CHAPTER 7 Flashcards
which ways can cells process information from the environment?
-the information can be a chemical or a physical stimulus
-EX: light
where cans signals come from?
-outside the organism or from neighboring cells
define signal transduction pathway
-a sequence of events that lead to a cell’s response to a signal
-signal transduction is highly regulated
what are the types of chemical signals?
-autocrine
-juxtacrine
-paracrine
-hormones
define autocrine
-signals affect the cells that made them
define paracrine
-signals affect nearby cells
define juxtacrine
-signals affect only adjacent (neighboring) cells
hormones
travel to distant cells, usually via the circulatory system
what are the elements of a signal transduction pathway?
-a signal, a receptor, and a response
-A cell’s response to a signal requires a receptor specific to that signal, often found at the cell membrane.
-Signal-receptor interaction occurs, amplifying the signal’s effects.
-Responses can involve activated or inactivated enzymes and transcription factors.
define crosstalk
-signal transduction pathways can be interconnected
How are signal transduction pathways interconnected?
Signal pathways can interact through crosstalk. This means that one activated protein might trigger multiple pathways, pathways can merge, and one pathway might be activated while another is deactivated.
receptor
-proteins have very specific binding sites for chemical signal molecules, or ligands
define ligands
-Any molecule that binds to a receptor site of another (usually larger) molecule.
-the ligands fit into a three-dimensional site on its receptor and causes the receptor protein to change shape
-the binding is reversible and the ligand is not altered
what can happen between molecules that are similar to ligands chemically?
they can both use the same receptor protein
what is the receptor ligand bonding formula
R + L ←→ RL
what does binding and dissociation have? what happens at equilibrium?
-they each have a rate constant
-at equilibrium rate of binding equals rate of dissociation
what is the equation of the equilibrium rate
k1[R][L] = k2[RL]
what is the formula for dissociation constant(KD)?
[R][L]/[RL] = k2/k1 = KD
what is the dissociation constant(KD) ?
-KD, is a measure of the affinity (attraction) of the receptor for its ligand.
what is the relationship between affinity and dissociation(KD) constant?
-having a lower dissociation content means you have greater affinity
-having a higher dissociation content means you have smaller affinity
what does low dissociation constant (KD) values allow?
-this allows them to bind to very low ligand concentrations
what is the dissociation constant value important for
-ligands functions as drugs
-the value is important when determining dosages
what are other chemicals that resemble ligands that can also bind to receptors?
-agonists
-antagonists
define agonists
-having the same effect as a the ligand
define antagonists
-(inhibitors) bind to the receptor, preventing the ligand from binding, but not setting off signal transduction
example of an antagonist and its ligand
-adenosine(ligand) initiates a signal transaction pathway in nerve cells that reduces brain activity and wakefulness
-caffeine is similar to adenosine and binds to the same receptors
-caffeine is an antagonist because it “ties up” the adenosine receptors, allowing continued nerve cell activity
define membrane receptors
-large or polar ligands (EX: insulin) bind to cell membrane receptors
define intracellular receptors
-for small or non polar ligands that can diffuse across the cell membrane (EX: estrogen)
what are the types of receptors eukaryotes have?
-protein kinase receptors
-G protein-coupled receptors
-intracellular receptors
define gated ion channels
-these allow ions to enter or leave a cell
-signal binding results in change in shape of the channel protein, and the channel opens
-the acetylcholine receptor on muscle cells is a ligand-gated ion chanell
define protein kinase receptors
-catalyze phosphorylation of themselves and/or other proteins, which changes their shapes
-the insulin receptor phosphorylates itself and other insulin response substrates, which initiates insertion of glucose transporters into the cell membrane
what is a phosphorylation include?
-a phosphate group
-OPO3 -
define G protein-coupled receptors
-signal binding to receptor activates a G protein, which then activates an effector protein
-G proteins have three subunit. when activated, one subunit moves through the cell membrane to an effector protein
define intracellular receptors
-respond to signals such as light or chemicals that can cross the cell membrane
-many transcription factors. after binding their ligands, they move to the nucleus, bind to DNA, and alter gene expression
what is the cascade event? what can the initial signal do?
-signals sometimes initiate a chain or cascade of events
-the initial signal can be amplified and distributed and result in several different cell responses
what do bladder cancer cells have?
-Bladder cancer cells have a abnormal G protein called Ras.
-This abnormal Ras is always stuck to GTP, leading to constant cell division.
-To prevent cell division, Ras inhibitors are used.
what is common in cancer cells?
