Cell Structure and Division - Prokaryotic Cells and Viruses

Question 1

List and describe the components of a prokaryotic cell and their functions.
(7)

Answer 1

CYTOPLASM:
of a prokaryotic cell has NO membrane-bound organelles (unlike a eukaryotic cell).
It has RIBOSOMES – but they’re SMALLER than those in a eukaryotic cell.

PLASMA MEMBRANE:
Just like in a eukaryotic cell, it is mainly made of LIPIDS and PROTEINS.
It CONTROLS the MOVEMENT of substances INTO and OUT of the cell.

CELL WALL:
SUPPORTS the cell and prevents it from changing shape.
Made from MUREIN.
MUREIN is a GLYCOPROTEIN (a protein with a carbohydrate attached).

CAPSULE:
Some prokaryotes (e.g. BACTERIA) have a capsule.
Made up of a secreted slime.
Helps to PROTECT BACTERIA from attack by cells of the immune system.

PLASMIDS:
Small hoops of DNA that aren’t part of the main circular DNA molecule.
Contain genes for things like ANTIBIOTIC RESISTANCE, and can be passed between prokaryotes.
NOT ALWAYS PRESENT in prokaryotic cells.
SOME prokaryotes have several.

CIRCULAR DNA:
No nucleus. 
DNA floats freely in the cytoplasm.
One long, coiled-up strand.
Not attached to any histone proteins.

FLAGELLUM:
A long, hair-like structure that rotates to make the prokaryotic cell MOVE.
NOT ALWAYS PRESENT in prokaryotic cells.
Some have more than one.

Question 2

What is a virus made up of?

Answer 2

Viruses are just NUCLEIC ACIDS surrounded by PROTEIN.
They’re not even alive.

• Viruses contain a core of genetic material – either DNA or RNA.
• The protein coat around the core is called the capsid.
• Attachment proteins stick out of the edge of the capsid.
  These let the virus cling on to a suitable host cell.

______________________________
They’re even smaller than bacteria – e.g. HIV is about 0.1 micrometres across.

Unlike bacteria, viruses have no plasma membrane, no cytoplasm and no ribosomes.

Question 3

Prokaryotic cells replicate via …

Answer 3

Prokaryotic cells replicate by

BINARY FISSION.

Question 4

Describe the process in which prokaryotic cells replicate.

Answer 4

In BINARY FISSION, the cell replicates its GENETIC MATERIAL,
before physically SPLITTING into two daughter cells.

1 - The circular DNA and plasmid(s) replicate.
The main DNA look is only replicated once.

2 - The cell gets bigger and the DNA loops move to opposite ‘poles’ (ends) of the cell.

3 - The cytoplasm begins to divide (and new cell walls begin to form).

4 - The cytoplasm divides and two daughter cells are produced.
Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s).

Question 5

How do viruses replicate?

Answer 5

1 - Viruses use ATTACHMENT PROTEINS to BIND to COMPLEMENTARY RECEPTOR PROTEINS on the surface of HOST CELLS.

2 - Different viruses have different attachment proteins and therefore require different receptor proteins on host cells. As a result, some viruses can only infect one type of cell (others can infect lots of different cells).

3 - Because they’re not alive, viruses DON’T undergo cell division.
Instead, they inject their DNA or RNA into the host cell – this hijacked cell then uses its own ‘machinery’ (e.g. enzymes, ribosomes) to do the virus’s dirty work and replicate the viral particles.