Meningitis and Phase Variation Recap genes and proteins

Meningitis and Phase Variation

Recap: genes and proteins G A C T C T G A C U G A T A C A T G A U G DNA RNA Proteins

Recap: immunity Molecules on the surface of bacteria are called antigens B cells

Recap: immunity Molecules on the surface of bacteria are called antigens Cells of the immune system recognise antigens and produce antibodies Antibodies bind to the bacteria’s antigen and kill them B cells

What is Meningitis Infection of the membranes around the brain and spinal cord Main cause is a bacteria called Neisseria meningitidis

What are the symptoms? Fever Headache Neck stiffness

Neisseria meningitidis Found in the throats of healthy people. Only causes disease in rare cases. Must have a way for its antigens to go unnoticed until it causes disease Microscope image of N. meningitidis

Phase variation = switching genes ON or OFF. Caused by reversible mutation Off On Mutation

What does phase variation look like? One cell will divide into two daughter cells With every division, there is a chance they will mutate (mutation rate) Mutation is random. Like rolling a dice This mutation will be passed down to the daughter cells

What does phase variation look like? It is a reversible process

What does phase variation look like? Many bacteria have more than one phase variable gene Both genes can mutate at the same time Mutation isn’t this quick in real bacteria.

How does this make the population look? All of the different cells have the same DNA but have different antigens expressed.

How does phase variation happen? -Slippery DNA Poly G tract THE CAT AND THE DOG 6 G’s Deletion 5 G’s GGG AGC CGA CCG THE ATA STOP NDT HED OG GGA GCC GAC CG - ON Reversible OFF

How can phase variation benefit bacteria?

How can phase variation benefit bacteria? Switching some genes off can help the bacteria to escape the immune system.

What genes can be phase variable? There are lots of different genes that can be phase variable Some examples in N. meningitidis are genes involved in: Taking up nutrients such as iron Sticking to the host cells Many of these genes are involved in causing disease