Lytic Lifecycle of a Virus

AHL BiologyOption F

Let´s REVIRUS!!! (revise the virus)

• How many questions can you get right on this quiz?

11

DNAviruses

RNAviruses

ds DNA ss RNA ss RNAss DNA

RNA DNAviruses

ss RNA(Retroviruses)

ds DNA(hepadnaviruses)

Viral genomes

• genome is template for mRNA

• genome is template for DNA synthesis ("retrovirus")

• Requires reverse transcriptase to change RNA into DNA

Virulent phages only undergo a lytic cycle

Temperate phages can follow both cycles

Prophage can exist in a

dormant state for a long time

It will undergo the lytic cycle

Bacteriophage

Lytic phages – add notes to your diagram as we go through the next few slides

Clockwise: Pseudomonas aeruginosa phage; Aeromonas phage; Shigella K II phage; Listeria phage

Life Cycle of a Lytic Phage

Step 1 Adsorption: virus attaches to the cell wall surface

Step 2 Penetration: entry of the viral DNA

Phage T4 adsorption to the cell wall of E. coli

Life Cycle of a Lytic Phage

Step 3 Synthesis of early viral proteins

Step 4 Replication of viral DNA

Phage T2 attacks E. coli

Life Cycle of a Lytic Phage

Step 5 Synthesis of late viral proteins

Step 6 Assembly

Step 7 Lysis and release of mature viruses

Lysis of E. coli cell by Phage T4

Life Cycle of a Lytic Phage

Antibiotics and their mode of action

MRSA

•Methicillin-resistant Staphylococcus aureus

•Resistance to beta-lam antibiotics which include the penicillins and cephelasporins

•MRSA is especially troublesome in hospitals where patients with open wounds, invasive devices and weakened immune systems are at greater risk of infection than the general public.

Superbug gone rogue…

Questions to consider….• What is the situation with regard to MRSA?

-Is it emerging? -Highly prevalent? -Why do you think the issue has gained so much press right recently?

• Do you think that the message that recent articles about MRSA disease highly publicised in the news were talking about risks associated with sick, hospitalized patients and not the public at large came through?

• Do you think that the media has portrayed a reliable representation of the threat of MRSA?