Stages in multiplication of T4 bacteriophage.PPT

Morphology: Icosahedral head and helical tail
Tail has contractile tail sheath.
Genome: ds DNA with terminal redundancy
Has unusual base ‘5-hydroxymethyl cytosine’.
Host: Non-motile strain B of E. coli
Stages involved in multiplication:
1. Adsorption
2. Penetration
3. Biosynthesis
4. Assembly
5. Release

1. Multiplication of T4
bacteriophage

2. Bacteriophage
Bacteriophage:Bacteria eating viruses
Two types of bacteriophages:
1.Lyticphage (Virulent/ non-temperate)
2.Lysogenicphage (Avirulent/ temperate)

3. T4 bacteriophage
Morphology: Icosahedralhead and helical tail
Tail has contractile tail sheath.
Genome: dsDNA with terminal redundancy
Has unusual base ‘5-hydroxymethyl cytosine’.
Host: Non-motile strain B of E. coli

5. Steps in multiplication cycle of T4 bacteriophage
1.
•Adsorption
2.•Penetration
3.•Biosynthesis
4.•Assembly
5.•Release

6. 1. Adsorption
Antireceptorsites:
Tail fibres, tail proteins, icosahedronspikes
Receptor sites:
T
3, T
4 and T
7-Lipopolysaccharidecomponents
T
2, T
6–Lipoprotein components
T
5–Both lipoprotein and lipopolysaccharide

7. Adsorption occurs by random collision between phage and host cell.
Tail fibres are folded by whiskers.
Unfolding requires tryptophan.
Tail fibres recognize receptor site during attachment.
Attachment occurs by electrostatic force of interaction.

9. Pinning:
Initial attachment is weak and reversible.
When tail pins comes in contact with lipopolysaccharide.

10. 2. Penetration
1.Tail contraction:
Tail sheath contracts, becomes
short and thick.
2. Core penetration:
Tail tube passes through the
cell wall.
3. Injection of DNA
DNA injected like syringe.

11. Biosynthesis
Divided into 3 steps:
A.Early mRNA translation
1. Immediate early mRNA translation
2. Delayed early mRNA translation
B. Replication of phage genome
C. Late mRNA translation

12. A.Early mRNA translation:
1.Immediate early mRNA translation
Nucleases: Exonucleaseand endonucleases
The α-subunit modifying enzyme:
ADP ribosyl
NADP

13. 2. Delayed early mRNA translation
Deoxycytidylatehydroxymethylase: Hydroxymethylcytosine
Polymerase and ligase
DNA glycosyltransferase: Glycosylationof HMC
Sigma subunit modifying enzyme for late mRNA transcription.

14. Replication
Begins after 6 minutes of infection and reaches at 10-12
minutes.
Initial replication is bi-directionaland semi-discontinous.
Later on replication occurs by “rolling circle mechanism”.

15. Bidirectional replication

16. Rolling circle replication

17. C. Formation of late proteins
After replication of phage DNA, transcription of late mRNA
occurs.
These mRNA translate to different proteins.
These proteins includes:
Structural proteins, proteins involved in assembly, holin
proteins

18. 4. Assembly
The process of assembling is also known as “maturation”.
4 pathways leads to formation of phage particle:
a.Base plate formation
b.Tail tube and sheath formation
c.Tail fibres formation
d.Head formation

20. 5. Release
Release of newly formed phage particles occurs by sudden
bursting of host cells.
Lysisbegins after 22 minutes.