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Bio1MGC > Cell communication > Flashcards

Cell communication Flashcards

1
Q

quorum sensing

A

bacteria secrete molecules that allow them to monitor the number (concentration) of other bacteria around them
allows bacteria to coordinate their behaviour e.g. biofilm / secretion of toxins to create antibiotic resistance

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2
Q

paracrine signalling

A

type of local signalling in ANIMAL cells
cells secrete molecules that acts on nearby cells
e.g. growth factors - compounds that stimulate nearby target cells to grow and divide
occurs through diffusion

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3
Q

growth factors

A

secreted by cells to communicate with other nearby cells and tell them to grow and divide

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4
Q

synaptic signalling

A

occurs in the animal nervous system
an electronic signal along a nerve cell triggers the secretion of neurotransmitter molecules
these diffuse across the synapse (space between nerve cell and target cell) triggering a response in the target cell

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5
Q

cell junctions used for signalling

A

cell junctions directly connect the cytoplasms of adjacent cells
signalling substances dissolved in the cytosol can pass freely between neighbouring cells

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6
Q

cell to cell recognition

A

animal cells may communicate via direct contact between membrane bound cell-surface molecules
embryonic development and immune response

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7
Q

hormones

A

used for long distance signalling in animals and plants

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8
Q

endocrine signalling

A

hormone signalling in ANIMALS

specialised cells release hormones which travel in the circulatory system to target cells that can recognise them

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9
Q

plant hormones

A

may travel through tubes
move through cells
released as a gas e.g. ethylene

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10
Q

three stages of cellular communication

A

reception
transduction
response

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11
Q

reception

A

target cell detects signalling molecule

signalling molecule binds to a specific receptor protein located on the cell’s surface

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12
Q

transduction

A

converts signal to a form that can bring about cellular response
sequence of changes - signal transduction pathway

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13
Q

signal transduction pathway

A

activation of receptor molecule causes a sequence of changes in a series of different molecules to relay signal
molecules are often called relay molecules

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14
Q

response

A

the transduction signal changes cellular behaviour / can be almost any cellular activity

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15
Q

ligand

A

a molecule that specifically binds to another (often larger) molecule
ligands bind and dissociate many times
the ligand concentration outside the cell determines how many times a ligand is bound and initiates signalling

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16
Q

what causes reception

A 
signalling molecule (ligand) is specific - complementary in shape to a specific site on the receptor (the receptor may be plasma membrane proteins or inside the cell)
ligand binding causes a change in shape of the receptor protein
shape change causes other proteins to react and causes chain of reactions
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17
Q

G protein coupled receptors (GPCR)

A

cell surface transmembrane receptors

the largest family of cell surface receptors

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18
Q

what is the structure of GPCRs

A

seven transmembrane alpha helices with loops that extend outside and inside the cell
the loops outside the cell form the binding site
the loops inside bind to G proteins

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19
Q

what types of cells have GPCRs

A

embryonic development

senses - vision, smell and taste depend on GPCRs

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20
Q

diseases related to GPCRs

A

bacterial infections - cholera, whooping cough, botulism produce toxins that interfere with G protein function

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21
Q

process for signalling using GPCRs

A

GDP is attached to G protein -the G protein in inactive
signalling molecule binds to receptor
receptor is activated and changes shape
cytoplasmic side of the receptor binds to G
binding causes GDP to change to GTP - activates the G protein
G protein dissociates from the receptor and binds to enzyme to trigger next steps
G protein hydrolyses its bound GTP to GDP and is inactive again

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22
Q

RTKs - receptor tyrosine kinases

A

plasma membrane receptor that functions as an enzyme
the side of the RTK that is in the cytoplasm catalyses the transfer of phosphate to the amino acid tyrosine

RTKs can trigger many different pathways and cellular responses

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23
Q

how are GPCRs and RTKs different

A

RTKs can set off multiple transduction pathways

GPCRs - single transduction pathway

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24
Q

what is the structure of RTKs (receptor tyrosine kinases)

A

receptors are monomers that consist of extracellular binding site. a helix spanning the membrane and an intracellular tail containing multiple tyrosines.

