Bacteria and viruses

Bacteria and Viruses•Distinguish between the structure of bacteria and viruses•Describe the role of microorganisms in the decomposition of organic matter and recycling of carbon

Bacteria

Main features of prokaryotes

Key features• No nucleus• DNA in simple ring structure free in cytoplasm• Cell wall present, not made of cellulose but peptidoglycans

( polymer of sugar and amino acids)• Cell membrane controlling passage of substances into and out of

the cell• Lack of membrane bound organelles• Infolding of the cell membrane called mesosome is the site of

respiration• Ribosomes (18nm diameter) free in cytoplasm are the sites of

protein synthesis• Cell size – 0.5 and 5 µm• Cells divide by binary fission with no spindle formation

Gram positive and gram negative bacteria

One of the major differences between types of bacteria is the ability to stain their cell walls using a procedure called Gram staining.Bacteria which have cells walls which take up the stain = Gram positiveThose that do not = gram negative

Useful as both types of bacteria respond differently to antibiotics.

Gram Negative bacteria

E.g. E-Coil

Thinner layer of peptidoglycan and no teichoic acid between two layers of membrane, then outer layer of lipopolysaccharides

Stain does not stick

Viruses

• Smallest microorganism• 0.02-0.3µm across• 50x smaller than average bacterium• Not cells• Arrangement of protein and genetic material• Invade other cells take over biochemistry to

make more copies.

Viruses

Viruses

Features of viruses• Have a protein coat (capsid) around a core

containing nucleic acid and virus enzymes• Lack of internal membranes, cytoplasm and

ribosomes• Some have an outer envelope taken from the

host’s cell surface membrane – it contains lipids and proteins

• Viral envelopes have glycoproteins which are recognised by the host immune system – helps virus attach to cell and penetrate the membrane