ch 7

Transmembrane Proteins

• Description:

  • Pinkish-looking rod that goes through and traverses the entire membrane.

  • Functions as a transmembrane protein.

Extracellular Attachments

• Sugars or polysaccharides are attached to the transmembrane protein in the extracellular space.

• Proteoglycans:

  • Similar to transmembrane proteins with sugars attached.

  • Key feature: sugars have sulfates attached to serine.

Differences Between Proteoglycans and Glycoproteins

• Proteoglycans:

  • Attachments include sulfate-bearing sugars.

• Glycoproteins:

  • Lack sulfate; contain different types of sugars.

• Distinction: based solely on the type of sugar attached.

Additional Sugar-Protein Interactions

• Glycosaminoglycans:

  • Joint lubricants that have sugars attached to proteins.

  • These are not free-floating polysaccharides.

• Glycosphingolipids:

  • Sugars attached to lipids instead of proteins.

  • Differ from glycoproteins in attachment type.

Functions of Sugars on Cell Surfaces

• Cell Signaling:

  • Sugars create a "sugar code" helping cells communicate their experiences.

• Adhesive Properties:

  • Sugars help cells stick together, allowing for close cell proximity.

  • Analogy: Sugars function like interlocked Legos.

• Viral and Bacterial Interaction:

  • Viruses and some bacteria can recognize and attach to cells based on the sugar code.

  • This can facilitate entry into the host cell, causing potential damage.

Examples of Protein-Sugar Interactions

• Enzyme Signaling:

  • Enzyme with sugar on it helps in its identification for exit from the Golgi apparatus.

  • Blue receptors recognize the sugars and facilitate the transport of the enzyme.

Summary of Key Learning Points

• Importance of sugars on cell surfaces for signaling purposes.

• Understand the similarities (presence of sugars) and differences (types of sugars) between glycoproteins and proteoglycans.

• Focus on mastering the fundamentals rather than intricate structural details.