleeding from all orifices.

• Who is at risk? Persons on the southeast coast of Africa, Congo,Sudan, Zaire, and Uganda

• Treatment: No known treatment• Disease: Ebola Hemorragic Fever• Surveillance: CDC SPECIAL PATOGENS UNIT,

WHO EbolaOutbreakhistory

Infected? With What?How can you tell?• Start with Symptoms: Myalgia, fever,

headache, extreme tiredness, dry cough, sore throat, runny or stuffy nose, and muscle aches.

• Who is at risk? Everyone

• Treatment: Bed Rest and Fluids

• Disease: Influenza

• Surveillance: CDC and WHO

How the fluChanges.

Avian FluPBS

AntigenicShifts

The Bacteriophageor Phage

• Viruses that attack bacteria

Viruses: Are They Alive?

T4Invasion

Characteristics of Viruses

• Much smaller than a bacterium.• Have 2 essential structural

features: Nucleic Acid (DNA or RNA) and Protein Coat called a capsid surrounding it.

• Must have a host (host range) in order to propagate itself.

Viral Shapes Fig 19.3

Grouping VirusesFig 19.1

• Presence of a Capsid and Envelope

• Whether they contain RNA or DNA

• Shape

Virus Reproduction• DNA viruses can immediately

produce RNA to construct new viruses or become part of host’s DNA.

• RNA viruses must uses reverse transcriptase.

Hiv Replication

HIV is a retrovirus: uses reverse transcriptase.

Provirus: integrated viral DNA

Phage Lysogenic Cycle DetailsFig 19.6

• Virus replicates without destoying the host cell. – Prophage: Dormant virus within host (HIV)– Prophage switches to lytic phase.– Temperate viruses are capable of both lytic

and lysogenic cylces within a bacterium.

The Lysogenic Cycle

The LysogenicCycle

Phage Lytic cycle details.

• DNA replication produces more viral DNA

• Transcription and translation produce protein coats and glycoprotein spikes

The Lytic Cycle

Virus Evolution• Plasmids (circular DNA in bacteria and

Yeast), or Transposons (mobile DNA segments) may have escaped.

• May have originated when fragments of host genes escaped or were expelled from cells or from prions.

• Can mutate quickly.

• Treated with antivirals

• Prevented by vaccines.

Other non-life forms Viroids and Prions

• Viroids: the smallest particles that are able to replicate.

• A short, circular RNA that has no capsid

• They disrupt plant cell metabolism

• Prions: (PREE-ahnz) are misfolded proteins that clump together inside a cell. Normal proteins begin to fold and clump as well. The clumping kills the cell. Fig. 19.11

• Composed of about 250 amino acids and have no associated nucleic acid.

• Indestructible. Can’t destroy or deactivate through normal cooking temperatures.

• Prions cause scrapie in sheep, mad cows disease, and Creutzfeld-Jakob disease in humans

Good reviewClips

Of GeneralConcepts

Infected? With What?How can you tell?

• Start with Symptoms: Severe abdominal pain, weight loss, stomach ulcers, nausea and vomiting.

• Who is at risk? Everyone

• Treatment: Antibiotics

• Disease: Stomach Ulcers caused by H. Pylori

• Surveillance: Both National and International By CDC and WHO How it

Works

What are bacteria?

• Single celled microscopic prokaryotes

• Circular DNA condensed into a nuceoid. (no nuclear membrane)

• With or without a peptidoglycan in cell wall.

• Autotrophs or heterotrophs

How are bacteria named?

Shape:

Group Arrangement: Strepto= Chains Staphylo= Clusters

Parts of a bacteria.• All have a Cell Wall and Plasma

Membrane

• Cytoplasm, Pilli, Plasmid

• Some have Flagella and Capsules • May make Endospores when

dormant for protection.Bacterial

ConjugationDon’t Look!

Donating DNA

Conjugation:

primitive sexual method. Bacterial transformation. Discovered by Frederick Griffith 1927.

How do bacteria reproduce?

• Binary Fission = asexual.

• Replicate their DNA in Both directions from a single point of origin= Theta Replication, because it looks like Θ.

• Very few mutations. But reproduce often enough that mutations show up quickly.

What is a plasmids and what do they do?

• Plasmid: foreign, circular, self-replicating DNA molecule in a bacterium.

• Bacterium may have more than one plasmid.

• Express genes they carry– Create pilli = F plasmid– Resist antibiotics = R plasmid

What is an Operon?

• A set of genes found in bacteria and phages that combined with the promoter and operator express those genes.

• A gene regulation mechanism.• Jacob and Monod (1940) discovered the first

operon in E.coli. They found 2 types:– Lac operon: Inducible operon. Always off– Tryptophan operon: Repressible operon. Always on.– The correct signal will switch the Lac on or the

Tryptophan off.

Operon Operations

• Terms to know:

• Promoter: RNA polymerase binds to this region of the DNA

• Repressor: binds to operator preventing RNA polymerases attachment. Noncompetitive inhibition.

• Operator: Where the repressor attaches at the start of the bacterial operon.

Lac Operon Overview

The AP Version of the Lac Operon

The Lac operon: Inducible

• Job of the Lac operon: to utilize lactose turning it into glucose and glactose.

• Three enzymes necessary to do this:– B-galactosidase, permease, and transacetylase

• RNA polymerase must bind to the promoter to allow the cell to utilize lactose.– Allosteric effector, allolactose, acts as an inducer.

Allolactose binds to the repressor causing a conformation of the repressor. It can not longer repress.

• If a repressor binds to the operator (noncompetitive inhibition) lactose can not be utilized.

Tryptophan Operon: Repressible

• Continuously on unless switched off by a corepressor.

• rRNA polymerase binds to the promoter and transcribes.

• Repressor combines with the corepressor on the tryptophan gene it changes conformation, binds to the operator = RNA polymerase can not bind and transcription is blocked.

• Turned off when tryptophan levels are high, negative feedback.

Tryp Operon

What is an Allosteric effector?

• Tryptophan: Tryptophan Operon

• Lactose: Lac Operon

• The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.