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cell structure and function mid term 1 > mid term 2 > Flashcards

mid term 2 Flashcards

1
Q

what are the modes of cell signaling

A

gap junctions, contact cell- cell signaling, secreted molecules

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2
Q

how do gap junctions work

A

this is how neighboring cells communicate with each each other, gap junctions connect the cytoplasms of neighboring cells via protein channels that allows the passage of small molecules and ions

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3
Q

contact cell cell signaling

A

the signal is though touch, cells communicate through surface proteins, the cells can make direct physical contact with each other though proteins in the cell cortex, they use receptor molecules in their plasma membrane

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4
Q

important role of contact inhibition in direct cell cell contact signaling

A

wound healing, cells stop growing when they touch each other and the wound is closed, also important in maintaining adult tissue

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5
Q

what are classic examples of cell cell recognition

A

sperm head coming into contact with the egg which send signal to the egg to build wall so no more sperm can penetrate, phagocytic cells when they come in contact with bacteria surround bacteria to phagocyte it

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6
Q

what are the 4 categories of secreted molecules and what makes them different?

A

the difference comes in how far they secreted molecule travels, you have autocrine, paracrine, endocrine and synaptic

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7
Q

paracrine signaling

A

secreted molecule only travels a short distance, the secreted molecule travels though the extracellular fluid and acts on nearby cells

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8
Q

synaptic signaling

A

signaling between neurons, occurs when neurotransmitter is released into the synaptic cleft and the responding signal is taken up by post synaptic neuron

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9
Q

autocrine signaling

A

self signaling, the cell releases a signal and then responds to the signal itself

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10
Q

endocrine signaling

A

long distance cell signaling, between organs, the molecules/ chemicals that are sent are hormones which are produced by endocrine glands, hormones are secreted into the blood stream and travel to their specific destination in the body

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11
Q

what does the ability of a cell to respond to a signal depend on

A

if they have the receptor for that signal or not

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12
Q

types of hormones

A

lipid (steroid) hormones, Gas (NO), Peptide and Protein hormones

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13
Q

lipid hormones

A

small hydrophobic molecules that can diffuse across the membrane and bind to intracellular receptors in the cytosol or nucleus

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14
Q

examples of steroid hormones

A

most of the sex hormones, cortisol, thyroid hormones

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15
Q

Gas hormones (NO)

A

small molecules, can diffuse across plasma membrane, main molecules for paracrine signaling, released by cells in blood vessels to vasodialate smooth muscle around the blood vessels

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16
Q

peptide and protein hormones

A

can not cross plasma membrane on surface of target cell so they act by binding to surface receptors

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17
Q

reception

A

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

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18
Q

transdiction

A

binding of the signal to the receptor alters the receptor, confirmational change in the receptor initiating the signal transduction pathway

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19
Q

response

A

transduced signal triggers a specific response in the target cell, responses can vary based on receptor type

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20
Q

molecular switches

A

turn on and off the signaling process, when on the signal is relayed when off it is not, commonly: GDP bound off, GTP bond on; phosphorylated (on), dephosphorylated (off)

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21
Q

what are the two mechanisms for adding phosphates

A

direct phosphorylation and attaching GTPs

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22
Q

direct phosphorylation and what enzyme catalyzes the reaction

A

in direct phosphorylation, a phosphate from ATP is directly attached to an amino acid, the reaction is catalyzed by a protein kinase

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23
Q

what does a protein kinase do

A

add a phosphate group, adding of the phosphate to proteins makes them turn on and start spreading the signals