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25
Q

how does a RTKs work

A

RTK is a monomer
signal binds causing two monomers to dimerise
dimerisation activates the tyrosine kinase region
tyrosine kinase adds a phosophate from ATP to a tyrosine on the tail of the other monomer
recognised by relay proteins - triggers transduction pathway

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26
Q

ion channel receptors

A

ligand binds to the channel receptor causing the gate to open or close - allowing or blocking the flow of ions such as sodium or calcium

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27
Q

give examples of where ligand gated ion channels function

A

nervous system - neurotransmitter molecules bind as ligands to ion channels on the receiving cell

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28
Q

what diseases are associated with cell surface receptors

A

cancer heart disease asthma

29
Q

what are intracellular receptors

A

found in the cytoplasm or the nucleus of target cells
signalling molecule must pass through the plasma membrane (need to be hydrophobic or small)
If hydrophilic cannot pass through the plasma membrane

30
Q

how do intracellular receptors work?

A

hormone enters cell - binds to intracellular receptor and changes it into a hormone receptor complex - causes a response
e.g. aldosterone (adrenal gland) - receptors only in kidneys - enters the nucleus and turns on specific genes that control water and sodium flow

31
Q

how does the transduction process in multiple steps benefit the cell

A

can quickly amplify the signal - one molecule transmits the signal to numerous molecules - geometric rise
multistep pathways provide more opportunities for coordination and control

32
Q

what molecules are most involved in signal transduction

A

protein

protein-protein interactions are the major theme of cell signalling

33
Q

what is a signalling pathway

A

falling dominoes - relay molecules
signal activated receptor activates another molecule which activates another molecule and so on until the protein that produces the final response is activated

34
Q

what causes the proteins at each step of a transduction pathway to change

A

shape change most often caused by phosphorylation

35
Q

what is a protein kinase

A

an enzyme that transfers phosphate groups from ATP to a protein

36
Q

how does receptor tyrosine kinase act as a protein kinase

A

RTKs is a specific kiind of protein kinase that transfers phosphates from ATP to the tyrosine on the other receptor

37
Q

what proteins are most often phosphorylated in transduction pathways

A

with RTK its tyrosine
more often it is either of two amino acids - serine or threonine
serine /threonine kinases are widely involved in signalling pathways in animals, plants and fungi

38
Q

phosphorylation cascade

A

the signal is transmitted by a cascade of protein phosphorylations each causing a change in shape in the phosphorylated protein
the shape change alters the function of the protein, most often activating it

39
Q

protein phosphatases

A

enzymes that can rapidly remove phosphate groups from protein - dephosphorylation
turn off the signal transduction pathway when the initial signal is no longer present

40
Q

second messengers

A

small, water soluble non-protein molecules or ions involved in signal transduction pathways
e.g. cyclic AMP and calcium ions

41
Q

cAMP

A

second messenger
ligand (adrenalin) binds to GPCR - activates G protein - activates adenylyl cyclase which catalyses the synthesis of cAMP - cAMP broadcasts signal

42
Q

Calcium as a second messenger

A

Calcium is even more widely used than cAMP as a second messenger

43
Q

what is being passed along the signal transduction pathway

A

information
the signal that is being transduced is the information that a signalling molecule is bound to a cell surface receptor
information is transduced by way of sequential protein to protein interactions that change protein shapes causing them to function in a way that passes the information along

44
Q

in what ways does the cell change as a result of signal transduction

A

protein synthesis - usually by turning specific genes on or off in the nucleus
if turns a gene on - becomes a transcription factor

45
Q

what is a transcription factor

A

turns genes on resulting in transcription - synthesis of one or more specific mRNAs which will be translated into proteins

46
Q

signal amplification

A

enzyme cascades amplify the cell’s response to a signal

at each step the number of activated products can be much greater …

47
Q

how can two cells (e.g. heart and liver) respond to the same signal differently

A
  • different kinds of cells have different collections of proteins
    two cells that respond differently to the same signal differ in one or more proteins that respond to the signal
48
Q

different types of signalling pathway

A

single pathway with one response
branched pathway with two different responses
cross talks (interaction) between two pathways

