ProteinSorting part 1

Summary

This transcript covers the fascinating topic of intracellular compartments and protein sorting within eukaryotic cells. It explains how proteins are directed to specific compartments, such as the cytosol, endoplasmic reticulum, and mitochondria, using post-translational modifications. These modifications, like phosphorylation, acetylation, and ubiquitination, determine a protein's fate, such as forming complexes, activating specific genes, or even being targeted for degradation. The role of these modifications in cellular functions like metabolism, DNA repair, and membrane association is highlighted, offering insights into the dynamic processes that regulate protein behavior within cells.

Takeaways

• 😀 Cells are compartmentalized, with different organelles performing various functions in eukaryotic cells.
• 😀 The cytosol occupies the largest volume in cells, particularly in liver cells where it can occupy more than 50% of the total cell volume.
• 😀 The endoplasmic reticulum (ER) is a significant compartment, occupying about 12% of the cell's total volume, despite its singular nature.
• 😀 Mitochondria are essential in cells with high metabolic activity, such as liver cells, and can occupy up to 22% of the cell volume.
• 😀 Organelles like peroxisomes, lysosomes, and endosomes are present in large numbers but occupy a small percentage of the cell's volume (around 1%).
• 😀 Protein targeting to specific cellular compartments is regulated by post-translational modifications, which guide the proteins to their destinations.
• 😀 Post-translational modifications include adding various molecules to proteins, such as phosphates, acetyl groups, and ubiquitin, which affect the protein's fate.
• 😀 Phosphorylation of proteins on serine, threonine, or tyrosine residues can signal the formation of protein complexes.
• 😀 Acetylation of lysine residues on proteins can influence gene activation by modifying histone proteins and chromatin structure.
• 😀 Ubiquitination of proteins can lead to their degradation (via proteasome) or regulate cellular processes like DNA repair, depending on the pattern of ubiquitin attachment.

Q & A

What is the concept of cellular compartmentalization in eukaryotic cells?

Cellular compartmentalization refers to the division of the cell into distinct regions or compartments, each with specific functions. In eukaryotic cells, this includes structures like the cytosol, endoplasmic reticulum, mitochondria, and others, each occupying different volumes within the cell.

How does the volume occupied by different cell compartments vary?

The volume occupied by each compartment varies depending on the cell type. For example, the cytosol can occupy over 50% of the cell volume in liver cells, while the endoplasmic reticulum accounts for around 12%. Mitochondria, despite being smaller in number, can occupy up to 22% of the cell volume.

What role do mitochondria play in the liver cells?

In liver cells (hepatocytes), mitochondria are essential for providing energy required for various metabolic processes, including the storage of glycogen, fatty acid metabolism, and detoxification activities.

Why are smaller organelles like peroxisomes, lysosomes, and endosomes less significant in terms of volume?

Although these smaller organelles are numerous within the cell, they occupy a much smaller percentage of the cell's total volume, typically around 1%, due to their smaller size and specialized roles.

What is the importance of post-translational modifications (PTMs) in protein function?

PTMs are crucial for directing proteins to their correct cellular locations and regulating their activity. They alter the protein's structure, function, or interactions with other molecules, ensuring proper cellular processes like gene activation, protein complex formation, or membrane attachment.

What are some examples of post-translational modifications discussed in the script?

The script discusses several types of PTMs, including phosphorylation, acetylation, palmitoylation, and ubiquitination. Each modification serves a unique function, such as activating proteins, regulating gene expression, or targeting proteins for degradation.

How does phosphorylation affect protein function?

Phosphorylation involves the addition of phosphate groups to amino acids like serine, threonine, or tyrosine. This modification often signals that the protein should bind with other proteins, forming larger complexes to carry out specific functions.

What is the role of acetylation in protein activity?

Acetylation, the addition of an acetyl group to lysine residues, is involved in regulating gene expression. It helps activate genes by modifying histones, proteins that package DNA in the cell nucleus.

What does palmitoylation do to proteins?

Palmitoylation involves adding palmitic acid to cysteine residues in proteins, which often helps anchor the protein to the cell membrane, influencing its location and function within the cell.

How does ubiquitination affect proteins and their degradation?

Ubiquitination involves attaching ubiquitin molecules to proteins, marking them for degradation. Depending on the type of ubiquitin chain formed, it can either signal the protein for destruction or regulate other cellular processes like DNA repair.