membrane note 2

Transport Variations

• Molecule Movement Directionality: Different proteins influence the direction of molecule movement, and these movements have specific names.

  • Uniport:

    • Involves the movement of one type of molecule in one direction across a protein channel.

    • Uni means one, and port refers to the utilization of a protein channel.

  • Symport (Cotransport):

    • Involves two or more different types of molecules moving through a channel in the same direction.

    • Also known as cotransport, with "co" signifying two things moving together.

  • Antiport (Counter Transport):

    • Involves two or more different types of molecules moving through a channel in opposite directions. One moves in, and another moves out.

    • Also known as counter transport, which better illustrates the opposing directions.

• Active Transport Exclusivity: These transport mechanisms (UniPort, symport, antiport) are generally exclusive to active transport processes.

  • Uniport and Primary Active Transport:

    • Uniport is generally exclusive to primary active transport, which requires ATP.

    • Example: Calcium ATPase pump, which moves only calcium ions in one direction.

  • Antiport in Primary and Secondary Active Transport:

    • Antiport can occur in both primary and secondary active transport.

    • Example: Sodium-potassium ATPase pump (primary active transport) and Sodium-Calcium exchanger.

  • Symport and Secondary Active Transport:

    • Symport is exclusive to secondary active transport.

    • Example: Sodium-glucose pump.

Cell Membrane Functions

• Primary Functions:

  • Moving substances in and out of the cell.

  • Cellular communication.

• Importance of Communication:

  • Cellular communication is crucial for homeostasis.

  • Medications rely on cellular communication to work.

Chemical Communication

• Cells respond to various signals such as voltage, light, pressure, and temperature.

• Chemical communication or chemical signals involve molecules that facilitate action.

• The nervous system uses chemical communication.

• Neurons communicate through electrical impulses and chemical signals via neurotransmitters.

• Ligands:

  • Chemical signals are also known as ligands.

  • Ligands are chemical messengers, including neurotransmitters and hormones.

• Phosphorylation:

  • Phosphorylation is an action related to a phosphate, and it generally leads to activation.

  • Phosphorylation requires energy, typically from ATP.

  • $ATP$ (Adenosine Triphosphate) is a molecule that provides energy for phosphorylation.

  • GTP (Guanosine Triphosphate) is another energy source used in communication.

  • When $ATP$ or $GTP$ is used, they turn into lower energetic states (ADP or GDP), and the energy comes from breaking the bonds between the phosphates.

Types of Chemical Communication by Distance

• Autocrine Signaling:

  • A cell releases a chemical that signals itself.

• Signaling via Gap Junction:

  • Gap junctions are tubes that physically connect two cells, allowing direct transport of substances without using the cell membrane.

  • Commonly found in cardiac muscle.

• Paracrine Signaling:

  • A cell signals a neighboring cell by releasing chemicals that reach the adjacent cell directly.

  • An example of paracrine signaling: Smooth muscle blood cells secrete nitric oxide to signal themselves and nearby cells to dilate rapidly.

• Endocrine Signaling:

  • Involves distant signaling where chemicals are put into the bloodstream to reach cells somewhere else in the body.

  • Brain cells releasing hormones that affect ovaries or testes are an example of distant signaling.

• Juxtacrine Signaling:

  • Requires contact between cells.

  • Involves physical bumping into a cell, with communication occurring via receptors and proteins.

Ligands and Receptors

• Ligands must bind with a specific receptor on a cell to cause action.

• Cells only respond to ligands if they have the appropriate receptors.

• Hormones float around in the bloodstream until they encounter the proper receptors on cells, such as in the kidneys for antidiuretic hormone.

• How hormones transported

  • Majority of the Hormones are using the blood

Chemical Properties of Ligands

• Toolkit of Terms:

  • **Water-like (Polar):
    **

    • Polar

    • Hydrophilic

    • Water soluble

    • Lipophobic

  • **Fat-like (Nonpolar):
    **

    • Nonpolar

    • Hydrophobic

    • Fat soluble

    • Lipophilic

  *Note: Like dissolves like, Watery mixes with watery, oily mixes with oils.

• Movement of Ligands in the Body:

  • Water-like messengers may be secreted via exocytosis or transported by proteins; they dissolve easily in the bloodstream.

  • Fat-like messengers can pass through membranes but need carrier proteins in the blood.

• Receptors and Communication:

  • Water-loving external receptors, fat-loving internal receptors.

  • Water-like messengers bind to receptors outside the cell. Fatty messengers bind to receptors inside the cell after carrier protein release.

• Examples of Chemical Messengers:

  • Most hormones are protein-based and water-like.

  • Steroid hormones (e.g., estrogen and testosterone) are fat-like.

  • Eicosanoids, such as prostaglandins, are also fat-like and involved in inflammation and swelling.

Communication to Action

• Steps:

  1. Reception: A ligand binds to a receptor.

  2. Transduction: The signal is amplified.

  3. Response: The amplified signal causes a cellular response.

• Transduction Amplification:

  • Message transferred very quick.

    • Involves phosphorylation, using ATP or GTP.

    • The cascade makes the overall message transfer very quick

  • Cellular response generally involves the activation of a gene to synthesize protein (transcription and translation).

Receptor Types

• Four Categories of Receptor Types:

  • Ligand-gated ion channel receptors

  • Enzyme-linked receptors

  • G protein-linked receptors

  • Integrin receptors

• These receptors are essential because many medications interact with them.

• Dysfunctions in chemical communication are often involved in diseases like cancer.

Ligand-Gated Ion Channel Receptors

• Mechanism: A channel that is closed unless a ligand binds to the receptor on that channel to open it, allowing ions to pass through.

• Example: Acetylcholine receptors at muscles contract in response to these

Integrin Receptors

• Integrin proteins often have two subunits.

• Mechanism: Binding of ligand to a receptor causes a conformational change,

• Involve actions of proteins like collagen that affect aging and dysfunction.

Enzyme-Linked Receptors

• Mechanism: Receptor is linked to an enzyme.

• Example: Tyrosine kinase receptor, which are the most common and will be found on quizzes.

• Kinases are enzymes to phosphorylate which will active.

• Process: Proper ligand binds to receptors so there is a dimerization in which the receptor is fully activated and the system is ready to communicate, which leads to signal transduction. After there is the cellular response.

G Protein-Coupled Receptors (GPCRs)

• Structure: Loops on exterior and interior of the cell.

• Binds to things at N terminal.

• Signal Process:

  • GDP active, GTP is ready to work

  • Ligand then binds to G Protein and there is a confirming change in shape.

  • GPT gives signal and moves to cyclase.