3 Cells:
Prokaryotic Cells
❖ No true nucleus, only area where DNA is found
❖ Pro DNA is not associated with proteins
❖ Some DNA may be in the form of circular strands called plasmids
❖ No membrane – bunded organelles
❖ No chloroplasts, only bacterial chlorophyll associated with the cell-surface membrane
in some bacteria
❖ Ribosomes are smaller (70s)
❖ Cell wall made of murein (peptidoglycan) may have an outer mucilaginous layer
called capsule
Eukaryotic Cells
❖ Distinct
nucleus, with nuclear envelope
❖ DNA is associated with proteins called histones
❖ No plasmids and DNA is linear membrane-bounded organelles (mitochondria)
❖ Chloroplasts present in plants and algae
❖ Ribosomes are larger (80s)
❖ When present, cell wall is made of cellulose
❖ No capsule
Methods to study cells
Cell Fractionation
1. Tissue is cut up and kept in cold, buffered solution. The cold solution is to stop enzyme
activity and the buffer is to keep a constant pH and water potential.
2. The cut-up tissue is further broken up I homogeniser. The resultant fluid is homogenate.
3. Homogenised tissue is spun in an ultracentrifuge at a low speed for 10 minutes.
, Differential Centrifugation
Prokaryotic Cells
❖ No true nucleus, only area where DNA is found
❖ Pro DNA is not associated with proteins
❖ Some DNA may be in the form of circular strands called plasmids
❖ No membrane – bunded organelles
❖ No chloroplasts, only bacterial chlorophyll associated with the cell-surface membrane
in some bacteria
❖ Ribosomes are smaller (70s)
❖ Cell wall made of murein (peptidoglycan) may have an outer mucilaginous layer
called capsule
Eukaryotic Cells
❖ Distinct
nucleus, with nuclear envelope
❖ DNA is associated with proteins called histones
❖ No plasmids and DNA is linear membrane-bounded organelles (mitochondria)
❖ Chloroplasts present in plants and algae
❖ Ribosomes are larger (80s)
❖ When present, cell wall is made of cellulose
❖ No capsule
Methods to study cells
Cell Fractionation
1. Tissue is cut up and kept in cold, buffered solution. The cold solution is to stop enzyme
activity and the buffer is to keep a constant pH and water potential.
2. The cut-up tissue is further broken up I homogeniser. The resultant fluid is homogenate.
3. Homogenised tissue is spun in an ultracentrifuge at a low speed for 10 minutes.
, Differential Centrifugation
