cell signaling unit 5 content questions

Question 1

general principles of cell signaling

Answer 1

all cells receive and respond to signals from their environments or from other cells

Question 2

cell signaling

Answer 2

how cells communicate with eachother

Question 3

gap junctions

Answer 3

cells may communicate directly with their immediate neighbor through gap junctions

Question 4

what do gap junctions connect

Answer 4

the cytoplasm of neighboring cells via protein channels which allow the passage of ions and small molecules behind them
example is coordinated contraction of cardiac muscle cells

Question 5

contact cell cell signaling

Answer 5

the signal is to touch, they communicate though cell surface proteins, the cells make direct physical contact with each other though proteins in cell cortex

they use receptor molecules in plasma membrane

Question 6

example of contact cell cell signaling: wound healing

Answer 6

important role in wound healing, cells stop growing when they touch together and wound is closed, important in maintenance of adult tissues

Question 7

cell cell regognition: sperm and egg

Answer 7

signal touch sperm head, the sperm has arrived, response the egg forms a wall so no more sperm can penetrate

Question 8

cell cell recognition: phagocytic cells recognizing the microbe

Answer 8

signal: touch phagocytic cell with bacteria, response: pseduopod formation to surround bacteria and phagocytize it

Question 9

cell cell signaling during embryonic development

Answer 9

allow adjacent cells that are initially smaller becomes specialized to form different cell type.

Question 10

how do most cells communicate with eachother

Answer 10

secreted molecules which can be divided into three general categories based on distance which signals are transmitted

Question 11

paracrine signaling

Answer 11

short distances
cells communicate using secreted chemicals that travel through extracellular fluid and act on nearby cells molecules that travel only short distances, signal molecules diffuse locally through extracellular fluid

Question 12

examples of paracrine signaling

Answer 12

in immune cells many signals that regulate inflammation at site of an infection, Gas NO that relaxes muscle around blood vessels, synaptic signaling

Question 13

synaptic signaling in synapses (between neurons)

Answer 13

occurs in nervous system when a neurotransmitter is released in synaptic cleft in response to an action potential, each electrical signal stimulates the nerve terminal for release of neurotransmitter

Question 14

autocrine signaling

Answer 14

self signaling, secreted signal acts back on the same group of cells it was secreted from

Question 15

example of autocrine signaling

Answer 15

t cells respond to antigen stimulation by synthesizing growth factors that drive their own proliferation increasing the number of T cells and amplifying immune response

Question 16

endocrine signaling

Answer 16

long distance signaling, chemical signals are transmitted over long distances from one organ to another, these chemicals are hormones

Question 17

how does endocrine signaling work

Answer 17

cells that make and release chemicals in endocrine signaling are endocrine cells that make up endocrine glands, hormones are secreted to the blood and they get to their target cells via the circulatory system

Question 18

ability of cells to respond to signal

Answer 18

depends on whether or not they have a receptor specific to that signal

Question 19

lipid hormones (steroid hormones)

Answer 19

small hydrophobic molecules, able to diffuse across plasma membrane, bind intracellular receptors located in cytosol or in nucleus known as nuclear receptor superfamily
- many are cholesterol derived

Question 20

Gas hormones

Answer 20

NO
small molecule, like steroids, able to diffuse directly across plasma membrane, major paracrine signaling molecule in circulatory system, released by cells in blood vessels to vasodilate

Question 21

peptide and protein hormones

Answer 21

widest variety of signaling molecules are proteins ranging in size from only a few peptide to more than 100,
most are secreted and participate in paracrine, autocrine, and endocrie cell signaling

Question 22

how do peptide and protein hormones bind

Answer 22

they cant cross plasma membrane on target cell so they act by binding to cell surface receptors

Question 23

three stages of cell signaling process

Answer 23

reception, transduction, response

Question 24

reception

Answer 24

target cell detects a signaling molecule that binds to a receptor protein on the cell surface

Question 25

transduction

Answer 25

the binding of the signal causes change in receptor initiating a signal transduction

Question 26

when does transduction begin

Answer 26

when the receptor protein on a target cell receives an incoming extracellular signal and converts it to the intracellular signals that produce a response in the cell

Question 27

response

Answer 27

transduced signal triggers specific response in target cell, various types cell responses can occur

Question 28

molecular switches

Answer 28

the signaling process once it reaches the inside of the cell requires molecular switches, proteins that can be turned on and off, reception of a signal causes flip of switch when on proteins can relay the signal and turn on other protein in signaling pathway

Question 29

most common way to activate molecular switches

Answer 29

phosphorylation

Question 30

why does phosphorylation change shape of protein activating it

Answer 30

phosphorylation changes shape bc phosphate groups are highly negative and the phosphorylation of a protein alters its charge which can alter the confirmation of the protein and its activity

Question 31

how can you add a phosphate

Answer 31

direct phosphorylation, attaching GTP in G protiens

Question 32

direct phosphorylation

Answer 32

a phosphate group from ATP is attached to an AA in the protein, the enzyme that catalyzes this reaction is protein kinases, protein phosphatase removes phosphate group to dephosphorylate

Question 33

phosphorylation cascades

Answer 33

one protein kinase activated by phosphorylation, phosphorylates the next protein kinase in the sequence, and so on transmitting the signal onward

Question 34

two main types of protein kinases operate in intracellular signaling pathways

Answer 34

serine/threonine kinases which phosphorylate proteins on serines or theronines, 2. tyrosine kinases which phosphorylate tyrosines

