BIOL Chapter 11
How is phosphorylation important in a signal transduction cascade?
Phosphorylation will change the activity of target proteins, which triggers another response in the cell.
Plasmodesmata
Small channels between cells that are otherwise surrounded by walls; enable movement of water and solutes between cells; plant
Gap Junctions
Small channels that form across the plasma membranes of adjacent cells; especially important in intercellular communication; animal
Based on nuclear transport, What type of signal would be exposed on the cytosolic receptor after the steroid hormone changes the receptor's conformation?
The conformational change would likely expose a nuclear localization signal on the receptor, which is required for the protein to be transported into the nucleus.
types of signal molecules
-nuertransmitters open or close ion channels in plasma membrane of distant cells changing electrical properties of membrane -hormones- secreted by cells in body fluids & act on distant target cells. small molecules including peptides, steroids, and even gases.
Enzyme-linked receptors transduce hormonal signals by directly catalyzing a reaction inside the cell ex. RTKs 1-3
1. Hormone binds to 2 subunits of an RTK & causes them to form dimer. 2. The change in RTK turns on its catalytic activity, and phosphates itself at (t)yrosine reidues using ATP inside the cell. 3.proteins inside the cell bind to the phosphoryated RTK, foring bridge between receptor & Ras, a single subunit G protein. Forming the RTK bridge activates Ras when it makes it exchange its bound GDP for GTP.
types of transduction and amplification systems
1. g-protein-coupled receptors initiate the production of intracellular "second messengers" when then amplify the signal 2. enzyme-linked receptors amplify the signal by triggering the activation of a series of proteins inside the cell, through the addition of phosphate groups
G protein coupled receptors trigger the production of a second messenger
1. signaling molecule arrives and binds to a receptor in the plasma membrane. the receptor is a transmembrane protein whose intercellular portion is coupled to a G protein composed of multiple subunits 2. response to binding signal molecule, changes shape and activates G protein, allowing GTP to bind to the protein. when GTP is bound, G protein will change shape radically: the active GTP-binding subunit splits off
each collagen protein
3 polypeptide chains wound around eachother to form rod-like component in ECM
RTK's 4-5 Phosphorylation cascade (all with MAPKs)
4. activated ras phosphorates and activates second kinase, which phosphorates and activates a third kinase. the third kinase triggers cell responses by phosphorating additional proteins
Why does a hormone act only on specific cell types in an organism and not others?
A cell must have the appropriate receptor before it can bind to the hormone.
How can a hormone that is present in very small quantities within the bloodstream elicit such a large response within a cell?
The message from the hormone is amplified many times within the cell.
The type of cell-cell attachment that resembles quilting, with proteins acting as stitches, is _____.
Tight Junctions
Cellulose
A polysaccharide used to synthesize cell walls, which protect cells and help maintain their shape; plant
Why would the same signal for adreniline recieved by the same receptors trigger different responses in the organs? (heart rate in hearts, glucose release in liver)
After adrenaline binds to the receptor in heart and liver cells, the signal is processed via distinct signal transduction pathways that activate different proteins and thus result in different cell responses.
How is a signal turned off with a G protein?
An activated g protein turns on a downstream enzyme, its bound GTP is hydrolyzed to GDP + Pi, making it inactive again. it stops activating its downstream target, and the second messanger stops producing. if it wants to continue, it must reactivated by the signal receptor or it shuts down.
Why is it important for signal transduction systems to trigger a rapid response within a cell and be able to be shut down quickly?
Cells often have to respond very quickly to changes in their internal and external environments.
The most abundant protein found in the extracellular matrix of animal cells is _____.
Collagen
2 Where are protein components of the extracellular matrix synthesized?
a. (all proteins in the ECM made in rough ER & secreted into EC)
5 how do the extracellular fibers in plants differ from those in animals?
b.
4 What does it mean to say that a signal is transduced?
c.
best studied second messangers (several activate kinases-in/activate proteins by adding phosphate
cGMP opens ion channels; DAG IP3; opens calcium ion channels cAMP CA2+ binds to receptor Ca2+/calmodulin complex activates proteins
rods/filaments
effective at withstanding tension (stretching and pulling)
Because cell walls consist of a cross-linked network of long filaments embedded in a stiff surrounding material, they can be called _____.
fiber composites
7 suppose yiu were to model amplificcation by the phosprylation cascade in 11.16 using a penny for each kinase 1, nickel for kinase 2, dime for kinase 3. suppose Raas and each kinase can activate 10 proteins. how much money?
for each Ras-GTP you would need 10 pennies for kinase 1 ($0.10), 100 nickles for kinase 2 ($5), 1000 dimes for kinase 3 ($100), so it would cost $105.10
receptors can be blocked
for example, beta-blockers bin to adrenaline receptors. when it binds to receptors in heart cells, it stimulates rapid and forceful contractions. if a physician wants to reduce heart cell contractions to reduce blood pressure, they'd prescribe a beta-locker.
