Structure and function of mitochondria, endoplasmic reticulum, Golgi apparatus, ribosomes

1. Introduction

1. Cell organelles are specialized structures within a cell that perform distinct functions.
2. They can be classified as membrane-bound (mitochondria, ER, Golgi apparatus) or non-membranous (ribosomes).
3. Each organelle plays a crucial role in maintaining cellular functions like energy production, protein synthesis, and transport.

2. Mitochondria

1. Known as the powerhouse of the cell, mitochondria generate energy in the form of ATP through cellular respiration.
2. They have a double membrane: an outer membrane and a highly folded inner membrane called cristae.
3. The cristae increase the surface area for ATP production.
4. The inner fluid-filled space is called the matrix, which contains DNA, ribosomes, and enzymes for energy metabolism.
5. Mitochondria have their own DNA, supporting the endosymbiotic theory (they originated from ancient bacteria).
6. They play a role in cellular respiration, including the Krebs cycle and Electron Transport Chain (ETC).

3. Endoplasmic Reticulum (ER)

1. The endoplasmic reticulum (ER) is a network of membranes involved in protein and lipid synthesis.
2. It is classified into two types: Rough ER (RER) and Smooth ER (SER).
3. Rough ER has ribosomes attached to its surface, making it responsible for protein synthesis.
4. Smooth ER lacks ribosomes and is involved in lipid synthesis, detoxification, and calcium storage.
5. The ER acts as a transport system, sending materials to the Golgi apparatus for further processing.

4. Golgi Apparatus

1. The Golgi apparatus is a stack of membrane-bound sacs responsible for modifying, packaging, and sorting proteins and lipids.
2. It receives proteins from the Rough ER via small transport vesicles.
3. It modifies proteins by adding carbohydrate or phosphate groups (glycosylation and phosphorylation).
4. The processed proteins and lipids are packed into vesicles and sent to their final destinations.
5. The Golgi apparatus also produces lysosomes, which contain digestive enzymes.
6. It plays a crucial role in secretion, especially in glandular cells.

5. Ribosomes

1. Ribosomes are the protein factories of the cell.
2. They are composed of ribosomal RNA (rRNA) and proteins.
3. They exist as free ribosomes in the cytoplasm or attached to the Rough ER.
4. Free ribosomes synthesize proteins used within the cell.
5. ER-bound ribosomes synthesize proteins for export or membrane insertion.
6. They consist of two subunits: a large subunit and a small subunit.
7. They use mRNA as a template to assemble amino acids into proteins.

6. Summary

1. Mitochondria: Powerhouse of the cell, ATP production.
2. Endoplasmic Reticulum: Rough ER for protein synthesis, Smooth ER for lipid synthesis and detoxification.
3. Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.
4. Ribosomes: Site of protein synthesis.