Cell Biology: Endomembrane System & ER

Tour of the Cell 2

• The lecture covers the endomembrane system, protein trafficking, and metabolic functions within cells.
• The endomembrane system is like a cellular factory.
• The endoplasmic reticulum (ER) is responsible for production, biosynthesis and other functions.
• The rough ER has ribosomes attached, making proteins for secretion, and often glycosylating them.
• The smooth ER lacks ribosomes and produces lipids and hormones.
• The Golgi apparatus processes and packages proteins, and adds sugar chains to them, before, often exporting them to lysosomes.
• Vesicles transport materials within the cell.

Endoplasmic Reticulum (ER)

• The ER is a network of membranes within the cytoplasm.
• It has a large surface area, with a convoluted structure.
• The inside of the ER is called the lumen.
• The ER has specialized environments to control specific processes.
• ERs are of two types: smooth ER and rough ER.
• The rough ER is studded with ribosomes, aiding protein production.
• The smooth ER is responsible for lipid production, and lacks ribosomes.

Rough ER

• Ribosomes are attached to the rough ER.
• Ribosomes translate mRNA into proteins.
• Proteins produced by rough ER are often secreted out of the cell or are transported to other parts of the cell.
• Many proteins produced on the rough ER are glycosylated , which is adding sugars.
• Proteins are processed within the membrane of the rough ER.
• Leader signal polypeptides can target proteins to the ER.
• Proteins are integrated into the ER interior, where they are processed.

Golgi Apparatus

• The Golgi apparatus is a series of flattened sacs.
• It has a cis (receiving end) and trans (shipping end).
• Materials move from cis to trans within the Golgi.
• Sugars are added to proteins in the Golgi.
• Proteins are exported or directed to lysosomes.
• It is like a sorting and modification center for proteins in cells.

Lysosomes

• Lysosomes are sacs filled with hydrolytic enzymes.
• They are produced by the Golgi and involved in waste recycling.
• They degrade biomolecules and damaged materials.
• The enzymes in lysosomes are ready to degrade biomolecules.
• Lysosomes merge with vesicles from the outer (cell) membrane to digest material in phagocytosis.
• Lysosomes merge with vacuoles containing damaged materials in autophagy.

Energy Organelles - Mitochondria

• Mitochondria convert chemical energy into ATP.
• They have two membranes. The outer membrane is smooth, and the inner membrane is folded (cristae) to increase surface area.
• They contain their own DNA and ribosomes.
• Processes like respiration produce ATP, the cells' energy currency.

Energy Organelles - Chloroplasts

• Chloroplasts convert light energy into chemical energy (sugars).
• They have two membranes and thylakoids (internal membrane stacks).
• Thylakoids contain chlorophyll for photosynthesis.
• Chloroplasts contain their own DNA and ribosomes.

Energy Organelles - Peroxisomes

• Peroxisomes contain enzymes for chemical oxidation.
• They protect cells from toxic substances like hydrogen peroxide (H₂O₂).
• Peroxisomes are involved in alcohol detoxification.

Endosymbiotic Hypothesis

• Mitochondria and chloroplasts were once free-living prokaryotes (bacteria) that formed relationships with early eukaryotic cells.
• This theory explains why they have double membranes, their own DNA, and their unique ribosomes.

Mitochondria (detailed)

• Mitochondria have two membranes.
• The outer membrane is smooth.
• The inner membrane is folded into cristae to increase surface area.
• The spaces within are the intermembrane space and the matrix.
• Mitochondrial processes happen in these two spaces.

Chloroplasts (detailed)

• Chloroplasts also have two membranes.
• The thylakoids are inside, interconnected sacs.
• Grana are stacks of thylakoids.
• The stroma is the fluid around the thylakoids.
• The sites of photosynthesis are primarily in the stroma, thylakoid membranes contain chlorophyll.

Cytoskeleton

• The cytoskeleton maintains cell shape and enables cell movement.
• There are three types of cytoskeleton filaments: Microtubules, Actin filaments, and Intermediate filaments.
• Microtubules are hollow tubes, help maintain cell shape, are involved in cell division and cell motility.
• Actin filaments are solid rods, also helpful in cell shape, cell contraction and motility .
• Intermediate filaments are more diverse and also assist in cell structure, helping to withstand tension in anchoring structures.
• A variety of proteins interact with the cytoskeleton to direct the movement and actions of cell components.

Extracellular Connections

• Extracellular matrix is a complex of glycoproteins, carbs, and fibrous proteins.
• It provides structure and support for animal cells.
• Collagen, one major protein in the extracellular matrix, is a major part of the human protein matrix, making up nearly 40%.
• Integrins are cell surface proteins that connect cells to the extracellular matrix.
• Junctions between animal cells include tight junctions, desmosomes, and gap junctions.
• Tight junctions prevent leakage between cells.
• Desmosomes provide strong adhesion between cells.
• Gap junctions allow for intercellular communication.

This quiz explores the intricacies of the endomembrane system, focusing on structures like the endoplasmic reticulum (both smooth and rough) and the Golgi apparatus. Understand how proteins are synthesized, processed, and transported within the cell. Ideal for students delving into cellular biology.