Studied by 4 peoplefour steps of communication
stimulus, the release of a signal, signal reception, and response
signaling molecules
a chemical messenger that functions in cell communication by affecting activities of other cells
target cell
a cell that has receptor proteins that can bind to a specific signaling molecule
ligands
a signaling molecule with a molecular shape and distribution of charge that allows it to match up with and bind to a complementary receptor protein
stimulus
something that evokes a specific functional reaction
quorum sensing
density-dependent production of signal molecules in bacteria that leads to population responses, such as bioluminescence of DNA uptake; part of prokaryotic signaling
hormone
a type of signaling molecule that is transported in the circulatory system by endocrine signaling
long-distance signaling
often carried in the circulatory system
endocrine signaling
signaling by hormones that travel through the circulatory system; ex. of long-distance signaling
paracrine signaling
signals that move by diffusion, when there is a concentration difference between two regions with movement from regions of high concentration to low concentration, and stimulate neighboring cells; ex. of short-distance signaling
autocrine signaling
the signaling cell and the target cell are the same; autocrine signaling occurs in bacterial quorum sensing
contact-dependent signaling
a form of signaling which requires two communicating cells to be in physical contact with each other
gap junctions
protein channels embedded in the membranes of two neighboring cells; signaling molecules and ions can travel directly from one cell to the next through gap junctions, allowing neighboring cells to communicate rapidly with one another directly
plasmodesmata
connections between two adjacent plant cells that permit molecules and other substances to pass directly from the cytoplasm of one cell to the cytoplasm of another
sensor
in homeostasis, the component that detects a stimulus
set point
in homeostasis, the typical physiological value of a particular parameter, such as body temperature or blood glucose levels, which is actively maintained by the body with very little fluctuation
negative feedback
a process in which the response or output of a system opposes the initial stimulus therefore turning off the signal, resulting in steady conditions aka homeostasis
positive feedback
a pattern of response in which the output or signal of a communication system increases the activity in the same system that produced the signal
signal transduction steps
the receptor is activated when it binds to the signal; the information in the signal is relayed within the cell; the cell responds to the signal; and the response to the signal is terminated
Specific binding in cell communication
receptor proteins must match the signaling molecules in molecular structure, shape, and charge distribution in order for the receptor and signal to fit together so they can bind to one another
tissue-specific responses
a signaling molecule can lead to different responses in different cells and tissues; one signal can trigger different tissue-specific responses
The hormone adrenaline circulates in the blood and so has access to all parts of an animal’s body. Describe why some cells in the body are affected by adrenaline and others are not.
some cells in the body are affected by adrenaline and others are not because only cells with receptor proteins that bind adrenaline will respond to adrenaline. cells absent in receptor proteins will not be affected by adrenaline, while for instance, target cells in the heart with receptor proteins that bind with adrenaline will respond by increasing heart rate
Describe two events that cause an inactive receptor protein to become activated
An inactive receptor protein becomes activated by two events which is when the receptor binds to the signal, and then the information in the signal is transferred within the cell
Signal transduction of hydrophilic signaling molecules
hydrophilic signaling molecules cannot pass through the cell membrane to enter the cell, and so bind to ligand-binding domains of membrane-bound receptor proteins. The activated receptor then initiates a signal transduction pathway, leading to a cellular response
G protein-coupled receptors
a receptor protein in cell membranes that is associated with a G protein that in turn alters activity of adenylyl cyclase and other generators of second messengers in responding cells; a hydrophilic signaling molecule
amplification
the process in which a small number of signaling molecules can generate a very large response; increase in volume
second messenger
an intermediate signaling molecule that amplifies a response inside a cell
G protein-coupled receptor activation
when a signal binds to the extracellular part of the receptor protein (top), the G protein binds to the signal–receptor complex inside the cell (middle). As a result of binding to the complex, the G protein’s GDP is exchanged for GTP. The G protein then binds to and activates a target protein (bottom). The active target protein produces intracellular events, leading to a cellular response.
