BIOL215 Exam 4

signal transduction

reception: cell perceives an extracellular signal and ligand(first messenger/signaling molecule) binds to PM receptor protein; conformational change of receptor protein

transduction: cascade of signaling/relay molecules that pass message along in cell

response: triggers a change in the cell (gene expression, some type of movement)

how can a signal molecule that does not enter a cell alter cell activities

primary messengers do not enter the cell. secondary messengers trasnmit message from primary messengers

extracellular ligand

interacts with the plasma membrane bound receptor. signaling molecule doesn’t actually enter the cell

cytoplasmic ligand

signaling molecules like steroids can enter the cell through simple diffusion (nonpolar\[hydrophobic\] or small)

once in the cell, targets intracellular receptor

receptor-ligand interactions

signaling molecule- ligand- binds to specific receptor in ligand-binding domain

conformation change in receptor triggers cascade

compare receptor-ligand interactions to other intermolecular interactions discussed in class

enzyme-substrate: cell will only respond if it has the right receptor and relay molecules

solute-transporter: fixed number of receptors limit response like vmax

different levels of signaling that occur in a cell or a multicellular organism

local: target neighboring cells like cell junctions, cell to cell contact, and secretion and diffusion of signals

long distance: multicellular organisms with transport system

paracrine hormone

paracrine signaling through localized diffusion when secretory vesicle releases and regulator diffused through extracellular fluid and goes to target cell

close and localized

endocrine hormone

long distance

synthesized in one particular location, secreted int the blood, travels long distance, induces a response in target cell/tissue located long distance from original source

signal amplification and its significance in cell signaling

small amount of ligand is enough to elicit a response from target cell because at each step, signaling intermediate stimulates the production of many molecules needed for next step(during transduction) - signal amplification

longer cascade = more amplification

GCPRs

G-protien linked receptors interact with G proteins, multipass integral membrane protein, once ligand binds to extracellular face and caused receptor change, it activates a particular G-protein

structure: 7 membrane spanning domains, ligand binding domain, G-protien interaction domain

cAMP

adenosine-3, 5-cyclic monophosphate

ATP + adenine = cAMP

catalyzed by adenylyl cyclase

phosphodiesterase cleaves cAMP to AMP, deactivating cAMP and stops cascade of intermediates

outline signal transduction pathway involving cAMP

1. ligand binds to receptor
2. conformational change caused GDP to switch to GTP (attached to alpha subunit)
3. alpha separates from other 2 subunits
4. G protein is activated
5. alpha hydrolyzes GTP back to GDP
6. subunits recombine and cascade is initiated

how are cAMP levels regulated by adenylyl cyclase and phosphodiesterase

once G protein is inactivated, adenylyl cyclase stops making new cAMP, cAMP remaining is turned into AMP by phosphodiesterase

kinase

adds inorganic phosphate involved with ATP

phosphorylase

adds organic phosphate

phosphatase

removes phosphate

pathways for glycogen metabolism

phosphorylysis of glycogen to release G1P by glycogen phosphorylase (adds inorganic phosphate)

mechanisms involved in regulating glycogen phosphorylase enzyme

active when phosphorous is attached by phosphorylase kinase

inactive when phosphorous not attached by phosphorylase phosphatase

signaling cascade involved in fight or flight response

perceived threat by hypothalamus to pituitary gland to adrenal gland in kidney. releases epinephrine hormone, travels long distance in blood to heart and liver cells. leads to increased heart rate and breakdown of liver glycogen

cAMP activates inactive PKA. phosphorylase phosphatase breaks down glycogen, releasing G1P

blood glucose level converts G6P to glucose and PKA inactivates glycogen synthase and activates phosphorylase kinase

IP3/DAG signaling pathway

1. ligand binds to GPCR and G protein is activated
2. Ga binds to phospholipase C (integral membrane protein)
3. triggers release of PIP2 from membrane which makes IP3 (soluble and released from membrane) and DAG(remains in membrane)
4. triggers release of calcium

basal cytoplasmic \[Ca2+\]

normal or resting level of calcium

compare basal cytoplasmic \[Ca2+\] to \[Ca2+\] in ER and/or the extracellular space

high concentration in ER so most stored here

low concentration in extracellular space

structure of calmodulin protein

calmodulin binds to four calcium ions triggering conformational change. two globular hands of the complex wrap around a binding site on a target protein

regulation of calmodulin involving calcium levels

When calcium levels rise in the cytoplasm, calmodulin conformational change which enables it to interact with a variety of target proteins

list and describe the signaling components involved in calcium-mediated signaling

calmodulin: conformational change when bound to calcium

NO synthase: release arginine, citruilline, and nitric oxide

guanylyl cyclase which convert GMP to cyclic cyclic GMP which then target protein kinase G

general tissue structure of a blood vessel

endothelial cells line blood vessel

smooth muscle layer surround endothelial cell which allows muscle to constrict and dilate

detail steps involved in calcium-mediated vasodilation

1. ligand binds to GPCR and G-protein is activated
2. G-alpha binds to phospholipase C (integral membrane protein)
3. triggers release of IP3 from membrane which then triggers release of calcium into cytoplasm
4. calmodulin activated and targets nitric oxide synthase
5. nitric oxide is release into smooth muscle layer of tissues
6. activates guanylyl cyclase which makes cyclic GMP
7. activates protein kinase G (PKG)


