Ch.11 Cell Communication Flashcards
describe the basic signal-transduction pathway used for mating in yeast.
Explain the evidence that these pathways evolved before the first multicellular organisms appeared on Earth.
each yeast cell secretes a mating factor that binds to receptors on the other cell type. Binding of the factors to receptors induces changes in the cells that lead to their fusion. The nucleus of the fused cell includes all the genes from the a and alpha cells.
explain the evidence that these pathways evolved before the first multicellular organisms appeared on Earth.
the similarities in animal, plant, and bacteria cell signaling provide proof the pathways evolved before organisms became multicellular.
explain how plant and animal hormones travel to target cells
- plant: travel in vessels, move through cells,
diffuse through air as a gas - animal: circulatory system (bloodstream)
list the three stages of cells signaling
- reception
- transduction
- response
describe the reception step of the cell signaling process
the target cell detects a signal from outside the cell by the signal binding to a receptor on the target cell’s plasma membrane or inside the cell
describe the transduction step of the cell signaling process
the binding of the signal changes the receptor protein’s shape and initiates transduction, this is where the signal is converted to a form that brings about a specific cell response `
describe the response step of the cell signaling process
the transduced signal triggers a specific cellular response: catalysis of enzymes, rearrangement of cytoskeleton, transcription of genes
describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system
signaling molecule(ligand) shape is specific to the binding site of its receptor. binding causes a receptor protein to undergo a change in shape which either activates the receptor, enabling it to interact with other molecules. Or, causes the aggregation of two or more receptor molecules leading to further molecular events inside the cell
state where signal receptors may be located in target cells
in/on the plasma membrane or inside cell(cytoplasm)
compare and contrast G-protein-linked receptors, tyrosine-kinase receptors, and ligand-gated ion channels
G-protein-linked receptors: plasma membrane receptor that works with the help of a G-protein. G protein uses energy of GTP to activate, and then activate an enzyme that triggers a cellular response
Tyrosine-kinase receptor: dimerize upon ligand-binding, and use ATP to activate tyrosine kinase regions. Multiple relay proteins act upon the regions and become activated, leading to a cellular response.
Ligand-gated ion channels: ligand binds and a gate opens or closes, allowing or blocking the flow of ions through a channel across the membrane. Change in concentration leads to a cellular response
list two advantages of using a multistep pathway in the transduction stage of cell signaling
- greatly amplifies the signal
- provides more opportunities for coordination and regulation than simpler systems
explain how an original signal molecule can produce a cellular response when it may not even enter the target cell
the original signal molecule information is passed on through the relay molecule pathway
describe how phosphorylation propagates signal information
The signal is transmitted by a cascade of protein phosphorylations, each causing a shape change because of the interaction of the newly added phosphate groups with charge or polar amino acids on the protein being phosphorylated. The change in shape alters the function of the protein, most often activating it. The added phosphates amplify the signal by the end
explain why a single cell may require hundreds of different protein kinases
each kinase is specific for a different substrate protein
explain how protein phosphates turn off signal-transduction pathways
remove phosphate groups from proteins, deactivating the protein kinases so no initial signal is present
define second messenger. briefly describe the role of these molecules in signaling pathways
second messengers are small, non-protein, water-soluble molecules that can spread easily by diffusion. They participate in pathways that are initiated by both G protein-linked receptors and receptor tyrosine kinases. The two most widely used are cyclic AMP and calcium ions
describe how cyclic AMP is formed and how it propagates signal info in target cells
cyclic AMP is formed from the binding of epinephrine to the plasma membrane of a liver which elevates the cytosolic concentration of cyclic AMP. When it is created cAMP broadcasts the signal to the cytoplasm
describe how the cytosolic concentration of Ca2+ can be altered and how the increased pool of Ca2+ is involved with signal transduction
in plant cells, a wide range of hormonal and environmental stimuli can cause brief increases in cytosolic Ca2+ concentration, triggering various signaling pathways. In response to a signal relayed by a signal transduction pathway, the cytosolic calcium level may rise, usually by a mechanism that releases calcium from the cell’s ER. The pathways leading to calcium release involve two other second messengers, IP3 and DAG
describe how signal info is transduced into cellular responses in the cytoplasm and in the nucleus
pathways of reactions, one protein binds to another, which binds to another, and so on, until it reaches its target and produces a cellular response in nucleus
describe how signal amplification is accomplished in target cells
elaborate enzyme cascades amplify the cell’s response to a signal. At each catalytic step in the cascade, the number of activated products can be much greater than in the preceding step
explain why different types of cells may respond differently to the same signal molecule
the particular proteins a cell possesses(relay,receptor,and response) determine what signaling molecules it responds to and the nature of the response. The proteins are different because they code for different genes
explain how scaffolding proteins help to contribute a cell’s response to incoming signals
scaffolding proteins are large relay proteins to which several other relay proteins are attached. It carries all these proteins with it when binding to a receptor, thus facilitating the transduction of these molecules
describe the roles of ced-3, ced-4, and ced-9, in apoptosis during embryonic development in Caenorhabditis elegans
ced-3 and ced-4 are two key apoptosis genes that encode proteins essential for apoptosis. ced-3 a protease triggers a cascade of reactions leading to activation of nucleases and other proteases.
ced-9:a protein in the outer mitochondrial membrane acts as a brake in the absence of a signal promoting apoptosis.
When a death signal is received by the cell, Ced-9 is inactivated and ced-3/4 are uninhibited
describe the events that may trigger signals from within a cell to trigger apoptosis
- signal is generated from the nucleus when the DNA is has suffered irreparable damage
- ER signals when excessive protein misfolding occurs
describe the role of apoptosis in normal development and degenerative disease in vertebrates
cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components. The cell shrinks and becomes loved and the cell’s parts are packaged up in vesicles that are engulfed and digested by specialized scavenger cells. This is needed because it is essential for normal development of the nervous system, normal operation of the immune system, and for normal morphogenesis of hands and feet in humans and paw in other mammals.