cyclic adenosine monophosphate (cAMP)
derived from ATP and serves as an intracellular second messenger in many signal transduction pathways; is a second messenger that binds to and activates protein kinases
kinase
an enzyme that, when activated, catalyzes the transfer of phosphate groups from ATP to another molecule such as proteins
signaling cascade
a series of chemical reactions inside of a cell that are initiated by a signal and are typically amplified to produce a large cellular response
termination of the signaling pathway
The release of adrenaline from the receptor protein causes the conversion of GTP to GDP on the G protein. The inactive G protein then separates from adenylyl cyclase, inactivating adenylyl cyclase and halting cAMP production. The ongoing breakdown of cAMP terminates the activation of the kinases. The inactivated kinases no longer activate target proteins. Ongoing phosphatase activity removes phosphates from active target proteins, and nonphosphorylated proteins no longer contribute to responses
receptor-protein kinase
a receptor protein in cell membranes that have kinase activity that is activated after binding to an extracellular signaling molecule; a hydrophilic signaling molecule
ligand-gated channel
receptor proteins in cell membranes that alter membrane permeability to ions after binding to an extracellular hydrophilic signaling molecule; a hydrophilic signaling molecule
Ligand-gated channel (figure)
binding a ligand changes the shape of the ligand-gated ion channel, opening a channel through which ions can flow across the cell membrane. Until it binds the ligand, the receptor is in its inactive, closed conformation. Binding the ligand activates the receptor, opening the channel
gene expression
the production of a functional gene product, such as a protein; the “turning on” of a gene
steroid hormones
hydrophobic signaling molecules that are lipids derived from the molecule cholesterol; travel to target cells using bloodstream
hydrophilic signaling
rapid, short lived cell response; receptor proteins include G protein-coupled receptor, receptor-protein kinase, and ligand-gated ion channel
hydrophobic signaling molecule
slow and long-lived cell response, receptor proteins include intracellular receptor protein
adenyl cyclase
target protein for active G proteins that converts ATP into cAMP when activated, which then activates protein kinases
endogenous ligands
ligands produced by the body
exogenous ligands
ligands from outside the body
agonist
a ligand that binds a receptor and leads to a response
antagonist
a ligand that binds a receptor and inhibits a response; doesn’t allow any other ligand to bind to the receptor so the cell’s response to the signaling molecule is suppressed
altered proteins in cell communication
mutations in DNA can lead to mutant proteins. Mutations in proteins involved at any of the four points in the cell communication pathway shown can disrupt cell communication. Mutant proteins can inhibit ligand binding or the activation of any of the second messenger or target proteins, altering the cell’s response to the signal
negative feedback
maintains homeostasis by transmitting responses which restore steady conditions; Negative feedback maintains homeostasis. After an initial stimulus causes the release of a signal from a sensor, the effector elicits a response. The response in turn feeds back on the sensor, turning off further production of the signal. The result is that the system maintains steady conditions over time
positive feedback
signals become amplified after a signaling system has been initiated; In positive feedback, responses are amplified. A stimulus acts on a sensor to release a signal. The signal acts on an effector to cause a response. The response in turn stimulates more signal release from the sensor, amplifying the overall response to the initial stimulus over time
cell division
the process by which a parent cell gives rise to two daughter cells; basically cells make more cells
binary fission
what prokaryotes divide by, resulting in two daughter cells by the division of a single cell into two cells.
steps of binary fission
asexual reproduction
the reproduction of organisms in which an offspring inherits DNA from a single parent; cell division in prokaryotes is a form of asexual reproduction
mitosis
the stage of M phase that produces two identical nuclei during the eukaryotic cell cycle; divides the nucleus
cytokinesis
the stage of M phase in which the cytosol, organelles, and duplicated nuclei from one eukaryotic cell divide into two daughter cells; is after mitosis
chromosomes
cellular structures containing the genetic material in cells, consisting of a single DNA molecule with associated proteins
cell cycle
the collective name for the steps that make up the life cycle of a eukaryotic cell, including DNA replication and mitotic cell division
M phase
one of two major phases of the eukaryotic cell cycle, consisting of mitosis and cytokinesis; this phase is where the parent cell divides into two daughter cells
interphase
one of two major phases of the eukaryotic cell cycle, in which the cell copies its DNA and synthesizes proteins necessary for mitosis
S phase
the phase during interphase in which the cell copies its DNA; the S phase follows the G1 phase but precedes the G2 phase
sister chromatids
the two copies of a chromosome resulting from DNA duplication that remain connected at the centromere
centromere
a region of DNA where sister chromatids can be held together, it is also the place where the mitotic spindle attaches to drive chromosome movement during mitosis
interphase (continued)
Interphase consists of three phases: G1 phase, S phase, and G2 phase. During G1, the cell prepares for DNA replication. In S phase, DNA synthesis takes place, duplicating each chromosome. In G2, the cell prepares for M phase
G1 phase
the phase during interphase in which the cell synthesizes regulatory proteins controlling the eukaryotic cell cycle
G2 phase
the phase during interphase after DNA has been replicated, characterized by increases in cell size and protein contents
G0 phase
the phase in the cell cycle in which cells pause between M phase and S phase; it may last for periods ranging from days to more than a year
chromatin
inside the eukaryotic nucleus, chromatin refers to the assemblage of DNA, RNA, and protein that fills the nucleus
prophase
the first stage of mitosis in which the chromosomes condense and become visible through the microscope
prometaphase
the second stage of mitosis where the nuclear envelope breaks down and the microtubules of the mitotic spindle attach to chromosomes
mitotic spindle
a structure in the cytosol made up predominantly of microtubules that pull the chromosomes into separate daughter cells
kinetochores
the protein complex on a chromatid where the mitotic spindle attaches
metaphase
the third stage of mitosis in which the chromosomes align in the middle of the dividing cell
anaphase
the fourth stage of mitosis in which sister chromatids separate and travel to opposite poles
telophase
the phase of mitosis in which the nuclei of the daughter cells are formed and the chromosomes uncoil to their original state
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