Endoplasmic reticulum, Golgi, vesicles

Overview of Cellular Transport Processes

  • Background on physical transport processes in cells.

  • Importance of visual aids for understanding complex mechanisms.

Chromosomal Structure and Function

  • Chromosomes: Contain regions associated with nucleoli, where ribosomal RNA is made.

  • Ribosomes: Sites of protein synthesis, abundant in cells that produce a lot of protein, such as those with large nucleoli.

    • Most ribosomes are found free in the cytoplasm.

Protein Translation and Polypeptide Trafficking

  • Translation of mRNA to polypeptides can lead to three destinations:

    • Lumen of the Endoplasmic Reticulum (ER):

      • Proteins destined for secretion or incorporation into other organelles.

    • ER Membrane:

      • Proteins that must be embedded in membranes (integrated into the lipid bilayer).

    • Cytoplasm:

      • Proteins that function within the cytoplasm (e.g., tubulin, actin).

Endoplasmic Reticulum (ER) Structure

  • ER is located near the nucleus and divided into:

    • Rough ER:

      • Contains ribosomes; involved in protein synthesis for secretion or membrane insertion.

      • Comprises a network of tubules and can account for a significant cell volume.

    • Smooth ER:

      • Involved in lipid biosynthesis (e.g., phospholipids).

    • Both types are interconnected, supporting different cell functions.

Functions of Different Cell Types

  • Cells with high ER content:

    • Liver Cells: Engage in detoxification and lipid metabolism.

    • Produce testicular hormones in reproductive organs where larger amounts of ER are needed for synthesis tasks.

Post-Translational Modifications

  • Modifications occur in the rough ER and can include:

    • Glycosylation (addition/removal of sugar units).

    • Lipid synthesis, notably phospholipids for membranes.

    • Secretion of proteins is often regulated and occurs at the cell membrane.

  • Glycogenolysis vs gensis

    • Glycogen breakdown is muscle &liver

    • glycogen converted to glucose

    • smooth ER contains glucose 6-phosphate

    • glucose production from non-carbon sources

Golgi Apparatus: Structure and Function

  • Structure: Composed of stacked disc-like structures (cisternae).

    • Contains a cis face (receiving side) and a trans face (shipping side).

    • Modifications of proteins happen here before they are sent to their final locations.

  • Function:

    • Processes, modifies, and sorts proteins from the ER.

    • Involves additional glycosylation and phosphorylation of proteins.

    • Directs proteins to proper organelles or to the cell membrane for secretion.

Lysosomes and Cellular Recycling

  • Lysosomes are formed from Golgi vesicles and contain enzymes that:

    • Digest cellular debris and recycle components.

    • Maintain an acidic environment necessary for enzyme function (pH ~5).

  • Peroxisomes

  • 0.5-1 micrometer its a single membrane called microbodies

  • it gets rid of hydrogen peroxide

  • they have b-oxidative enzymes for the breakdown of fatty acids

Vesicular Transport Processes

  • Constitutive secretion: Constantly occurring process where vesicles release materials to the cell exterior.

  • Regulated secretion: Vesicles are held until a signal is received (example: insulin release).

  • Importance of cargo receptors on vesicles and their interactions with the cytoskeleton for a directed pathway.

Ion Channel Dynamics in Cells

  • Changes in membrane potential influence ion channels:

    • Potassium (K+) channels can close in response to increased ATP, affecting membrane potential.

    • Calcium (Ca2+) channels open when the membrane depolarizes, allowing Ca2+ influx necessary for vesicle transport.

Summary

  • A comprehensive understanding of cellular transport relies on the interplay of structures such as the ER and Golgi apparatus.

  • Cellular functions are intricately tied to the modifications and destinations of synthesized proteins, playing crucial roles in physiology and metabolism.