Prokaryotic cellsBacteria

The parts of a prokaryotic cell

Cell wallMade of a peptidoglycan called murein. This is laid down as a network of polysaccharide fibres.

A strong layer that prevents the cell from bursting and excludes certain substances

Cell surface membrane Normal fluid mosaic structure

Controls the passage of substances in and out of the cell. Can be folded inwards to give additional surface area to house molecules involved in respiration reactions

Genetic material A circular strand of DNA To control the cell

Ribosomes These are a smaller type (70S) than those found

in eukaryotic cells

Protein synthesis

Capsule Protects against chemicals and

desiccation. Also protects the bacterium

from attack by phagocytic cells such as our white blood cells.

flagellum Made of a single, long fibre up to 20 µm long. These may be present singly, at one or both

ends or even all over the cell.

Parts continued

pili Fine threadlike structures attached to

the capsule or cell wall. Up to 1 µm long

For attachment to surfaces

plasmids Small loops of DNA Carry some additional genes. This is where genes giving antibiotic resistance would be found. Used in genetic engineering for

transferring foreign genes into bacterial cells

Oil droplets/glycogen granules

As a food store

Parts continued

Microorganisms can cause disease by damaging the cells of the host and by producing toxins

Mycobacterium tuberculosis is a Gram-positive, rod-shaped bacterium and the cause of

tuberculosis in humans

Tuberculosis is primarily an airborne disease; it is spread from person to person

by droplet infection when an active TB sufferer coughs and sneezes

The most common salmonellosis is enterocolitis, caused principally by Salmonella enteriditis and

Salmonella typhimurium.

Food poisoning caused by S. enteriditis and S. typhimurium occurs when these bacteria are present in sufficient numbers in consumed food. A bacterial load of 100,000 per gram of food is

sufficiently high for many of the bacteria to survive the digestion process, and to continue multiplying within the gut.