Topic 2 Cells :2.1.2 Structure of prokaryotic cells and of viruses

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

Question 2

Describe the general structure of prokaryotic cells

Answer 2

sometimes present :
- capsule
- plasmids
- flagella

always present :
- cell surface membrane
- cell wall
- 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 cell :

Has membrane-bound organelles
eg. mitochondria, endoplasmic reticulum

Has a nucleus
Containing DNA

DNA is long & linear
& associated with histone proteins

Larger (80S) ribosomes (in cytoplasm)

Cell wall only in plants, algae and fungi
Containing cellulose or chitin

Plasmids / capsule never present
(sometimes flagella)

Larger overall size

Prokaryotic Cell :

No membrane-bound organelles
eg. no mitochondria, endoplasmic reticulum

No nucleus
DNA is is free in cytoplasm

DNA is short & circular
& not associated with proteins

Smaller (70S) ribosomes

Cell wall in all prokaryotic cells
Containing murein, a glycoprotein

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
● Non-living - have no metabolism, cannot independently move

Question 5

Describe the general structure of a virus particle

Answer 5

1. Nucleic acids surrounded by a capsid
   (protein coat)
2. Attachment proteins allow attachment
   to specific host cells
3. No cytoplasm, ribosomes, cell wall,
   cell-surface membrane etc.
4. Some also surrounded by a lipid
   envelope eg. HIV