C2.1 Chemical Signalling Flashcards
Define ligand.
Ligands are signalling molecules that cause biochemical reactions that lead to a specific response.
Outline the structure and function of receptor molecules.
Structure:
- Receptor molecules exhibit specificity to ligands due to the structure of their binding sites
Function:
- Chemical signalling helps maintain homeostasis, development, immune response, neural function and metabolic regulation by receiving signals from outside the cell and passing the signals to the inside
Outline the relationship between receptor and a specific ligand.
Receptors and ligands interact either directly or indirectly
Directly:
- involving cell-to-cell contact
Indirectly:
- occurs through the secretion of molecules by one cell that are transported to the target cells
Describe the 6 stages of chemical signalling in cells
- Synthesis and release of ligand from signalling cell
- Transport and diffusion - Ligand transports to target cell (for instance, in the blood)
- Receptor binding - Binds to receptor on target cell
- Signal Transduction - binding to receptor causes a series of reactions within the cell
- Cellular response - the cell produces a response (for instance, expressing certain genes)
- Signal termination - ligand is degraded in order to terminate the signal
Describe the process of quorum sensing in a population of bacteria, including the role of signaling molecules, receptors and a threshold for gene expression.
- Bacteria involved in quorum sensing release small signalling molecules called autoinducers which diffuse in their environment
- once the population threshold for bacteria is reached, the bacteria coordinate the expression of genes with the help of autoinducers binding to receptors and inducing or stopping gene expression.
What are the 2 different types of bacteria and what do they use to communicate
Gram +ve bacteria
- Use processes oligopeptides
Gram-ve bacteria
- Use Acylated homoserine lactones (generally)
What is an example of Quorum sensing in bacteria
Bioluminescence in Vibrio Fischeri
What type of bacterium is vibrio fischeri
Gram -ve
Outline the process of bioluminescence in Vibrio fischeri as an example of quorum sensing in bacteria (6 stages)
- As a response to population density of the bacterium rising, VF releases an autoinducer called Acylated homoserine lactones
- The autoinducer induces the lux operon which, thus, produces more autoinducers
- When autoinducers get to a certain concentration, the enzyme luciferase is expressed also (it’s part of the lux operon)
- Luciferase catalyses a reaction which oxidises luciferin to oxyluciferin. This releases light
- As the release of light energy intensifies, this process ensures that light’s only released when numbers of bacteria are high
What are 3 applications of quorum sensing other than bioluminescence
- Medicine: Blocking quorum sensing can prevent biofilms from forming. Quorum sensing blockers could be used as alternatives to antibiotics
- Bioremediation: Which is being used to breakdown pollutants from the environment
- Food Spoilage: Autoinducers can be blocked in bacteria which causes food spoilage and biofilms to form
What chemical triggers bioluminescence in Vibrio fischeri
Acylated homoserine lactones
List the 4 main categories of signalling molecules in animals
List 2 extra signalling molecules
- Hormones
- Neurotransmitters
- Cytokines
- Calcium ions
Extra:
- Phermones: Communicate with members of the same species
- cAMP: act as secondary messengers in the signalling cascade
WARLD of hormones (action etc) - a signalling molecule in animals
Hormones:
- What: Regulate metabolic functions of other cells
- Action: act on tissues which possess receptors
- Release: Hormones secreted by endocrine glands into extracellular fluid
- Location: Receptors may be intracellular or on the surface membrane
- Duration: Effects remain for a prolonged period of time
WARLD of Neurotransmitters (action etc) - a signalling molecule in animals
Neurotransmitters:
- What: Transmit signals between neurones
- Action: Carry signals from one neurone to the other or from one neurone to a target cell like muscle cells
- Release: Released into the synaptic cleft
- Location: Signal is transmitted in only one direction
- Duration: Actions are short lived
WARLD of Cytokines (action etc) - a signalling molecules in animals
Cytokines:
- What: Small proteins involved in the immune response
- Action: They activate the lymphocytes at the site of inflammation.
- Release: Released by white blood cells
- Location: They activate lymphocytes at sites of infection
- Duration: Duration of action ranges from less than a second to several hours
WARLD of Calcium 2+ ions (action etc) - a signalling molecule in animals
Calcium 2+ ions:
- What: Act as ligands - can bind to proteins and activate them
- Action: They can bind and activate proteins
- Release: As they move in and out of cells via calcium pump in the plasma membrane
- Location: Can be found intracellular and extracellular
- Duration: Not considered
Outline the properties shared by all signalling chemicals.
- Specificity
- Reception
- Transmission
- Cellular Response
List the 3 main chemical categories of hormones.
- Amine hormones
- Peptide hormones
- Steroid or Lipid-derived hormones
Properties of amine hormones
- Small molecules derived from the amino acids tyrosine and tryptophan
- Mostly not lipid soluble so they bind to receptors on surface of target cells
- Bind to surface receptors
Give 3 main examples of amino acid derived hormones; If can, where they are secreted by too
- Noradrenaline and Adrenaline; Secreted by medulla of adrenal gland
- Thyroxin; Secreted by the thyroid gland
- Melatonin; Secreted by pineal gland situated in the brain - helps to maintain circadian rhythm
- Seratonin; Secreted by the tryptophan
Properties of peptide hormones
- They are in the form of polypeptide chains, small proteins, glycoproteins
- Not Lipid soluble
- Bind to surface receptors
Give 4 main examples of peptide hormones; If can, where they are secreted by and what they do too
- Insulin; Secreted by the pancreas in response to blood glucose level and promotes the uptake of glucose
- Oxytocin
- FSH
- Growth hormone
Properties of Lipid-based hormones
- Lipid Soluble
- They are derived from cholesterol
- Steroid hormones are insoluble: Require carrier proteins to be transported via blood
- Remain in circulation for longer
- Can cross membrane directly into the cell
Give 4 main examples of lipid-derived hormones; If can, where they are secreted by and what they do too
- Oestradiol; Secreted by female reproductive organs
- Testosterone; Secreted by male reproductive organs
- Cortisol and Aldosterone; Secreted by the cortex of the adrenal gland
What molecule has a dual function; It can act both as a hormone and a neurotransmitter. Where is it secreted from too
- Epinephrine (also called adrenaline) which is secreted from the medulla of the adrenal glands
What are neurotransmitters
- Neurotransmitters are chemicals that transmit signals across a synapse
- They are synthesised in the neurones and stored in thin-walled sacs called synaptic vesicles.
List chemical categories of neurotransmitters.
- Amino acids
- Gases
- Esters
- Amines (modified amino acids)
Properties of amino acid as neurotransmitters
- Involved in fast synaptic transmission
- Glycine, Glutamate and GABA are examples
Properties of peptides as neurotransmitters
- Responsible for a number of physiological and homeostatic processes - increases the motivation to eat food
- Neuropeptide Y is an example
Properties of amines as neurotransmitters. Give 3 e.g. and explain them
- They are modified amino acids that have different functions
- Serotonin, an example, regulates the mood
- Dopamine, an example, is involved in reward and movement regulation in the brain
- Noradrenaline, an example, controls the fight or flight response
The one property of nitrous oxide as a neurotransmitter
- Acts as a moderator of neuronal functions