Bacterial cell

Bacterial cell

The structure of a bacterial cell is studied at IGCSE and at A level.

At IGCSE you mainly need to be able to label up a bacterial cell and have a basic knowledge of what the different parts do. At A level you need to have a much greater understanding.

This is the structure of a typical bacterial cell. Image supplied by Alila Medical media. Click on the link to see more images of cells.

Bacteria structure

Capsule

The bacterial cell is covered in a slime capsule. This capsule helps to protect the bacteria against attack from antibiotics. Antibiotics are naturally produced by other microorganisms. However, we as humans have used this information to produce antibiotics as drugs.

Cell Wall

The cell wall of a bacterial cell is not made of cellulose like a plant cell wall. It is also not made of Chitin like a fungal cell wall is made. Instead a bacterial cell wall is made up of peptidoglycan or murein.

Cell Membrane

This controls the movement of substances into and out of the bacterial cell.

Flagella

These allow the bacterium to propel itself forward.

Ribosomes

These carry out protein synthesis. However, it should be noted that in a bacterial cell they are slightly smaller 70s.

DNA

The DNA in a bacterial cell is not in a nucleus, nor are there any membrane bound organelles. Instead the DNA is as a single loop chromosome.

 Cytoplasm

This is a jelly like material where all of the cells chemical reactions take place.

AQA Biology only – Cholera

Cholera is caused by the bacterium Vibrio cholerae. The bacterium are normally present in contaminated water. This can be a problem where sewage has entered drinking water. Once the person ingests the contaminated water or food, the infection will begin. Most bacteria are killed by the acidic conditions of the stomach. However, some maybe resistant or the pH of the stomach maybe too high.

sewage

© Dmitry Vereshchagin – Fotolia.com

Once inside the gut they propel themselves through the mucus lining of the small intestine wall. The bacteria will produce a toxin which splits itself into two. One part binds to receptors on the epithelial cells. The other part enters the epithelial cells and causes the ion channel of the cell surface membrane to open.  This lets chloride ions move into the lumen of the gut from the epithelial cells. As a result the water potential of the gut will be much lower and so water moves by osmosis from the epithelial cells into the lumen of the gut. Also, due to the concentration gradient it will cause water from the blood and surrounding tissues to move into the lumen of the small intestine. This excess water in the small intestine will cause diarrhoea and dehydration.