Unit 6: Cell Signaling and Hormones
secretory cell
(1) The physiological process of synthesizing and eventually releasing substances from the interior of a cell to its exterior. (2) The substance secreted. Supplement. In eukaryotes, cells primarily involved in secretion have well-developed endoplasmic reticulum and Golgi apparatus.
steroid hormones
(estrogen, testosterone...) lipid soluble, and acn go through the cell membrane and attach to cytoplasmic recpetors to begin signal responses
protein hormones
(insulin, glucagon), water soluble, cannot go through the cell membrane, must attach to specific membrane receptor to effect a response
secondary messengers
(like cAMP), diffuse readily through the cytosol and thus help broadcast signals quickly. Many G proteins activate adenylyl cyclase, which makes cAMP from ATP.
Effects of lipid-soluble hormones:
-In most cases, lipid-soluble hormones stimulate the synthesis of new kinds of proteins by altering gene expression in the target cell. -The synthesis of new kinds of proteins leads ultimately to anatomical, physiological, or behavioral changes.
Two effects of epinephrine?
1) The mobilization of fuel reserves, which can be used by the animal to either defend itself (fight) or escape whatever elicited a scare (flight).
regulation of a thyroid gland
1. Hypothalamus reacts to you eating a big meal by secreting a hormone TRH. 2. TRH travels to the pituitary gland, which in turn secretes TSH 3. TSH hormone travels though the blood stream to target cells in the thyroid gland, which are signaled to release TH which goes to regulate the metabolism of food 4. TH builds up in blood, and "turns off" production of TRH by hypothalamus (negative feedback)
Describe the event that sets off phosphorylation cascade inside of a cell
A ligand attached to an active site in a recepetor protein in a cell membrane
What event begins the process of producing a cellular response?
A ligand attached to the active site of a receptor protein molecule
leaf abscission
Abscission, as defined by Merriam-Webster, is the shedding away or cutting off of different body parts of an organism, generally in terms of a plant. When you see a plant dropping its leaves or its fruits, this is a form of abscission. Leaf abscission is simply when a plant drops its leaves.
Absciscis acid (ABA)
Almost all plant cells have the ability to synthesize abscisic acid, ann its presence has been detected in every major organ and living tissue; may be transported in the phloem or xylem.
What advantage would there be to an organism if the signal transduction pathway had several amplification steps?
Amplification allows the reception of a single ligand to cause a response in several places in the cell, which allows an organism to respond to a stimulus more quickly.
Antidiuretic hormone/ADH/vasopressin
Antidiuretic hormone (ADH): A relatively small (peptide) molecule that is released by the pituitary gland at the base of the brain after being made nearby (in the hypothalamus). ADH has an antidiuretic action that prevents the production of dilute urine (and so is antidiuretic).
neurotransmitters
At synapses, neurons secrete molecules called neurotransmitters that diffuse a very short distance to bing to receptors on the target cells
Difference between lipid-soluble hormones and water-soluble hormones:
Because lipid-soluble hormones stimulate the synthesis of new kinds of proteins, rather than serving to modify existing proteins, their actions are slower and last longer then those of water-soluble hormone
cGMP
Both cGMP and Ca2+ must be produced for a complete de-etiolation response. Many second messengers, including these, activate protein kinases directly.
What is the function of the endocrine system?
Chemical signaling by hormones. The endocrine system is one of the two basic systems of communication and regulation through the body.
Brassinosteroids
Compounds present in all plant tissues, although different intermediates predominate in different organs. Internally produced brassinosteriods act near the site of synthesis .
Describe what amplification steps mean in terms of the signal transduction pathway example
Each kinase can activate more than one of the next kinase enzymes in a sequence
etiolation
Etiolation is a process in flowering plants grown in partial or complete absence of light. It is characterized by long, weak stems; smaller leaves due to longer internodes; and a pale yellow color (chlorosis).
Describe the type of diffusion that is used to get the secondary messengers into the cell
Facilitated diffusion
long-day (short-night) plant
Flowers only if the night is shorter than a critical dark period. A brief flash of light artificially interrupts a long dark period, thereby inducing flowering.
short-day (long-night) plant
Flowers when night exceeds a critical dark period. A flash of light interrupting the dark period prevents flowering.
Ethylene
Gaseous hormone can be produced by most parts of the plant. Produced in high concentrations during senescence, leaf abscission, and the ripening of some types of fruits. Synthesis is also stimulated by wounding and stress.
gravitropism
Gravitropism (also known as geotropism) is a turning or growth movement by a plant or fungus in response to gravity. It is a general feature of all higher and many lower plants as well as other organisms.
What was Sutherland's team investigating at Vanderbilt?
How the animal hormone epinephrine (adrenaline) stimulates the breakdown of the storage polysaccharide glycogen within liver cells and skeletal muscle cells.
Negative feedback example
Hypothalamus--pituitary--thyroid gland signaling during food metabolism
What is the main purpose of Abscisisc acid?
