Cytoplasm and Cytoskeleton Study Guide

🗻 Big Picture: Cell division, polarity, and contraction all rely on the structure of cytoplasm and cytoskeleton, part of the cell. To get the whole picture, keep reading.

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The cytoplasm consists of everything inside the cell membrane excluding the nucleus. This means that the components of the cytoplasm include everything from the mitochondria, Golgi apparatus, endoplasmic reticulum, etc to the jelly like fluid that surrounds these organelles. This entire unit is termed the cytoplasm.

The cytoskeleton provides structural support to the cell, very similarly to how the human skeleton provides the main framework for our bodies. This guide dives deeper into these two critical parts of a cell.

What is cytoplasm?

The Cytoplasm comprises everything else that is contained within the cell's membrane, except the nucleus. All the cellular organelles are surrounded by a watery gel-like substance known as Cytosol, which is ALSO a considered a part of the cytoplasm. Therefore, cytoplasm = cell organelles (except the nucleus) + cytosol + macromolecules/granules suspended in the cytosol!

Cytoplasm Functions

The cytoplasm is responsible for several vital functions, one of which is maintaining cell structure. Cytoplasmic functions also include the following:

  • Presence of cytosol, which surrounds and protects the cell's internal organelles, and is a jelly-like fluid made mostly of salt and water.

  • The chemicals and enzymes needed to break down waste are found in the cytoplasm.

  • Provides a site for most cellular functions such as cellular respiration, mitosis, meiosis, glycolysis etc.

  • Works to keep organelles in position, it acts as a lubricant. It also allows for the movement of chemicals such as hormones between organelles.

Cytoplasm Structure

Cytoplasm Source

What is a cytoskeleton?

The Cytoskeleton is made up of a system of filaments that are present in the cytoplasm, and can be thought of as the 'skeleton of the cell'. The eukaryotic cytoskeleton is a network of long, thin protein fibers that contribute to the cell's structure and function in several ways. The cytoskeleton is composed of 3 types of filaments: microfilaments, microtubules, and intermediate filaments.

Cytoskeleton Functions

The cytoskeleton hase several important functions as the 'skeleton' of the cell. These include:

  • Organization of the components of the cell

  • Maintains cell shape

  • Enables cell locomotion, and controls the movement of organelles within the cell


A Microtubule is one of the thickest structures in the cytoskeleton, and while they are fairly strong, they are not too flexible. They are made up of alpha and beta tubulin that are typically found radiating from an area near the nucleus (the centrosome). Tubulin dimers consisting of both alpha and beta types, come together to form the cylinder-like structure that is observed in the below visual.

  • Microtubules help the cell maintain its shape.

  • They allow cell organelles to move around while still holding them in place (like an anchor)

  • They play a large role in the metaphase stage of mitotic cell division, through the formation of spindle fibers

  • Microtubules are found in cilia and flagella which aid the movement of the cell

Microtubule Source


Microfilaments are often called actin filaments since they’re primarily composed of two actin chains that are wound around each other. Microfilaments are the narrowest of the 3 filament types. Actin in microfilaments interacts with myosin to contract your muscles and both actin and myosin are found in abundance in muscle cells.

  • Microfilaments help cells maintain some rigidity and cell structure, and are found in almost every cell of the body

  • They can disintegrate and reassemble quickly and allow the cell some flexibility (white blood cells make great use of this property while engulfing a pathogen)

Actin Filament Source

Intermediate Filaments

These fibres make up the nuclear envelope and hold the organs of the cell together. They also provide strength and support to the cell, and differ in structure among different cell types. Keratin is a well-known protein that makes up intermediate filaments in nails, skin, and hair.

intermediate filament Source

✅ Conclusion

  • The cytoplasm consists of everything inside the cell membrane excluding the nucleus.

  • The cytoplasm is responsible for maintaining cell structure. It also holds the enzymes needed to break down waste, provides a site for cellular functions, keeps the organelles in place, acts as a lubricant, and allows for the movement of chemicals between organelles.

  • The cytoskeleton is responsible for preserving the cell's form while facilitating mobility inside the cell. Thicker than any other cytoskeleton component, microtubules provide structural support for the cell.

  • Polymer filaments made up of alpha, and beta tubulins are common. Intermediate filaments aid in the cell's internal structure and protect and preserve organelles.

  • When comparing cytoplasm and cytoskeleton, it's important to remember that each cellular component has a unique structure and function.


1. What is the cytoskeleton?

The cytoskeleton comprises protein filaments and tubules positioned inside the cell's cytoplasm and provides structural support.

2. What are the functions of the cytoplasm and the cytoskeleton?

The cytoplasm is a defined medium for the biological activities inside cells. The cytoskeleton maintains cell structure while regulating cell movement. The cytoplasm and cytoskeleton are fundamentally diverse in their structure and function.

3. Is cytoplasm part of the cytoskeleton?

The cytoplasm is highly organized despite its lack of form and structure. The cytoskeleton is a protein scaffolding network that holds the cytoplasm and the cell together.

4. How does the cytoskeleton play a role in cell division?

The cytoskeleton facilitates intracellular transport and cell division. Microtubules help cells maintain their shape. When cells split, they form the mitotic spindle, strengthening and shifting organelles.

6. Do prokaryotic cells have a cytoskeleton?

Both eukaryotes and prokaryotes have a cytoskeleton. Bacterial cytoskeletons are composed of tubulin-related proteins FtsZ and MreB/Mbl.

8. What is the cytoplasm?

The cell membrane encloses the cytoplasm, a viscous substance that fills each cell. Water, salts, and proteins make up the majority of the composition. The nucleus, endoplasmic reticulum, and mitochondria are all included inside the cytoplasm.

9. What are the functions of the cytoplasm?

The cytoplasm is a medium for chemical reactions. It serves as a platform for the cell's other organelles. A cell's cytoplasm is responsible for all expansion, growth, and replication functions.

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