Cell Signaling Flashcards
List 5 reasons cell signaling is important
- information processing
- self-preservation (eg. reflexes)
- voluntary-movement
- homeostasis
Which two main types of cells are responsible for cell signaling and what are the differences between both?
- nerve fibres from central & peripheral nervous system = rapid, almost instantaneous response (nervous system like e-mail)
- blood vessels of the cardiovascular system = slower but more versatile regulation (endocrine system like postal delivery)
What is endocrine communication & what are 2 examples?
hormone travels in blood vessels to act on a distant target cell
eg. physiological response to hypoglycemia (glucagon secreted, travels in blood vessels, stimulates glycogenolysis & gluconeogenesis)
insulin in pancreas -> liver, muscle cells & adipose tissue
adrenaline from adrenal glands-> trachea
What is paracrine communication & 2 examples?
hormone acts on an adjacent cell
eg. physiological response to hyperglycemia (glucose->insulin secreted in pancreas acts beta cells on adjacent alpha cells = inhibits glucagon secretion in liver)
- nitric oxide produced by endothelial cells in blood vessels = vasodilation
- osteoclast activating factor is produced by adjacent osteoblasts during bone formation
What is communication between membrane receptors + 2 examples?
signalling/interaction between two proteins on the plasma membrane
eg. antigen presenting cell detecting blood borne virus (eg hep C) within the blood stream & digests the pathogen then expresses major histo-compatibility (MHC) class II which a T-lymphocyte interacts with using its t-cell receptor
- HIV GP120 glycoprotein -> CD4 receptors on t-lymphocytes
- COVID-19 attaches to angiotensin II receptor on cells
What is autocrine communication & 2 examples?
signalling when molecule acts on the same cell
eg. activated T-cell expressing IL-2 receptor on surface then releasing IL-2 (interleukin 2) to be detected on the IL-2 receptor on the same cell
- growth factors from tumour cells causing mitogenesis
What are ligand-gated ion channel receptors aka ionotropic receptors and 1 example?
transmembrane with a central pore in their quaternary enzyme structure, its conformation changes when the appropriate ligand attaches to its ligand-binding domain which makes the pore open allowing ions to go through the receptor, they follow the concentration gradient
-eg nicotinic acetylcholine on skeletal muscle cells-> muscle contraction
or in cognitive enhancement in neurons
What are G protein-coupled receptors & 1 example?
- known as 7-transmembrane receptors because the channel protein crosses the cell membrane 7 times
- linked to an intracellular G protein complex
What is the process for G protein activation ?
alpha and beta subunits + GDP molecule (G protein complex) close to receptor
-> ligand binds & changes conformation of receptor = G protein complex attaches to receptor = GDP phosphorylated or exchanged to GTP
(GDP becomes active)
- > alpha subunit (Gα) dissociates from alpha-gamma subunit (Gβγ) = Gα (+GTP) and Gβγ can act as separate messengers to target protein
- > ligand leaves = GTPase on alpha subunit (+GTP) hydrolyses GTP to GDP -> Gα and Gβγ re-associate and near receptor again, do not always bind to the same subunit again
What does a G protein complex consist of?
an alpha (α) subunit, a beta-gamma (βγ) subunit and a GDP molecule (heterotrimeric, Gα and Gβγ)
How many G-protein complexes can bind to the receptor and what are the conditions?
multiple, as long as the ligand remains bound to the receptor and it remains in its active configuration
What are enzyme-linked receptors?
- one transmembrane domain, which has the ligand-binding domain on the outside and specialised enzymes (usually tyrosine kinase enzymes) on the inside
- require clustering of more than one receptor protein to activate the intracellular enzyme which trigger a signaling cascade within the cell
What are intracellular receptors?
transcription factors (regulate mRNA and protein synthesis) in the cytoplasm
What are the 2 types of intracellular receptors and what are the differences between them + similarities?
both have cell-membrane permeable steroid hormone ligands, both intracellular
Type I receptors = in cytoplasm and are associated with chaperone molecules called heat shock proteins (hsp), once hormone binds to the receptor, hsp protein dissociates, 2 hormone bound receptors come together to form a homodimer -> move to nucleus and attaches to DNA
Type 2 receptors = inside nucleus & often already bound to DNA, when hormone ligand binds there is direct transcriptional regulation by activated hormone-receptor complex