Inhibits growth; promotes stomatal closure during drought stress; promotes seed dormancy and inhibits early germination; promotes leaf senescence; promotes desiccation tolerance.
What are "antagonistic" hormones which work together to regulate glucose.
Insulin & Glucagon
What followed up Darwin's experiment?
Later on, Boysen-Jensen's results suggested that the signal for the bending is a light-activated mobile chemical.
gibberellin
Meristems of apical buds and roots, young leaves, and developing seeds are the primary sites of production.
Where do the phosphate groups come from that are aded to the proteins during phosphorylation?
Phosphate groups comes from ATP molecule that converts to ADP
What would need to occur int he cell to deactivate the protein kinase enzymes?
Phosphate groups would have to be removed
Major functions of ethylene?
Promotes ripening in many types of fruit, leaf abscission, and the triple response in seedlings)inhibition of stem elongation, promotion of lateral expansion, horizontal growth); enhances the rate of senescence; promotes root and root hair formation; promotes flowering in the pineapple family.
protein kinases
Proteins are phosphorylated by a wide variety of protein kinases
seed dormancy
Seed dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination. These conditions are a complex combination of water, light, temperature, gasses, mechanical restrictions, seed coats, and hormone structures.
Although signal transduction pathways vary among species, there are several common elements. Explain how a biologist might use details about signal transduction pathways used in different species as evidence for evolutionary relatedness
Species that use the same replay proteins, receptor proteins, and the same ligands are probably closely related by evolution.
de-elotation
Stem elongation slows; leaves expand; roots elongate; and the shoot produces chlorophyll. The response is an example of how a plant cell's reception of a signal--in this case, light--is transduced into a response (greening).
Two types of animal hormones?
Sterioid and protein
cytokinins
Synthesized primarily in roots and transported to other organs.
What did Sutherland's team discover?
That epinephrine stimulates glycogen breakdown by somehow activating a cytosolic enzyme, glycogen phosphorylase.
What did Sutherland's early work suggest?
That the process going on at the receiving end of a cellular conversation can be dissected into 3 stages: RECEPTION, TRANSDUCTION, AND RESPONSE.
What are associated with many human diseases?
The activity of all three types of receptors is crucial to proper cell functioning and abnormal GPCRs and RTKs are associated with many human diseases.
What activates or opens the transport protein channel that allows the secondary messengers to enter the cell?
The membrane channels is opened by the activated relay protein, which attaches to an active site on the transport protein.
Process of water-soluble hormones
The receptors have a binding domain that projects beyond the outside of the plasma membrane and a catalytic domain that projects into the cytoplasm of the cell. -Directly or indirectly, most receptors initiate cellular responses by activating protein kinases, which catalyze the transfer of phosphate groups from ATP to specific proteins. -Phosphorylation of specific proteins causes them to become activated or de-activated, thereby leading ultimately to anatomical, physiological, or behavioral changes.
secretory vesicle
The secretory vesicle is a vesicle that mediates the vesicular transport of cargo - e.g. hormones or neurotransmitters - from an organelle to specific sites at the cell membrane, where it docks and fuses to release its content.
auxin
The term auxin is used for any chemical substance that promotes elongation of coleoptiles, although auxins have multiple functions in flowering plants. Auxin is produced predominantly in shoot tips and is transported from cell to cell down the steam at a rate of about 1 cm/hour.
What is the cell's reponse to a signal?
The transcription of a segment of DNA is started
Darwin's experiment
They observed a grass seedling ensheathed in its coleoptile could bend toward light only if the tip of the coleoptile was present. If the tip was removed, the coleoptile did not curve. It was the tip of the coleoptile, the Darwins concluded, that was responsible for sensing light.
Process of lipid-soluble hormoenes
They pass readily through the lipid-rich plasma membrane that surrounds the target cell, and bind to receptors in the cytoplasm or nucleus of the cell.
main purpose of cytokinins?
They regulate cell division in shoots and roots; modify apical dominance and promote lateral bud growth; promote movement of nutrients into sink tissues; stimulate seed germination; delay leaf senescence.
What are the major functions of gibberellins?
They stimulate stem elongation, pollen development, pollen tube growth, fruit growth, and seed development and germination; regulate sex determination and the transition from juvenile to adult phases.
Water-soluble hormones:
Water-soluble hormones: -do NOT pass readily through the lipid-rich plasma membrane that surrounds the target cell. -Instead, they bind with receptors on the surface of the target cell. -The receptors are glycoprotein complexes.
What did Went conclude at the end of the experiment?
Went concluded that the agar block contained a chemical produced in the coleoptile tip, that this chemical stimulated growth as it passed down the coleoptile, and that a coleoptile curved toward light because of a higher concentration of the coleoptile. For this chemical messenger, or hormone, Went chose the name AUXIN.
Fritz Went's work with coleoptiles growth
Went extracted the chemical messenger for phototropism by modifying the experiments of Boysen-Jensesn. Went removed the coleoptile tip and placed it on a cube of sugar, a gelatinous material. When the block was placed off center, the coleoptile began to bend away from the side with the agar block, as though growing toward the light.