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24
Q

what does a protein phosphatase do

A

removes phosphate

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25
what are the two main types of protein kinases and how do they operate
the two main types are serine/threonine kinases which phosphorylate protein on serines and theronines the second group are tyrosine kinases which phosphorylate tyrosines, they both work through intracellular signaling pathways
26
two categories of extracellular signal molecules
large hydrophilic, small hydrophobic large hydrophilic can not cross the membrane so they are recognized by receptors on the plasma membrane where as small hydrophobic molecules can cross the membrane so they are normally recognized by receptors in the cytosol or the nucleus
27
what are the two receptors that bind extracellular signal molecules
GPCRs, RTKs
28
what type of signal molecules do GPCR recieve?
large hydrophilic molecules: Peptides and proteins
29
what is the structure of GPCRs
all GPCRs have the same structure, they are made of a single polypeptide chain that threads across the membrane 7 times by 7 membrane spanning alpha helicies
30
what do the loops that form form in the structure of the 7 membrane spanning alpha helicies do
the loops form so that the signaling molecules bind on the outside and the inner loops bind the G proteins on the cytoplasmic side
31
what happens when an extracellular signal binds to a GPCR
when an extracellular signal binds to a GPCR, the receptor protein undergoes a conformational change which enables it to activate the G protein which is located in the cytosolic face of the plasma membrane, the activated G protein then dissociates and carries the signal to the intracellular target
32
the subunits on G proteins
G proteins have three subunits, alpha, beta, gamma, the alpha and gamma subunits are attached to the plasma membrane the beta is between the two. GDP/GTP bind to the alpha subunit, when GDP bound the protein is inactive
33
what does the change of being GDP bound to GTP bound do
when the extracellular ligand binds, it activates the G protein exchanging GDP for GTP, the conformational change in the protein causes the alpha subunit to detach creating two active molecules
34
what causes people with cholera and pertussis to be sick
the bacteria that causes the diseases interferes with G protein function
35
cholera
bacteria causes the G protein to no longer be able to be hydrolyzed back to GDP so in active state indefinetly which cases prolonged and excess outflow of Cl- and water into the gut which leads to diarrhea and dehydration
36
whooping cough
bacteria locks the G protein into inactive GDP state resulting in inappropriate signal stimulates coughing and interfering with normal cell functioning
37
Structure of RTK
RTKs are transmembrane proteins they have an extracellular binding domain where they bind the ligand on the outer surface of the plasma membrane and their enzyme binding domain on the inner surface towards the cytoplasm, they normally act in pairs they have only one transmembrane segment which spans the lipid bilayer as a single helix
38
direct structure of each RTK receptor
there is an N terminal extracellular ligand binding domain, a single transmembrane alpha helix and a cytosolic C terminal domain with tyrosine kinase activity
39
what happens when a growth factor binds to the RTK
when the growth factor binds it induces dimerization which results in autophosphorylation as the two polypeptide chains cross phosphorylate one another
40
activation of RTKs
normally occurs in pairs, the ligand binds and you have ligand induced receptor dimerizations: two receptors come together forming cross linked dimers, the contact between the two receptors activates their kinase function and you get the autophosphorylation, one subunit phosphorylates the other subunit at tyrosine specific portion on the cytosolic tail
41
what do proteins that are activated by TKRs have
they have specific protein domains called SH2 domains that are able to recognize and bind to specific phosphorylated Tyr
42
can more than one protein with SH2 domain get activated on the same receptor
yes, many proteins with SH2 domains will come by and attached and become activated so multiple proteins get activated at the same time
43
what can SH2 domains do
each phosphorylated tryosine serves as specific binding site for a different intracellular signaling protein that has an SH2 domain which then relays the signal into the cell interior
44
how is the signal from tyrosine phosphorylations terminated
protein tyrosine phosphatases remove phosphates from RTKs and other signaling proteins
45
Mutations on RTKs
if its over activation of certain cells, it can make cells become cancerous as signals for proliferation become out of control
46
second messengers
small water soluble molecules or ions that spread though out a cell by diffusion
47
what type of pathways do second messengers participate in
all type of receptor pathways: GPCr and RTKs
48
what are common examples of second messengers
cAMP, IP3, Dag, Ca2+
49
