Endoplasmic reticulum and golgi apparatus | Cells | MCAT | Khan Academy

Summary

This educational video script delves into the endoplasmic reticulum, a vital cell organelle connected to the nucleus. It distinguishes between the rough and smooth ER, detailing their roles in protein synthesis and lipid production. The script explains the secretory pathway, highlighting the Golgi apparatus's role in protein modification and sorting. It also touches on post-translational modifications and the movement of proteins to their destinations, such as lysosomes or the cell membrane, emphasizing the interconnectedness of cellular organelles in the secretory process.

Takeaways

• 📍 The endoplasmic reticulum (ER) is an organelle connected to the nucleus and has two parts: rough and smooth.
• 🛢️ The smooth ER synthesizes lipids, including those for the cell membrane and secreted hormones like steroid hormones.
• 🍬 The smooth ER also metabolizes carbohydrates and aids in detoxifying drugs and toxins.
• 🏭 The rough ER, studded with ribosomes, is the site of protein synthesis and contains proteins that will be secreted or become part of cellular structures.
• 🔍 Proteins synthesized in the cytoplasm typically remain in the cytoplasm or are destined for other organelles like the nucleus or mitochondria.
• 🔗 Proteins made in the rough ER follow the secretory pathway, which includes post-translational modifications like disulfide bridge formation.
• 📦 The secretory pathway describes the journey of proteins from synthesis to their final cellular destination, either secretion or integration into membranes.
• 🔑 Proteins intended for the secretory pathway have a signal sequence that directs them to the rough ER for synthesis.
• 📚 The Golgi apparatus modifies, sorts, and directs proteins to their correct destinations, including secretion or use in other organelles like lysosomes.
• 🚀 Vesicles transport proteins from the ER to the Golgi apparatus, where they undergo further modifications before being sent to their final destinations.
• 🔄 The ER, Golgi apparatus, lysosomes, and cell membrane are all part of the cell's secretory pathway, facilitating the transport and integration of proteins.

Q & A

What is the endoplasmic reticulum and how is it related to the nucleus?

The endoplasmic reticulum (ER) is an organelle in the cell that is connected to the nucleus. It has a lumen that is continuous with the space within the nuclear envelope, which is a double membrane structure.

How many parts does the endoplasmic reticulum have and what are they?

The endoplasmic reticulum has two parts: the rough endoplasmic reticulum, which is studded with ribosomes, and the smooth endoplasmic reticulum, which lacks ribosomes.

What is the primary function of the smooth endoplasmic reticulum?

The smooth endoplasmic reticulum synthesizes lipids, including those that become part of the cell membrane or are secreted from the cell, such as steroid hormones. It also metabolizes carbohydrates and aids in the detoxification of drugs and toxins.

What role does the rough endoplasmic reticulum play in protein synthesis?

The rough endoplasmic reticulum is the site of protein synthesis. It contains ribosomes and is responsible for synthesizing proteins that will either be secreted, become part of the cell membrane, or remain within the cell's organelles like the ER, Golgi apparatus, or lysosomes.

How does the rough endoplasmic reticulum differ from ribosomes in the cytoplasm?

Proteins synthesized in the cytoplasm by free ribosomes typically remain in the cytoplasm or are destined for organelles like the nucleus or mitochondria. In contrast, proteins synthesized in the rough endoplasmic reticulum often follow the secretory pathway and are destined for secretion or incorporation into the cell membrane.

What is a signal sequence and how does it relate to protein synthesis in the rough endoplasmic reticulum?

A signal sequence is a specific sequence of amino acids in a protein that indicates it should be synthesized in the rough endoplasmic reticulum. This sequence is detected during translation, causing the ribosome to attach to the ER and complete protein synthesis there.

Can you explain the secretory pathway in the context of protein synthesis?

The secretory pathway describes the route a protein takes from its synthesis in the rough endoplasmic reticulum to its final destination, which could be secretion out of the cell, incorporation into the cell membrane, or residence in organelles like the Golgi apparatus or lysosomes.

What is the role of the Golgi apparatus in the secretory pathway?

The Golgi apparatus modifies, sorts, and directs proteins to their correct destinations. It receives proteins from the endoplasmic reticulum, modifies them, and then packages them into vesicles for transport to their final destinations, such as lysosomes, the cell membrane, or secretion out of the cell.

How does a protein move from the rough endoplasmic reticulum to the Golgi apparatus?

A protein synthesized in the rough endoplasmic reticulum is packaged into a vesicle that buds off from the ER. This vesicle then fuses with the Golgi apparatus, delivering the protein to the cis face of the Golgi, where it begins its journey through the Golgi's stacks.

What happens to a protein within the Golgi apparatus?

Once inside the Golgi apparatus, a protein undergoes further modifications in the cis, medial, and trans stacks. After modification, it is packaged into a vesicle that buds off from the trans face of the Golgi, destined for its final location such as the lysosome, cell membrane, or extracellular space.

Why are the endoplasmic reticulum, Golgi apparatus, lysosomes, and cell membrane grouped together?

These organelles are grouped together because they are all part of the cell's secretory pathway, which handles the synthesis, modification, and transport of proteins and lipids to their final destinations within or outside the cell.