exam revision - cellular signals Flashcards
what is homeostasis
involves processes that are responsible for maintaining a relatively constant environment, ie, it provides cells with a relatively stable environment so that cells can function properly
explain the stimulus response model
stimulus (environment change)–> receptor (specialised cells)–> control centre (brain, CNS)–> effector (muscle, gland)–> response (opposite to the initial stimulus)
what are the two ways chemical messages can occur in animals
nervous system (synapse) endocrine system (hormones)
describe the nervous system
the nervous system consists of specialised cells that carry on action potential (nerve impulses) from one nerve to another or from one to a muscle or gland. The action potential is passed from one nerve to another across a synaptic cleft.
describe the endocrine system
regulates the bodies processes by releasing chemical messengers called hormones into the bloodstream. Hormones are produced in minute quantities yet can have a large effect on metabolism. Endocrine organs may be stimulated by a hormonal, humeral or neural stimulus.
What are types of signalling molecules
hormones, neurotransmitters, neurohormones, cytokines, pheromones
what are neurotransmitters
produced by neurones and cross the synapse.
what are pheromones
chemicals produced by animals and secreted into the external environment
what are hormones
steroids or peptides that are produced mainly in endocrine glands.
what is a signal transduction pathway
is the process that occurs in order for the chemical messengers to bind to a receptor site, in order to begin a chemical pathway (a cascade effect).
1. reception 2. transduction 3. response
what are the two types of signal transduction pathways
steroid hormones (small) peptide hormones (big)
how do steroid hormones undergo signal transduction
steroid hormones have a lipid base and are able to pass through cell membranes that are phospholipid in nature. They usually activate protein syntheses, steroids enter the cell directly where they interact with a receptor. This receptor hormone complex moves into the nucleus to interact with DNA. This interaction “turns on” specific genes to produce a protein in response to the initial stimuli.
how do peptide hormones undergo signal transduction
unlike steroids, they cannot pass through the phospholipid bilayer. The receptor site is therefore on the cell surface, this is where the hormone receptor complex begins, which produces a cascade effect inside the cell to produce a response to the initial stimuli.
What are two examples of signalling molecules and explain them
CYTOKINES- are international signalling molecules and come in many types. Cytokines act as cell messengers in a number of ways for eg; stimulate cells to reproduce; initiate transduction pathways; inhibit cells from reproducing.
PHEROMONES- external signalling molecules. They are released into the surrounding environment with the hope to find target cells in other organisms
What are the five major groups of plant growth regulators (hormones)
auxins, gibberellins, ethylene, cytokinins, abscisic acid
