Lect 10. Energy & Metabolism - Cell Signalling
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Cell communication focuses on how a cell ____ from its ____ and ____ and how it transmits messages to other cells.
Cell communication focuses on how a cell receives messages (chemical and physical signals) from its environment and surrounding cells and how it transmits messages to other cells.
Cell Communication in Prokaryotes Cell-cell communication in bacteria is called
quorum sensing
Responses to signalling in prokaryotes (by quorum sensing)
• sporulation • conjugation (sex) • bioluminescence (light emission) in symbiosis • virulence: secretion of proteins that allow the bacteria to attack multicellular hosts and cause disease • production of biofilms - hard, polysaccharide-rich substances that encase the cells and attach them to a surface (like plaque)
Types of Signalling in Eukaryotes (plants and animals)
• Direct Signalling a) cell junctions b) cell-cell recognition • Local Signalling (Paracrine signalling) (neurotransmitters) • Long Distance Signalling
Long Distance Signalling in Eukaryotes The activities of cells, tissues, and organs in different parts of a multicellular organism are coordinated by
hormones, which are bound by target cells.
Steps of Cell Signalling (Eukaryotes) cell-cell
• Signal Reception • Signal processing • Signal response • Signal deactivation
Hormones only affect cells that have the precise:
receptors
Hormones can bind receptors in a variety of target cells; different kinds of cells can respond differently to the ____ hormone.
Hormones can bind receptors in a variety of target cells; different kinds of cells can respond differently to the ** same** hormone.
ex of hormones that have a wide range of targets:
sex hormones
ex of hormones that have a narrow range of targets:
gastrin in the stomach
Hormones can come into contact with virtually all body cells since the cardiovascular system transports hormones throughout the body. But, a hormone was designed to affect only specific cells which often have receptors on the cell surface or inside the cell that are specific to one hormone. These cells are called:
target cells. Some target cells only have receptors for 1 hormone only, others can respond to as many hormones as it has receptors for.
Hormone Receptors 2 general reception methods used by hormones (depending on structure):
• cell surface receptor-mediated signaling: conversion of an extracellular chemical signal into an intracellular response • intracellular receptor-mediated signaling: involves transcription factors.
Cell surface receptor-mediated signaling Hormones using this method are ____ & ____, therefore cannot ____.
Hormones using this method are hydrophilic & polar (non-lipid soluble), therefore cannot diffuse into the cell.
Cell surface receptor-mediated signaling Hormones bind to receptor on cell surface, which activates the receptor. This activation of the receptor in turn activates a ____ leading to activation of a ____.
Hormones bind to receptor on cell surface, which activates the receptor. This activation of the receptor in turn activates a signal transduction pathway leading to activation of a target protein (ex: an enzyme).
Cell surface receptor-mediated signaling These hormones are made from ____, they are called:
These hormones are made from amino acids: peptide hormones
Cell-surface receptor-mediated signalling In a ____, molecules relay the signal. This adds complexity.
signal transduction pathway transduction, step before response
Intracellular receptor-mediated signaling Hormones using this method are ____, ____ or ____, ____, therefore can ____.
Hormones using this method are hydrophobic, lipid-soluble or small, non polar, therefore **can diffuse into the cell.
Intracellular receptor-mediated signalling Hormones bind to receptors inside the cell; receptor-hormone complex acts as a:
transcription factor ex: steroid and thyroid hormones, hormonal form of vitamin D
Steps of intracellular receptor-mediated signaling
• Hormone passes through PM • Hormone binds to a receptor protein in the cytoplasm, activating it • Hormone-receptor complex enters the nucleus and binds to specific genes (target gene DNA) • The bound protein stimulates the transcirption of the gene into mRNA • The mRNA is translated into a specific protein
step 2 of cell signaling in eukaryotes Signal processing (signal transduction pathways) involve 2 key elements:
• Second messengers • Phosphorylation cascades
Second Messengers The hormone that binds to the receptor is a pathway’s ____. Second messengers are:
The hormone that binds to the receptor is a pathway’s first messenger. Second messengers are small, non-protein, water-soluble molecules or ions that spread throughout a cell by diffusion.
ex: What is one of the most widely used second messengers in signal transduction pathways?
Cyclic AMP (cAMP) Adenylyl cyclase converts ATP to cAMP in response to an extracellular signal.
ex: a signal molecule binds to a ligand-gated ion channel, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor. These ions act as:
second messengers.
In many pathways, the signal is transmitted by a series of:
protein phosphorylations (phosphorylation cascade)