cytoplasm and cellular organelles

1. Cytoplasm and Cytosol

In high school biology, think of the cytoplasm as everything inside the cell membrane except for the nucleus. Within the cytoplasm is a jelly-like fluid called cytosol.

• What's in it?: It is mostly water ($70\%--80\%\text{ water}$) mixed with salts, sugars, and proteins.

• What does it do?: It holds all the organelles in place and is where many chemical reactions, like breaking down sugar (glycolysis), happen.

2. The Nucleus: The Control Center

The nucleus is like the brain of the cell because it stores the instructions (DNA) for everything the cell needs to do.

• Nuclear Envelope: A double layer that surrounds the nucleus. It has tiny holes called pores that let materials move in and out.

• Nucleolus: A dark spot inside the nucleus where ribosomes are made.

• Chromatin: This is DNA wrapped around proteins. When the cell isn't dividing, it looks like a blurry mass of spaghetti.

3. Ribosomes: Protein Builders

Ribosomes are the "factories" that build proteins. They can be found in two places:

• Free Ribosomes: Floating in the cytosol; they make proteins used inside the cell.

• Bound Ribosomes: Stuck to the endoplasmic reticulum; they make proteins that are either sent out of the cell or put into the cell membrane.

4. The Endomembrane System

This is the cell's internal system for making and shipping products.

• Endoplasmic Reticulum (ER): A network of tubes.

  • Smooth ER: No ribosomes. It makes lipids (fats) and helps detoxify things like drugs or alcohol.

  • Rough ER: Covered in ribosomes. It helps fold and modify proteins.

• Golgi Apparatus: The "post office" of the cell. It receives, sorts, and packages proteins from the ER into bubbles called vesicles to be sent where they are needed.

• Lysosomes: The cell's "trash crew." They are filled with enzymes and acid (pH of about $5.0$) to break down waste or old cell parts.

5. Energy Centers

• Mitochondria: The "powerhouse." They take energy from food and turn it into a form of energy the cell can use, called $\text{ATP}$.

• Chloroplasts: Found only in plants. They act like solar panels, catching sunlight to make food through photosynthesis. They contain the green pigment chlorophyll.

6. The Cytoskeleton

This is a network of protein fibers that gives the cell its shape and acts like a highway for moving organelles around.

1. Microtubules: Thickest tubes ($25\text{ nm}$). They help the cell keep its shape and pull chromosomes apart during cell division.

2. Microfilaments: Thinnest rods ($7\text{ nm}$). Made of actin, they help the cell move and contract (like in muscle cells).

3. Intermediate Filaments: Medium-sized ($8\text{--}12\text{ nm}$). They are very strong and hold organelles like the nucleus firmly in place.

7. Peroxisomes

These are small sacs that break down fatty acids and toxins. A byproduct of their work is hydrogen peroxide ($\text{H}<em>2\text{O}</em>2$), which they quickly turn into harmless water.