Salters-Nuffield AS Biology - Topics 3 - Cells

Prokaryotic Cells:

• Bacteria and cyanobacteria (photosynthetic bacteria) are prokaryotic.
• These cells have no membrane bound organelles. (including NO nuclei!)
• The DNA in prokaryotic cells is not associated with any proteins, but free in the cytoplasm.

ALWAYS HAVE:

Cell Wall
Cytoplasm
Cell Surface Membrane
Infoldings in Cell Surface Membrane- these are the site of respiration
Circular DNA (free in cytoplasm)
Ribosome

SOME PROKARYOTIC CELLS HAVE:

Capsule - slimy outer layer for protection, and to prevent dehydration
Pili - Thin protein tubes protruding from the cell which allow the bacteria to adhere to surfaces
Flagellum - ((looks like a tail, moves like propeller)) Hollow, cylindrical, thread-like structure which rotates tomove the cell around
Plasmid - small circle of DNA

Eukaryotic Cells:

• DO have membrane bound organelles.
• Four groups: animals, plants, fungi and protocists (e.g. unicellular organismsand the seaweeds)
• Larger than prokaryotic cells.
• Not all eukaryotics have cell walls.

Nucleus - Contained within the nuclear envelope (two membranes perforated bypores) andcontains the nucleolus and DNA which contains genes that code for proteins.
Nucleolus - Dense body within the nucleus where ribosomes are made.
Rough Endoplasmic Reticulum - Interconnected, membrane bound flattened sacs, with ribosomes attatched to them. When protein is made (by the ribosomes) it is transported through the endoplasmic reticulum to other parts of the cell.
Smooth Endoplasmic Reticulum - Like the Rough ER, without ribosomes. Smooth ER makes lipids and steroids.
Golgi Apparatus - Stacked membrane bound sacs, formed from fused vesicles. When proteins reach the golgi apparatus from the ER, the golgi apparatus modifies them then packages them into vesicles.
Cell Surface Bilayer - Phospholipid bilayer which contains proteins and other molecules. Partially permeable membrane (allows substances to travel in and out).
Ribosome - Made from RNA and protein. Protein synthesis occurs here.
Lysosome - Spherical sacs containing digestive enzymes bound by a single membrane. Involved in the break down of organelles, or whole cells (when old cells are replaced, or during development)
Centrioles - Cylinders made up of nine protein tubules. Form the spindle during nuclear division.
Mitochondrion - The inner membrane is folded inwards, to form projections called cristae. This is the site of later aerobic respiration.

1. Name two types of prokaryotic organism.
   
2. Name two types of eukaryotic organism.
   
3. Outline the main differences between prokaryotic and eukaryotic cells.
   
4. What is the function and structure of the pili?
   
5. What is the function and structure of a lysosome?