Topic 2---A: Cell structure and Division- 2.Prokaryotic Cells and Viruses

Question 1

What are prokaryotes?

Answer 1

• They are single-celled organisms.
• Bacteria (like E. coli) are examples of prokaryotes.

Question 2

What is the difference between prokaryotic and eukaryotic cells?

Answer 2

• Prokaryotic cells are much smaller and simpler than eukaryotic cells.
• Prokaryotic cells don’t have any membrane-bound organelles in their cytoplasm.
• Cell wall is made out of murein which is a glycoprotein.
• They don’t have a nucleus so they have circular DNA molecule that is free in the cytoplasm.
• It isn’t associated with proteins.

Question 3

What is in a prokaryotic cell?

Answer 3

• Slimy capsule
• Plasmids
• Cell wall
• Cell-surface membrane
• Cytoplasm
• Flagellum
• DNA (long coiled up strand).

Question 4

Slimy capsule

Answer 4

• Some prokaryotes (e.g. bacteria) also have a capsule made up of secreted slime.
• It helps to protect the bacteria from attack by cells of the immune system.

Question 5

Plasmids

Answer 5

• Small loops of DNA that aren’t part of the main circular DNA molecule.
• They contain genes for things like antibiotic resistance, and can be passed between prokaryotes.
• There not always present in prokaryotic cells but some have several.

Question 6

Cell wall (prokaryotic cell)

Answer 6

• It supports the cell and prevents it from changing shape.
• It is made up of a polymer called murein.

Question 7

What is murein?

Answer 7

• Cell wall in a prokaryotic cell is made from it.
• It’s a glycoprotein which is a protein with a carbohydrate attached to it.

Question 8

Flagellum

Answer 8

• Long hair-like structure.
• It rotates to make the prokaryotic cell move.
• Not all of them have them but some have more than one.

Question 9

Cytoplasm (prokaryotic cell)

Answer 9

• It contains ribosomes but they’re smaller than those in a eukaryotic cell.

Question 10

DNA (prokaryotic cell)

Answer 10

• Prokaryotic cell doesn’t have a nucleus.
• So the DNA floats free in the cytoplasm.
• It’s circular DNA and it’s present as one long coiled up strand.
• It’s not attatched to any histone proteins.

Question 11

Cell surface membrane (prokaryotic cell)

Answer 11

• It’s mainly made up of lipids and proteins.
• It controls the movement of substances into and out of the cell.

Question 12

How big is a prokaryotic cell?

Answer 12

less than 2 micro metres in diameter

Question 13

What is the process by which prokaryotic cells replicate by?

Answer 13

Binary fission so the cell replicates it’s genetic material before physically splitting into two daughter cells.

Question 14

What is the process of binary fission?

Answer 14

1) The circula DNA and plasmids replicate. The main DNA loop is only replicated once but the plasmids can be replicated loads of times.
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 they can have a variable number of copies of the plasmids.

Question 15

What is the structure of a virus?

Answer 15

• They have a protein coat called a capsid with attatchment proteins sticking out from it.
• Capsid is made up of protein units called capsomeres.
• Core of genetic material (either DNA or RNA).

Question 16

What do the attatchment proteins allow the virus to do?

Answer 16

They let the virus cling onto a suitable host cell.

Question 17

Why are viruses said to be accellular?

Answer 17

• They don’t have a cellular structure like other organisms do.
• They only invade and reproduce inside the cells of other organisms (host cells).

Question 18

What is a virus?

Answer 18

They are just nucleic acids surrounded by a protein.

Question 19

What are the differences between a virus and bacteria?

Answer 19

• Unlike bacteria, viruses have no plasma membrane, no cytoplasm, no ribosomes.
• They’re even smaller than bacteria (e.g. HIV is 0.1 micro metres across).

Question 20

What are some examples of viruses?

Answer 20

• HIV (causing AIDS)
• Influenza (causing flu)
• Rhinoviruses (causing colds)

Question 21

Why do viruses replicate?

Answer 21

-Because they are not alive so they don’t undergo cell division.
- So instead they inject their DNA or RNA into the host cell.

Question 22

What are the stages of viral replication?

Answer 22

1. The virus attatches to the host cells surface by using their attachment proteins which binds to the complementary receptor proteins on the cell-surface membrane of the host cell.
2. The genetic material from the virus is released into the host cell.
3. Genetic material and proteins are then replicated by the host cells ‘machinery’ (e.g. enzymes and ribosomes).
4. The viral components assemble.
5. Replicated virus is released from the host cell.

Question 23

Why can some viruses only infect one type of cell?

Answer 23

• Because different viruses have different attatchement proteins so require different receptor proteins on a host cell in order for them to be replicated.