plant ground
gelatinous polysaccharides such as pectins. theyre hydrophillic and attract & hold water to keep the cell wall moist. produced by ER and golgi, secreted into extracellular space.
when plant cells first form they secrete an initial fiber composite called a primary cell wall (produced by complex of enzymes in plasma membrane)
long strands of cellulose are bundled into stout microfibrils crosslinked to other polysaccaride filaments via hydrogen bonds.
apoplast
region outside the plasma membrane. (cell walls, middle lamella, air spaces).
tight junctions
seal cells together
Plasma membrane
seperates life from nonlife, phospholipid bilayer. proteins are integral or periphial in this membrane and enforce function of the membrane: creating internal cell enviornment diffrent from outside by regulating subsance transport
inside receptors
most lipid-solouble signaling molecules can diffuse across the hydrophobic region of the membrane and enter the cytosol of their target cells, the receptors inside the cells.
A bacterium lacking the receptor for responding to quorum-sensing signals would be unable to ________
mount a coordinated response with other microbes. Quorum sensing allows bacteria to sense the population density and engage in population-wide behaviors such as biofilm formation
demosomes are
similar to rivets holding sheet metal together. they consist of integral membrane attachment proteins that form bridges between anchoring proteins in the cytoplasm, forming continous structural support system to all the cells in the tissue
selective adhesion example
sponge grouped together based on their origin-to cells of the same tissue type.
processing lipid soluble signaling molecules
steroids are hydrophobic and would be carried in the bloodstream through hydrophillic proteins, after reaching the target cells, the molecules are released from the carrier proteins and enter the cytosol. it is often carried by a hormone receptor complex into the nucleus, to trigger gene expression and produce different proteins thus the functions/shape of the cell
what would happen to a plant cell if cell wall was removed?
turgor pressure would cause it to swell and burst instead of growing and expanding
cells communicate
via diffusion of cytosolic ions and small molecules from cell to cell in a tissue and other signals. 1. may regulate gene expression, altering protein production 2. may activate or inactivate proteins existing in the cell (involved in metabolism, transport, secretion and the cytoskeleton) changes cell activity dramatically
stiff ground substance
withstand pressing forces (compression)
how is the "dehydration" signal sent to just certian kidney cells even though it told to the whole body
only they have the receptor that binds to that molecule
Liquid insoluble signal molcules
hormones that cant diffuse will not directly change gene expression. they have a signal that arrives at the cell surface, triggering signal transduction- conversion of a signal form. converts extracellular signal to intracellular.
1. why only certain cells respond to particular signaling molecules that are sent throughout the body 2. explain how some signals are amplified by cells
(1) Each signaling molecule binds to a specific receptor protein. A cell can respond to a signaling molecule only if it has the appropriate receptor. Only certain cell types will have the appropriate receptor for a given signaling molecule. (2) Signals are amplified if one or more steps in a signal transduction pathway, involving either second messengers or a phosphorylation cascade, result in the activation of multiple downstream molecules
what responces would occur in cells exposed to the following signaling molecules (1) A +B,(2) A+C (3) C alone
(1) cell responses A, C, and possibly B at a low level; (2) cell responses A, B, and C; (3) cell responses B and C.
what would happen if all the cells in a developing frog embreyo expressed the same type of cadherin on their surfaces
All of the cells in the embryo would be capable of attaching to one another, regardless of the cell type. This would severely affect the development of different tissues and organs. The embryo would likely die.
describe structure and function of plasmodesmata and gap junctions
At plasmodesmata, the plasma membranes of adjacent plant cells are continuous, and the cells share portions of the smooth endoplasmic reticulum. Gap junctions connect adjacent animal cells by forming protein-lined pores. Both structures are openings between cells that allow cytosol, including ions and small molecules, to be shared.
A spy arrives at a castle gate. the castle guard recieves a note from the spy, but he cant read the coded message of the note, so he gives it to the queen. She reads it and summons the commander of the guard, who sends soldiers out in the castle to warn others of approaching danger.
The spy is the signaling molecule that arrives at the cell surface (the castle gate). The guard is the G-protein-coupled receptor in the plasma membrane, and the queen is the G protein. The commander of the guard is the enzyme that is activated by the G protein to produce second messengers (the soldiers)
Collagen
Long fibers of protein found in the extracellular matrix that provide structural support for cells; animal
Demosomes
Membrane protein complexes that strengthen the adhesion between adjacent cells, like rivets, to protect against pulling forces; Animal
Tight Junctions
Membrane proteins that create a watertight seal between cells; animal
Compare and contrast the molecular compisition of the animal cell ECM and cell walls of plant cells
Plant cell walls and animal ECMs are both fiber composites. In plant cell walls, the fibrous component consists of cross-linked cellulose fibers, and the ground substance consists of polysaccharides such as pectins. In animal ECMs, the fibrous component consists mainly of collagen fibrils, and the ground substance consists of proteoglycans.