-many cancers have abnormalities in signal transduction pathways causing an abnormal growth of cells
what happens in a protein kinase cascade?
one protein kinase activates the next one, and so on. (on and on event)
in a protein kinase cascade:
-the signal is amplified at each step
-information that arrived at the cell membrane is communicated to the nucleus
-multiple steps provide specificity
-different target proteins provide variation in the response
second messengers?
-small molecules that mediate some steps in a cascade
-ex: cyclic AMP (cAMP)
-they amplify and distribute the signal, known as “helpers”
what can lead to the production of cAMP?
binding of one signal molecules to a receptor can lead to this, which also activates many enzyme targets
what are second messengers involved in?
-they are involved in crosstalk
-Crosstalk means these messengers don’t just stick to one pathway. They can jump between different pathways within the cell, influencing how they work. For example, a messenger produced in response to one signal might affect another pathway, altering how the cell responds overall.
where are some second messengers formed?
-some are formed from membrane phospholipids
-hydrolysis of PIP2(in membrane) results in two second messengers
what are the two second messengers you need to know?
-IP3 (released to cytoplasm)
-DAG (in membrane)
what doe IP3 and DAG activate?
they activate protein kinase C (PKC)
what is protein kinase C (PKC)
PKC is a group of proteins in cells that can change many other proteins by adding a tag called phosphate (phosphorylate). This tag alters how these proteins work, causing different reactions in the cell.
information about Ca 2+ ion
-they can be second messengers
-its pumped out the cytoplasm, keeping concentration low
-IP3 and other signals open Ca 2+ channels, causing Ca 2+ concentrations to rise quickly. This increase in calcium activates a protein called protein kinase C.
information about Nitric oxide
-(NO) gas is a second messenger between acetylcholine (a neurotransmitter) and the relaxation of smooth muscle in blood vessels, allowing more blood flow
how is the concentration of NO and Ca 2+ regulated?
-NO is regulated by how much is made
-Ca 2+ depends on activity of membrane pumps and ion channels(open?closed?)
what are enzymes used for? what does it regulate?
-The cellular response to a signal depends on the balance between enzymes that turn on and enzymes that turn off the signal transducers.
-protein kinases, G proteins, and cAMP are all regulated by enzymes
how can the balance of enzymes be altered
-balance can be altered by synthesis or breakdown of the enzymes; or other molecules inhibit or activate enzymes
how do celles repsond to singlas?
-by opening ion channels
-by changing enzyme activity
-by differential gene expression
how can ion channels function?
-they can function as single receptors, and respond to signals by opening or closing
-EX: oxytocin can cause ion channels to open
enzymes may be modified in signaling pathways:
-phosphorylation by a protein kinase changes enzyme shape
-cAMP binds noncovalently to an enzyme to change its shape
(when you change the shape the enzyme loses its function or gets a new function)
-in the protein kinase cascade in liver cells stimulated by epinephrine, two enzymes are phosphorylated:
-glycogen synthase is inhibited: prevents glucose from being stored as glycogen
-phosphorylase kinase is activated: activates glycogen phosphorylase which catalyzes breakdown of glycogen
what doe signal transduction often target?
Signal transduction often targets transcription factors, which are like switches for genes. They can turn genes on or off by binding to specific DNA sequences.
ex: in the Ras signaling pathway, a protein kinase called MAPK goes into the nucleus and tells genes to start dividing cells.
what are the specialized intercellular junctions that cells within a tissue use to communicate directly?
-gap junctions in animals
-plasmodesmata in plants
define gap junctions
-channels between neighboring cells crated by connexons
-two connexons come together to span the gap and link the cytoplasms of the two cells
-this channel is too small for proteins but wide enough for ions and small molecules
define plasmodesmata
-These are tunnels that go through cell walls, made from the fused cell membranes
-the desmotubule, derived from the ER, fills the space in the plasmodesmata channels
-only small metabolites and ions move between plant cells (typically)
what plasmodesmata important for? how does it help with diffusion?
-they are important for circulation of materials; similar in function to capillaries in animals
-rapid diffusion of hormones through plasmodesmata to ensure that all cells respond to a signal at the same time
evolution of multi-cellular organisms took up to a billion years and probably occurred in steps of?
-aggregation of cells into a cluster
-intercellular communication
-specialization of some cells
-organization of specialized cells into tissues
evolution of intercellular communication
-this is a key event
The volvocine line of green algae shows how multicellularity may have developed.
It includes organisms starting from single-celled Chlamydomonas to groups with more cells.
Volvox, for instance, has around 1000 cells, with different cells for somatic and reproduction.
Many of these cells cannot survive or divide alone anymore.
