Topic 2.2 Prokaryotic Cells

Question 1

2.2.1 Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.

Answer 1

Question 2

2.2.2 What is the function of a cell wall?

Answer 2

• Rigid outer layer of peptidoglycan (carbohydrate-protein complex) that maintains shape and protects cell from damage or bursting if internal pressure is high
• Some bacteria have additional layer of a type of polysaccharide outside cell wall (allows bacteria to adhere to structures e.g. teeth, skin and food)

Question 3

2.2.2 What is the function of a plasma membrane?

Answer 3

• Semi-permeable membrane inside cell wall with similar composition to membranes of eukaryotic cells
• Controls movement of materials in and out of the cell
• Involved in binary fission

Question 4

2.2.2. What is the function of cytoplasm?

Answer 4

• Fluid component which contains enzymes needed for all metabolic reactions
• Occupies complete interior of cell
• No compartmentalization in cytoplasm ∴ all cellular processes in prokaryotic cells occur in cytoplasm

Question 5

2.2.2 What is the function of pili (sin. = pilus)?

Answer 5

Hair-like growth on outside of cell wall

• Attachment pili: shorter length, allow bacteria to adhere to one another or to available surfaces
• Sex pili: longer length, joins bacterial cells to allow for the exchange of DNA via a process called bacterial conjugation

Question 6

2.2.2 What is the function of flagella (sin. = flagellum)?

Answer 6

Long, slender projection containing a motor protein which spins the flagella like a propellor, enabling cell motility

Question 7

2.2.2 What is the function of ribosomes?

Answer 7

• Composed of 2 subunits equal to 70S in prokaryotes
• Sites of protein synthesis

Question 8

2.2.2 What is the function of the nucleoid?

Answer 8

• Region of cytoplasm which contains prokaryotic DNA (genophore)
• DNA is single, long, continuous, circular, double stranded thread
• Cell control and reproduction

Question 9

2.2.2 What is the function of plasmid?

Answer 9

• Small, circular, double stranded DNA molecules existing and replicating independently from genophore
• Not required under normal conditions, but may help cell adapt to unusual circumstances (e.g. key carry antibiotic resistance gene)
• Can be transmitted between bacterial species

Question 10

2.2.3 Identify structures from 2.2.1 in electron micrographs of E. coli.

Answer 10

Question 11

2.2.4 How do prokaryotic cells divide?

Answer 11

By binary fission.

(Circular DNA is copied → two daughter chromosomes become attached to different regions on plasma membrane → membrane elongates and divides (cytokinesis) into 2 genetically identical daughter cells. Includes partitioning of newly produced DNA by microtubule-like fibres made of protein called FtsZ.)