how do you get cAMP
a hormone binds which promotes the interaction of the receptor with a G protein, the now activated G protein alpha subunit dissociates from the receptor and stimulates adenylyl cyclase which catalyzes conversion ATP to cAMP
50
how is the cAMP signal turned off
by phosphodiesterase which breaks the ring of cAMP and turns it back into AMP
51
what allows the same cAMP second messenger to produce different responses in different contexts
PKA is found in many different cells and has different target proteins in each different cell
52
what activates PKA
cAMP
53
what to protein kinases do (PKA)
transfer a phosphate from ATP to a protein
54
what is one important cell response controlled by cAMP
stress response: adrenal glands release adrenaline which circulates in the blood and binds GPCRs which help prepare the body for flight or flight reaction
55
what does adrenaline trigger
a rise of intracellular cAMP which stimulates PLA which leads to activation of the enzyme that promotes glycogen breakdown which has the effect of producing the max amounts of glucose available as fuel for muscle activity
56
what is the relationship between cAMP and gene transcription
binding of signal to GPCR leads to activation of adenylyl cyclase and rise in concentration of intracellular camp that activates PKA which goes to nucleus and phosphorylates specific transcription regulators allowing gene transcription
57
CREB
transcription factor leading to the recruitment of coactivators and expression of cAMP inducible genes
58
how is IP3 and DAG formed
phospholipase C cuts a membrane phospholipid called PIP2 which is present in cytoplasmic region of plasma membrane
59
what is DAG
lipid that remains embedded in the plasma membrane
60
IP3
sugar phosphate that diffuses into the cytosol
61
what protein kinase can DAG activate
Dag stays in the plasma membrane and can activate PKC which cases a phosphorylation cascade
62
what does IP3 bind to
IP3 diffuses into the cytoplasm and binds to ligand gates calcium channels in SER: binding of IP3 opens the calcium channels
63
what is the relationship between PKC and Ca+2
PKC not only need the binding of DAG to be active but also needs to bind Ca2+ to become active, PKC then operates similar to PKA
64
where is calcium stored
compartments of ER
65
cellular effects of an increase in calcium concentration
1. exocytosis: calcium signaling in beta cells of the pancrease leads to release of insulin 2. activation of motor proteins, increase in calcium stimulates neuron firing
66
what is the most common calcium response protein
calmodulin
67
where is calmodulin found
in cytosol of all eukaryotic cells
68
what happens when calcium binds to calmodulin
calmodulin undergoes a confirmational change which allows it to wrap around range of target proteins altering their cellular activities. once one calcium is bound the alpha helix jackknifes around the target protein Calmodulin (CaM) is a calcium-binding protein that plays a crucial role in cell signaling by acting as a calcium sensor. When calcium levels rise inside the cell, calmodulin binds to Ca²⁺ ions, changing its conformation. This activated form can then interact with and regulate various target proteins, including kinases, phosphatases, ion channels, and enzymes.
69
what is the shape of calmodulin
it is a dumbell shape with two globular ends connected by long flexible alpha helix, each end has two calcium binding sites
70
what is one important target for calmodulin
CaM kinases, when they are activated they influence other processes in the cell by phosphorylating and regulating proteins
71
what activates Akt
PIP3
72
what happens once Akt is activated
it will phosphorylate target proteins will the effect of promoting cell survival and inhibiting apoptosis
73
Ras
a small gtp binding protein found in cytoplasmic face of plasma membrane, similar to trimeric g proteins
74
how is ras linked to the membrane
though lipid tails, it is active when GTP is bond and inactive when GDP is bound
75
what gets Ras to exchange GDP for GTP
when it interacts with RTK
76
how does ras get activated
though an adaptor protein with an SH2 domain that docs on a phosphorylated tyrosine on the activates RTK, activated ras stimulates downstream signaling pathway
77
what does activated ras promote
phosphorylation cascade involving MAP kinase proteins where MAP kinase phosphorylates various effector proteins including ones that deal with trascription regulators or altering gene transcription stimulating cell proliferation to promote cell survival or induce cell death
78
what binds to cell surface receptors
any hydrophilic molecule or one that can not cross the membrane
79
what are the cell surface receptors
GPCR and RTK
80
what binds to intracellular receptors
steroid hormones, lipid soluble hormones, anything that can cross the membrane
81
what do intracellular receptors act as?
transcription factors, once activated they bind directly to DNA and regulate gene expression for slow but long lasting effects

cell structure and function mid term 1 (8 decks)

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