Cell parts

1. Nucleus

• Function: The control center of the cell, containing most of the cell’s genetic material (DNA). It regulates cell activities like growth and reproduction.

• Key Structures:

  • Nuclear Envelope: Double membrane that encloses the nucleus.

  • Nucleolus: Located inside the nucleus, responsible for producing ribosomes.

  • Chromatin: The form in which DNA exists when the cell is not dividing (a mix of DNA and proteins).

2. Ribosomes

• Function: Protein synthesis. Ribosomes read mRNA and assemble amino acids into proteins.

• Location:

  • Free Ribosomes: Found floating in the cytoplasm, synthesize proteins used within the cell.

  • Bound Ribosomes: Attached to the Rough Endoplasmic Reticulum (ER), synthesize proteins for export or membrane insertion.

3. Endoplasmic Reticulum (ER)

• Function: A network of membranes involved in the production, processing, and transport of proteins and lipids.

• Types:

  • Rough ER: Studded with ribosomes, involved in protein synthesis and modification.

  • Smooth ER: Lacks ribosomes, involved in lipid synthesis, detoxification of drugs and poisons, and storage of calcium ions.

4. Golgi Apparatus

• Function: The “post office” of the cell. It modifies, sorts, and packages proteins and lipids made in the ER for delivery to their destination (inside or outside the cell).

• Structure: Flattened sacs called cisternae.

5. Lysosomes

• Function: Contain digestive enzymes to break down waste materials, cellular debris, and foreign substances (like bacteria). They play a key role in autophagy (the recycling of the cell’s own components).

• Structure: Membrane-bound vesicles containing enzymes.

6. Vacuoles

• Function: Storage organelles that hold water, nutrients, and waste products. In plant cells, the central vacuole also helps maintain turgor pressure (structural support).

• Structure: Large vesicles found in plant and some animal cells.

7. Mitochondria

• Function: The powerhouse of the cell, responsible for cellular respiration (the process of converting glucose into ATP, the cell's energy currency).

• Structure: Double-membraned with an inner membrane folded into cristae to increase surface area for ATP production. It contains its own DNA.

8. Chloroplasts (Plant Cells Only)

• Function: Site of photosynthesis, where light energy is converted into chemical energy (glucose).

• Structure: Contains a double membrane and stacks of thylakoids (called grana) where light reactions take place. Also contains its own DNA.

9. Cytoskeleton

• Function: A network of fibers that provides structural support, helps in cell movement, and organizes organelles.

• Components:

  • Microtubules: Involved in cell division (form the mitotic spindle), movement of organelles, and structural support.

  • Microfilaments: Involved in muscle contraction, cell shape changes, and cytoplasmic streaming in plants.

  • Intermediate Filaments: Provide mechanical support and maintain cell shape.

10. Plasma Membrane (Cell Membrane)

• Function: A selectively permeable barrier that controls the movement of substances in and out of the cell. It maintains homeostasis by regulating the internal environment.

• Structure: Composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

11. Cell Wall (Plant Cells and Prokaryotes)

• Function: Provides structural support and protection. It helps maintain the shape of the cell and prevents excessive water uptake.

• Structure: Made of cellulose in plants, chitin in fungi, and peptidoglycan in prokaryotes.

12. Peroxisomes

• Function: Contain enzymes that break down fatty acids and detoxify harmful substances like hydrogen peroxide (H₂O₂) by converting it into water.

• Structure: Small membrane-bound organelles with enzymes.

13. Cytoplasm

• Function: The jelly-like fluid inside the cell that holds organelles in place. It is the site for many biochemical reactions.

• Structure: Composed of water, salts, and organic molecules.

14. Centrosomes and Centrioles

• Function: Play a key role in organizing microtubules during cell division to form the mitotic spindle.

• Structure: Centrosomes contain a pair of centrioles in animal cells (not found in plant cells).

15. Cilia and Flagella

• Function: Involved in cell movement or moving fluids over the surface of the cell.

• Structure:

  • Cilia: Short, hair-like projections that move in coordinated waves.

  • Flagella: Longer, whip-like structures that propel the cell (e.g., sperm cells).

Prokaryotic Cell Components

• Nucleoid: The region in prokaryotic cells where the DNA is located (not membrane-bound).

• Ribosomes: Smaller than eukaryotic ribosomes, but also involved in protein synthesis.

• Cell Wall: Made of peptidoglycan in bacteria, provides structural support.

• Plasma Membrane: Controls the entry and exit of substances.

• Capsule: A sticky outer layer that protects the cell and helps it adhere to surfaces (in some bacteria).

• Pili: Hair-like projections used for attachment and DNA exchange (conjugation) in bacteria.

• Flagella: Used for locomotion.

Endomembrane System Overview

The endomembrane system regulates protein and lipid traffic within the cell. It includes:

• Nuclear Envelope

• Endoplasmic Reticulum (ER)

• Golgi Apparatus

• Lysosomes

• Vesicles

• Plasma Membrane

Function: Proteins and lipids are synthesized in the ER, modified in the Golgi, and then sent to their destination (either inside the cell or secreted out).