3.2.1.2 Structure of prokaryotic cells and of viruses

What are the organelles that are always present in a bacterial cell?

• Cell wall- containing peptidoglycan

• Cell-surface membrane

• Cytoplasm

• Circular DNA

• Ribosomes

What are the organelles that are sometimes present in a bacterial cell?

• Flagellum- motion

• Capsule-protection

• Infolding of cell surface membrane - may allow photosynthesis or carry out nitrogen fixation

• Plasmid- small circle of DNA

• Pili- for attachment to other cells or surfaces, involved in sexual reproduction

Sizes

• Prokaryotic cells are extremely small, less than 0.002 mm

• Eukaryotic cells can be up to 50 times bigger, around 01 mm

Similarities in eukaryotic and prokaryotic cells

• Ribosomes

• DNA

• Cytoplasm

• Cell membrane

• Some have flagella

What process do prokaryotic cells replicate by?

Binary fission, where the cell replicates its genetic material, before physically splitting into 2 daughter cells

Binary fission - step 1

• The circular DNA and plasmids replicate

• The main DNA loop is only replicated once, but plasmids can be replicated a lot of times

Binary fission - step 2

The cell gets bigger and the DNA loops move to opposite poles (ends) of the cell

Binary fission - step 3

The cytoplasm begins to divide and new cell wall begins to form

Binary fission - step 4

• The cytoplasm divides and 2 daughter cells are produced

• Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmids

Viruses

• Not alive

• Acellular

• Nucleic acids surrounded by protein

• Invade and reproduce inside the cells of other organism

• Smaller than bacteria

Viruses - structure

• Attachment proteins

• Capsid

• Genetic material ,either DNA or RNA

Virus division - 1

• Attachment : the virus attaches to the surface of the host cell

Virus division - 2

• Entry: the viral DNA/RNA enters the host cell

Virus division - 3

• Replication: viral DNA/RNA replicates and new viral proteins are made ( forming new capsids)

Virus division - 4

• Assembly: new viral particles are assembled

Virus division - 5

• Release: host cell lyses (bursts) releasing the newly made viruses