3.2.1.2 Stucture of prokaryotic cells and of viruses (3.2 cells)

Question 1

What are the distinguishing features of prokaryotic cells ?

Answer 1

• Cytoplasm lacking membrane - bound organelles
• So genetic material not enclosed in a nucleus
Examples of prokaryotic organisms : bacteria and archaea

Question 2

Describe the general structure of prokaryotic cells

Answer 2

Sometimes present :
- Capsule
- Plasmids = small rings of DNA
- Flagella

Always present :
- Cell surface membrane
- Cell wall = contains murein , a glycoprotein
- Cytoplasm
- Small ribosomes
- Circular DNA = free in cytoplasm , not associated with proteins

Question 3

Compare and contrast the structure of eukaryotic and prokaryotic cells

Answer 3

Eukaryotic:
• Has membrane bound organelles
• Has a nucleus
• DNA is long and linear and associated with histone proteins
• Larger ribosomes
• Cell wall only in plants , algae and fungi containing cellulose or chitin
• Plasmids / capsule never present
• larger overall size

Prokaryotic :
• No membrane bound organelles
• No nucleus , Dna is free in cytoplasm
• DNA is short and circular and not associated with proteins
• Smaller ribosomes
• Cell wall in. all prokaryotic cells containing murein
• Plasmids , flagella and a capsule sometimes present
• Much smaller overall size

Question 4

Explain why viruses are described as acellular and non living

Answer 4

• Acellular = not made of cells , no cell membrane / cytoplasm /organelles
• Non living = Have no metabolism , cannot independently move / respire / replicate / excrete

Question 5

Describe the general structure of a virus particle

Answer 5

1) nucleic acids surrounded by a capsid
2) Attachment proteins allow attachment to specific host cell
3) no cytoplasm , ribosomes , cell wall , cell surface membrane
4) Some also surrounded by a lipid envelope