Insulin
When secreted acts to lower blood glucose by allowing it to enter body cells and exit the blood stream
target cell
a cell that bears receptors for a hormone, drug, or other signaling molecule, or is the focus of contact by a virus, phagocyte, nerve fiber, etc.
list several possible reasons that could occur due to a signal being received by a cell
a gene is turned on, a protein channel is opened, a protein is produced, a cell divides/dies
amine
an organic compound derived from ammonia by replacement of one or more hydrogen atoms by organic groups.
tropism
any growth response that results in plant organs curving toward or away from stimuli
steroid
any of a large class of organic compounds with a characteristic molecular structure containing four rings of carbon atoms (three six-membered and one five). They include many hormones, alkaloids, and vitamins.
G protein-coupled receptor
cell-surface transmembrane receptor that works with the help of a G protein , a protein that binds the energy-rich molecule GTP.
aptoptosis
cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components. The cell shrinks and becomes lobed, and the cell's parts are packaged up in vesicles that are engulfed and digested be specialized scavenger cells, leaving not trace. CELL SUICIDE.
pheromones
chemicals that are released into the external environment. Pheromones serve a wide range of functions that include defining territories, warning of predators, and attracting potential mates.
day neutral plants
day-neutral plant. A plant that flowers regardless of the length of the period of light it is exposed to. Rice, corn, and the cucumber are day-neutral plants
negative feedback
for many hormones, the response pathway involves negative feedback, a loop in which the response reduces the initial stimulus.
where are nephrons located?
in the kidneys
does the signal transduction pathway occur inside or outside?
inside
phytochromes
is a photoreceptor, a pigment that plants, and some bacteria and fungi, use to detect light. It is sensitive to light in the red and far-red region of the visible spectrum.
What class of enzymes perform phosphorylation?
kinases
local regulators
molecules that act over short distances and reach their target cells solely by diffusion
neurohormones
molecules which travel through the bloodstream to target cells
response
often the transcription of a certanin genes and thus protein synthesis, but can also be the secretion of ions or other reponse
Many hormone pathways work by a negative feedback mechanism because...
once you start a response in the body, you need to be able to stop it
WHEN A LIGAND IS RELEASED, WHAT PREVENTS ALL OF THE CELLS IN THE BODY FROM BEING AFFECTED?
only the target cells like epinephrin has to have to correct shape/receptor cells for it
ligand-gated ion channels
open or close in response to binding by specific signaling molecules, regulating the flow of specific ions across the membrane
protein phosphatases
phosphate groups are removed by other enzymes called protein phosphatases.
Do only animals have cell signaling?
plants
What are the major functions of brassinosteroids?
promote cell expansion and cell division in shoots; promote root growth at low concentrations; inhibit root growth at high concentrations; promote xylem differentiation and inhibit phloem differentiation; pr0mote seed germination and pollen tube elongation.
positive feedback...
reinforces a stimulus
CAMP is the...
secondary messenger that carries its message to the kinase, which is the next molecule
Thyroid gland...
secretes thyroid hormone (T3 and T4)
compare shape of ligand to shape of receptor protein
shapes of the ligand and receptor proteins go hand in hand; the ligand will fir into the active site on the receptor protein
reception
signal molecule attaches to a receptor molecules and causes a conformational change in the receptor which begins further changes in the cell
neuroendocrine signaling
specialized neurons called neurosecretory cells secrete molecules that diffuse from nerve cell endings into the bloodstream.
kinase
sticks phosphate on something
paracrine signaling
target cells lie near the secreting cell
once the response is achieved in a call, what would need to occur to stop the response?
the activated relay proteins would need to be deactivated
senescence
the condition or process of deterioration with age. loss of a cell's power of division and growth.
phototropism
the growth of a shoot toward light or away from it
signal transduction pathway
the received signal is converted to a specific cellular response in a series of steps
photoperiodism
the response of an organism to seasonal changes in day length.
propose a definition for transduction
the signal moves through the cell to the location where the response will occur
transduction
the signal travels through the cytoplasm often in the form of phosphorylated and dephosphorylated moleulces until a response
autocrine signaling
the target cell is the secreting cell itself
Describe what would occur in the cell if the activated protein kinase enzymes continued to be active for a long period of time
the transcription factor would continue to transcribe the DNA strands as long as the protein kinases were active
thigmotropsim
the turning or bending of a plant or other organism in response to a touch stimulus.
negative feedback
there is an initial response chemical which goes to signal release of other response chemicals. the final response chemical as it builds up, when it reaches a certain concentration serves to "turn off' the initial response chemical thus stopping the response
Anterior pituitary secretes...
thyroid-stimulating hormone (TSH, also known as thyrotropin)
Hypothalamus secretes...
thytroptin-releasing hormone (TRH)
Glucagon
when secreted acts to raise blood glucose by causing the breakdown of glycogen in the liver and muscles, so glucose is then raised into the blood.