49
Q

scaffolding proteins

A

increase the efficiency of a pathway
large relay proteins to which several other relay proteins are simultaneously attached - hold together networks of signalling pathway proteins - rate of protein-protein interaction is not limited by diffusion

scaffolding proteins hold molecular components of signalling pathways in a complex with each other

50
Q

apoptosis

A

programmed cell death / cell suicide
cellular agents chop up DNA, fragment the organelles
cell shrinks and becomes lobed (blebbing)
cells parts are packed up in vesicles and engulfed by scavenger cells

51
Q

homeostasis

A

the tendency of an organism or cell to regulate its internal environment and maintain equilibrium

52
Q

what is the effect of a ligand binding to a receptor

A

conformational change

when a receptor is stimulated by a ligand the receptor always changes conformation

53
Q

phosphorylation

A

the transfer of phosphate groups to amino acids within a protein. Used to regulate the activity of the protein

54
Q

autophosphorylation

A

the phosphorylation of the kinase by itself

often occurs upon dimerisation of two units of the kinase

55
Q

phosphatase

A

an enzyme that REMOVES a phosphate group from its substrate

protein phosphatases are important for regulating the activity of other proteins

56
Q

dephosphorylation

A

the removal of a phosphate group

57
Q

autocrine signalling

A

the cell signals to receptors on its own surface

the cell that is releasing the signal is the same cell that is receiving the signal

58
Q

juxtacrine signalling

A

signals that are sent through direct contact between two cells

59
Q

what types of ligands are there

A

ligands can be hydrophillic (water soluble like adrenaline)
hydrophobic - not water soluble so can pass through the plasma membrane e.g. testosterone
protein e.g. human growth hormone
ions

60
Q

how do signals cross the cell membrane?

A

hydrophobic - go freely across
most small molecules and ions require the assistance of proteins to cross
ions can’t cross because of their charge
proteins are too big

61
Q

what types of receptor activation are there

A

agonist - activates the receptor
inverse agonist - the receptor goes back to its inactive state
antagonist - blocks the receptor and does not allow the agonist to bind

62
Q

difference between agonist and antagonist

A

agonist - turns the receptor on

antagonist - turns the receptor off

63
Q

structure of the GPCR

A

7 transmembrane domains

heterotrimeric - made up of three subunits - alpha, beta and gamma subunit

64
Q

how does a GPCR work

A

An agonist (ligand) is a substance which binds to a receptor and brings about a cellular response. For G-protein coupled receptors, this consists of 5 main steps.

Ligands bind to the extracellular portion of the G-protein coupled receptor, binding either at the N-terminus or a binding site within the transmembrane region.
Binding at the extracellular ligand binding site causes a conformational change in the GPCR, resulting in release of GDP from the α-subunit of the G-protein.
Released GDP is then replaced with a GTP
This activates the G-protein, causing the α-subunit and bound GTP to dissociate from the transmembrane portion of the GPCR and βγ-subunit.
These α-subunit interacts with its relevant effectors and cause downstream effects, e.g. ion channel opening or enzyme activity regulation.

65
Q

types of second messengers

A

cAMP
ions - calcium Ca2
inosital triphosphate (IP3)
diacyl glycerol (DAG)

66
Q

kinase

A

kinases catalyse protein phosphorylation
phosphate groups are generally added to amino acid groups like serine, tyrosine, threonine (have hydroxyl groups in their side chain)

67
Q

how does phosphorylation work

A

alters the charge (makes negative)
changes the shape of the protein so that it can interact with or attract partner proteins
by phosphorylating a protein you can change the qualities of that protein

68
Q

how does cAMP work

A

signalling molecules e.g. adrenaline lead to the activation of adenylyl cyclase by G proteins
formation of cAMP
elevation of cAMP activates protein kinase A (serine/threonine kinase)
activated protein kinase A phosphorylates other proteins

Bio1MGC (11 decks)

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