Question 35

Molecular switch 2: GTP bound

Answer 35

GTP active, GDP inactive, once activated by gtp binding these proteins can give phosphates and phosphorylate and activate protiens

Question 36

GTPase

Answer 36

intrinsic GTP hydrolyzing GTPase activity the shut themselves off by hydrolyzing their bound GTP to GDP

Question 37

what are protein kinases

Answer 37

enzymes that add phosphates to target proteins, adding phosphates makes the proteins turn on

Question 38

extracellular signal molecules fall into two categories

Answer 38

large hydrophilic signals that are recognized by receptors on the membrane of the target cells small hydrophobic signals which have receptors in cytosol or nucleus of cell

Question 39

types of receptors that bind extracellular ligands

Answer 39

GPCR and RTK

Question 40

GPCR

Answer 40

reception of large hydrophobic molecules, peptides and proteins, largest group of cell receptors

Question 41

Structure of GPCR

Answer 41

single polypeptide change that goes though membrane 7 times by membrane spanning alpha helices, specific loops form binding sites outside of the cell for signaling molecules and inside the cell they bind g protien

Question 42

how to G protein coupled receptors work

Answer 42

when extracellular signal binds to GPCR receptor protein undergoes confirmational change that enables it to activate a G protein located in cytosolic face of plasma membrane, the activate g protein then dissociates from the receptor and carries the signal to intraceullular target

Question 43

what do activated G proteins activate

Answer 43

activate target enzyme close to plasma membrane, leads to production of second messenger

Question 44

G proteins and cholera

Answer 44

this protein enters the cells that line the intestine and modifies alpha subunit of G protein in way that it can no longer hydrolyze its bound GTP the altered alpha subunit this remains in the active state indefinitely

Question 45

G protein whooping cough

Answer 45

protein alters alpha subunit of different type of G protien and disables it by locking into its inactive GDP bound state resulting in generation of prolonged inappropriate signal that stimulates cough

Question 46

Receptor tyrosine kinases

Answer 46

Transmembrane proteins that display their ligand binding domains on the outer surface of the plasma membrane and use their enzyme domains on inner surface toward cytoplasm

Question 47

Structure of RTK

Answer 47

Extracellular ligand binding domain and intracellular domain that can act as an enzyme, have only one transmembrane segment which spans the lipid bilayer as single helix

Question 48

Activation of RTK

Answer 48

RTKs works in pairs, the first step in signaling is the ligand induced receptor dimerizes with happens when the extracellular signal binds causing two receptors to come together

Question 49

An active RTK is what

Answer 49

Phosphorylated

Question 50

When RTKs are phosphorylated what is their function

Answer 50

Phosphorylated intracellular activated sections will serve as docking platforms for many intracellular proteins

Question 51

Protein domains for TKRs

Answer 51

SH2 domains, they are able to recognize ad bind to specific phosphorylated Tyr

Question 52

Important role of RTK

Answer 52

Important role in responses to extracellular growth factors which regulate cell growth, proliferation, differentiation

Question 53

Abnormal functioning of RTKs

Answer 53

Associated with many types of cancers

Question 54

How is the signal from tyrosine phosphorylations terminated

Answer 54

By protein tyrosine phosphatases which remove phosphates from RTKs and other signaling proteins

Question 55

Second messengers

Answer 55

Small water soluble molecules or ions that spread throughout a cell by diffusion, they participate in pathways initiated by all types of receptors

Question 56

How are second messengers generated

Answer 56

In cascades of reactions, the first message comes from extracellular signal

Question 57

Examples of second messengers

Answer 57

CAMP, IP3, Ca2+

Question 58

How is cyclic AMP synthesized

Answer 58

By the enzyme adenylyl cyclase

Question 59

How is camp turned off

Answer 59

By enzymes called phosphodiesterases which breaks the ring of cAMP and turns it back to AMP

Question 60

What mediates the affects of cAMP

Answer 60

PKA

Question 61

Pk/ what do they do

Answer 61

Protein kinases transfer phosphates from ATP to protein, a process called phosphorylation

Question 62

Stress response and cAMP

Answer 62

Adrenaline triggers a rise of intracellular cAMP which activates PKA which leads to activation of an enzyme that promotes glycogen breakdown and the inhibition of enzyme that drives glycogen synthesis, the affect is max amts glucose available for anticipated muscle activity

Question 63

Activation of phospholipase c

Answer 63

Activated alpha subunit of G protein activates a different nearby enzyme

Question 64

What does phospholipase C do

Answer 64

Cuts membrane phospholipid called PIP2 which is present in cytoplasmic region forming DAG and IP3

Question 65

DAG

Answer 65

Lipid that remains embedded in the plasma membrane, can activate protein kinase C

Question 66

IP3

Answer 66

Sugar molecule that diffuses into cytosol and binds to ligand gated calcium channels in SER they open the Ca2+ channels in the membrane of SER

Question 67

Cellular effects of an increase in Ca2+

Answer 67

Promotes exocytosis signaling in B cells of pancreas to release insulin and activation of motor proteins

Question 68

Most common Ca2+ responsive proteins

Answer 68

Calmodulin, which is present in the cytosol of all eukaryotic cells

Question 69

What happens when calmodulin binds to Ca2+

Answer 69

Protein undergoes conformational change that allows it to wrap around a wide range of target proteins in the cell altering their activities

Question 70

Important target for calmodulin

Answer 70

caM kinases

Question 71

PIP3 and Akt

Answer 71

PIP3 can bind to Akt and activate it which once activated will phosphorylate a number of target proteins with effect on promoting cell survival inhibiting apoptosis