2.1.2 structure of prokaryotic cells and viruses

Question 1

what are examples of prokaryotic organisms

Answer 1

bacteria and archaea ( always unicellular )

Question 1

what are the distinguishing features of prokaryotic cells

Answer 1

cytoplasm lacking membrane bound organelle so genetic material is not enclosed in a nucleusn

Question 2

describe the general structure of prokaryotic cells

Answer 2

• cell surface membrane
• cell wall containing murein and a glycoprotein
• cytoplasm
• small ribosomes
• circular DNA which is free in cytoplasm and not associated with any proteins
• capsule ( sometimes present )
• plasmids which are small rings of DNA ( sometimes present )
• flagella

Question 3

compare and contrast the structure of eukaryotic and prokaryotic cells

Answer 3

• eukaryotic cells have membrane bound organelles such as mitochondria whereas prokaryotic cells dont
• eukaryotic cells have a nucleus containing DNA whereas prokaryotic cells dont and their DNA is free in the cytoplasm
• DNA in eukaryotic cells is long, linear and associated with histone proteins whereas in prokaryotic cells DNA is short circular and not associated with proteins
• eukaryotes have larger 80s ribosomes in the cytoplasm whereas prokaryotes have smaller 70s ribosomes
• in eukaryotes only plants, algae and fungi have cell walls which contain cellulose or chitin whereas in prokaryotes they all contain a cell wall containing murein and a glycoprotein
• in eukaryotes plasmids and capsule are never present however sometimes present in prokaryotic cells
• eukaryotes have a larger overall size than prokaryotes

Question 4

why are viruses described as acellular and non living

Answer 4

• they are acellular because they are not made out of cells since there is no cell membrane, cytoplasm or organelles
• they are non living because they have no metabolism, cannot independently move, respire, replicate or excrete

Question 5

describe the general structure of a virus particle

Answer 5

• nucleic acid surrounded by a capsid ( protein coat )
• attachment proteins allowing attachment to specific host cells
• no cytoplasm, ribosomes, cell wall or cell surface membranes
• some surrounded by a lipid envelope eg. HIV