A Level Biology Revision "Cell Fractionation"

Summary

This video from Free Science explains cell fractionation, a technique for studying cellular organelles. It starts with homogenizing tissue to break cells open, using a buffer to maintain pH and prevent organelle damage. The homogenate is then centrifuged at increasing speeds to separate organelles by size: nuclei, mitochondria, lysosomes, and ribosomes. The process requires keeping samples cool and acknowledges challenges in achieving complete separation.

Takeaways

• 🔬 **Cell Fractionation Importance**: Cell fractionation is a technique crucial for studying the functions of different cell organelles.
• 🧪 **Tissue Homogenization**: The process begins with homogenizing tissue to break it up and open cells, which can be done using a blender or a homogenizer.
• 🧊 **Use of Buffer Solution**: A buffer solution is used to maintain pH and prevent organelles from bursting due to osmotic water movement.
• ❄️ **Cooling the Sample**: Keeping the homogenizer on ice slows down enzymes, protecting the organelles from damage.
• 🔄 **Breaking Cells**: The plunger in the homogenizer is used to disrupt the tissue and break open cells, creating a cell homogenate.
• 🔽 **Organelle Sizes**: The relative sizes of organelles play a key role in their separation, with larger ones like the nucleus being easier to separate.
• 🌀 **Centrifugation**: A centrifuge is used to separate organelles by spinning the homogenate at different speeds, causing them to settle at different rates.
• 🧲 **Pellet Formation**: Larger organelles form a pellet at the bottom of the tube after centrifugation, while smaller ones remain in the supernatant.
• 🔁 **Sequential Spins**: Multiple spins at increasing speeds are required to separate organelles of different sizes, from nuclei to ribosomes.
• ⏳ **Time and Temperature**: Keeping pellets on ice is crucial to prevent enzymatic damage, and complete separation of organelles is challenging.

Q & A

What is the purpose of cell fractionation?

Cell fractionation is a technique used by scientists to separate cell organelles so that they can study their functions individually.

What is homogenization in the context of cell biology?

Homogenization is the process of breaking up tissue and breaking open cells to create a cell homogenate, which contains all the organelles found in the cell.

Why is it important to maintain a constant pH during homogenization?

Maintaining a constant pH is important because changes in pH could cause enzymes within the cell organelles to denature, which would affect their function.

What is the role of the buffer solution in homogenization?

The buffer solution maintains a constant pH and has the same water potential as inside the cell, preventing water from moving into the organelles by osmosis and causing them to burst.

How does cooling the sample during homogenization help protect the organelles?

Cooling the sample slows down the activity of enzymes, which helps prevent any destructive enzymes from damaging the organelles during the homogenization process.

What equipment is typically used to homogenize tissue samples?

A homogenizer, which is a glass tube containing a plunger, is commonly used to homogenize tissue samples.

How does a centrifuge aid in the separation of organelles during cell fractionation?

A centrifuge spins the sample, and the organelles are flung towards the bottom of the tube by the forces generated. Larger organelles move faster than smaller ones, allowing for separation by size.

What is the first organelle to be pelleted during the centrifugation process?

The first organelle to be pelleted during the centrifugation process is the nucleus, as it is the largest organelle.

Why is it difficult to separate organelles fully during cell fractionation?

It is difficult to separate organelles fully because some organelles of different sizes may have similar densities, and the process may not be able to differentiate them completely.

Why do we need to keep the pellets on ice after they are separated?

Keeping the pellets on ice slows down enzyme activity, which helps prevent damage to the organelles before they are used for further study.

What other organelles might be present in the fractions besides the ones mentioned in the script?

Other organelles such as the endoplasmic reticulum and Golgi apparatus might be present in the fractions, although they are not the primary focus of this script.