Ultrastructure and Function of Organelles

Ultrastructure of Organelles

Nucleus

The nucleus is the control centre of a cell and contains genetic material in the form of DNA.
It is surrounded by a double membrane known as the nuclear envelope, which controls the entry and exit of substances.
Within the nucleus are chromosomes, long molecules of DNA wrapped around proteins, which carry the genes.
The nucleus also contains a structure called the nucleolus, where ribosome assembly begins.

Mitochondria

Mitochondria are oval-shaped organelles that are the site of aerobic respiration, where energy is produced.
They contain a double membrane; the inner membrane is highly folded into structures called cristae to increase its surface area for respiration reactions.

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a network of tubules used for protein and lipid synthesis.
Rough ER has ribosomes on its surface and is involved in the synthesis and transport of proteins, while smooth ER does not have ribosomes and synthesises lipids.

Ribosomes

Ribosomes are tiny, spherical structures where protein synthesis occurs.
They can be found free-floating in the cytoplasm or attached to the rough ER.

Golgi Apparatus

The Golgi apparatus modifies, sorts, and packages proteins and lipids for transport out of the cell.
It is a series of flattened, membrane-bound sacs called cisternae.

Lysosomes

Lysosomes are small, round organelles filled with enzymes.
They play a crucial role in cellular digestion and the breakdown of waste materials.

Chloroplasts (plant cells)

Chloroplasts are found in the cells of green plants and are responsible for photosynthesis, the process by which light energy is converted into chemical energy.
Like mitochondria, they are surrounded by a double membrane and have an inner membrane system called thylakoids.

Cell Wall (plant cells)

The cell wall is a rigid layer surrounding the plant cell, providing strength and support.
It is principally made up of cellulose, a complex carbohydrate.

Functions of Organelles

Understanding the different structures found within the eukaryotic cell is essential. Each organelle has a specific function crucial to the survival of the cell:

Nucleus controls the cell activity and houses DNA.
Mitochondria provide the cell with energy through respiration.
Endoplasmic reticulum synthesises proteins and lipids.
Ribosomes are the site for protein synthesis.
Golgi apparatus modifies, sorts, and packages cellular products for transport.
Lysosomes perform cellular digestion and waste removal.
Chloroplasts (plant cells) carry out photosynthesis to create food for the plant cell.
Cell wall (plant cells) provides structural support to the plant cell.

Each organelle has a unique structure which is optimised for its specific function, an important concept to understand in cell biology.