What is paracrine signalling?
A local form of signalling where the signalling molecule is released from the signalling cell into the local area like the matrix between a tissue. The target cell for these local mediators are cells with the specific receptors that are close by.
What is synaptic signalling?
A specialized form of electrochemical communication where neurons transmit signals to other neurons, muscles, or glands across a tiny gap called a synapse. An example of these signallers are neurotransmitters.
What is endocrine signalling?
Endocrine signalling utilises hormones synthesised in various tissues + organs within our bodies. Hormones are released in the bloodstream and travel through the blood to their target cells and they target cells that could be a range of cells throughout the body.Involves glands like the hypothalamus, pituitary gland, pineal gland, parathyroid gland, thyroid gland, thymus, adrenal gland, pancreas, kidney, testis and ovary.
What is intracellular signalling?
As a whole, intracellular signalling occurs once the external/extracellular signalling molecule reaches the cell and triggers a signalling pathway or the activation of a signalling pathway within the cell. Once the signalling molecule reaches the receptor, it triggers the activation of a pathway within the cell that could actually include quite a number of different signalling molecules. Several molecules may be involved before effector proteins are actually activated.
What are effector proteins?
Effector proteins carry out the role that the signalling protein is intending to perform. These effector proteins contribute to the target/desired cell responses, e.g. metabolic enzyme (altered metabolism), cytoskeletal protein (altered cell shape/movement) & transcription regulator (altered gene expression). Examples of effector proteins include metabolic enzymes, cytoskeletal protein and transcription regulators
What are the 4 types of signalling?
Contact-dependent (signal requires a membrane-bound signal molecule), paracrine, synaptic, and endocrine.
What are key features of cell signalling?
The specific targets of cell signalling allows for coordinated, and tightly controlled responses. It describes situations in which signal molecules fit the binding site on its complementary receptor whilst other signals do not fit. The activation of a receptor by a single signalling molecule quickly generates or activates an enzyme cascade, meaning that the no. of affected molecules increases geometrically. So, 1 signalling molecule can activate multiple enzymes
What is amplification in regards to enzymes?
Each time the next target enzyme is activated, the number of activated molecules increase. In an example, 1 molecule of glucagon doesn’t result in the generation of only 1 cAMP as that would fail in generating this cascade. This results in 10,000 molecules of glucose being generated
What is feedback in regards to enzymes?
Occurs when the downstream effect of a stimulus signals back to the signalling cell and either turns off or enhances the signal further. Provides feedback to the original cell responding to the stimulus. Once the stimulus enters a system, a particular signalling molecule may be released. Positive = increases change, negative = decreases/counteracts change
What is signal transduction?
The response time to this cell signalling can either be rapid (almost instant) or taking several hours. A fast response will occur if the signalling molecule works to activate/alter the function of a protein that might already be present in the cell. Slower reactions involve synthesising new proteins (transcription, translation or post-translational modifications) which is why the response takes longer. But, some reactions have both slow and fast elements
what are the fundamental where and whats of adrenaline?
the site of origin is the adrenal gland and it acts to increase blood pressure/ heart rate/metabolism. also, it is a derivative of the amino acid tyrosine
what are the fundamental where and whats of insulin?
found in the B cells of the pancreas, is a protein by nature. it works to stimulate glucose uptake, protein synthesis and lipid synthesis in various cell types
what are the 3 main classes of hormones?
Hormones can be divided into 3 main classes: polypeptide/protein hormones (insulin), amine (epinephrine), and steroid hormones (estrogen/testosterone)
what does the hypothalamus do?
Hypothalamus synthesises and release many releasing factors that act on the anterior pituitary.
what are polypeptides or protein hormones?
Once synthesised they’re stored in secretory vesicles for up to 1 day. Many are stored as prohormone. Vesicles fuse with the membrane which are released by exocytosis of secretory granules into the extracellular matrix. Secretion is regulated by other hormones, metabolites and CNS. They circulate freely in the blood. Have a lifetime of minutes
Is insulin a protein?
Yes, it’s a small protein that consists of 2 polypeptide chains (a and B). when it’s translated it is translated as a long single chain called proinsulin. When it’s synthesised it undergoes some post-translational modifications in the ER and is ultimately packaged into vesicles in the form of proinsulin. Once glucose levels rise and the beta cells within the pancreas need to secrete insulin, proinsulin is cleaved into mature insulin and released into the bloodstream.
What are peptide-amine hormones derived from tyrosine?
Amine = nitrogen base. Epinephrine & norepinephrine are synthesised in the Adrenal medulla. These are stored for several days, are secreted in response to signals from the CNS and are free in the blood with a lifetime of seconds.
Thyroxine and triiodothyronine are synthesised in the thyroid gland by the process of iodination of tyrosine residues followed by further modifications within the protein thyroglobulin. They are released by proteolytic cleavage.
what are lipophillic hormones?
They can diffuse straight through the cell membrane and pass directly through without needing to bind to a cell surface receptor. The receptors for these hormones are intracellular and examples are steroids (cortisol,testosterone, estradiol) and vitamin D
what is intracellular signal transduction?
Activation of a cell surface receptor initiates a relay, amplified, distributed, and modulated signal into the cell
how is phosphorylation used as a molecular switch?
Particular signalling molecules can be turned on through phosphorylation. Phosphatases remove phosphate groups. Some enzymes are turned off when phosphorylated and turned on when dephosphorylated
how are GTPases used as molecular switches?
Some molecules need to bind to GTP to become active. A GTPase is a molecule that becomes active upon the exchange of GDP for GTP. It functions to activate subsequent signalling molecules. In its inactive form, GTPase remains bound to GDP and a Guanine Nucleotide Exchange Factor (GEF) is required to promote the removal of GDP and exchange for GTP which in-turn facilitates the activation of GTPase. GAP (GTPase-activating protein) increases the rate at which a GTPase hydrolyses GTP to GDP. This converts the GTPase from its active (GTP-bound) form to its inactive (GDP-bound) form. After hydrolysis, GDP remains tightly bound to the GTPase, keeping it inactive until it is exchanged for GTP again.
what is the Ras family?
There is a Ras family of GTPases with examples like H-Ras, K-Ras, and N-Ras that promote cancer by causing an an overactive stimulation of cell grown & survival pathways but it overall functions to relay signals from RTKs
what are receptors? how many types are there, and what are they?
There are either cell-surface receptors or intracellular receptors which differ greatly in size (the first sends signals from its membrane whereas the second sends them from its nucleus). Cell surface receptors typically have 3 regions, an extracellular region, transmembrane, and intracellular region
Intracellular receptors are found either within the nucleus or within the cytoplasm. The ligands/molecules that will bind to these are generally lipophilic and can pass directly through the membrane into the cell where the receptor is.
what are cell surface receptors?
in this sub-class, there are ion-channel-coupled receptors, G-protein-coupled receptors, and enzyme-coupled receptors. In ion channel-coupled receptors, the signalling molecule induces the opening or closing of an ion channel that allows ions to pass through. This is common for neurotransmitters + signalling related to neuronal cells.
In enzyme-coupled receptors, receptors are enzymes themselves or very closely associated with an enzyme. When the signalling molecule binds it leads to the activation of those enzymes, which in-turn leads to the propagation of that signal
