Cell Components and Their Functions

Posted on Jan 13, 2025 in Biology

Cell Organelles: Structure and Function

1. Plasma Membrane (Cell Membrane)

Structure: A bilipid membranous layer composed of proteins and carbohydrates. It is fluid-like.

Function: The cell membrane separates the cell from its external environment and is selectively permeable, controlling what gets in and out. It protects the cell and provides stability. Proteins are found embedded within the plasma membrane, with some extending all the way through in order to transport materials. Carbohydrates are attached to proteins and lipids on the outer lipid layer.

2. Cytoplasm

Structure: The jelly-like substance composed mainly of water and found between the cell membrane and nucleus. The cytoplasm makes up most of the “body” of a cell and is constantly streaming.

Function: Organelles are found here, and substances like salts may be dissolved in the cytoplasm.

3. Nucleus

Structure: The largest organelle in the cell. It is dark and round and is surrounded by a double membrane called the nuclear envelope or membrane. In spots, the nuclear envelope fuses to form pores which are selectively permeable. The nucleus contains genetic information (DNA) on special strands called chromosomes.

Function: The nucleus is the “control center” of the cell, for cell metabolism and reproduction.

4. Endoplasmic Reticulum (ER)

The endoplasmic reticulum is a network of membranous canals filled with fluid. They carry materials throughout the cell. The ER is the “transport system” of the cell.

There are two types of ER:

• Rough Endoplasmic Reticulum: Lined with ribosomes, giving it a rough appearance.
• Smooth Endoplasmic Reticulum: Contains no ribosomes and has a smooth appearance.

Functions:

• Produces proteins and lipids.
• Detoxifies, helping liver cells.
• Sends proteins through vesicles to the Golgi apparatus.

5. Ribosomes

Ribosomes are small particles which are found individually in the cytoplasm and also line the membranes of the rough endoplasmic reticulum. Ribosomes produce protein. They could be thought of as “factories” in the cell. Tiny structures floating around in the cytoplasm or ER that make protein from amino acids.

6. Golgi Body (Apparatus)

Golgi bodies are stacks of flattened membranous stacks (they look like pancakes!). The Golgi body temporarily stores protein which can then leave the cell via vesicles pinching off from the Golgi.

7. Lysosomes

Lysosomes are small, sac-like structures surrounded by a single membrane and containing strong digestive enzymes which, when released, can break down worn-out organelles or food. The lysosome is also known as a “suicide sac”.

8. Mitochondria

The mitochondria are round, “tube-like” organelles that are surrounded by a double membrane, with the inner membrane being highly folded. The mitochondria are often referred to as the “powerhouse” of the cell. The mitochondria release food energy from food molecules to be used by the cell. This process is called respiration. Some cells (muscle cells) require more energy than other cells and so would have many more mitochondria.

9. Vacuoles

Vacuoles are fluid-filled organelles enclosed by a membrane. They can store materials such as food, water, sugar, minerals, and waste products.

10. Centrioles

Centrioles: Organelles exclusive to animal cells, cylindrical. They function in cellular division.

11. Cilia and Flagella

Cilia and Flagella: Prolongations of the membrane. Cilia are numerous but short, while flagella are long and few in number. Similar to centrioles, they function in cellular movement.

12. Chloroplasts

Chloroplasts: Organelles that contain chlorophyll and produce photosynthesis. Formed by a double membrane, the exterior is smooth, and the interior is rough, full of sacs or thylakoids. They pile up, forming grana. The interior space is called the stroma.