2.1.2 Structure of Eukaryotic Cells

Key Organelles in Eukaryotic Cells:

1. Nucleus:

• Surrounded by a double membrane (nuclear envelope) with ~3000 nuclear pores, allowing molecules to move in and out.
• Contains:
• Chromatin: DNA and associated proteins.
• Nucleolus: Produces ribosomes.
• Nucleoplasm: Jelly-like substance that forms the bulk of the nucleus.

2. Rough Endoplasmic Reticulum (RER):

• A network of flattened sacs enclosed by a membrane.
• Surface is studded with ribosomes, giving it a "rough" appearance.
• Function: Folds and processes proteins synthesised by the ribosomes.

3. Smooth Endoplasmic Reticulum (SER):

• A network of membrane-bound sacs without ribosomes.
• Function: Synthesises and processes lipids.

4. Golgi Apparatus:

• A stack of fluid-filled, flattened, curved sacs, with vesicles at the edges.
• Function:
• Modifies, packages, and transports proteins and lipids.
• Produces lysosomes.

5. Mitochondria:

• Oval-shaped, surrounded by a double membrane.
• The inner membrane is folded into cristae, which increase the surface area for respiration.
• The internal space, called the matrix, contains enzymes needed for aerobic respiration to produce ATP.

6. Ribosomes:

• Made of two subunits (large and small).
• Found either free in the cytoplasm or attached to the RER.
• Function: Site of protein synthesis.

7. Lysosomes:

• Small vesicles bound by a single membrane, containing digestive enzymes.
• Function: Break down waste materials, old organelles, and pathogens.

8. Centrioles:

• Hollow cylinders made of microtubules, arranged at right angles to each other.
• Function: Organise the spindle fibres during cell division.