AQA A Level Biology Summary Notes
3.2.1.2 Structure of prokaryotic cells and viruses
Prokaryotic cells are much smaller than eukaryotic cells
- 10-100 times smaller
Compare the structure of eukaryotic and prokaryotic cells
1. Bacterial cells much smaller than a human cell
2. Bacterial cell has cell wall, human cell does not
3. Bacterial cell lacks a nucleus, human cell has a nucleus
4. Bacterial cell lacks membrane-bound organelles, but human cell has membrane-bound
organelles
5. Bacteria have 70S ribosomes, humans have 80S ribosomes
6. Bacterial DNA is circular, human DNA is linear
7. Bacterial DNA is ‘naked’, whereas human DNA is bound to histones
++
Prokaryotes carry extra DNA in the form of plasmids
Cell wall is made of murein – a glycoprotein
Prokaryotes have:
- flagellum (or several) for movement – LOCOMOTION
- capsule (MUCILAGINOUS slime layer) that helps bacteria stick together to form
colonies/films and protection from chemicals
- cell wall which is a physical barrier and prevents osmotic lysis
- cell surface membrane is partially permeable that controls entry and exit of chemicals
USE ‘whereas’ in the sentence
, Viruses are acellular and non-living. The structure of virus particles include genetic material
(RNA/DNA), capsid and attachment protein.
Viruses are not cells – they are viral/non living particles which are obligate parasites of cells as they
must enter a living cell to reproduce
Viruses are NOT prokaryotic OR eukaryotic = non living so cannot undergo cell division
Smaller than bacteria
Contain:
- genetic material (RNA/DNA)
- Capsid (protein coat)
- Attachment proteins (projecting from surface that allowing them to attach to host cell)
DIFFERENT VIRUSES HAVE DIFFERENT STRUCTURES
‘Lipid envelope’ is formed from the host cells plasma membrane. As the virus particle bursts from
the cell, it becomes coated with membrane. This helps it to bind and enter the host cell.
^ usually in HIV
Viral replication
- Virus attaches to host cell surface using attachment protiens (which are complementary to
receptor protiens on the host cells surface membrane)
- Viral DNA/RNA is injected into host cell
- Viral DNA/RNA is replicated and new viral protiens are made, forming new capsids
- New viral particles are assembled by host cell
- Newly replicated viruses are released from host cell causing it to lyse
3.2.1.2 Structure of prokaryotic cells and viruses
Prokaryotic cells are much smaller than eukaryotic cells
- 10-100 times smaller
Compare the structure of eukaryotic and prokaryotic cells
1. Bacterial cells much smaller than a human cell
2. Bacterial cell has cell wall, human cell does not
3. Bacterial cell lacks a nucleus, human cell has a nucleus
4. Bacterial cell lacks membrane-bound organelles, but human cell has membrane-bound
organelles
5. Bacteria have 70S ribosomes, humans have 80S ribosomes
6. Bacterial DNA is circular, human DNA is linear
7. Bacterial DNA is ‘naked’, whereas human DNA is bound to histones
++
Prokaryotes carry extra DNA in the form of plasmids
Cell wall is made of murein – a glycoprotein
Prokaryotes have:
- flagellum (or several) for movement – LOCOMOTION
- capsule (MUCILAGINOUS slime layer) that helps bacteria stick together to form
colonies/films and protection from chemicals
- cell wall which is a physical barrier and prevents osmotic lysis
- cell surface membrane is partially permeable that controls entry and exit of chemicals
USE ‘whereas’ in the sentence
, Viruses are acellular and non-living. The structure of virus particles include genetic material
(RNA/DNA), capsid and attachment protein.
Viruses are not cells – they are viral/non living particles which are obligate parasites of cells as they
must enter a living cell to reproduce
Viruses are NOT prokaryotic OR eukaryotic = non living so cannot undergo cell division
Smaller than bacteria
Contain:
- genetic material (RNA/DNA)
- Capsid (protein coat)
- Attachment proteins (projecting from surface that allowing them to attach to host cell)
DIFFERENT VIRUSES HAVE DIFFERENT STRUCTURES
‘Lipid envelope’ is formed from the host cells plasma membrane. As the virus particle bursts from
the cell, it becomes coated with membrane. This helps it to bind and enter the host cell.
^ usually in HIV
Viral replication
- Virus attaches to host cell surface using attachment protiens (which are complementary to
receptor protiens on the host cells surface membrane)
- Viral DNA/RNA is injected into host cell
- Viral DNA/RNA is replicated and new viral protiens are made, forming new capsids
- New viral particles are assembled by host cell
- Newly replicated viruses are released from host cell causing it to lyse
