Lecture 10: Internal Balance Flashcards
Hormone
Chemical messengers functioning in both cellular and organ activity and ultimately, maintaining the body’s homeostasis.
Intercellular Signaling
Communication between cells
Intracellular Signalling
Communication within a cell
Ligand
A molecule that binds another specific molecule, in some cases, delivering a signal in the process.
Signalling molecules
Small, usually volatile or soluble molecules
Interact with proteins (receptors) in target cells
Panacrine Signalling
A cell targets a nearby cell
Signals move by diffusion through the extracellular matrix.
Usually elicit quick responses that only last a short amount of time
Panacrine ligand molecules are normally quickly degraded by enzymes or removed by neighbouring cells in order to keep the response localized.
Endocrine Signalling
A cell targets a distant cell throughout the bloodstream.
Originate from endocrine cells
Usually produce a slower response but have a longer-lasting effect
Ligands released are called hormones
Hormones get diluted and are present in low concentrations when they act on. target cells
Autocrine Signalling
Produced by signaling cells that can also bind to the ligand that is released.
Means that the signalling cell and the target cell can be the same or similar cell.
Often occurs during the early development of an organism to ensure that cells develop into the correct tissues and take on proper function
Regulates pain sensation and inflammatory response
Direct Signalling across Gap Junctions
Gap junctions are connections between the plasma membrane of neighbouring cells. The water- filled channels allow small signalling molecules known as intracellular mediators to diffuse between the 2 cells.
Specificity of channels means that the cells remain independent but can quickly and easily transmit signals
Transfer of signalling molecules communicates the current state of the cell that is directly next to target cell: This allows a group of cells to coordinate their response to a signal that only one of them received.
Receptor
Protein molecules in the target cell or on its surface that bind ligands.
2 types: Internal and cell-surface
Internal Receptors
Intracellular/Cytoplasmic Receptors
Found in the cytoplasm of the cell and respond to hydrophobic ligand molecules that are able to travel across the plasma membrane
When inside the cell, many of the molecules bind to proteins that act as regulators of mRNA synthesis to mediate gene expression.
When ligand binds, a conformational change is triggered that exposes a DNA-binding site on the protein.
The Ligand receptor complex moves into the nucleus and binds to specific regulatory regions of the chromosomal DNA and promotes the initiation of transcription.
Can directly influence gene expression without having to pass the signal on to the other receptors or messengers.
Gene Expression
Cellular process of transforming the information in a cell’s DNA into a sequence of amino acids which ultimately forms a protein.
Transcription
Process of copying the information in a cells DNA into mRNA.
The information in mRNA is used by the cell to link specific amino acids in the correct order, producing a protein.
Cell-surface receptors
Known as Transmembrane receptors
Are cell surface, membrane anchored proteins that bind to external ligand molecules.
Spans the plasma membrane and performs signal transduction, in which an extracellular signal is converted into an intracellular signal.
Ligands for these receptors don’t have to enter the cell that they affect
Also called cell-specific proteins or markers because they are specific to individual cell types.
Each has 3 main components: an external ligand-binding domain (extracellular domain), a hydrophobic membrane-spanning region, and an intracellular domain inside the cell.
3 General Categories of Cell-Surface Receptors
Ion-channel linked receptors
G-protein Linked receptors
Enzyme-linked receptors
Ion-channel Linked receptors
Bind a ligand and open a channel through the membrane that allows specific ions to pass through
Many of the amino acids have an extensive membrane spanning region and are hydrophobic in nature.
