C2.1 Chemical signalling HL Flashcards
Explain why cell signalling is important for organisms.
In order to communicate and coordinate responses.
What is the purpose of chemical signalling in humans?
In humans, chemical signalling helps in maintaining homeostasis, development, immune response, neural function and metabolic regulation.
State the name of the molecules where signalling molecules can bind.
Receptors
State an alternative name for a signalling molecule.
Ligand
Name the step that occurs after a a ligand has bound to a receptor, but before the response has been brought about.
Signal transduction pathway
Describe the difference between autocrine, paracrine and endocrine signalling.
Autocrine is when a cell signals to itself, paracrine is signalling by diffusion between two cells close to each other and endocrine is communication over a large distance.
State two examples of responses.
Transcription of DNA and opening of ligand-gated channels in neurones.
How do cells communicate with each other?
Cells communicate with each other by sending and receiving chemical signalling molecules called ligands. Typically, one cell produces chemical substances as messengers, and another one (often called the target cell) receives them using a receptor.
What are ligands?
A ligand is a chemical signalling molecule which selectively bind to a specific site on another molecules.
What are the examples of ligands?
They include hormones, neurotransmitters, cytokines and growth factors.
What are receptors?
A receptor is a protein with a site to which the signalling chemical can bind. The binding causes changes in the receptor which stimulates a response to the signal.
What is a ligand-binding site?
The site on a receptor to which the signalling chemical binds is its ligand-binding site
How do receptors and ligands bind?
-Weak interaction at distance
-Conformational change increases molecular complimentarity
-Bonding of molecules
What are the similarities between enzymes and receptors?
The selectivity or specificity of binding is similar to enzyme-substrate specificity in enzymes:
In both enzymes and receptors, binding of the ligand occurs at a specific site.
The shape and chemical properties of the ligand-binding site match those of the ligand, preventing other substances from binding.
Both enzymes and receptors are unchanged by the binding of a ligand, even if there are temporary changes to induce fit.
What are the differences between enzymes and receptors?
There are also key differences between enzymes and receptors:
When a substrate binds to the active site of an enzyme, the substrate changes. It is converted chemically into the product and released. Another substrate can then bind to the active site, and this cycle can repeat many times per second. Binding is very brief.
In contrast, a signalling chemical may remain bound to a receptor for a long time because the ligand-binding site does not act as a catalyst and does not convert the signal chemical into a product. The signalling chemical is eventually released unchanged.
What are the stages of chemical signalling?
- Synthesis and release of a ligand from a signalling cell.
- Transport and diffusion – ligands travel through the bloodstream or by diffusion through the extracellular fluid to reach the target cells.
- Receptor binding – the signalling molecules bind to specific receptors on the surface of the target cell (called cell surface receptors) or, in the case of intracellular signalling, within the cytoplasm or nucleus of the target cell. Receptors are specific to ligands. For example, hormones such as insulin and glucagon have specific receptors on cells to which they bind.
- Signal transduction – when the ligand binds to its receptor, it causes a conformational change in the receptor, initiating a cascade of biochemical reactions allowing it to bind to other molecules.
- Cellular response – the activated signalling pathways lead to specific cellular responses, such as changes in gene expression, activation or inhibition of enzymes, alteration of ion channel activity, or modulation of cellular metabolism.
- Signal termination – the signalling molecule is either degraded or removed from the extracellular space, and the receptor is inactivated, bringing the signal transduction process to an end.
How is the quorum established?
-This quorum is perceived with the help of signalling molecules (autoinducers).
-These molecules diffuse freely between cells and bind to receptors in each cell.
-When there has been sufficient binding of the signalling molecules to receptors in a cell, gene expression is changed. This causes a switch in activities.
-At a low rate (due to the low number of cells) this will only result in individual behaviour to that chemical signal.
-As the population density rises, all cells receive more of the signalling chemical from other cells.
-At high concentrations (above a certain density), every cell in the population receives enough to cause the change in gene expression and the resulting switch in activity – they have sensed there is a quorum.
