Test 4 Review I Chapter 11 a External signals are converted to responses within the cell i Flight response epinephrine a k a adrenaline ii Apoptosis programmed cell death that integrates input from multiple signaling pathways iii 2 cell sexes 1 2 a iv Process 1 Each type secretes a specific factor that binds to receptors only on the other type of cell 2 When exposed to each other s mating factors a pair of cells of opposite type change shape grow toward each other and fuse mate 3 New a cell contains DNA of both cells in nucleus v Signal transduction pathway when a mating signal is changed transduced once being received by the yeast cell surface receptor into a form that brings about the cellular response of mating 1 Series of steps 2 Exist in both yeast and animal cells vi Quorum sensing the ability for bacteria to monitor the local density of cells by secreting molecules that can be detected by other cells allowing them to sense the concentration of such signaling molecules 1 Allows bacterial populations to coordinate their behaviors in activities that require a given number of cells acting synchronously a Ex The formation of a biofilm an aggregation of bacterial cells adhered to a surface i Slimy coating on logs or on leaves lying on the ground b Local and Long Distance Signaling i Cells can communicate via 1 Direct contact 2 Cell junctions a Free cytosol exchange 3 Cell cell recognition target cells to grow and divide iii Local signaling ii Growth factors local regulator in animals are compounds that stimulate nearby 1 Paracrine signaling when numerous cells simultaneously receive and respond to the molecules of growth factor produced by a single cell in their vicinity 2 Synaptic signaling occurs in animal nervous system when an electrical signal along a nerve cell triggers the secretion of neurotransmitter molecules c Three stages of cell signaling i Sutherland Nobel prize 1971 a These molecules act as chemical signals diffusing across the synapse the narrow space between the nerve cell and its target cell triggering a response in the target cell iv Both animal and plant cells use chemicals called hormones for long distance signaling 1 Endocrine signaling hormonal signaling in animals specialized cells release hormone molecules which travel via the circulatory system to other parts of the body where they reach target cells that can recognize and respond to the hormones a Ex Mammalian hormone insulin regulates blood sugar level and is a protein with thousands of atoms 2 Plant hormones plant growth regulators travel in vessels but more often reach their targets by moving through cells or by diffusing through cells or by diffusing through the air as a gas a Ex Plant hormone ethylene a pas that promotes fruit ripening and helps regulate growth is a hydrocarbon of only six atoms C2H4 small enough to pass through cell walls 1 Investigating how the animal hormone epinephrine stimulates the breakdown of the storage polysaccharide glycogen within liver cells and skeletal muscle cells a Team discovered that epinephrine stimulates glycogen breakdown by somehow activating a cytosolic enzyme glycogen phosphorylase i Glycogen phosphorylase could be activated by epinephrine only when the hormone was added to intact cells in a solution this told Sutherland 2 things 1 Epinephrine does not interact directly with the enzyme responsible for glycogen breakdown an intermediate step or series of steps must be occurring inside the cell 2 The plasma membrane itself is necessary for transmission of the signal to take place ii The process going on at the receiving end of a cellular conversation can be dissected into three stages from outside the cell 1 Reception the target cells detection of a signaling molecule coming a A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cells surface 2 Transduction the binding of the signal molecule changes the receptor protein in some way initiating transduction a Converts the signal to a form that can bring out a specific cellular response b Sometimes occurs in a single step but more often requires a sequence of changes in a series of different molecules a signal transduction pathway i Molecules in pathway are called relay molecules 3 Response almost any imaginable cellular activity such as catalysis by an enzyme ex Glycogen phosphorylase rearrangement of cytoskeleton or activation of specific genes in the nucleus a Helps ensure that crucial activities like these occur in the right cells at the right time and in the proper coordination with the activities of other cells of the organism d Reception A signaling molecule binds to a receptor protein causing it to change shape i Reception of the signal depends on the receiver 1 The signals emitted by an a yeast cell are heard only by its mate ii A receptor protein on or in the target cell allows the cell the hear the signal cells and respond to it 1 The signaling molecule is complementary in shape to a specific site on the receptor and attaches there like a key in a lock 2 Signaling molecule acts as a ligand molecule that specifically binds to another molecule often larger a Ligand binding changes the shape of the rp i Sometimes this activates the receptor enabling it to interact with other cellular molecules ii Sometimes this causes the aggregation of two or more receptor molecules leading to further molecular events inside the cell iii Most signal receptors are plasma membrane proteins but others are located inside the cell e Receptors in the Plasma membrane coupled receptors GPCRs i The largest family of human cell surface receptors are nearly 1000 G protein ii Most water soluble signaling molecules bind to specific sites on transmembrane receptor proteins that transmit information from the extracellular environment to the inside of the cell iii We see how cell surface transmembrane receptors work by looking at three major types 1 G protein coupled receptors GCPRs 2 Receptor tyrosine kinases 3 Ion channel receptors 1 Heart disease 2 Cancer 3 Asthma iv Cell surface receptor malfunctions are associated with many human diseases v G protein coupled receptor GPCR a cell surface transmembrane receptor that works with the help of a G protein 1 G protein a protein that binds the energy rich molecule GTP 2 Are all similar In humans vision smell and taste depend on GPCRs vi vii Malfunctions in G proteins are associated with human diseases like bacterial infections f Exploring
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