1 - Intro to Hormone Signalling Flashcards
Stimuli triggers what?
Signal transduction
What is signal transduction?
Signal transduction is a cascade of biochemical changes that occur inside the cell which mediates how a cell responds to a particular stimulus
What does stimuli include in humans?
Hormones, neurotransmitters, and growth factors (but also light photons, odorants, and taste)
What do growth factors refer to?
A particular type of hormone that controls cell growth and division and have an intimate role in cancer
What do stimuli bind to?
Most stimuli bind to receptor proteins in the target cell causing responses, i.e., signal transduction and biochemical changes that control the activity of a cell
Example of stimuli binding
Neurotransmitters allow nerve cells to communicate across synapses by interacting with post-synaptic receptors and opening ion channels (response). In this case, the stimuli of the neurotransmitters bind receptors and trigger responses, which is the opening of the ion channels, and the entry and exit of ions is the signal transduction which controls changes in cell behaviour
Steps of hormone-initiated signal transduction
- BIOSYNTHESIS of a hormone
- STORAGE and SECRETION of the hormone
- TRANSPORT of the hormone to target cell
- RECOGNITION by the hormone receptor protein
- RELAY and AMPLIFICATION of the signal that leads to defined biochemical sections within the target cell
- REMOVAL of the hormone
- BIOSYNTHESIS of a hormone
Biosynthesis in the endocrine gland
- STORAGE and SECRETION of the hormone
- stored in the endocrine gland until they are required for secretion
- storage primes the system - don’t need to rely on de novo synthesis of new hormones
- often they are already stored and ready for action in their particular endocrine gland
- TRANSPORT of the hormone to target cell
The transport of hormones can involve a particular transport protein - which allows the hormone to mix with the bloodstream
- RECOGNITION by the hormone receptor protein
Causes a conformational change to take place
- RELAY and AMPLIFICATION of the signal that leads to defined biochemical reactions within target cell
Translated and amplified by biochemical changes or signal transduction inside the target cell which causes changes in cell activity
- REMOVAL of the hormone
- it is important to switch off the signal once a desired effect has been reached
- if we don’t then it can lead to serious disease states, so we often have what’s called “negative feedback” effects, whereby the production of hormone will then lead to changes resulting in the same production being switched off
- removal of the hormone from the system so it’s no longer able to interact with target receptors
- removal can involve degradation of the hormone by particular enzymes
What are hormones?
Chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body
Where do hormones travel? (include example)
- hormones reach all parts of the body but only target cells have receptors for that hormone
- for example, insulin will be secreted from the pancreas - it will travel through the bloodstream but will only regulate cells that express insulin receptors on the cell surface
What is the function of the endocrine system?
Chemical signalling by hormones is the function of the endocrine system
What is the endocrine signalling system?
- a system of glands inside the body that produce and secrete hormones into the bloodstream
- “endo” because they secrete into the body
Give four examples of how cells communicate
- Direct
- Synaptic
- Paracrine
- Endocrine
What is direct communication? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]
- ions, small molecules
- direct movement through gap junctions linking the cytoplasm of adjacent cells
- ions flowing between cardio muscle cells
What is synaptic communication? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]
- neurotransmitters
- diffusion from a neutron across a narrow space (synaptic cleft) to a cell bearing the appropriate receptors
- acetylcholine
What is paracrine signalling? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]
- local hormones
- diffusion through extracellular fluid to nearby cells bearing the appropriate receptors
- prostaglandins
What is endocrine signalling? [include chemical messengers (1), mechanism of transmission (2), and examples(3)]
- hormones
- carried in the bloodstream to near or distant cells bearing the appropriate receptors
- insulin
What are the 3 major classes of hormones?
polypeptides, steroids, amines
What are polypeptide hormones?
- made up of strings of amino acids, and can range from about 10 amino acids up to hundred of amino acids
- insulin is included in this polypeptide hormone class
What are steroid hormones?
- derived from the chemical cholesterol
- these are a particular class of hormones which are largely non-polar
What are amine hormones?
- derived from animo acids
- generally water soluble like polypeptide hormones - travel through bloodstream
What is the signalling pathway of water soluble hormones?
- water soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors
- receptors need to be at the cell surface because they hormones can’t pass through the cell membrane
Give 2 examples of water soluble hormones
- insulin belongs to the polypeptide class of large water soluble proteins
- epinephrine (amine class) - derived from a single amino acid tyrosine
Give 2 examples of lipid soluble hormones
- thyroxine (thyroid hormone produced by the thyroid gland) - an amino acid hormone
- cortisol
What is thyroxine?
- thyroid hormone produced by the thyroid gland
- 2 separate tyrosine molecules that have been decorated with iodine (unusual- thyroid hormones are the only ones in the body with iodine attached to them)
- largely hydrophobic because of the two aromatic rings with iodines - tends to mix with the cell membrane and require transport proteins to allow it to travel through the bloodstream
Features of steroid hormones
- steroid hormones are classic examples of the lipid soluble hydrophobic hormones
- derived from the structure of cholesterol which gives the four ring structure - planar, very hydrophobic and that lends the hydrophobic properties to the molecules
- aliphatic in nature
- are able to pass through the cell membrane and interact with intracellular receptors
Give an example of a steroid hormone
- cortisol is a long term stress hormone nd is produced by the adrenal glands, but the steroid hormones also tend to have some charged residues attached, e.g., hydroxyls, which makes them behave a little bit like fats
What is the lipid soluble (steroid) hormone pathway?
- steroid hormones enter through the cell membrane
- secreted into the bloodstream
- travel through the bloodstream, bound to transport proteins
- recognise target cell by the intracellular receptor
- dissociate from the transport protein when they sense the receptor
- pass through the cell membrane of target cells and interact with the receptor inside the cell
What is the lipid soluble (steroid) hormone pathway?
- steroid hormones enter through the cell membrane
- secreted into the bloodstream
- travel through the bloodstream, bound to transport proteins
- recognise target cell by the intracellular receptor
- dissociate from the transport protein when they sense the receptor
- pass through the cell membrane of target cells and interact with the receptor inside the cell
How can steroid hormones directly stimulate transcription?
- directly stimulate transcription of genes to make certain protein
- the receptors become activated and interact directly with target genes and change gene expression
- this causes responses in the cytoplasm, leading to long term changes
Are steroid hormones or peptide hormones faster?
- because steroids work by triggering gene activity, the response is slower than peptide hormones