The long and complex series of events that occurs when a signal binds to the cell surface and is converted from one form to another is called _____.
Signal Transduction
compare and contrast the structure and function of the middle lamella of plants and the tight junctions and desmosomes of animals.
The three structures differ in composition, but their function is similar. The middle lamella in plants is composed of pectins that glue adjacent cells together. Tight junctions are made up of membrane proteins that line up and "stitch" adjacent cells together. Desmosomes are rivet-like structures composed of proteins that link the cytoskeletons of adjacent cells.
What happens when plants experience drought?
The tissues in the root system secrete a hormone called absicic acid, its travels through the apoplast. when it reaches the leaves, it binds to receptors of guard cells, which control the stomatal pores used in gas exchange. binding initiates transduction pathway that increases Ca concentration inside the guard cells, causing K to move out of the cells, creating an osmotic gradient that causes water to leave the guard cells & deflate & close the pores, preventing further water loss.
What role do plasmodesmata play in plant cells?
They serve as communication portals between neighboring plant cells, allowing the passage of small molecules between the two cells.
signal receptor
a protein that changes its shape and activity after binding to a signaling molecule. the shape change marks the signal transfer from the molecule to receptor protein.
gap junction
act as channel between cells in animal cells. allow water, ions, and small molecules like sugars, amino acids and nucleotide to move in between cells.
tight junctions are good at holding cells together but
are weak adhesions & easily broken. other adhesions required to hold cells together in a tissue.
dehydration?
cells in brain sense dehydration, brain cells release signal to kidney activating expression of water channels. water moves out of the urine and back into the blood, preventing further dehydration.
G proteins
closely associated with membrane-anchored proteins inside the cell called G proteins. activated by a signal receptor, trigger key tep in signal transduction: produces second messanger- a small, nonprotein signaling molecule that arrived at a cell surface. link the receipt of an extracellular signal to the production of an intracellular signal
proteoglycan complex
complexes of gelatinous proteoglycans branch off the core protein
demosome
connect the cytoskeletons of the cells. securley.
symplast
continous network of cytoplasm connected by the plasmdesmata
plasmodesmata
create gaps that connect plant cells. the plasma membrane and cytoplasm of two cells are continuous, direct contact. molecules can move through plant tissues without ever crossing the membrane
3 What charecteristics do demosomes bestow on tissues that use these adhesions to connect adjacent cells?
d.
primary cell walls
define shape of plant cell. when the cell's volulme is increased from osmosis, the plasma mebrane expierences turgor pressure and presses against the p cell wall. young plant cells secrete expansins to disrupt hydrogen bonds to allow microfibrils to slide past each other.
amplification
in the intercellular region, signal amplifies it and triggers larger response in cells. increased number of signals make it possible for hormones to affect different molecules in the cell. ipod does same thing, takes tiny music, plays to a room. some may dance, some may block ears. in general first signal results in secondary with many ions or molecules
outside receptors
large or hydrophillic signaling molecules are lipid insolouble, and most cant cross the plasma membrane. they haveto be recognized at the cell surface.
tj
long chain form watertight seal on surface of cell and then to adjacent cells by pulling the membranes closeley, resmebling a quilt, preventing solutions from flowwing inbetween the space.
indirect intercellular attachments
middle lamella- gelatinous polysaccharides, pectins that glue together walls of adjacent cells. in animals its reifocred by collagen to other cells.
example signal transduction
one major type of signal receptors that are also ion channels. signal transduction opens the channels, allowing ions to diffuse into the cytosol. in muscle cells, thi type of amplification occurs when calcium ions flood into the cytosol, causing the entire cell to contract as a whole.
antibody
protein produced by immune responce that binds specifically to a unique type of molecule. when it binds to that molecules, it can change its structure or interfere with its ability to interact with other molecules.
cadherins
proteins that link cells to demosomes. can only bind to cadheirns of the same type.
gap juntions are communication portals
they help adjacent cells coordinate their activities by allowing rapid pasage of regulatory ions or small molecules. in heart muscle cells, a flow of ions through gap junctions signal contractions.
animal ECM
structural support fiber composite most animal cells secrete. fiber is collagen. gel-forming proteoglycans is ground substance.
if an antibody binds to an adhesion protein
the adhesion protein can't bind to other adhesion proteins and attach all the cells to one another
receptors are dynamic
the number of receptors in a particular cell may decline if the hormonal stimulation occurs at high levels over a long time. the abilityy of a receptor to bind tightl to a signaling molecule may also decline in reponse to intensive stimulation. as a result, sensitivity to a particular hormone may change overtime.
G proteins derived from?
the type of guanine they are bound to. GDP or GTP. GTP is similar to ATP, high potential energy cause phosphate groups. When GTP binds to G protein, the negative charges alters the proteins shape, changin the activity. G proteins inactive when GTP turns to GDP.
how are extracellular structures like reinforced concrete?
they have a crosslinked latice of long fillaments embedded in a stiff surrounding material (ground substance). flexible and strong.