1. muscles relax and blood vessel dilates

effects of nitroglycerin and viagra on the vasodilation pathway. how do they influence the pathway? at which specific step are they involved?

nitroglycerin: catabolized to release NO, stimulates vasodilation

viagra: inhibits cGMP phosphodiesterase, prolongs vasodilation

cGMP-phosphodiesterase? how is involved in vasodilation pathway

enzyme that cleaves cGMP into GMP

in vasodilation pathway, deactivates cGMP, stopping vasodilation signal cascade

enzyme coupled receptor

transmembrane proteins, subunits of singlepass polypeptides

cytosolic domain

some have intrinsic enzymatic activity, while others directly associate with an enzyme

extracellular domani for ligand binding

function of receptor tyrosine kinases

add phosphate group (phosphorylate) tyrosine residues on themselves

growth factor

common ligands for RTKs

small molecules capable of stimulating cell growth, cell division, and/or cell differentiation

often requires specific combo of growth factors for right fucntion

outline events involved in a growth factor/RTK mediated pathway

1. ligand binds, causing dimerization of RTK
2. autophosphorylation: kinase domain phosphorylate each other, activating the RTKs
3. activates signaling cascade like phospholipase C
4. release IP3, triggering calcium release

in the context of regulating blood glucose, are glucagon and insulin functioning as endocrine or paracrine hormones

endocrine hormones

long distance pathway, start from pancreas to liver to blood, etc

systemize the signal transduction pathway involved in insulin mediated uptake of glucose and insulin mediated glycogenesis

1. insulin produced and secreted from pancreas because of high glucose levels
2. insulin binds to RTK which dimerizes and autophosphorylates
3. activates receptor and binds to phosphorylated IRS-1
4. activates PI3 kinase
5. PI3 phosphorylates PIP2 to form PIP3(integral membrane proteins)
6. which activates AK+ which activates glucose transporter and is inserted into membrane; also activates glycogen synthase which triggers glycogenesis (glucose to glycogen)

diabetes

high blood glucose levels

explain how defects in the insulin signal transduction pathway may lead to diabetes

in type I diabetes, pancreatic beta cells are destroyed so when glucose levels are high, insulin can’t be produced and the somatic cells can’t take up glucose from the blood

in type II diabetes, impaired insulin signaling at the cellular level leads to insulin resistance

differentiate between type I and type II diabetes

type I is juvenile onset, an autoimmune disease, can’t produce insulin

type II: insulin is produced but cells don’t react, caused by lifestyle

which type of diabetes is gestational diabetes

type II

list and describe the treatments available to treat diabetes

for type I: insulin injections, human cadaveric islet transplants, stem cells

for type II: special meal plans, physical activity, insulin injections, meds that increase insulin production, meds that increase sensitivity of target organs to insulin, decrease glucose absorption from GI tract or glucose release

list the functions of the cytoskeleton

mechanical strength, organize internal contents, motility (movement of cell itself and movement inside cell), cel division (cytokinesis), regulation(transmit mechanical signals from environment)

recall the three different elements that make up the cytoskeleton

microtubules, microfilaments, intermediate filaments

list the functions specific to microtubules

organization, intracellular transport

differentiate between cytoplasmic Mts and axonemal MTs

cytoplasmic: cell organization and intracellular movement

axonemal: components of motility structures (cilia and flagella)

describe in detail the structure of MTs

hollow tube of protofilaments comprised of tubular heterodimers

alpha and beta tubulins

each subunit bound to GTP but only beta has GTPase activity

one end has alpha, other has beta

plus end grows faster (beta)

define critical concentration as related to MTs

free tubulin in cytosol concentration at which rate of subunit Addison is equal to rate of subunit loss. plus end of MT has lower Cc requirements of free tubulin so it continues to grow in lower concentrations of free tubulin heterodimer

explain the effects of the critical concentration on MT assembly

as MT grows, free tubulin concentration decreases

minus end will stop growing because Cc is too low

how is critical concentration related to the polarized assembly of Mts

plus end continues to grow even at low Cc while minus end will stop growing

describe the process of dynamic instability and the role played by GTP in this process

