Prokaryotic cells and viruses

structures always present in bacteria

• murein/peptidoglycan cell wall

• cell-surface membrane

• cytoplasm

• circular DNA

• 70S ribosomes

structures found in SOME bacteria

• flagella

• capsule

• mesosomes (infolding of cell-surface membrane)

• plasmids

• pili

function of plasmids

the genes they contain can be passed between prokaryotes

function of capsule

protects the bacteria from drying out, protects it from attacks from immune system cells of the host organism

structure of viruses

• nucleic acid core

• capsid - protein coat

• some have a lipid envelope - usually formed from the membrane-phospholipids from the cell they were made in

• attachment proteins on the capsid/envelope - these allow the virus to identify and attach to the host cell

viral replication

• viruses are parasitic

• they use attachment proteins to complementary receptor proteins on the surface of a host cell

• they inject their DNA or RNA into the host cell

• the ribosomes in the host cell use this nucleic acid to build new viral particles

• the host cell bursts open, releasing all of the viral particles

• sometimes viral particles leave by budding, when they take a section of the cell-surface phospholipid membrane with them to become their envelope