Cells - Binary Fission and Viral Replication

Question 1

How does cell division take place in prokaryotic cells?

Answer 1

By a process called binary fission.

Question 2

What is binary fission?

Answer 2

1. The cell elongates and the circular DNA molecule replicates and both copies attach to the cell membrane.
2. The plasmids also replicate.
3. The cell membrane begins to grow between the two DNA molecules and begins to pinch inward, dividing the cytoplasm into two.
4. A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of the circular DNA and a variable number of copies of the plasmids.

Question 3

How do viruses replicate?

Answer 3

As viruses are non-living, they cannot undergo cell division. Instead they replicate by attaching to their host cell with the attachment proteins on their surface. They then inject their nucleic acid into the host cell. The genetic information on the injected viral nucleic acid then provides the ‘instructions’ for the host cell’s metabolic processes to start producing the viral components, nucleic acid, enzymes and structural proteins, which are then assembled into new viruses.

Question 4

Compare cell division in eukaryotes, prokaryotes, and viruses.

Answer 4

EUKARYOTES

• mitosis
• spindle fibres arrange chromosomes
• genes contain introns and exons
• cytoplasm divided between daughter cells
• organelles divided between daughter cells
• pairs of homologous chromosomes
• copied chromosomes pulled to ends of cell

PROKARYOTES

• binary fission
• no membrane bound organelles
• plasmids
• cytoplasm divided between daughter cells
• single circular chromosome
• copied plasmids shared between daughter cells
• genes don’t contain introns and exons
• copies chromosomes pulled to ends of cell

VIRUSES

• reproduced by a cell host cell
• no membrane bound organelles
• small linear DNA or RNA
• genes don’t contain introns and exons