MT grow and shrink very rapidly due to Cc

free beta tubulin has GTP in unbound state and then changes to GDP when in MT. GTP hydrolysis can cause destabilization and depolymerization of MT end occurs

growth happens when growth rate is faster than hydrolization rate

shrinkage happens when hydrolization rate is faster than growth rate

cells need dynamic instability to survive

what is the GTP cap and how does it influence MT stability

GTP caps protect against depolymerization of MTs and promotes growth

explain the function of MTOCs

microtubules organization center

site where MT assembly is initiated

anchors and organizes MTs

forms spindle apparatus in dividing cells

contains gamma tubulin ring complexes embedded in gel that forms MTOC and nucleation site for growth on MT on minus end

in animal cells: centrosome

describe the structure of the centrosome

centriole: two barrel shaped structures

pericentriolar material: gel matrix on outside of centrosome

explain how MTOCs are involved in cell shape/differentiation in polarized cells like neuron differentiation

in polarized cells like a neuron, axon only grows in plus direction and dendrite grows in both directions

polarization is determined by MT arrangement

describe the role of Tau and how it is correlated with some neurodegenerative diseases

MT associated protein found in axons: stabilizes MT, promotes polymerization, important in axon polarization

destabilization of MTs happen when kinase acts when targeting Tau: dephosphorylation of Tau stabilizes MTs

when Tau aggregates, paired helical filaments get into neurofibrillary tangles, leading to neurodegenerative diseases

describe the structure of microfilaments

right beneath plasma membrane

describe the similarities and differences between microtubules and microfilaments

plus and minus ends

all monomers orientated in same direction

structural polarity

plus end will polymerize faster

bound to ATP and hydrolyzed to ADP (destabilizes) once it joins MF

cell cortex: network of MF, meshwork underlying PM

cell shape changes by the difference in pressure that the cell cortex puts on the membrane

describe the structure of microvilli

formed from ordered arrays of MF bundles

prominent feature in cells with absorption function

what type of cells have lots of cilia

sperm, epithelial cells in the trachea

describe the structure of intermediate filaments

range in size from 8-12nm

variety of protein components

no variation in proteins that make up nuclear lamina

describe the function of intermediate filaments

structural support: tension bearing role(withstand pressures and tensions), very stable

nuclear lamina scaffolding: determine nuclear shape

describe the function of microvilli

digestion and absorption of intestinal contents

describe the function of microfilaments

responsible for cell shape and locomotion

distinguish cytoplasmic IFs from those that form the nuclear lamina

intermediate filaments are made of cell-specific proteins

compare the diameter sizes of the three cytoskeletal elements? why is there variation in the diameter of cytoplasmic IFs

MTs: 25nm outer and 15nm inner

MFs: 7nm

IFs: and 8-12nm

explain how and why cytoplasmic IFs can be used in tissue/cell-typing and why nuclear IFs or other cytoskeletal elements cannot

cytoplasmic IF proteins are cell/tissue specific

nuclear IF proteins are the same in every cell

describe the three different types of cell movement

intracellular movement: movement of contents within the cell

movement of the cell itself: swimming cel or a crawling cell

movement of environment past/through the cell: ciliated epithelial cell in the trachea moving mucus over their apical surface

recall the types of microtubules associated motor proteins and describe their general overall structural/functional domains

kinesins: move towards the plus end of MTs

dyneiens: move toward the minus end of MTs(toward centrosome)

have globular region that binds to MT(head) and the other end binds to cargo(tail)

both have 2 ATP binding domains

recall the direction of movement associated with each MT motor protein

can only move in one direction (plus or minus)

only attached to MF and MT because IFs are not poilarized

describe how vesicle based movement occurs in the cell. how are vesicles transported between the components of the end-membrane system Ising the different MT motor proteins. which motor protein would carry a visible to the PM? which motor protein would transport cargo from the ER to the Golgi

MTs and their motor proteins direct vesicle traffic of the end-membrane system. location of MTOC confers directionality to transport. dyneins carry cargo from PM during endocytosis and from ER to Golgi. kinesins carry cargo from Golgi to PM and from Golgi to ER

why are motor protein necessary? use examples from class

much faster than diffusion

it would take a membrane vesicle to reach the end of an axon 10 cm by diffusion almost 32 years

recall the rates of transport associated with motor proteins and with axonemal dyneins

2 um per second with motor proteins and 14 um per second with axonemal dyneins

describe the motor proteins associated with microfilaments (no need to memorize the different types of myosins)

myosins

what similarities do they share with microtubule-based motor proteins

both have structural polarity which allows the motor proteins to have directionality

explain why motor proteins are only associated with MTs and MFs, but not IFs? what is different about IF structure compared to the other cytoskeletal elements

