2.1.2 Strucute Of Prokaryotic Cells And Of Viruses

Question 1

What are the distinguishing features of a prokaryotic cell

Answer 1

• cytoplasm lacking membrane - bound organelles
• so genetic material not enclosed in a nucleus

Question 2

Describe the structures always present in prokaryotic cells

Answer 2

• cell membrane
• cell wall
  
  • contains murein
• cytoplasm
• small ribosomes
• circular DNA
  
  • free in cytoplasm
  • not associated with proteins

Question 3

Describe the structures sometimes present in prokaryotic cells

Answer 3

• capsule
• plasmids
• flagella

Question 4

Compare and contrast eukaryotic and prokaryotic cells

Answer 4

Eukaryotic:
- has membrane bound organelles e.g. mitochondria, endoplasmic reticulum
- has a nucleus containing DNA
- DNA is long & linear & associated with histone proteins
- larger (80s) ribosomes I’m cytoplasm
- cell wall only in plants, algae and fungi
- containing cellulose or chitin
- plasmids / capsule never present (sometimes flagella)
- larger overall size
Prokaryotic cells:
- no membrane bound organelles
- no nucleus
- DNA is free in cytoplasm
- DNA is short & circular & not associated with proteins
- smaller (70s) ribosomes
- cell wall in all prokaryotic cells
- containing murein
- plasmids, flagella and a capsule sometimes present
- much smaller overall size

Question 5

Explain why viruses are described as acellular and non living

Answer 5

• acellular - not made of cells, no cell membrane / cytoplasm / organelles
• non-living - have no metabolism / cannot independently move / respire / replicate / excrete

Question 6

Describe the general structure of a virus particle

Answer 6

1. Nucleic acids surrounded by a capsid
2. Attachment proteins allow attachment to specific host cells
3. No cytoplasm, ribosomes, cell wall, cell-surface membrane
4. So,et also surrounded by a lipid envelope e.g. HIV