IFs don’t have structural polarity. the ends are identical. no polarity for motor protein sterospecificity

compare and contrast the structure and function of cilia and flagella

cilia: many per cell and short

flagella: only one or few per cell and long

list and describe the three types of cilia found in eukaryotic cells. provide an example for each

motility: swimming cell, can move environment over cell

sensory: cellular antennas, involved in detecting external signals and present on many different types of specialized cells. ie. mechanoreceptors, chemoreceptors, and photoreceptors

nodal: cilia on surface of the embryo. movement of nodal cilia generate a unidirectional flow of embryonic fluid, activating a left side only gene cascade

describe the signal transduction pathway involved in odor detection

nasal cavity is lined by olfactory epithelium: inhalation of odorant molecule into nasal cavity

odorant molecules cross over the source of the OE and are detected by olfactory sensory neurons

odorant receptors in sensory cilia bind to odorant molecules which starts cascade that activates a neuron that makes you smell

what is the difference between cilia and microvilli

cilia are MT based and involved in cell movement

microvilli are MF based and function to increase surface area

describe the ultrastructural details of cilia and flagella

9+2 array of Mts with nine doublets arranged in a ring, surrounding a single pair of Mts (circle)

Mts are associated with many accessory proteins: bind at regular points along length of MT, some serve to X-link bundles, some generate forces to cause bending

axonemal dyneins: specialized motor proteins in axoneme structures

explain how the axonemal components interact to generate movement in cilia and flagella

one end of dynein binds to one MT and the other binds to adjacent MT which causes the pair to slide against each other and bend back and forth

situs inversus disorder

rare congenital abnormality which causes the several of organs in thoracic and abdominal cavities

explain underlying cause and the connection to the various issues that arise in an individual suffering from situs inversus

studies have revealed a defect in axonemal dyneins: due to defect in cilia, proper symmetry is not established during embryogenesis

can cause respiratory problems and infertility issue due to decreased sperm motility in males and problems with translocation of eggs in females

define cell locomotion

actin based cell movement involving MFs

how is cell crawling different from swimming cell

crawling is MF based and swimming is MT based

create a detailed model outlining the subcellullar events involved in cell locomotion

1. leading edge extends via polymerization of actin at its tip
2. new adhesions, anchored by actin, form on the undersurface of the lamellipodium
3. the trailing edge of the cell detaches, and is drawn forward by contraction of the cell body

explain the components involved in cell locomotion and how the microfilament arrangements contribute to this process

myosins: motor proteins

lamellipodium: extended sheet of cytoplasm at leading edge

filopodium: thin pointed protrusion

how are MFs attached to the PM to generate changes in cell shape

MFs are indirectly connected to the PM and exert force on it during cell locomotion and cell shape changes

explain how a disruption in MFs leads to a disruption in cell locomotion and other MF-based cell functions like white blood cells not being able to polarize towards a signal

in WAS, a genetic disorder involving a mutation in a MF-associated protein, defect would cause microvilli defects in intestinal epithelia

list and describe the various levels of organization in a multicellular organism

cell to tissue to organs to organ system

define a tissue

organized collection of cells

list and describe the structure and functions of the four major tissue types found in animals. include examples for each

epithelial: lines surface and cavities within the body; includes endothelial which line blood vessels

muscle: contractile (skeletal, cardiac, smooth)

nervous tissue: sensory input, control of system (brain, spinal cord, nerves)

connective: structure and support (tendons, bones, fat, blood)

describe the structure of endothelial tissue

lines blood vessels

describe the function of endothelial tissue

vasodilation

explain the events necessary for tissue formation

cell recognition, cell adhesion, and continued communication

describe ways that cells can adhere to one another

1. direct attachment to each other via transmembrane adhesion proteins
2. attachments through the ECM
3. or combo of above

list and describe the cell adhesion proteins discussed in class

selectin: type of carb binding protein with carb recognition domain, binds to glycoproteins on other cells; P-selectin, L-selectin; E-selectin

integrins: interact with other cell adhesion protein (ICAMS) and extracellular matrix components

outline and describe the events involved in leukocyte extravasation

1. rolling: L-selectins of leukocyte interact with P and E selectin on endothelial cells
2. stopping: signal received by leukocyte that activates interns that interact with ICAMs on endothelial cells (integrins are stronger than selectins)
3. exit blood vessel (extravasation)

describe the events in ”the inner life of a cell” video

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what is cancer

disease that arises from abnormalities of cell function

characterized by the uncontrolled growth and spread of abnormal cells

can result in death if not treated